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WO2009032996A2 - Imagerie par résonance sismique - Google Patents

Imagerie par résonance sismique Download PDF

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Publication number
WO2009032996A2
WO2009032996A2 PCT/US2008/075362 US2008075362W WO2009032996A2 WO 2009032996 A2 WO2009032996 A2 WO 2009032996A2 US 2008075362 W US2008075362 W US 2008075362W WO 2009032996 A2 WO2009032996 A2 WO 2009032996A2
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WO
WIPO (PCT)
Prior art keywords
seismic
waves
resonant
sensors
location
Prior art date
Application number
PCT/US2008/075362
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English (en)
Other versions
WO2009032996A3 (fr
Inventor
Valeri A. Korneev
Original Assignee
The Regents Of The University Of California
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Regents Of The University Of California filed Critical The Regents Of The University Of California
Publication of WO2009032996A2 publication Critical patent/WO2009032996A2/fr
Publication of WO2009032996A3 publication Critical patent/WO2009032996A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/10—Aspects of acoustic signal generation or detection
    • G01V2210/12—Signal generation
    • G01V2210/123—Passive source, e.g. microseismics
    • 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
    • G01V2210/67—Wave propagation modeling
    • G01V2210/679—Reverse-time modeling or coalescence modelling, i.e. starting from receivers

Definitions

  • the present invention relates to seismic imaging, and more particularly to imaging subsurface objects using resonant seismic emissions.
  • Imaging of shallow subsurface heterogeneities has a variety of important applications. Those applications include detection and location of different kinds of local inhomogeneities such as tunnels, pipes, buried containers, ground-filled excavations, unexploded ordinances (UXO), fluid-filled fractures, mine shafts, and the like. Being high contrast scatterers, these objects are capable of generating strong scattered waves where primary PP, PS, and SS waves carry away most of the energy which was brought by incident waves. This conclusion follows from numerical and analytical results obtained from canonical solutions for spheres and cylinders.
  • the primary scattered waves have the same order of magnitude as incident waves. While low-contrast objects (i.e. objects having an impedance relatively close to that of the embedding elastic medium [where impedance is defined as the product of velocity times density]) effectively radiate most of the energy soon after impact, high-contrast objects (i.e. objects having an impedance significantly different from that of the embedding medium) trap some fraction of incident wave energy in the form of durable circumferential waves, which propagate, rotating along the interface between the object and the embedding medium. The seismic energy from these waves is slowly released, long after the initial impact.
  • low-contrast objects i.e. objects having an impedance relatively close to that of the embedding elastic medium [where impedance is defined as the product of velocity times density]
  • high-contrast objects i.e. objects having an impedance significantly different from that of the embedding medium
  • This trapped energy occurs primarily as a resonant emission of shear waves and can be detected as sharp resonant peaks in amplitude spectrums of single records.
  • These circumferential waves include surface Rayleigh-type waves (propagating mostly in the embedding medium), Stoneley waves (propagating mostly in the fluid, if present), and Frantz waves (body waves trapped in the object because of its curvature). Strong impedance contrast ensures small radiation loss for circumferential waves, which slowly decay in amplitude while rotating inside and around the object.
  • Another class of wave-trapping objects are localized low- velocity zones, which can have a natural low velocity (like a part of a coal seam) or which result from some impact such as a filled excavation pit of loosened rock/soil which have smaller elastic modules compared with the embedding medium.
  • Still another class of wave trapping objects includes fluid-filled fractures in rocks. Stoneley slow waves can have very low velocities in such fractures which makes resonances possible even for seismic frequencies (with frequencies less than 100 Hz).
  • the present invention provides a method for detecting the subsurface presence of such features as have been described above, in situations where the transmission velocities between the feature and the embedding medium are sufficiently different such that the embedded feature generates resonant waves which can be detected.
  • a plurality of seismic detectors are placed over an area of surface to be examined for the presence of underground features.
  • the sensors in one embodiment can be disposed along a line when the orientation of the object is known or arrayed as an ordered two to three dimensional grid. In another embodiment they may be randomly dispersed over a generalized area.
  • a seismic source is provided for generating a seismic impulse wave.
  • the source may be a simple hammer and plate combination, an automatic hammer, an explosive charge, a motor vehicle or the like. Natural seismic noise, caused by a variety of possible unknown sources can similarly be used provided they generate over a long enough time for these waves to be recorded.
  • Each sensor is linked either by cable or wirelessly to a monitor/computer for recording/storing and displaying of the processed output of the sensors.
  • the seismic source is activated, generating an impulse wave which travels in all directions through the ground.
  • the seismic response at each of the sensors is recorded, and the initial response from the high energy direct incident waves ignored (though this information can be used for S- wave velocity (V s ) estimates).
  • V s S- wave velocity
  • This is done by recording the initial response of two sensors of known distance from the source, and calculating the velocity of the S- wave by dividing the difference of those distances by the travel time difference recorded at those sensors.).
  • the gain of the monitoring device is turned up so that any late arriving resonant wave responses can be detected.
  • the location of the buried feature can then be determined. This is done through a series of shot gathers taken either at predetermined times when using an active controlled source, or at randomly chosen times when using ambient noise waves.
  • the actuation of a seismic source is known as a shot
  • the set of recorded responses at various sensors/receivers is referred to as a shot gather.
  • Simultaneous detection of the noise waves by a set of sensors is also referred as a shot and all the records made after such detection also compose a shot gather.
  • several shot gathers are achieved, in one embodiment re-positioning the plurality of sensors until, based upon the observed responses, it is determined that several sensors/receivers record the same resonance emission of the buried feature. This determination is made by comparison of the responses of adjacent sensors, in the manner more fully explained below in the Detailed Description and the Example. In this manner the approximate lateral position of the subject feature is established.
  • the theoretical data for each potential feature/object position can be computed (assuming the presence of that feature generates monochromatic waves at the detected resonant frequency) and compared to the field recorded data.
  • the theoretical location that provides the best fit between computed and recorded data indicates the true location of the object.
  • the accurate location of the buried feature may be readily calculated. This is done, using a computer, by first computing a model of the subsurface system response, based upon the evaluated shear- wave propagation velocity V 8 of the embedding elastic medium, modeling expected sensor responses for different locations (as is later explained in the Detailed Description); and then matching the calculated responses to those measured in the field.
  • Figure 1 is a flow diagram of various steps utilized according to a method of this invention for identifying the location of embedded feature.
  • Figure 2 is a schematic illustration of a field arrangement for the detection of resonant emissions.
  • Controlled sources may be underground and/or at the surface.
  • Figure 3 shows the shot gathers in the Example for field data recorded above the buried barrel, the direct S-waves visible.
  • Figure 4 shows the amplitude spectrum of automatic gain controlled late arrivals with a sharp peak at 78 Hz.
  • Figure 5 shows the shot gathers after automatic gain control (AGC) and band-pass filtering around 78 Hz, showing hyperbolic signatures of a secondary source.
  • AGC automatic gain control
  • Figure 6 shows the image of a buried barrel.
  • Figure 7 shows the partial scattering cross-section for a fluid-filled sphere for P- incident waves (a) and for S- incident waves (b).
  • Figure 8 shows single shot gather for synthetic field computed for a fluid-filled tunnel model.
  • Figure 9 is a snap-shot showing propagation of circumferential waves along the object.
  • Figure 10 shows amplitude spectrum of automatic gain controlled late arrivals with a sharp peak at 53 Hz.
  • Figure 11 shows late arrivals of modeled data after AGC (automatic gain control) and band pass filtering around the resonance frequency, having repeating quasi-hyperbolic patterns similar to one observed for field data (Figure 5).
  • Figure 12 shows the migrated image of the modeled object is similar to one obtained from field data ( Figure 6).
  • Figure 13 shows theoretical resonances for a 1 mm thick, 4 m long fracture filled with water.
  • Figure 14 shows theoretical resonances for a 1 mm thick, 4 m long fracture filled with oil.
  • Figure 15 shows the partial scattering cross-section for a fluid-filled sphere for S- incident waves for extended frequency band.
  • the intent of a field investigation using the methods described herein is to determine the presence or absence of a buried feature such as a pipe, tunnel or fluid-filled crack within a selected area of examination. And if present, to the extent possible, determine both the location of the feature and its shape. Broadly, this is done by generating a seismic wave in step 104 initiated using the provided seismic source or ambient seismic noise (step 100), and analyzing the information in step 108 detected in step 106 by sensors deployed in step 102.
  • the seismic source may be literally anything that can generate a seismic wave.
  • the source can consist of no more than a metal plate laid upon the ground, and a sledge hammer which when brought into quick contact with the plate, generates a pulse.
  • the source can be a piezeo-electric device which when energized can create a propagating seismic wave, an automatic hammer, pile driver, a low level explosive device, vibrator truck, rifle and the like. The knowledge about the location of the source is not necessary. The nature of the source is not critical.
  • T be m is the source activation time
  • T be m is an arbitrarily chosen start time of recording.
  • exact knowledge about T b is not important.
  • the employed sensors can be any readily available commercial device, including vertical geophones, capable of sensing both reflected primary waves and the weaker resonant waves generated by the buried resonant object, or feature. These sensors by be physically linked, connected by electric cables to carry their detected responses to the seismic monitor.
  • the sensors are provide as a linked chain, each sensor spaced about a meter from its adjacent sensor and its connecting wire bundled with those of the other sensors of the linked line.
  • the number of linked sensors, and thus the length of the line itself are not critical. The longer the line however, the greater the area examined, and accordingly the more information gathered in each shot gather.
  • the sensors may be placed individually, linked to the seismic monitor by wireless transmitters associated with each sensor. In this embodiment, the sensors may more easily be placed, such as the intersection of multiple non-parallel grid lines or in an arbitrary grid configuration, to one that is random over a given surface area, to thus provide three-dimensional coverage.
  • the seismic recording station employed provides simultaneous recording for all sensors.
  • Such recording station devices can be readily obtained commercially, and the exact type or brand of such recording system is not critical to this invention so long as it is capable of performing the functions above described.
  • the computer used to perform the calculations can likewise be a standard item, programmed to perform the calculations required as described herein.
  • the recording station should also be capable of copying data into computer memory, which is the common case.
  • a number of sensors are laid out over the area to be investigated, connected to the seismic recording station (either, by wire or wirelessly), and the seismic source repeatedly positioned in the field.
  • the receivers can be left in the field with a stationary recording system where the "source” may consist of ambient noise, the system deployed for the long term monitoring of an area of interest, where the post deployment detection of stable resonant peaks indicates the appearance of new feature.
  • a multiplicity of shot gathers are conducted, and the responses recorded.
  • the source and its associated line of sensors can be moved incrementally, both longitudinally and transversely.
  • the source and line of sensors are moved after each single shot gather.
  • the source can be moved from one grid line to the next in the course of the investigation.
  • separate seismic sources can be positioned at an end of each of the grid lines.
  • the detection of resonant peaks indicates a presence of an object of potential interest in the vicinity of sensor installation.
  • For detection one can compute the complex spectrums -?,(/) of the records U 1 (Y) using an inverse Fourier transform. Spectrums s t (/) are the functions of frequency / .
  • Objects are identified by the presence of sharp frequency peaks of amplitude spectra J,(/)
  • the next step is to determine the object's exact position. This is done at step 112 by analysis of the seismic response patterns. Assuming that the seismic propagation velocity of the ground immediately around the buried object is fairly constant, it follows that the sensor directly above the buried object will be first to detect the resonant waves emitted by the object, the time of receipt of the same emitted wave by an adjacent sensor taking longer due to the greater distance of the object from the sensor.
  • a time of arrival plot manifests as a hyperbolic curve, with the trough or inflection point of the curve coinciding with the sensor positioned closest to the buried object.
  • the plot will manifest as a symmetrical hyperbolic curve with its inflection point at the center of the receiver's line as illustrated for the Example, Figure 5, shot position 51.
  • Points M k which provide a best fit of the modeled field data W lk (/ re4 ) with transformed recorded data S 1 (f ⁇ es ) localize the object. For example, localization can be done using maximums of imaging function
  • a passive system where ambient seismic waves are relied upon to provide the source of seismic excitation.
  • a line or grid of sensors can be laid out, either above or below the ground surface. These sensors in turn can be linked to a seismic monitor by wire or wirelessly. Any number of ambient sources can generate a seismic wave that can cause a buried feature of impedance contrast to resonate and the resonant wave detected.
  • Such seismic source could include a low intensity earthquake, a movement of vehicles in the vicinity of sensor grid, or active excavation underground in the area of the sensors, running machinery and vehicles, wind, walking people.
  • FIG. 2 Shown are two underground features, with resonant waves emanating from each in response to an incident seismic wave.
  • the array of source and receivers that is, sensors
  • the array of source and receivers shown at ground level is illustrative of the first embodiment described above.
  • a borehole can be drilled, and a controlled source and a line of receivers placed into the hole. Shot gathers are taken by activating the source.
  • This modality can be used in combination with surface examination, in that once the lateral location of a feature is determined, the borehole can be drilled, the controlled source and sensors placed. With these additional readings, the depth of an object can be accurately fixed using the same methodologies as described above.
  • the experiment was conducted to generate a test data set using the methods of this invention for subsurface object detection and imaging.
  • the soil comprised compacted, consolidated sand with a measured P- velocity of 500 m/s and S- velocity of 240 m/s.
  • the test object was a water-filled barrel 60 cm in diameter and 120 cm long. Some air bubbles were left inside the barrel before it was sealed.
  • the barrel was placed at a depth of 5-6 meter in a specially excavated pit which was then back filled with soil.
  • An in-line channel of 24 vertical geophones, spaced 0.5 m one from the other was used for every ground shot made by a sledge-hummer. The shot point was positioned at the first receiver of each line.
  • the field data is modeled with 2D finite-difference seismic wave propagation program using a 4Ox 12.5 m model with 0.05 m grid spacing. Background Vp and Vs velocities have the same values as in the field experiment.
  • the local object was modeled as a 1 m x 0.7 m rectangular containing liquid with 70 m/s velocity and 1 g/cm 3 density.
  • Ten shot gathers were computed using 3 m spacing for sources.
  • the surface receiver line was the same for all shots and had 61 sensors separated by 0.5 m.
  • a single shot gather for the shot #3 is shown on Figure 8, where similar to the field case, primary scattered waves rapidly decay after 0.2 seconds. The recording length was 1 second.
  • a snapshot image at 0.3 seconds shows that at a later time the propagating field is predominantly comprised of shear waves caused by circumferential waves in the object.
  • Spectral content of the late parts of the records shows the presence of a sharp peak at 53 Hz in all traces ( Figure 10).
  • AU the data were automatic gain controlled and band-pass filtered around the peak frequency leading to the images like that shown in the Figure 11 and revealing a quasi hyperbolic phase arrivals similar to the one based on real data (Figure 5).
  • the methods of this invention capitalize on the observation that high-contrast subsurface heterogeneities trap seismic energy and are capable of releasing that energy long after the recordings of primary scattered waves.
  • This trapped energy primarily consists of circumferential waves propagating along the perimeter of the object and radiate into the surrounding medium as slowly decaying body waves. The circumferential waves propagate in all directions around the object which potentially can create discontinuous travel time curves. Most of the energy irradiated back to the embedding medium is carried by shear waves.
  • This simple data pattern makes it attractive candidate for inversion techniques based on back-propagation principles where recorded traces are used as sources in reverse time, and a suitable program used to "collapse" the waves back to a point of resonant source origin. It is expected that multiple objects can be detected and imaged using separate resonant frequencies. It is clear that exact timing of the source excitation is not important and trapped energy radiation can possibly be observed in the presence of the background noise, leading to cost effective object detection techniques.

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  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)

Abstract

Le procédé décrit consiste d'abord à localiser des objets enfouis tels que des tuyaux, des fissures remplies de liquides, des munitions explosives non explosées (UXO), des tunnels et similaires, puis à en déterminer la position. Selon ce procédé, les réponses sismiques sont analysées afin de détecter la présence d'ondes secondaires retardataires générées par des objets résonants en réponse à un tir d'onde sismique. Après détection de telles ondes résonantes, qui indiquent la présence d'un objet enfoui, l'emplacement de l'objet peut être trouvé par la mise en correspondance d'un champ calculé et d'enregistrements de données. Un objet résonant enfoui peut être excité à distance par illumination d'une source active distante.
PCT/US2008/075362 2007-09-06 2008-09-05 Imagerie par résonance sismique WO2009032996A2 (fr)

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US60/970,471 2007-09-06

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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2473607A (en) * 2009-09-14 2011-03-23 Hannes Zuercher Locating hydrocarbons passively by observing a porous oil and gas saturated system giving off its characteristic resonance response to ambient background nois
GB2476788A (en) * 2009-09-14 2011-07-13 Hannes Zuercher Locating fluid saturated zones by applying low frequency excitation and analysing a characteristic resonant response
US8164983B2 (en) 2009-03-06 2012-04-24 Johnson David A Fish finder
US8253417B2 (en) 2008-04-11 2012-08-28 Baker Hughes Incorporated Electrolocation apparatus and methods for mapping from a subterranean well
WO2013057484A3 (fr) * 2011-10-17 2014-03-06 Seg Squared Limited Collecte et traitement de données d'étude sismique
US8797037B2 (en) 2008-04-11 2014-08-05 Baker Hughes Incorporated Apparatus and methods for providing information about one or more subterranean feature
US8841914B2 (en) 2008-04-11 2014-09-23 Baker Hughes Incorporated Electrolocation apparatus and methods for providing information about one or more subterranean feature
ES2524736A1 (es) * 2014-02-21 2014-12-11 Universidad Politécnica De Cartagena Sistema combinado para la adquisición de las velocidades de ondas de compresión y de ondas Rayleigh y para la generación de secciones Vs, Vp y de parámetros geomecánicos del subsuelo
US9097097B2 (en) 2013-03-20 2015-08-04 Baker Hughes Incorporated Method of determination of fracture extent
US9200507B2 (en) 2013-01-18 2015-12-01 Baker Hughes Incorporated Determining fracture length via resonance
US10087735B2 (en) 2010-02-20 2018-10-02 Baker Hughes, A Ge Company, Llc Apparatus and methods for providing information about one or more subterranean variables

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6236943B1 (en) * 1999-02-09 2001-05-22 Union Oil Company Of California Hybrid reservoir characterization method
AU2002230389A1 (en) * 2000-06-14 2002-04-29 Vermeer Manufacturing Company Utility mapping and data distribution system and method
US7254999B2 (en) * 2003-03-14 2007-08-14 Weatherford/Lamb, Inc. Permanently installed in-well fiber optic accelerometer-based seismic sensing apparatus and associated method
FR2868167B1 (fr) * 2004-03-23 2006-05-19 Inst Francais Du Petrole Methode pour imager dans une formation souterraine des interfaces geologiques fortement pentees, donnant lieu a des reflexions prismatiques

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8253417B2 (en) 2008-04-11 2012-08-28 Baker Hughes Incorporated Electrolocation apparatus and methods for mapping from a subterranean well
US8797037B2 (en) 2008-04-11 2014-08-05 Baker Hughes Incorporated Apparatus and methods for providing information about one or more subterranean feature
US8841914B2 (en) 2008-04-11 2014-09-23 Baker Hughes Incorporated Electrolocation apparatus and methods for providing information about one or more subterranean feature
US8164983B2 (en) 2009-03-06 2012-04-24 Johnson David A Fish finder
GB2476788A (en) * 2009-09-14 2011-07-13 Hannes Zuercher Locating fluid saturated zones by applying low frequency excitation and analysing a characteristic resonant response
GB2473607B (en) * 2009-09-14 2011-12-14 Hannes Zuercher Locate oil or gas passively by observing a porous oil and gas saturated system giving off its characteristic resonance response to ambient background noise
GB2476788B (en) * 2009-09-14 2012-01-04 Hannes Zuercher Locating fluid saturated zones in the earth by applying low frequency excitation and analysing the characteristic resonance response
GB2473607A (en) * 2009-09-14 2011-03-23 Hannes Zuercher Locating hydrocarbons passively by observing a porous oil and gas saturated system giving off its characteristic resonance response to ambient background nois
US10087735B2 (en) 2010-02-20 2018-10-02 Baker Hughes, A Ge Company, Llc Apparatus and methods for providing information about one or more subterranean variables
WO2013057484A3 (fr) * 2011-10-17 2014-03-06 Seg Squared Limited Collecte et traitement de données d'étude sismique
US9200507B2 (en) 2013-01-18 2015-12-01 Baker Hughes Incorporated Determining fracture length via resonance
US9097097B2 (en) 2013-03-20 2015-08-04 Baker Hughes Incorporated Method of determination of fracture extent
ES2524736A1 (es) * 2014-02-21 2014-12-11 Universidad Politécnica De Cartagena Sistema combinado para la adquisición de las velocidades de ondas de compresión y de ondas Rayleigh y para la generación de secciones Vs, Vp y de parámetros geomecánicos del subsuelo

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