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WO2017044978A1 - Appareil et procédé d'utilisation de données de mesure pendant le forage pour générer des propriétés de résistance mécanique de la roche et cartographier des propriétés de résistance mécanique de la roche le long d'un trou de forage - Google Patents

Appareil et procédé d'utilisation de données de mesure pendant le forage pour générer des propriétés de résistance mécanique de la roche et cartographier des propriétés de résistance mécanique de la roche le long d'un trou de forage Download PDF

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Publication number
WO2017044978A1
WO2017044978A1 PCT/US2016/051381 US2016051381W WO2017044978A1 WO 2017044978 A1 WO2017044978 A1 WO 2017044978A1 US 2016051381 W US2016051381 W US 2016051381W WO 2017044978 A1 WO2017044978 A1 WO 2017044978A1
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WIPO (PCT)
Prior art keywords
force
spectral
rock
data
time domain
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Inventor
James D. Lakings
Jesse B. HAVENS
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Fracture Id Inc
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Fracture Id Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
    • G01V1/44—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging using generators and receivers in the same well
    • G01V1/48—Processing data
    • G01V1/50—Analysing data
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B47/00—Survey of boreholes or wells
    • E21B47/26—Storing data down-hole, e.g. in a memory or on a record carrier
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2200/00—Details of seismic or acoustic prospecting or detecting in general
    • G01V2200/10—Miscellaneous details
    • G01V2200/16—Measure-while-drilling or logging-while-drilling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/62—Physical property of subsurface

Definitions

  • the present disclosure involves measurement while drilling techniques that provide mechanical rock properties, and from which wellbore rock properties and other may be identified and used to improve drilling and completion practices, including identification of hydraulic fracture entry points and hydraulic fracture stages, among other things.
  • hydrocarbons oil or gas
  • the production of hydrocarbons can be generally distilled into two primary steps - drilling a borehole to intersect hydrocarbon bearing formations or oil and gas reservoirs in the subsurface, and then completing the well in order to flow the hydrocarbons back to the surface.
  • the ability of a well to flow hydrocarbons that are commercially significant requires that the borehole be connected to oil and gas bearing formations with sufficient permeability to support the flow rates that are needed to account for the costs of developing the field. In many instances, however, commercially viable flow rates cannot be obtained without the use of various advancements including horizontal drilling and hydraulic stimulation due to the type of formation or reservoir being developed.
  • unconventional resource plays are areas where significant volumes of hydrocarbons are held in reservoirs with low primary permeability (nanodarcy to microdarcy) and low primary porosity (2 - 15%) such as shales, chalks, marls, and cemented sandstones that generally do not have sufficient primary permeability to yield commercial quantities of hydrocarbons.
  • unconventional reservoirs Compared to "conventional" reservoirs, unconventional reservoirs have a much lower hydrocarbon density per unit volume of rock and much lower unstimulated hydrocarbon flow rates, making commercial development impossible without hydraulic stimulation of the reservoir rock fabric.
  • unconventional reservoirs are often regionally extensive covering thousands of square miles and containing billions of barrel of oil equivalent (BOE) of potentially recoverable hydrocarbons.
  • BOE barrel of oil equivalent
  • horizontal drilling involves first vertically drilling down close to the top of the unconventional reservoir and then using directional drilling tools to change the orientation of the wellbore from vertical to horizontal in order to contact greater areas of the reservoir per well.
  • horizontal drilling as used herein is meant to refer to any form of directional (non- vertical) drilling.
  • Horizontal drilling although having been performed for many decades prior to intensive unconventional resource development in the early 2000's, has been evolved to provide cost effective provisioning of the long horizontal borehole sections (5,000' to 10,000+') required to contact commercially viable volumes of hydrocarbon bearing reservoir rock.
  • Hydraulic fracture stimulation involves pumping high volumes of pressurized fluid into the borehole and through targeted perforations in the wellbore to create large networks of cracks (fractures) in the formation that create enhanced reservoir permeability and so stimulate greater quantities of oil and gas production.
  • Proppant is usually pumped along with the fluid to fill the fractures so permeability is maintained after the pumping is stopped and the fractures close due to reservoir stresses.
  • Proppant can range from simple quarried sand to engineered man-made materials.
  • Isolation generally involves the use of some form to technology to focus where fracturing occurs at specific locations along the well bore rather than stimulating the entire length of an open wellbore.
  • dipole sonic or natural fracture image logs can identify and quantify this variability on a scale that is useful to completions design, but existing tools are currently too expensive to run on anything but a very small fraction of unconventional wells drilled.
  • Conventional techniques, such as dipole sonic and natural fracture image logs are based on inferred information and not involved directly measuring the interaction of the drill bit with the formation. Instead, dipole sonic involves the transmission of acoustic signals (waves) from a controlled active acoustic source, through the rock formation in the areas of the well bore to a receiver typically several feet from the source, to measure the velocity of the waves through the formation.
  • Natural fracture image logs involve measuring the resistivity of the formation along the walls of the wellbore. Natural fracture logs are of limited use in wells using oil based mud, which has an inherently high resistivity and masks some fractures. These techniques are often cost prohibitive and limited in effectiveness. As a result, almost all wells are completed using geometrically equal spacing of zones isolated (referred to as stages) and stimulated. Thus, for example, hydraulic fracturing is inadvertently performed routinely on individual stages with significantly varying rock properties along the isolated section, resulting in the failure to initiate induced fractures in less conducive rock and so potentially bypassing substantial volumes of hydrocarbon bearing rock.
  • aspects of the present disclosure involve a method of characterizing rock properties comprising accessing, by a processor, time domain force and motion data collected from sensors associated with a drill bit interacting with a rock formation while drilling a wellbore.
  • the method may involve receiving acoustical signals obtained from the sensors positioned on a component of a bottom hole assembly where the sensors (e.g., accelerometers or strain gauges) are in operable communication with at least one data memory to store the acoustical signals.
  • the acoustical signals which may also be considered vibrations, are generated from a drill bit interacting with a rock formation while drilling a wellbore.
  • the method may further involve accessing, by the processor, spectral pairings generated from transformations of the time domain force and motion data. Additionally, the method may involve generating, by the processor, a rock strength property from a distribution of the spectral pairings.
  • Another aspect of the present disclosure involves a method of characterizing rock strength properties comprising: accessing, using a processor, time domain force and motion data collected from a sensor associated with a drill bit interacting with a rock formation while drilling a wellbore.
  • the force and motion time domain data is captured over a rotation (partial, full or multiple) of the drill bit where the formation experiences elastic and plastic deformation.
  • the method further involves accessing, using the processor, spectral pairings of force amplitude and motion amplitude, the spectral pairings from transforming the time domain drill bit forces and motions data in frequency domain drill bit forces and motions data.
  • the forces may be in the form of amplitude of force (or ensemble of amplitudes) and an amplitude of motion (or ensemble of amplitudes) paired according to frequency.
  • the spectral pairings may be accessed or may be generated from Fourier transformations or otherwise.
  • the method may further involve generating, using the processor, an elastic plastic transition of the rock formation where the elastic plastic transition is from a distribution of the spectral pairings of force amplitude and motion amplitude.
  • the method may further involve identifying or otherwise generating, using the processor, a force at a point of the elastic plastic transition and identifying or otherwise generating, using the processor, a rock strength property from the force at the point of the elastic plastic transition.
  • Yet another aspect involves a method of characterizing rock strength properties comprising: accessing, using a processor, time domain force and motion data collected from sensors associated with a drill bit interacting with a rock formation while drilling a wellbore.
  • the method may further involve accessing, using the processor, spectral pairings of a ratio of motion/force amplitude and a motion amplitude, the spectral pairings from transforming the time domain forces and motions data into frequency domain drill bit forces and motions data and identifying or otherwise generating, using the processor, a critical strain energy release rate from a distribution of the spectral pairings, the critical strain energy based on a slope of the distribution at a point of elastic plastic transition and a force at the elastic plastic transition.
  • Another aspect involves an apparatus comprising a processing unit in communication with at least one tangible machine readable media including computer executable instructions to perform the operations of the various methods, or portions thereof, discussed herein.
  • the processing unit may be part of a measurement while drilling apparatus and/or a computing device configured to process data collected from the measurement while drilling apparatus.
  • Figures 1A-1 B Illustrate reservoir- to-well connectivity where brittle rocks are generally associated with larger fracture creation and better proppant support that is more permeable than ductile rock that produces smaller, less productive fractures which are prone to rapid compaction and closure and are less permeable.
  • Figure 2A-2B is a diagram of a drill bit assembly including sensors for measuring bit accelerations and forces on the bit, and which includes at least one processing unit and tangible storage media in which to store acceleration and/or force data, and which may also store processed acceleration and/or force data of the drill bits interaction with a formation while drilling.
  • Figures 3A-3C illustrate the cutting action of a drill bit, stick slip fracturing of a rock formation, torque-on-bit and weigh on bit forces, and related torque and displacement curves.
  • Figure 4 is a method of obtaining mechanical rock properties of a formation proximate a well bore from measurements of bit behavior taken while drilling.
  • Figure 5 is a stress displacement diagram plotting a spectral spectral pairings of ensemble averages of annular pressure and axial displacement based on time domain measurements from sensors obtaining and recording drill bit motions and forces while drilling.
  • Figure 6 is a force displacement diagram plotting an spectral pairings of ensemble averages of torque-on-bit and shear (e.g., angular) displacement based on time domain measurements from sensors obtaining and recording drill bit motions and forces while drilling.
  • shear e.g., angular
  • Figure 7 are representative power law curves from ensemble force displacement diagrams with the lower curve representing a power law curve for deformation where the mode of deformation can be considered ductile such that the rock becomes harder with increasing strain with the upper curve being a related strain hardening coefficient curve where the higher the strain hardening coefficient, the strong the rock becomes for an equivalent strain
  • Figure 8 is a Coulomb strength diagram generated from motion and force data collected while drilling.
  • Figure 9A is a force displacement diagram based on spectral pairings generated from torque-on-bit and angular displacement data, with an initial yield strength computed at the frequency associated with a point of maximum curvature of the diagram.
  • Figure 9B is a compliance length diagram based on spectral pairings of angular displacement / torque-on-bit and angular displacement for measurements coinciding with those of Fig. 9A, with the critical strain energy release rate based on the initial yield strength computed from the distribution of Fig. 9A.
  • Figure 10 is a diagram of a distribution of ensemble averages of spectral pairings of torque-on-bit and annular pressure, where a point of transition between elastic and plastic deformation involves forming the spectral pairs between the torque-on-bit and the annular pressure, fitting a line to the low-frequency pairs and fitting a line to the high frequency pairs and obtaining the intersection between the two lines.
  • Figure 1 1 is a diagram illustrating Vsand and Vclay with an overlay of initial yield strength where there is a high lYS the value of Vsand - Vclay increases and conversely a low value of lYS corresponds to low values of Vsand - Vclay.
  • Figure 12 is a special purpose computer programmed with instructions to execute methods described herein.
  • the present disclosure involves a novel and non-obvious way of using drilling motions representative of displacement, such as may be captured using an accelerometer measuring angular and/or axial drill bit motions, and drilling forces, such as may be captured using strain gauges measuring forces associated with the angular and/or axial drill bit motions, where the motions and forces are generated by the deformation of a rock formation related to a drill bit cutting a wellbore during a drilling operation.
  • the drilling motion and force measurements are transformed into the frequency domain. From the frequency domain, the amplitudes of two spectra, where one spectra represents a motion and the other spectra represents a force, are paired together at each frequency.
  • Spectral pairs may be generated and used to generate a distribution, such as a force-displacement diagram, which may be correlated to positions along the wellbore. From the force displacement diagram and the spectral pairs more generally, various rock properties may be derived and used in various operations. For example, the Initial Yield Strength (lYS) may be derived and correlated to positions along the wellbore. The lYS may be used to identify the nature and occurrence of fractures, fracture swarms and other mechanical discontinuities (boundaries) such as bedding planes and/or faults that offset or otherwise separate rock formations with different mechanical rock properties. This information may further be used in completitions, such as where to target stimulation, and in numerous other ways.
  • lYS Initial Yield Strength
  • the techniques and measurements from this disclosure are made using downhole tools that are simple and rugged, allowing for a magnitude in order reduction in logging cost to characterize near-wellbore rock mechanical properties and intersected existing fracture locations.
  • the low cost to log a well which may be less than 0.5% of the total well cost, allows for widespread use of the technique.
  • Detailed knowledge of rock property characteristics and variability along a wellbore allows for grouping like-for-like rock types in variable length stages, avoiding losing reserves due to a lack of fracture initiation relative to mixed rock strength stages, among other advantages.
  • knowledge of existing fractures will improve well economics overall as fractures can be targeted for stimulation to improve initial production if appropriate, or avoided for example when setting swell packer locations.
  • the technique may also be useful in characterizing properties of rotating members and related structures, such as rotating shafts and bearings, among other things.
  • the processing of drilling induced motions and forces when recorded using sensors deployed in a borehole in connection with a bottom hole assembly (BHA), such as may be provided from a measurement while drilling (MWD) assembly and a bit sub, and according to the methods disclosed here, can provide rock properties including the nature and occurrence of mechanical discontinuities, such as pre-existing fractures, which can be used to target sections of the well where the rock properties are conducive to economical hydraulic stimulation and to avoid sections that are viewed as sub-commercial, where the rock properties are not conducive to economical hydraulic stimulation.
  • BHA bottom hole assembly
  • MWD measurement while drilling
  • the rock strength e.g., IYS, fracture toughness, secant modulus, tangent modulus, uniaxial compressive and tensile strengths, and others
  • variations in the rock strength that are obtained while conducting drilling operations can be used for assisting, in real-time, the steering of the bottom hole assembly in order to maintain the tracking of the drill bit through geological formations as are targeted according to the desired mechanical rock properties, especially where the mechanical rock properties are relevant to the production of commercially significant hydrocarbons using hydraulic fracturing stimulation techniques.
  • Natural fracture identification also refines the process of hydraulic stimulation optimization by providing direct measurement of zones that offer higher permeability and higher hydrocarbon productivity.
  • aspects of the present disclosure involve methodologies that use broad band measurements (e.g., continuous, high resolution) of drilling motions, which may also be referred to as vibrations, and drilling dynamics data, such as forces, taken proximate the drill while conducting drilling operations to log the mechanical properties of a rock formation.
  • Drilling vibrations generated by the deformation and failure of a rock formation are generally related to the mechanical properties of the rock being drilled. It is generally understood that the depth of cut or the tooth penetration into the rock is inversely related to the strength of the rock.
  • rock formations that take a relatively long time to drill through or where the rate of penetration is slow are generally referred to strong or hard formations and have a lesser depth of cut in relation to rock formations that are relatively weaker and less rigid.
  • These basic principles have enabled the application and use of techniques that take measurements of the hardness of a rock formation by forcing a tool into a rock to make an indentation where the depth of the indentation relative to the force applied is used to obtain a hardness characteristic that is essentially a mechanical property of a rock formation.
  • Signal processing techniques are used to process the force displacement curves to identify locations along the wellbore where the rock strength or changes in the rock strength indicate that the drill bit has encountered a mechanical discontinuity (e.g., preexisting fractures) or geological boundary. If the changes in the drilling vibration and forces as expressed through the force displacements diagrams and rock information derived therefrom are rapid and discrete in both space and time, and then return back to a long-term trend or the levels that were recorded prior to the change in the drilling vibrations and forces as expressed through the amplitudes and frequencies of the forces and displacements, then it would indicate that that the drill bit has encountered and crossed a discrete mechanical discontinuity because mechanical rock properties that are discrete in both space and time are uniquely separated from the mechanical properties of a rock formation such as would be in the case of a drill bit penetrating a fracture face. If the changes in drilling information are rapid and discrete and continue over a short interval, then that would indicate multiple fractures or a swarm of fractures has been encountered.
  • a mechanical discontinuity e
  • the signal processing techniques indicate that the changes in the amplitudes and frequencies of the forces and displacements, as evidenced through the processing and analysis of the force displacement curves, are rapid, but then do not revert back to the level prior to the change and instead carry on at a new, significantly different level, then that indicates a mechanical boundary where the mechanical boundary that separates or offsets two different rock formations such as a bedding plane and or fault has been encountered and crossed as evidence by the change in rock strength across the boundary. Whether or not the boundary is related to a fault or a bedding plane depends on the inclination of the bit with respect to the orientation of the stratigraphy of the rock formation being drilled.
  • the description provides a method to evidence the presence of fractures, fracture swarms and other mechanical discontinuities such as faults and bedding planes that offset or otherwise separate rock formations with different rock properties.
  • the approach uses geophysical signal processing techniques that are sensitive to changes in the drilling motions and forces where the changes are relative to some baseline, such as a normalized preceding set of drilling data, and whether or not the changes are discrete and then return back to the level prior to the change or are maintained at a new level that is different than the level observed prior to the change.
  • the present disclosure involves an innovative, new system, apparatus and method to specify, in general, the mechanical properties of a rock formation from an analysis of drilling vibrations generated by the cutting action of the bit and the deformation of the formation in response to the forces acting on the rock formation in connection with the drill bit and drilling fluid system while conducting drilling operations.
  • Deformation may include elastic deformation, plastic deformation, and failure of the rock, which may be considered fracturing.
  • aspects of the present disclosure involve obtaining information associated with the drilling of a borehole, while drilling, to identify mechanical rock properties of the formation being drilled.
  • Such mechanical rock properties may be used, in some examples, to identify the presence of natural fractures or rock properties more or less susceptible to stimulation techniques.
  • knowing mechanical rock properties along a borehole or the presence of natural fractures along a borehole may be used to optimize hydraulic fracturing operations by focusing such fracturing on areas where it will be most effective, among other advantages.
  • Mechanical rock properties may include strength measurements such as IYS and others discussed herein.
  • the mechanics of drilling a well provide a natural, in-situ, means to measure the deformation of a rock formation and gather data suitable for determining mechanical rock properties, because the penetration of the drill bit is in and of itself accommodated by repeatedly fracturing the rock formation by using the bit to generate forces on the rock formation that are sufficient to overcome the failure strength of the rock, measurements of such forces in relations to motions that accompany the forces, in relation to the methods described here may be used in predictable ways to determine the presence of natural (in situ) fractures, fracture swarms (cluster of fractures), bedding planes, fault boundaries, and other information. In some instances, variations in mechanical rock properties are used to identify fractures, bedding planes and the like.
  • FIG. 1 is a simplified diagram illustrating the difference between fractures induced in a relatively brittle rock formation, and which may be include naturally occurring fractures, versus fractures induced in a relatively ductile rock formation, which may include fewer or no natural fractures.
  • a horizontal section 10 of a borehole has been drilled through relatively brittle rock 12 and hydraulically fractured.
  • Fig. 1 B illustrates a horizontal section 14 of a borehole drilled through relatively ductile rock 16 and hydraulically fractured.
  • the fractures 18 created in the relatively brittle rock tend to penetrate deeper into the reservoir than the fractures 20 in ductile rock. Moreover, reservoir rock trending to the brittle end of the normal range tends to have higher initial production rates and lower decline rates.
  • the techniques described in this disclosure will provide new information for selecting hydrocarbon bearing zones by differentiating between brittle rocks generally associated with larger fracture creation and better proppant support that is more permeable than ductile rock that produces smaller, less productive fractures which are prone to rapid compaction and closure and are less permeable.
  • techniques discussed herein may also identify areas where natural fractures may exist provide similar advantages as brittle rock.
  • Fig. 2 is a diagram of a BHA portion 21 of a drill string where the bottom hole assembly includes a drill bit 23, a mud motor 24, a bit sub 26 including various measurement components positioned between the drill bit and the mud motor, and sections of pipe 28 within a horizontal section 30 of a borehole 31 , also referred to herein as a wellbore.
  • the section 30 may include brittle rock 12 (Fig.
  • Fig. 1A ductile rock 14
  • Fig. 1 B ductile rock 14
  • the vibration data used in the described methodologies may be recorded as close to the source (drill bit) as practical to avoid attenuation through the BHA. Forces may also be measured from components in the bit sub.
  • One possible location for recording is directly behind the drill bit and ahead of the mud motor 24 using the bit sub 23, although multiple bit subs may be used along the drill string for geophysical processing of the desired signal.
  • Drilling a wellbore involves using a force of the weight of the drill string, known as weight-on-bit (WOB), to push the drill bit into a formation 33.
  • WOB weight-on-bit
  • the rotating force on the drill bit can be generated from the surface or from a mud motor close to the drill bit.
  • drilling mud is pumped down the drill string until it encounters the power drive section of the mud motor where a portion of the mud pressure and flow is converted into a rotational force, which is mechanically coupled to the bit to thereby place rotational torque on the bit 22 to turn the bit.
  • the rotational force on the bit can also be augmented by or come exclusively from mechanisms at the surface on the drilling rig.
  • the WOB and the TOB may be measured through strain gauges associated with some portion of an MWD apparatus, such as the bit sub, or more generally the BHA 21.
  • the objective of the drilling process is to break the rock down into fragments that are small enough that they can be lifted and evacuated from the wellbore with drilling fluids in order to continue to accommodate the forward motion of the bit.
  • the action of the drill bit on a rock formation causes the fracturing of the rock formation along the borehole to drill the hole, and in the formation immediately adjacent the borehole.
  • the drill may encounter existing fractures 34 while drilling.
  • Hydraulic fracturing is a process that occurs during the completion phase by injecting fluid into the borehole, typically with perforation clusters 22 (see Figs. 1A and 1 B) in the casing, to initiate fractures 18/20 into the formation surrounding the bore hole.
  • the casing may be perforated to facilitate fracturing based on rock strength characteristics generated from the compute and drilling measurement systems and methods discussed herein.
  • the bit sub 26 is shown between the bit 22 and the mud motor 24.
  • the bit sub is a cylindrical component that is operably coupled between the mud motor 24 and the drill bit 22 in a way that allows the mud motor to turn the bit.
  • the bit sub provides a housing, typically in a cylindrical shape, or mechanism to support various possible measurement components 36 including strain gauges, one or more accelerometers, pressure sensors, which may measure the pressure of the mud flow, temperature sensors which may measure the circulating temperature of the mud or other temperatures and which may be used to provide correction or offset of measurements or calculations that vary with temperature, gyroscopes which may be used to measure inclination and/or directional changes of the bit and string, and/or other components to measure or derive the information discussed herein.
  • strain gauges typically in a cylindrical shape, or mechanism to support various possible measurement components 36 including strain gauges, one or more accelerometers, pressure sensors, which may measure the pressure of the mud flow, temperature sensors which may measure the circulating temperature of the mud or other temperatures and which may be used to provide correction or offset of measurements or calculations that vary with temperature, gyroscopes which may be used to measure inclination and/or directional changes of the bit and string, and/or other components to measure or derive the information discussed herein
  • the strain gauges are mounted on the bit sub to determine the TOB and the WOB (the force turning the bit and the force pushing the bit into the rock formation).
  • the strain gauges or combinations of strain gauges, are possible.
  • accelerometers are placed to measure axial, rotary, and/or lateral acceleration of the bit. Note, the bit axis is in the center of the circle, whereas axial acceleration may be measured somewhat offset from the axis depending on the placement of the accelerometer. Acceleration measurement may be accomplished by using one or more multi- axis accelerometers.
  • accelerometers In the case of using accelerometers to measure the drilling induced motions, it may be useful to use multiple accelerometers where the some of the axes of the accelerometers are oriented at right angles or oriented in opposing fashions. This is because a single accelerometer mounted tangentially to the drill collar contains both angular and linear accelerations. By summing measurements of the opposing the accelerometers together it is possible to cancel the lateral motion and obtain an angular acceleration. The angular acceleration is then transformed into the frequency domain where it can then be integrated to obtain an angular velocity and then integrated again to obtain an angular displacement.
  • the bit sub may also include a processor and memory to store computer executable instructions to implement various possible methodologies as well as a power source which may be one or more batteries.
  • Data storage such as the memory or other data storage mediums, is also provided to store the collected data.
  • the bit sub may also include processors and methods to preprocess data the data.
  • the processor or an additional purpose specific digital signal processor may transform time domain motion and force data in the frequency domain for storage on the bit sub, which may provide for larger data storage capacity particularly if data is gathered at frequencies at or exceeding 1 KHz.
  • the measurement components alone or in various possible combinations, may be provided in other locations of the drill string in the general proximity of the drill bit.
  • Figs. 3A-3C are a sequence of diagrams illustrating a close up view of a cutter 32 portion of a drill bit 23 in a borehole, slipping, sticking on a portion of rock, and then slipping loose when the forces on the bit are sufficient to overcome the rock causing the rock to fracture and the bit to rotate - collectively referred to as stick slip behavior.
  • the rock deformation mode for a PDC bit is shearing as opposed to a roller cone bit which is punching.
  • Models that describe drilling behavior are in a large part informed on the mechanics of drilling with a roller cone bit and while these models have been extended for the application and use of PDC bits, they suffer uniquely from their inherent inability to reconcile the fundamentally different nature of rock deformation.
  • the innovative, new techniques disclosed here seek to advance the application and use of PDC bits, as well as other bits, to characterize mechanical rock properties and in particular for the identification of the nature and occurrences of fractures.
  • the figures describe the depth of cut in relationship to the area and displacement of the fractures created in response to the forces acting on the bit.
  • the cutting action of a particular type of bit but should not be construed to limit the method in the use of other types of drill bits that generate acoustic emissions from rock failure in response to the forces acting on the geometry and configuration of the bit.
  • the interaction of the bit with the rock formation at any instant in time produces a complex distribution of forces acting on the formation in connection with the bit and drilling fluid system (e.g., the mud motor) where the orientation and magnitudes of the forces acting on the rock formation are related to the configuration and geometry of the cutters on the bit.
  • drilling is not a smooth and consistent process. Instead, depending many things including the axial force on the bit, rotational torque on the bit, rock properties, and presence or absence or existing fractures, the bit cuts, gouges, spins, snags, and otherwise drills the borehole in a very complicated and varying fashion, and motions (or vibrations) of the bit are simultaneously occurring.
  • the complex distribution of forces acting on the formation is insufficient to initially overcome the strength of the rock formation in relation to the cutting action of the bit and the bit will stop rotating or stick.
  • bit Regardless of whether and the extent of stick slip behavior is experienced, deformation and failure of the rock cause the bit to vibrate.
  • stored elastic strain energy is released in the form of acoustic emissions.
  • the bit is fracturing rock and may intersect fractures and existing mechanical discontinuities.
  • the bit may reactivate existing fractures, which may itself generate a distinct acoustical signal in the form of an induced bit vibration.
  • the force data and vibration (motion) data are captured and stored.
  • a drill bit 23 typically includes many cutters 32 arranged with a geometry and configuration designed to generate sufficient forces to overcome the failure strength of the rock formation 33 based on the nature of the rock formation expected to be encountered when drilling a well.
  • the tool may include various possible mechanisms, including a reed switch or gyroscopes, which measure revolutions per minute and provide information of each rotation of the bit.
  • a reed switch or gyroscopes which measure revolutions per minute and provide information of each rotation of the bit.
  • the implementation of the method discussed herein may use statistical methods and signal analysis tools.
  • the Fourier transform is understood to separate the modes of deformation, where relatively higher frequency measurements have low displacements and generally describe the forces acting on the rock formation in connection with a drill bit during elastic deformation, while relatively lower frequencies with larger displacements generally represent the forces acting on the bit in relation to plastic deformation.
  • the implementation of the technique as described uses signal processing techniques, such as Fourier transforms, bandpass filtering or other filtering, or combinations thereof, to calculate the motion of the bit and the forces on the bit.
  • the motions of the bit are captured from the amplitudes and frequencies of the acoustical signals recorded by the MWD apparatus (e.g. bit sub 26) that are generated in response to the cutting action of the bit (e.g., the drilling vibrations propagate up the drill string as acoustic waves sometimes referred to as collar waves or tool mode, where they are recorded as acoustical signals by the MWD apparatus).
  • Forces on the bit are also measured using strain gauges, in one possible implementation.
  • the amplitudes and frequencies of the motions of the bit and the forces on the bit are used to generate a distribution, including a force displacement diagram, which facilitates the computation of mechanical rock properties.
  • Mechanical rock properties such as IYS
  • a baseline such as an average IYS over some wellbore distance
  • rock properties may be used to identify such locations through computations based on assumptions of the rock formation, and comparisons thereof, or otherwise.
  • the acoustical emissions associated with the deformation and failure of the rock formation while drilling are generally too minute and/or too attenuated by the intervening rock to be detectable at the surface (which may be hundreds or thousands of feet above the borehole). Because of the amount of energy released is generally expected to be slight and of relatively high frequency, the radiated waves are best viewed when transmitted from the cutting face through the bit and bottom hole assembly where they propagate along the drill string through acoustically conductive steel as a direct tool arrival and contribute to the vibration of the drill string. The drilling vibrations and forces can be recorded on instrumentation that is sensitive to their nature and presence.
  • one aspect of the present disclosure involves a drilling tool assembly including sensors and processing electronics (e.g., the accelerometers and/or strain gauges in the bit sub 26 proximate the bit 22) that are positioned to detect and record the radiated waves from the drilling induced fracturing, which may further involve identification and/or characterization of existing mechanical discontinuities, such as fractures or geological boundaries, such as faults or bedding planes.
  • sensors and processing electronics e.g., the accelerometers and/or strain gauges in the bit sub 26 proximate the bit 22
  • a form of measurement while drilling (MWD) system or tool is employed.
  • the MWD system uses sensors designed to measure vibrations.
  • the MWD system may also measure forces on the bit, and other parameters such as bit speed, which may be expressed as revolutions per minute, the fluid pressures, and temperature of the drilling mud or environment proximate the bit sub.
  • the system may also include gyroscopes to obtain the orientation of the cutting face of the drill bit, in some implementations.
  • the MWD tool includes at least one receiver, accelerometers which may include strain gauges mounted on or proximate the bottom hole assembly to record the drilling vibrations and associated acoustic emissions.
  • the MWD may further include electrical, mechanical, and/or other filtering mechanisms to processes the data to remove unwanted noise or to record the data without unwanted noise.
  • stages of filtering may be applied both prior to recording, and after recording but prior to processing, to remove unwanted data, or as much as necessary or possible.
  • the signals may be transmitted to the surface for storage and processing.
  • the results are correlated back to the measured depth of the well using precise measurements of the length of drill string components as they are lowered into the well.
  • Gamma ray LWD and casing collar measurements can further be used to correlate the absolute location of data processed from the BHA collection point or points to determine a more reliable location of the bit in relation to the subsurface.
  • mechanical rock properties are obtained from the processing and analysis of forces and motions of a drill bit, or other component, interacting with a geological formation, such as a rock formation.
  • the forces and motions may be measured from an arrangement of appropriate sensors, such as provided from the MWD apparatus positioned proximate the drill bit as discussed above. Such forces and motions may be measured continuously and at a high sample rate.
  • the forces and motions are used to obtain, such as through Fourier transformations, spectral estimates of the forces and motions of the bit.
  • the spectral estimates may then be used to construct innovative, new force-displacement diagrams representing the deformation and failure of a geological formation, such as a rock formation being drilled through for an oil or gas well, as a result of a drill bit interacting with the formation.
  • the force-displacement diagrams are understood to represent the constitutive elastic and plastic behavior and the elastic-plastic transition of the material when being cut by a bit.
  • the method further elaborates on objective techniques to obtain the point of the elastic-plastic transition from the force-displacement diagram and to further use the values of the forces and displacements at the elastic-plastic transition to obtain rock strength and other properties.
  • the use of the force-displacement construction is extended to include an innovative new way to construct a compliance-length diagram.
  • the compliance length diagram can be used, in general, to determine the resistance of a rock formation to a propagating crack or in a particular application to obtain a fracture toughness which is a measure of the resistance to a propagating hydraulic fracture in connection with a well completion operation. Understanding the resistance of a formation to a propagating crack can be used to select hydraulic fracture entry points and thus used for casing and perforation determinations among other ways to use the information.
  • the method to obtain the force-displacement diagram pertains to any piece of rotating machinery.
  • the force- displacement diagram obtained by continuous, high-resolution measurements would be related to the interaction of the rotating shaft with the bearing assembly. Variations in the force- displacement diagrams could be used to describe the deformation and failure of the bearings. Accordingly, while the methods discussed herein are primarily discussed relative to rock properties and drilling operations, the techniques have broad applicability in other fields.
  • MWD data can be recorded using downhole measurements made with strain gauges and accelerometers, among other things.
  • strain gauge measurements can be processed to obtain measurements of WOB and TOB.
  • the measurements can be sampled continuously at high frequency and the measurements stored in a memory of the MWD recording apparatus.
  • the motion (vibration) of the bit, while drilling may be captured through an arrangement of accelerometers on the MWD recording system.
  • the accelerometers may be arranged in orthogonal recording configurations that when combined together using addition and subtraction can be used to separate the angular (rotational) and linear motions of the bit.
  • the method begins with receiving and storing, at and by a processor and an associated data memory, acoustical and force signals, in the time domain, obtained from the sensors of the MWD apparatus or otherwise (operation 400).
  • the method may begin with accessing, by the processor, time domain force and motion data collected from the sensors associated with a drill bit interacting with a rock formation while drilling a wellbore.
  • Processing, continuous high-frequency measurements while drilling (MWD) data in the manner described by the method provides innovative, new techniques to generate the constitutive relationships that can be used to obtain properties of mechanical rock strength that are useful to characterize the deformation and failure of a rock as it progresses from elastic to plastic behavior.
  • the constitutive relationship between the angular forces and angular motions of the drill, and mechanical rock strength properties of the rock formation being drilled through are used to predict the deformation and failure of the rock formation when subject to the forces associated with hydraulic fracture completion operations.
  • a rock formation interacting with multiple cutters on a drill bit undergoes multiple modes of deformation simultaneously including both elastic and plastic behavior in the same instant of time.
  • the deformation and failure of a rock formation is generally understood to involve (i) an initial loading and elastic deformation of the rock formation up to the point (ii) where the strain energy required to accommodate further deformation requires the onset of plastic deformation caused by activation of small dislocations in the rock matrix (iii) that localize into microcracks with dimensions on the order of micrometers that (iv) link together to cause through going shear fractures that undergo (v) shear displacements and ultimately (vi) the cataclysmic failure of the rock formation followed by (vii) unloading of the bit and (viii) the bit slipping along the new evacuated surface until which point (ix) the dislocation is arrested as the bit re-engages the rock formation at its cutting edge and repeat the process all over again.
  • the onset of the elastic to plastic transition usually occurs with the activation of small dislocations.
  • any one or more of the cutters may be engaged in any one or more of the behaviors that constitute the elastic deformation and plastic deformation or failure of the rock formation.
  • Most of the cutting behavior of a rock is plastic deformation and the elastic deformation is small and on the order of micrometers.
  • the cutting face is understood to be defined by the distribution of area where the cutters are in contact with the rock formation. At the location of each cutter along the cutting face, the rock formation is experiencing either elastic or plastic behavior or the rock formation there is undergoing a transition between the two. As the bit turns, multiple modes of rock deformation and failure in relation to the cutting action of the bit are superimposed on each other through constructive and destructive interferences and the state of deformation in relation to each and every cutter is seemingly unknowable.
  • the MWD records of the forces and the motion of the bit interacting with the rock formation have a chaotic, seemingly unpredictable character that makes it difficult to (i) not only separate the specific types behaviors describing the various components of rock deformation and rock failure, (ii) but also extract any meaningful information from the raw MWD records in relation to mechanical rock-strength properties of the rock formation.
  • the techniques discussed herein are able to extract mechanical properties of the rock formation, such as the elastic plastic transition, from this chaotic soup of data captured from the multiple cutter heads individually interacting with the rock formation and each generating their own signals.
  • the method further involves transforming the acoustical and force signals to obtain spectral estimates of the motions and forces on the bit (operation 410).
  • techniques set out herein provide meaningful descriptions of rock strength through the application and use of geophysical signal processing techniques to transform the MWD data into novel and non-obvious, force-displacement diagrams, which may be correlated with a position of the bit in relation to the well bore to characterize the rock formation along the well bore.
  • the force-displacement diagrams are analyzed to obtain a point at which the material deformation undergoes a transition from elastic and plastic behavior in response forces and motions of a drill bit when interacting on the rock formation.
  • the transition from elastic to plastic deformation usually occurs when the rock begins to deform along discrete failure surfaces and is commonly referred to as the Initial Yield Strength (IYS).
  • IYS Initial Yield Strength
  • innovative new techniques are used to obtain various different measurements of rock strength, along the well bore, using the forces on the bit and motion of the bit interacting with a rock formation at the point of elastic to plastic transition.
  • the method which may involve obtaining rock strength through the application and use of force-displacement diagrams, first involves collecting and storing vibration (acoustical) and force signals generated from the bit cutting the well bore into the formation (operation 400).
  • the acoustical and force signals may be locally stored in a data memory associated with the BHA generally or the MWD apparatus more specifically, or any other device positioned to capture and record the data. Further processing may be necessary to convert the force and acoustical signals into representations of forces on the bit and accelerations of the bit.
  • the forces on the bit of interest relate to TOB and the vibrations of the bit of interest relate to angular accelerations.
  • the method further involves transforming the data, which may be continuously sampled, high-rate MWD data, using geophysical signal processing techniques to (i) obtain the spectral estimates of the forces of the bit interacting on rock formation in connection with the drilling apparatus and drilling fluid system, and (ii) obtain the spectral estimates of the motions of the bit (displacements) in relation to the deformation and failure of the rock formation (operation 410).
  • the geophysical signal processing involves (i) obtaining a spectral representation of the forces acting on the rock formation in connection with the drilling apparatus, such as the TOB and WOB, and drilling fluid system such as the annular pressure and (ii) the displacement of the bit caused by the deformation and failure of the rock formation also as a function of frequency.
  • the spectral representations are generated for the TOB and angular displacement.
  • geophysical signal processing uses techniques related to spectral estimation, such as Fourier transform methods, to obtain the amplitude spectra of the forces and displacements from the MWD data.
  • MWD systems capable of storing high-frequency data can be used in connection with the method, where the data is retrieved from the memory of the MWD system when the drilling operations have been completed and then subjected to further processing and analysis.
  • the data may be stored in the time domain.
  • onboard digital signal processing (DSP) of the data in accordance with the techniques presented here enables the method to be implemented at higher sample rates than can be currently afforded owing to the limitations and constraints of recording in hostile downhole environments.
  • DSP digital signal processing
  • the MWD apparatus and the onboard DSP system are positioned near the bit to acquire the forces and motions of the bit interacting with a rock formation with less attenuation and noise as compared to a device where the MWD apparatus is positioned behind the mud motor or otherwise further from the drill.
  • the displacement of the bit as a function of frequency can be calculated by integrating the acceleration spectra twice in the frequency domain to obtain the displacement spectrum.
  • Fig. 5 illustrates a spectral estimate of the angular displacement spectra where the spectral estimate is obtained by processing an angular acceleration obtained by first sampling at a high rate either (i) a sensor sensitive to changes in the velocity or otherwise an accelerometer or (ii) a gyrometer or sensor sensitive to an angular velocity measurements, and then transforming the measurements into the frequency domain using Fast Fourier Transform (FFT) techniques.
  • FFT Fast Fourier Transform
  • Other spectral estimation techniques such as wavelet transforms can also provide a basis to transform the time series data into the frequency domain.
  • the angular displacement spectrum can be obtained by transforming the measurements of the gyrometer or angular velocity of the bit typically referred to in terms of revolutions per minute (RPM) into the frequency domain and then performing and integration of the angular velocity spectra to obtain the angular displacement spectra.
  • RPM revolutions per minute
  • the estimates of the spectral amplitudes used to form the data pairs can be further improved by obtaining multiple consecutive Fourier transforms such as by using a time window corresponding to one turn of the bit and then averaging the amplitude spectra for each of the time windows to create spectral ensembles.
  • multiple amplitude spectra describing the forces and displacements as a function of frequency are averaged for each frequency.
  • Increasing the number of amplitude spectra used to generate the spectral ensemble reduces the variance in the spectral estimation and improves the spectral estimate by averaging out any noise in the measurements.
  • the variance of the ensemble spectral estimate is expected to decrease by 9K/11 where K is the number of spectra used in the ensemble.
  • the number of spectra used in the ensemble depends on the resolution of the smallest degree of heterogeneity that is wished to be resolved. The more spectra used to generate the ensemble represent more drilling time and will average heterogeneity of the mechanical rock strength properties. In practice the number of spectral data windows used to calculate the average or ensemble spectral may depend on the resolution of the lowest frequency needed to adequately describe the low frequency behavior of the rock formation. [0076] Returning to Fig. 4, the spectral representations of the displacements and forces are paired according to frequency (operation 420). More particularly, a computing system, where the originally obtained drilling data is available and has been transformed, pairs the transformed force-displacement data by frequency to obtain a distribution, which may be a force- displacement distribution.
  • the force-displacement diagram is constructed by (i) decomposing the MWD data into the spectral domain and (ii) then forming the spectral pairs between the forces and the displacements. Analyzing the distribution of the spectral pairs with stress-strain constitutive relationships provides a method to identify the transition between elastic and plastic behavior of the rock formation experienced by the cutting action of the bit.
  • Force-displacement pairs are made for each frequency using the amplitude or an ensemble of the appropriate amplitude spectra.
  • force-displacement data pairs may be comprised of a frequency pair of TOB (f) and angular displacement (f) or a frequency- pair or WOB (f) and axial displacement.
  • Fig. 5 is a plot of the distribution of spectral pairs formed between the annular pressure and the axial displacement.
  • the spectral pairs are formed from an ensemble average annular pressure spectra and ensemble average of the axial displacement spectra. In this case, the ensemble averages are formed by averaging 38 spectra.
  • Each spectral estimate was obtained using a series of 512 sample windows lagged by 256 samples. On a log-log scale, the distribution of the spectral pairs forms a linear relationship suggesting that the distribution of spectral pairs between the annular pressure and axial displacement can be described using a power-law.
  • the distribution of force-displacement spectral pairs is found to follow a constitutive relationship used to describe the deformation and failure of a wide range of materials known as the Holloman-Ludwig equation.
  • This equation is conventionally used to parameterize stress-strain (force-displacement) curves in laboratory settings.
  • the force-displacement pairs are obtained as a function of time (not frequency) and the power law relationship describes the distribution of the force-displacement in time as the rock deformation experiment progresses.
  • a laboratory loading apparatus a sample of material is subject to loading using a hydraulic press with gauges to measure the load applied to a sample.
  • Fig. 6 is a linear cross-plot of spectral pairs formed between ensemble average of the downhole measurements of TOB and angular displacements, and is one example of spectral pair distributions taking advantage of TOB and angular displacements. The distribution of spectral pairs can be described by the power-law relationship shown by the curved line.
  • the force-displacement distribution may be analyzed using parametric relationships useful to describe the constitutive stress-strain behavior of a rock formation.
  • Holloman-Ludwig power-law relationships may be used to represent the constitutive stress- strain behavior of the rock formation during deformation and failure associated with the cutting action of the bit, obtain mechanical rock-strength properties at the transition from elastic to plastic deformation of the rock formation in relation to (a) the IYS, (b) the angle of internal friction, (c) uniaxial compressive strength and uniaxial tensile strength (d) the secant modulus and tangent modulus, (e) an offset yield modulus, (f) peak strength, (g) the modulus of toughness or the work under the force-displacement curve, (h) the modulus of resilience, (i) the critical strain energy release rate and (j) the stress-intensity factor, any of which and others may be considered "Mechanical Rock Properties".
  • a first star is taken to represent a point along the curvature representative of the transition between elastic and plastic deformation.
  • the value of TOB at the first star is the IYS, which is discussed in more detail below.
  • the tangent modulus is defined by the slope of the power-law curve at the first starred point, and the slope from the origin through the star is the secant modulus.
  • a line drawn from any angular displacement on the x-axis parallel to the secant modulus to the intersection of the power-law curve is the offset yield modulus. In engineering nomenclature, the offset yield modulus is taken as the point of 0.02 strain.
  • the distribution of the force-displacement pairs is analyzed using a linear power-law relationship of the form: n
  • the force is given is a function of frequency by the spectral estimate of the TOB and the displacement is given as a function of frequency is the spectral estimate of the angular displacement of the bit.
  • geophysical processing of the MWD data is used to transform the forces on the bit and the motion of the bit in an unexpected way into a Holloman-Ludwig equation used to describe the nature of the deformation and failure of a wide range of materials including rock.
  • the C coefficient is related to the material strength and the n exponent is often referred to as the strain hardening exponent.
  • Fig. 7 is a diagram illustrating a representation of power-law curves for various strength scalars and strain hardening exponents.
  • Most materials exhibit a hardening exponent between 0.25 and 0.5 when undergoing deformation that involves a transition from elastic-plastic behavior as shown in Fig. 5.
  • the spectral frequency pairs naturally distribute into a constitutive relation describing the deformation and failure of the rock formation in relation to the forces and motions on a drill bit interacting with a rock formation. While not being constrained by theory, it is believed that this is possible through the method described here, because the higher frequencies represent early times associated with onset of loading and small displacements associated with elastic deformation, while the lower frequency data pairs represent the forces and motions at later times and plastic deformation up until after rock failure.
  • the transition between these two types of constitutive behavior is often referred to as the elastic-plastic transition, and the captured data and processing of the same includes elastic deformation, plastic deformation and the transition there between.
  • the point of maximum curvature also determines the frequency in the data at which the elastic to plastic transition occurs. Note that the frequency of the data is not used to obtain the point of maximum curvature only that the distribution of the spectral pairs with respect to power law are used to determine this point and it is not obvious that (i) the spectral pairs obtained in this manner should follow the power law constitutive behavior observed in laboratory material deformation experiments (ii) it is only through a high-rate near-bit MWD recording apparatus that this relationship is possible, and (iii) that the IYS is determined as the value of the torque-on-bit (TOB) at the point of maximum curvature.
  • TOB torque-on-bit
  • the mechanical rock-strength property that relates to the transition between elastic and plastic (sometimes referred to incorrectly as the brittle-ductile transition) is often referred to as the Initial Yield Strength of the rock formation and occurs at the onset of critical fracture propagation.
  • the determination of the IYS from the constitutive stress-strain relationship provided in connection with a high rate MWD recording apparatus and/or DSP processing system according to the method provides innovative, new techniques to obtain mechanical rock properties.
  • the data set captured should cover sufficient rotation of the drill bit to capture data representative of the elastic, plastic and transitions between elastic and plastic behavior. The rotation may be less than one complete revolution of the bit.
  • an objective way to separate the elastic and plastic regions and obtain the elastic-plastic transformation of the force-displacement diagram would be to calculate the point of maximum curvature of the power-law relationship used to describe the distribution of the force-displacement data pairs.
  • the coefficients of the power-law or Holloman-Ludwig relationship can be obtained by (i) transforming the spectral data pairs using a log-log transformation and (ii) using linear regression techniques to find a line that describes the log-log transformed data pairs where the strain hardening coefficient is related to the slope of the line and the strength coefficients is related the intercept of the line.
  • the point of maximum curvature can be obtained by taking the derivative of the equation that describes the curvature of a line in relation to the power-law and setting the value of that derivative function to zero.
  • the point may also be determined by identifying the WOB value from the closest measured spectral pair to the computed maximum curvature.
  • the frequency that corresponds to the data pair at the point of maximum is used to select the value of the torque at the transition between the elastic and plastic deformation.
  • the value of this particular torque value obtained in this method is understood to be the IYS of the rock and the angular displacement is understood to be a critical displacement as evidenced by the forces on the bit and the motion of the bit while interacting with a rock formation.
  • the rock deformation behavior is more often ductile than brittle and this ductility results in a gradual flattening to the slope of the force-displacement curve with decreasing frequency or longer periods of the bit interacting with the rock.
  • This type of behavior lends itself naturally to a technique where the point of maximum curvature on the force-displacement curve can be used to determine the IYS.
  • the offset yield stress at a given turn of the bit or for example a 0.2% percentage of a revolution can also be used to approximate the IYS from the force- displacement diagram as constructed in the manner presented here.
  • the IYS is identified as the value of the TOB at the point of maximum curvature of the force displacement diagram based on a distribution of the spectra for TOB and angular displacements.
  • the point of maximum curvature as previously described can be obtained in one example by using regression techniques to find the power-law curve that best describe the distribution of spectral pairs.
  • the data pairs are obtained by the spectral estimation of the TOB and angular displacement measurements.
  • the frequency of which the point of maximum curvature occurs it is also possible to obtain the other values of the forces such as the WOB and/or the annular pressure value at the point of the elastic-plastic transformation or at the same frequency as the IYS.
  • obtaining the IYS using only the distribution of the TOB and angular displacement spectral pairs to obtain the point of transition from elastic to plastic deformation can provide estimates of the other forces and motions of the bit interacting with the rock formation at the elastic-plastic transition.
  • the values of IYS are obtained when the rock deformation transitions from elastic to plastic deformation as evidenced by the power-law distribution of the TOB and angular displacement spectral pairs, it is understood that in relation to the method that the IYS is related to the maximum principal stress at failure and the amplitude of the WOB or AP spectra at that the elastic-plastic transition would be understood to be related to the confining pressure exerted by the bit on the rock formation at failure.
  • the TOB value when normalized by the contract area of the bit would correspond to the principle stresses sigma one and the WOB or annular pressure value at the frequency of maximum curvature when normalized by the contact area of the bit would correspond to sigma three.
  • Values of sigma sub 1 and sigma sub 3 obtained by this method can be analyzed in terms of a rock failure model generally known Coulomb strength profile according to the following, while drilling a well.
  • the forces and motions from multiple turns of the bit are observed by the high-rate MWD recording apparatus while drilling a well.
  • the principal stresses at the transition between the elastic and plastic deformation can be determined according to the method.
  • the principal stresses, sigma sub 1 and sigma sub 3, obtained for each turn of the bit can be plotted on a diagram.
  • the distribution of data principal stresses defines a failure envelope known as the Coulomb strength envelop in terms of principal stresses.
  • Fig. 8 is a plot of sigma sub 1 versus sigma sub 3, providing a Coulomb strength criterion. Construction of a Coulomb strength criterion using MWD measurements, for each turn of the bit or each consecutive window of drilling data, involves (i) obtaining a distribution of spectral pairs and in particular where the spectral pairs are formed between the TOB and the angular-displacement spectra at each frequency, (ii) obtaining the point of maximum curvature at the point of transition between elastic and plastic deformation, (iii) obtaining the frequency at the point of maximum curvature,
  • Tan phi ( 1 + sin theta ) over ( 1 - sin theta )
  • the intercept of the principle stress failure envelope when the confining pressure is zero is the uniaxial compressive strength of the rock formation.
  • the uniaxial compressive strength of the rock formation Sigma sub c can be related to both the internal cohesion and angle of internal friction through:
  • Peak Yield Strength is not necessarily the same as the IYS, though in terms of the constitutive behavior in terms of the force-displacement curves peak yield strength can be approximated as an offset yield strength where the offset yield corresponds to the maximum deformation that can be sustained by the rock formation.
  • Another measure of rock strength is the ability of the rock to resist propagation of a fracture. In some instances, this is referred to as fracture toughness.
  • the ability of a rock to resist the cutting action of the bit can be obtained by further extending the method of constructing a force-displacement diagram in order to construct a compliance-length diagram as shown in Fig. 9B, which is based on the force displacement diagram depicted in Fig. 9A.
  • the compliance is the ratio of deformation to applied load. In a particular example, the deformation is the angular displacement of the bit and applied load is the TOB.
  • the compliance as a function of length can be constructed in connection with high-rate MWD recording apparatus.
  • a method to obtain fracture toughness, using a computing device, through the application and use of force-displacement and compliance-length diagrams involves transforming continuous high-rate MWD data using geophysical signal processing techniques to (i) obtain the spectral estimates of forces of the bit interacting on rock formation in connection with a drilling apparatus and drilling fluid system, (ii) obtain the spectral ensemble of the motions of the bit displacements in relation to the deformation and failure of the rock formation, (iii) pair force-displacement points by frequency for each frequency to obtain a force-displacement distribution, (iv) analyze the distribution of the force-displacement pairs using parametric relationships useful to describe the constitutive stress-strain behavior of a rock formation (v) and in particular use a power-law relationship in the form of the Holloman-Ludwig relationship to fit a curve to the force displacement pairs thereby representing the constitutive stress-strain behavior of the rock formation during deformation and failure associated with the cutting action of the bit, (vi) obtain the point of elastic-plastic deformation from
  • the critical strain energy release rate is related to the critical load or the IYS required to propagate a fracture of length given by the angular displacement at the point of transition between the elastic and plastic deformation.
  • the critical energy release rate G sub c can be related to the fracture toughness parameter K as: Where E is the Young's modulus of elasticity in the case of plane stress. Other modulus
  • the modulus of toughness can be calculated as the area under the force-displacement curve described by the distribution of all spectral pairs that correspond to all frequencies below the point of elastic plastic transition or the mode of deformation and failure that is governed by plastic deformation where the onset of plastic deformation can be determined from the point of maximum curvature and the modulus of resilience is the area under the force-displacement curve corresponding to elastic deformation, where the elastic limit can be determined as the area under the curve described by the distribution of all spectral pairs that correspond to frequencies higher than the frequency of maximum curvature or all frequencies higher than the point of elastic plastic transition.
  • the area under the curves can be determined by integration.
  • n In instances with the strain hardening coefficient, n, is greater than 0.5 then there is no point of maximum curvature for a power low-relationship.
  • two lines are fit to the distribution of spectral pairs. This is known as a bi-linear approximation.
  • the bilinear approximation is accomplished by fitting a line to the spectral pairs that are (i) below a critical strain which can be informed by a frequency of the spectral pairs and by fitting a line to the spectral pairs below a critical strain which can be informed by a certain frequency of the spectral pairs. More specifically, referring to Fig.
  • the graph represents a distribution of ensemble averages for TOB and Annular Pressure.
  • the low frequency data distribution represented by the rotated squares, generates a first line
  • the high frequency data distribution represented by squares, generates a second line.
  • the intersection of the first line and the second line, at the star, value of TOB at the intersection is taken as the IYS.
  • the distribution of low frequency spectral pairs corresponds to values below 45 Hz and the high frequencies distribution of spectral pairs corresponds to the spectral pairs formed at frequencies above 45 Hz.
  • the rock properties obtained by the method discussed herein may be used in various possible drilling and completing operations (operation 440).
  • a force- displacement curve for brittle rocks is typically linear over the entire range where catastrophic failure occurs before the onset of any appreciable plastic deformation.
  • the concept of brittle rock behavior can be expressed through the mechanical rock-strength properties in a variety of ways. In the simplest case the coefficients of the power-law fit to the force-displacement diagram provide a key diagnostic between brittle and ductile behavior where higher hardening coefficients corresponds to increasingly brittle behavior.
  • the coefficients of the Holloman Ludwig equation C and n are found to correspond to Vsand - Vlclay as shown in Fig. 11.
  • the coefficients of C and n are related to the IYS where the coefficients are used to determine the point of maximum curvature from a force- displacement diagram from which the IYS is obtained as the TOB at the point of maximum curvature.
  • the red curve in Fig. 1 1 shows the IYS plotted against the Vsand - Vclay relationship black. Where there is a high IYS the value of Vsand - Vclay increases and conversely a low value of IYS corresponds to low values of Vsand - Vclay.
  • the IYS can be used to describe the forces sufficient to initiate failure in a rock formation.
  • its calculation provides a high- resolution continuous strength profile along the length of the borehole that can be used to characterize geological heterogeneity in order to understand production variability. Rapid changes in strength may be indicative of the locations of weak rock formations where the rock formations may contain numerous fractures.
  • Systematic identification of strong and weak zones and brittle and ductile zones along the length of a lateral can be used to identify and group perforation locations in the stimulation and treatment of unconventional resources.
  • the IYS may be used to identify the locations within an unconventional reservoir likely to initiate fractures in relation to the emplacement of hydraulic fractures during a hydraulic fracture stimulation treatment operation.
  • an interval of the well is isolated using packers. These packers would ideally be set in zones of high yield strength to ensure that the inflation of the packers and the pressures used to hold it in place would not cause the rock formation to failure and provide a means for the fluids to bypass and escape from the interval or stage being pumped into.
  • the stage would consist of rock type with varying initial yield stress, where zones with low yield strength would be understood to provide preferential zones to target stimulation and treatment through the selection of perforations.
  • Zones of lower yield strength would be easier to break and preferred locations for perforations than zones with high IYS.
  • fluid pressures are expected to vary as the viscosity of the fluid is changed with the introduction of proppant.
  • the proppant is understood to embed itself in the newly formed fractures to prop or otherwise keep it open.
  • the fracture toughness can be understood in terms of the critical strain energy release rate or the critical stress intensity factor which can be related to the initial yield strength. As the fracture toughness increases, it requires greater pumping pressures to propagate a fracture. In similar plug and pert completion designs it would be desirable to have all the perforation locations grouped into rocks with similar toughness so that pressure drops during pumping operations would not cause preferential flow in the fluids into the hydraulic fractures initiated in rocks with lower fracture toughness. This would help promote uniform fracture geometries and uniform fracture heights within a stage along the length of a lateral.
  • FIG. 12 is a block diagram of a machine in the example form of a computer system 1200 within which instructions 1206 for causing the machine to perform any one or more of the methodologies discussed herein may be executed by one or more hardware processors 1202.
  • the machine operates as a standalone device or may be connected (e.g., networked) to other machines.
  • the machine may operate in the capacity of a server or a client machine in server-client network environment, or as a peer machine in a peer-to-peer (or distributed) network environment.
  • machine shall also be taken to include any collection of machines or controllers that individually or jointly execute a set (or multiple sets) of instructions 1206 to perform any one or more of the methodologies discussed herein, including that set out in Fig. 4 as well as the various methodologies discussed herein to obtain and compute, axial displacement, rotary displacement, axial and rotary accelerations, bit displacement, force measurements, spectral pairings, force displacement distributions, and various rock strength properties derived therefrom, as well as methods to use the rock strength properties in various possible ways including completions, fracture identification, packer placements, drill bit steering and others.
  • the example computing system 1200 may include one or more hardware processors 1202, one or more data storage devices 1204, one or more memory devices 1208, and/or one or more input/output devices 1210.
  • Each of these components may include one or more integrated circuits (ICs) (including, but not limited to, field-programmable gate arrays (FPGAs), application-specific ICs (ASICs), and so on), as well as more discrete components, such as transistors, resistors, capacitors, inductors, transformers, and the like.
  • ICs integrated circuits
  • FPGAs field-programmable gate arrays
  • ASICs application-specific ICs
  • Various ones of these components may communicate with one another by way of one or more communication buses, point-to-point communication paths, or other communication means not explicitly depicted in FIG. 12.
  • various peripheral controllers e.g., an input/output controller, a memory controller, a data storage device controller, a graphics processing unit (GPU), and so on
  • a power supply e.g., a fan, and a fan.
  • a ventilation fan e.g., a fan, and a fan.
  • an enclosure for encompassing the various components may be included in the example computing system 1200, but are not explicitly depicted in Fig. 12 or discussed further herein. Aspects of the computing system may be integrated in a measurement while drilling apparatus or otherwise included in a drilling tool.
  • the at least one hardware processor 1202 may include, for example, a central processing unit (CPU), a microprocessor, a microcontroller, and/or a digital signal processor (DSP). Further, one or more hardware processors 1202 may include one or more execution cores capable of executing instructions and performing operations in parallel with each other. In some instances, the hardware processor is within the bit sub, and others it is part of another separate processing system.
  • CPU central processing unit
  • DSP digital signal processor
  • the one or more data storage devices 1204 may include any non-volatile data storage device capable of storing the executable instructions 706 and/or other data generated or employed within the example computing system 1200.
  • the one or more data storage devices 1204 may also include an operating system (OS) that manages the various components of the example computing system 1200 and through which application programs or other software may be executed.
  • OS operating system
  • the executable instructions 1206 may include instructions of both application programs and the operating system.
  • Examples of the data storage devices 1204 may include, but are not limited to, magnetic disk drives, optical disk drives, solid state drives (SSDs), flash drives, and so on, and may include either or both removable data storage media (e.g., Compact Disc Read-Only Memory (CD-ROM), Digital Versatile Disc Read-Only Memory (DVD-ROM), magneto-optical disks, flash drives, and so on) and non-removable data storage media (e.g., internal magnetic hard disks, SSDs, and so on).
  • removable data storage media e.g., Compact Disc Read-Only Memory (CD-ROM), Digital Versatile Disc Read-Only Memory (DVD-ROM), magneto-optical disks, flash drives, and so on
  • non-removable data storage media e.g., internal magnetic hard disks, SSDs, and so on.
  • the one or more memory devices 1208 may include, in some examples, both volatile memory (such as, for example, dynamic random access memory (DRAM), static random access memory (SRAM), and so on), and non-volatile memory (e.g., read-only memory (ROM), flash memory, and the like).
  • a ROM may be utilized to store a basic input/output system (BIOS) to facilitate communication between an operating system and the various components of the example computing system 1200.
  • BIOS basic input/output system
  • DRAM and/or other rewritable memory devices may be employed to store portions of the executable instructions 1206, as well as data accessed via the executable instructions 1206, at least on a temporary basis.
  • one or more of the memory devices 1208 may be located within the same integrated circuits as the one or more hardware processors 1202 to facilitate more rapid access to the executable instructions 1206 and/or data stored therein.
  • the one or more data storage devices 1204 and/or the one or more memory devices 1208 may be referred to as one or more machine-readable media, which may include a single medium or multiple media that store the one or more executable instructions 1206 or data structures.
  • the term "machine-readable medium” shall also be taken to include any tangible medium that is capable of storing, encoding, or carrying instructions 1206 for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present invention, or that is capable of storing, encoding, or carrying data structures utilized by or associated with such instructions 1206.
  • the input/output devices 1210 may include one or more communication interface devices 1212, human input devices 1214, human output devices 1216, and environment transducer devices 1218.
  • the one or more communication interface devices 1212 may be configured to transmit and/or receive information between the example computing system 1200 and other machines or devices by way of one or more wired or wireless communication networks or connections.
  • the information may include data that is provided as input to, or generated as output from, the example computing device 1200, and/or may include at least a portion of the executable instructions 1206.
  • Examples of such networks or connections may include, but are not limited to, Universal Serial Bus (USB), Ethernet, Wi-Fi®, Bluetooth®, Near Field Communication (NFC), and so on.
  • One or more such communication interface devices 1210 may be utilized to communicate one or more other machines, either directly over a point- to-point communication path or over another communication means. Further, one or more wireless communication interface devices 1212, as well as one or more environment transducer devices 1218 described below, may employ an antenna for electromagnetic signal transmission and/or reception. In some examples, an antenna may be employed to receive Global Positioning System (GPS) data to facilitate determination of a location of the machine or another device.
  • GPS Global Positioning System
  • the one or more human input devices 1214 may convert a human-generated signal, such as, for example, human voice, physical movement, physical touch or pressure, and the like, into electrical signals as input data for the example computing system 1200.
  • the human input devices 1214 may include, for example, a keyboard, a mouse, a joystick, a camera, a microphone, a touch-sensitive display screen ("touchscreen”), a positional sensor, an orientation sensor, a gravitational sensor, an inertial sensor, an accelerometer, and/or the like.
  • the human output devices 716 may convert electrical signals into signals that may be sensed as output by a human, such as sound, light, and/or touch.
  • the human output devices 1216 may include, for example, a display monitor or touchscreen, a speaker, a tactile and/or haptic output device, and/or so on.
  • the one or more environment transducer devices 1218 may include a device that converts one form of energy or signal into another, such as from an electrical signal generated within the example computing system 1200 to another type of signal, and/or vice-versa. Further, the transducers 1218 may be incorporated within the computing system 700, as illustrated in FIG. 12, or may be coupled thereto in a wired or wireless manner.
  • one or more environment transducer devices 1218 may sense characteristics or aspects of an environment local to or remote from the example computing device 1200, such as, for example, light, sound, temperature, pressure, magnetic field, electric field, chemical properties, physical movement, orientation, acceleration, gravity, and so on. Further, in some embodiments, one or more environment transducer devices 1218 may generate signals to impose some effect on the environment either local to or remote from the example computing device 1200, such as, for example, physical movement of some object (e.g., a drill bit interacting with a formation), receiving or processing accelerometer data, strain gauge data, gyroscopic data, and the like.
  • some object e.g., a drill bit interacting with a formation
  • the spatial variations in the MWD data in in particular the MWD vibrations as obtained through a combination of one or more of the measurements are used to describe variations in mechanical rock properties where the variations and occurrences of the can be described as fractures based on the methods used here.
  • calculations made using signal processing techniques are used to generated force displacement distributions among other useful representations of spectral pairings, from which mechanical rock strength properties may be derived for a formation along a well bore and otherwise.
  • the method discloses how the spatial variations in one or more or a combination of the mechanical rock properties as can be obtained from the rock strength properties used to identify the nature and occurrence of fractures, fracture swarms and other mechanical discontinuities (boundaries) such as bedding planes and/or faults that offset or otherwise separate rock formations with different mechanical rock properties.
  • the present disclosure uses an innovative, new methodologies to determine the deformation of a rock formation by systematically relating forces acting on a rock formation in connection with the drill bit and drilling fluid system to the geophysical signal processing of drilling forces and motions generated by the fracturing of the rock in response to the cutting action of the bit to obtain a strain measurement.
  • This approach allows spectral representations of the force and motion data to be used to identify rock strength properties of a formation through which a drill bit drills a well bore.

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  • Life Sciences & Earth Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Geology (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geophysics (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Mining & Mineral Resources (AREA)
  • Acoustics & Sound (AREA)
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  • General Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
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  • Earth Drilling (AREA)

Abstract

La présente invention concerne l'obtention de données de force et de mouvement à partir d'un appareil de mesure pendant un forage ou similaire ayant des capteurs mesurant les forces et les mouvements du foret pendant le forage d'un puits. Les données de force et de mouvement sont transformées en combinaisons spectrales à partir desquelles des distributions, telles que la relation force-déplacement et la loi de puissance, sont générées. À partir des distributions, diverses propriétés de résistance de la roche le long du puits de forage peuvent être déduites et utilisées dans divers processus de complétion, comme le positionnement de perforations et le positionnement de garnitures d'étanchéité.
PCT/US2016/051381 2015-09-10 2016-09-12 Appareil et procédé d'utilisation de données de mesure pendant le forage pour générer des propriétés de résistance mécanique de la roche et cartographier des propriétés de résistance mécanique de la roche le long d'un trou de forage Ceased WO2017044978A1 (fr)

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CN110219700A (zh) * 2019-07-07 2019-09-10 于广东 一种识别煤矿巷道顶板岩石性质的方法及装置
CN112483076A (zh) * 2019-09-11 2021-03-12 中国石油化工股份有限公司 一种用于识别钻井施工复杂情况的系统
CN113283069A (zh) * 2021-05-18 2021-08-20 长江大学 一种钻井套管可靠性预测方法及系统
CN115807620A (zh) * 2023-02-06 2023-03-17 山东省地质矿产勘查开发局八〇一水文地质工程地质大队(山东省地矿工程勘察院) 一种钻探设备及钻探方法
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CN110219700A (zh) * 2019-07-07 2019-09-10 于广东 一种识别煤矿巷道顶板岩石性质的方法及装置
CN112483076A (zh) * 2019-09-11 2021-03-12 中国石油化工股份有限公司 一种用于识别钻井施工复杂情况的系统
CN112483076B (zh) * 2019-09-11 2024-04-02 中国石油化工股份有限公司 一种用于识别钻井施工复杂情况的系统
US12050297B2 (en) 2020-09-11 2024-07-30 Saudi Arabian Oil Company Method and system for determining energy-based brittleness
CN113283069A (zh) * 2021-05-18 2021-08-20 长江大学 一种钻井套管可靠性预测方法及系统
CN113283069B (zh) * 2021-05-18 2022-10-14 长江大学 一种钻井套管可靠性预测方法及系统
CN115807620A (zh) * 2023-02-06 2023-03-17 山东省地质矿产勘查开发局八〇一水文地质工程地质大队(山东省地矿工程勘察院) 一种钻探设备及钻探方法
CN119221902A (zh) * 2024-10-15 2024-12-31 北京德物钻探工程技术有限公司 一种用于钻探设备的自动化控制方法及系统

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