WO2025038779A1 - A method to determine wellbore placement based on fracture orientations and stress conditions - Google Patents

Abstract

Wellbore placement and design can have a strong impact on the recovery efficiency of energy from subsurface reservoirs. In reservoirs where much of the flow occurs through fractures, the interactions between state of stress and fracture deformation controls fluid flow behavior. The present invention relates to methods to determine wellbore engineering designs based on a combination of state of stress, preexisting fractures, and newly formed fractures.

Description

A METHOD TO DETERMINE WELLBORE PLACEMENT BASED ON FRACTURE ORIENTATIONS AND STRESS CONDITIONS

CLAIM OF PRIORITY

[0001] This international application claims the benefit of U.S. Provisional Patent Application Serial No. 63/532,834, filed on August 15, 2023, titled “A METHOD TO DETERMINE WELLBORE PLACEMENT BASED ON FRACTURE ORIENTATIONS AND STRESS CONDITIONS,” the contents of which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to determine the engineering design of one or more wellbores for applications in industries such as oil and gas, mining, and geothermal energy.

BACKGROUND

[0003] Wellbores are commonly used to inject or extract fluids in subsurface reservoirs. Typical wellbore designs include vertical, deviated, and horizontal geometries. Wellbore design and placement is critical to effectively implement reservoir engineering strategies to control fluid recovery. Engineering design decisions can be driven by a variety of factors. Vertical wellbores can be used to target several permeable strata in layered sedimentary formations that contain oil or gas. Five-spot patterns of injection and production wellbores are common in waterflood and enhanced oil recovery projects. Horizontal wellbores can be used to target a single formation and can be drilled in the orientation of the minimum principal stress to encourage hydraulic fractures to form transverse to the wellbore during hydraulic stimulation treatments. In hydrothermal reservoirs, wellbores can be drilled with some deviation from vertical to intersect permeable faults that have been identified previously from geological or geophysical methods. In low-permeability reservoirs, where much of the fluid flow occurs through fractures, it is particularly important to consider how stress and fractures interact to affect flow to and from wellbores. Techniques to improve the permeability of fractured reservoirs include hydraulic fracturing methods, where the goal is to create new tensile fractures, and hydroshearing methods, where the goal is to enhance the permeability of preexisting fractures through hydromechanical processes such as shear-slip-induced- dilation. The prior art has been focused on targeting either hydraulic fracturing or hydroshearing, neglecting how wellbores can be designed to take advantage of how stress interacts differently with distinct fracture sets. The prior art has typically only considered the stress-related effects of fractures that intersect the wellbore directly, as opposed to fractures that exist or are newly created at significant proximity away from the wellbore. [0004] The state of stress at a location requires knowledge of the magnitudes and orientations of the three principal stresses. A variety of techniques exist to obtain measurements, estimates, or constraints on the state of stress. These techniques include wireline density logs, leakoff tests, extended leakoff tests, minifrac tests, diagnostic fracture injection tests, analysis of wellbore breakouts, step-rate injection tests, analysis of drilling-induced tensile fractures, stress inversions based on earthquake focal mechanisms, stress relief methods based on strain cells, and core-based methods. Based on the relative magnitudes of the three principal stresses, the state of stress can be broadly characterized into normal faulting, strike-slip faulting, reverse faulting, or transitional faulting regimes.

[0005] A variety of techniques exist to evaluate and characterize the properties of preexisting faults or fractures in the subsurface. These techniques include seismic reflection surveys, wellbore acoustic image logs, wellbore resistivity image logs, wireline temperature/pressure/spinner logs, microseismic methods, fluid injection tests, methods based on earthquake focal mechanisms, and analog outcrop studies.

[0006] These prior techniques have many failings, including limited applicability based upon well type and problem, other adverse or unexpected results, cost, potential for lost production time, inoperability, limited success rates (both qualitative and quantitative). Thus, for these and other reasons they have not meet the long-standing need for enhanced and greater efficiency in the recovery of resources from the earth. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various examples discussed in the present document.

[0008] FIG. 1 A illustrates an example of a natural resource system, in accordance with examples described herein.

[0009] FIG. IB illustrates an example of multizone stimulation, in accordance with examples described herein.

[0010] FIGS. 2A-2C illustrate example techniques, in accordance with examples described herein.

[0011] FIG. 3 illustrates an example of a block diagram of a machine upon which any one or more of the techniques discussed herein may perform in accordance with examples described herein.

DETAILED DESCRIPTION

[0012] The systems and techniques described herein may be used for determining wellbore placement based on fracture orientations and stress conditions with applications in oil and gas, mining, and geothermal energy activities.

[0013] There has been a long-standing and unfulfilled need for enhanced methods to recover resources from the earth. In particular, there has been a long standing and unfulfilled need for greater predictability in planning, designing and operation wells and fields, and geothermal energy plants. The present inventions, among other things, solve these needs by providing the systems, materials, articles of manufacture, devices and processes taught, disclosed and claimed herein.

[0014] Accordingly, in an example, lateral offset between two horizontal wells is determined based on strike-slip faulting stress conditions.

[0015] In an example, vertical offset between two horizontal wells is determined based on normal faulting stress conditions. [0016] In an example, lateral and vertical offset between two horizontal wells is determined based on transitional normal faulting / strike-slip faulting stress conditions. [0017] Typically, in the production of natural resources from formations within the earth a well or borehole is drilled into the earth to the location where the natural resource is believed to be located. These natural resources may be a heat source for geothermal energy, a hydrocarbon reservoir, containing natural gas, crude oil and combinations of these; the natural resource may be fresh water; or it may be some other natural resource that is located within the ground.

[0018] These resource-containing formations may be a few hundred feet, a few thousand feet, or tens of thousands of feet below the surface of the earth, including under the floor of a body of water, e.g., below the sea floor. In addition to being at various depths within the earth, these formations may cover areas of differing sizes, shapes and volumes.

[0019] Unfortunately, and generally, when a well is drilled into these formations the natural resources rarely flow into and out of the formation, and into the well at rates, durations and amounts that are economically viable. This problem occurs for several reasons, some of which are well understood, others of which were not as well understood, some of which may not yet be known, and several of which, prior to the present inventions were incorrect. These problems can relate to the viscosity of the natural resource, the porosity of the formation, the geology of the formation, the formation pressures, and the perforations that place the production tubing in the well in fluid communication with the formation, to name a few.

[0020] Typically, and by way of general illustration, in drilling a well an initial borehole is made into the earth, e.g., the surface of land or seabed, and then subsequent and smaller diameter boreholes are drilled to extend the overall depth of the borehole. In this manner as the overall borehole gets deeper its diameter becomes smaller; resulting in what can be envisioned as a telescoping assembly of holes with the largest diameter hole being at the top of the borehole closest to the surface of the earth.

[0021] Typically, when completing a well, it is necessary to perform a perforation operation. In general, when a well has been drilled and casing, e.g., a metal pipe, is run to the prescribed depth, the casing is typically cemented in place by pumping cement down and into the annular space between the casing and the earth. (It is understood that many different down hole casing, open hole, and completion approaches may be used.) The casing, among other things, prevents the hole from collapsing and fluids from flowing between permeable zones in the annulus. Thus, this casing forms a structural support for the well and a barrier to the earth.

[0022] While important for the structural integrity of the well, the casing and cement present a problem when they are in the production zone. Thus, in addition to holding back the earth, they also prevent the resources or fluid from flowing into and out of the well and from being recovered. Additionally, the formation itself may have been damaged by the drilling process, e.g., by the pressure from the drilling mud, and this damaged area of the formation may form an additional barrier to the flow of resources. Similarly, in most situations where casing is not needed in the production area, e.g., open hole, the formation itself is generally tight, and more typically can be very tight, and thus, will not permit the flow of resources into and out of the well.

[0023] To address, in part, this problem of the flow of resources e.g., geothermal, hydrocarbons, etc. into the well being blocked by the casing, cement and the formation itself, openings, e.g., perforations, are made in the well in the area of the pay zone. Generally, a perforation is a small, about 1/4" to about 1" or 2" in diameter hole that extends through the casing, cement and damaged formation and goes into the formation. This hole creates a passage for the resource to flow from the formation into the well. In a typical well, a large number of these holes are made through the casing and into the formation in the pay zone.

[0024] As used herein, unless specified otherwise, the term "earth" should be given its broadest possible meaning, and includes, the ground, all natural materials, such as rocks, and artificial materials, such as concrete, that are or may be found in the ground, including without limitation rock layer formations, such as, granite, basalt, sandstone, dolomite, sand, salt, limestone, rhyolite, quartzite and shale rock.

[0025] As used herein, unless specified otherwise, the term "borehole" should be given it broadest possible meaning and includes any opening that is created in a material, a work piece, a surface, the earth, a structure (e.g., building, protected military installation, nuclear plant, offshore platform, or ship), or in a structure in the ground, (e.g., foundation, roadway, airstrip, cave or subterranean structure) that is substantially longer than it is wide, such as a well, a well bore, a well hole, a micro hole, slimhole, a perforation and other terms commonly used or known in the arts to define these types of narrow long passages. Wells would further include exploratory, production, abandoned, reentered, reworked, and injection wells. Although boreholes are generally oriented substantially vertically, they may also be oriented on an angle from vertical, to and including horizontal. Thus, using a vertical line, based upon a level as a reference point, a borehole can have orientations ranging from 0° i.e., vertical, to 90°, i.e., horizontal and greater than 90° e.g., such as a heel and toe and combinations of these such as for example "U" and "Y" shapes. Boreholes may further have segments or sections that have different orientations, they may have straight sections and arcuate sections and combinations thereof; and for example, may be of the shapes commonly found when directional drilling is employed. Thus, as used herein unless expressly provided otherwise, the "bottom" of a borehole, the "bottom surface" of the borehole and similar terms refer to the end of the borehole, i.e., that portion of the borehole furthest along the path of the borehole from the borehole's opening, the surface of the earth, or the borehole's beginning. The terms "side" and "wall" of a borehole should to be given their broadest possible meaning and include the longitudinal surfaces of the borehole, whether or not casing or a liner is present, as such, these terms would include the sides of an open borehole or the sides of the casing that has been positioned within a borehole. Boreholes may be made up of a single passage, multiple passages, connected passages and combinations thereof, in a situation where multiple boreholes are connected or interconnected each borehole would have a borehole bottom. Boreholes may be formed in the sea floor, under bodies of water, on land, in ice formations, or in other locations and settings.

[0026] Boreholes are generally formed and advanced by using mechanical drilling equipment having a rotating drilling tool, e.g., a bit. For example, and in general, when creating a borehole in the earth, a drilling bit is extending to and into the earth and rotated to create a hole in the earth. In general, to perform the drilling operation the bit must be forced against the material to be removed with a sufficient force to exceed the shear strength, compressive strength or combinations thereof, of that material. Thus, in conventional drilling activity mechanical forces exceeding these strengths of the rock or earth must be applied. The material that is cut from the earth is generally known as cuttings, e.g., waste, which may be chips of rock, dust, rock fibers and other types of materials and structures that may be created by the bit's interactions with the earth. These cuttings are typically removed from the borehole by the use of fluids, which fluids can be liquids, foams or gases, or other materials know to the art.

[0027] As used herein, unless specified otherwise, the term "advancing" a borehole should be given its broadest possible meaning and includes increasing the length of the borehole. Thus, by advancing a borehole, provided the orientation is not horizontal, e.g., less than 90° the depth of the borehole may also be increased. The true vertical depth ("TVD") of a borehole is the distance from the top or surface of the borehole to the depth at which the bottom of the borehole is located, measured along a straight vertical line. The measured depth ("MD") of a borehole is the distance as measured along the actual path of the borehole from the top or surface to the bottom. As used herein unless specified otherwise the term depth of a borehole will refer to MD. In general, a point of reference may be used for the top of the borehole, such as the rotary table, drill floor, well head or initial opening or surface of the structure in which the borehole is placed.

[0028] As used herein, unless specified otherwise, the terms "workover," "completion" and "workover and completion" and similar such terms should be given their broadest possible meanings and would include activities that place at or near the completion of drilling a well, activities that take place at or the near the commencement of production from the well, activities that take place on the well when the well is producing or operating well, activities that take place to reopen or reenter an abandoned or plugged well or branch of a well, and would also include for example, perforating, cementing, acidizing, fracturing, pressure testing, the removal of well debris, removal of plugs, insertion or replacement of production tubing, forming windows in casing to drill or complete lateral or branch wellbores, cutting and milling operations in general, insertion of screens, stimulating, cleaning, testing, analyzing and other such activities. These terms would further include applying heat, directed energy, preferably in the form of a high power laser beam to heat, melt, soften, activate, vaporize, disengage, desiccate and combinations and variations of these, materials in a well, or other structure, to remove, assist in their removal, cleanout, condition and combinations and variation of these, such materials.

[0029] Generally, the term "about" and the symbol

as used herein unless stated otherwise is meant to encompass a variance or range of ±10%, the experimental or instrument error associated with obtaining the stated value, and preferably the larger of these.

[0030] As used herein, unless specified otherwise, the terms "formation," "reservoir," "pay zone," and similar terms, are to be given their broadest possible meanings and would include all locations, areas, and geological features within the earth that contain, may contain, or are believed to contain, the desired resource, e.g., geothermal heat, hydrocarbons, etc.

[0031] As used herein, unless specified otherwise, the terms "field," "oil field" "geothermal field" and similar terms, are to be given their broadest possible meanings, and would include any area of land, sea floor, or water that is loosely or directly associated with a formation, and more particularly with a resource containing formation, thus, a field may have one or more exploratory and producing wells associated with it, a field may have one or more governmental body or private resource leases associated with it, and one or more field(s) may be directly associated with a resource containing formation.

[0032] As used herein, unless specified otherwise, the terms "conventional gas", "conventional oil", "conventional", "conventional production" and similar such terms are to be given their broadest possible meaning and include hydrocarbons, e.g., gas and oil, that are trapped in structures in the earth. Generally, in these conventional formations the hydrocarbons have migrated in permeable, or semi-permeable formations to a trap, or area where they are accumulated. Typically, in conventional formations a non-porous layer is above, or encompassing the area of accumulated hydrocarbons, in essence trapping the hydrocarbon accumulation. Conventional reservoirs have been historically the sources of the vast majority of hydrocarbons produced. As used herein, unless specified otherwise, the terms "unconventional gas", "unconventional oil", "unconventional", "unconventional production" and similar such terms are to be given their broadest possible meaning and includes hydrocarbons that are held in impermeable rock, and which have not migrated to traps or areas of accumulation.

[0033] As used herein, unless specified otherwise, the terms "hydrocarbon exploration and production", "exploration and production activities", "E&P", and "E&P activities", and similar such terms are to be given their broadest possible meaning, and include surveying, geological analysis, well planning, reservoir planning, reservoir management, drilling a well, workover and completion activities, hydrocarbon production, flowing of hydrocarbons from a well, collection of hydrocarbons, secondary and tertiary recovery from a well, the management of flowing hydrocarbons from a well, and any other upstream activities.

[0034] As used herein, unless specified otherwise, the terms "poroelastic", "poroelasticity", "poroelastic stresses", "poroelastic forces" and similar such terms should be given their broadest possible meanings and would include the forces, stresses and effects that are based upon the interaction between fluid flow and solid deformation within a porous medium. Typically, in evaluating poroelastic effects Darcy's law, which describes the relation between fluid motion and pressure within a porous medium, is coupled with the structural displacement of the porous matrix.

[0035] As used herein, unless specified otherwise, the terms "geothermal", "geothermal well", "geothermal resource", "geothermal energy" and similar such terms, should be given their broadest possible meaning and including wells, systems and operations that recover or utilize the heat energy that is contained within the earth. Such systems and operations would include enhanced geothermal well, engineered geothermal wells, binary cycle power plants, dry steam power plants, flash steam power plants, open looped systems, and closed loop systems.

[0036] The ability of, or ease with which, the natural resource can flow out of the formation and into the well or production tubing (into and out of, for example, in the case of engineered geothermal wells, and some advanced recovery methods for hydrocarbon wells) can generally be understood as the fluid communication between the well and the formation. As this fluid communication is increased several enhancements or benefits may be obtained: the volume or rate of flow (e.g., gallons per minute) can increase; the distance within the formation out from the well where the natural resources will flow into the well can be increase (e.g., the volume and area of the formation that can be drained by a single well is increased, and it will thus take less total wells to recover the resources from an entire field); the time period when the well is producing resources can be lengthened; the flow rate can be maintained at a higher rate for a longer period of time; and combinations of these and other efficiencies and benefits.

[0037] Fluid communication between the formation and the well can be increased by the use of hydraulic stimulation techniques. The first uses of hydraulic stimulation date back to the late 1940s and early 1950s. In general, hydraulic treatments involve forcing fluids down the well and into the formation, where the fluids enter the formation and crack, e.g., force the layers of rock to break apart or fracture. These fractures create channels or flow paths that may have cross sections of a few microns, to a few millimeters, to several millimeters in size, and potentially larger. The fractures may also extend out from the well in all directions for a few feet, several feet and tens of feet or further. It should be remembered that the longitudinal axis of the well in the reservoir may not be vertical: it may be on an angle (either slopping up or down) or it may be horizontal. The section of the well located within the reservoir, i.e., the section of the formation containing the natural resources, can be called the pay zone.

[0038] Although hydraulic stimulation has been used in geothermal wells, the use of proppants has generally not been used, and its use has been discredited by those in the art. [0039] Generally, in prior geothermal wells, even those that have been hydraulically stimulated, the performance and efficiency of the well, and geothermal power plant, has been less than desirable and suboptimal. This suboptimal performance has hindered the adoption of geothermal energy, making its replacement of hydrocarbon energy sources difficult. This suboptimal performance has reduced the ability of geothermal energy, which is a clean, carbon free energy source, from being widely adopted and replacing carbon emitting, e.g., coal, oil, natural gas, power generation sources.

[0040] This low efficiency or lack of performance in geothermal wells is also seen in the inefficiency of the recovery of oil and natural gasses from hydrocarbon wells, i.e., wells that are production hydrocarbons.

[0041] In general, the present invention is directed to industries such as oil and gas, mining, and geothermal energy that is directed to determine the engineering design of one or more wellbores used to inject or extract fluid based on how the interactions between stress and fractures affects subsurface fluid flow.

[0042] The present invention has application to oil and gas activities, such as waterflooding, steam flooding, steam assisted gravity drainage, and enhanced oil recovery. The present application has application to geothermal energy activities, where thermal energy is extracted from subsurface formations by circulating a working fluid, such as water or carbon dioxide, through the formation and recovering the heated fluid. [0043] The commercial viability of a geothermal power system depends on the long-term thermal sustainability of the reservoir. Thermal energy recovery efficiency is defined as the amount of heat recovered over the lifetime of a project relative to the initial amount of heat in place. Thermal breakthrough is defined as the time at which the temperature of the produced fluid has dropped by a threshold amount, which is controlled by the rate at which the thermal front propagates through the reservoir. The present invention relates to methods to design geothermal reservoir systems to control heat recovery efficiency and thermal breakthrough to improve the system's thermal sustainability.

[0044] It should be understood that while this Specification focuses on the recovery of geothermal resources and hydrocarbon resources from beneath the surface of the earth, its applications are not so limited. Thus, the present well systems, methods of drilling and completing wells, and well configurations may find applicability in the recovery of minerals and ores, and other resources within the ground.

[0045] In general, examples of the present well configurations have one, two, three, four or more wells. These wells can be vertical, vertical with horizontal section, vertical with sloped section, branched configurations, comb configurations, combinations and variations of these, and other configurations known to or later developed by the art and combinations and variations of these. These wells can have a TVD of from about 1,000 feet (ft) to about 20,000 ft, from about 2,000 ft to about 10,000 ft, about 2,000 ft to about 15,000 ft, and all values within these ranges, as well as larger and smaller values. These wells can have MD from about 1,000 feet (ft) to about 25,000 ft, from about 2,000 ft to about 10,000 ft, about 2,000 ft to about 15,000 ft, and all values within these ranges, as well as larger and smaller values. [0046] Flow between a well bore and a formation can be influenced by a range of factors that can depend on the type of well bore completion and the properties of the formation. Examples of the present inventions find application in one, many and preferably across numerous types, and in particular across the types that are found in a particular field. In this manner, in an example, a single type of the present solutions can find applicability in an entire field.

[0047] The present invention involves designing wellbore location, geometry, and extent based on how the interaction between stress and fractures affects subsurface fluid flow to improve injection or extraction of fluids. In some examples, the method can be used to isolate wellbores from communicating hydraulically from nearby wells. In other examples, the method can be used to encourage hydraulic communication from nearby wells.

[0048] The state of stress in the subsurface can vary with location and with time. The presence of fractures in subsurface formations, as well as their hydraulic, mechanical, and frictional characteristics, can depend on location, depth, stress state, lithology, tectonic history, and other geologic conditions. The interaction between stress and fractures can strongly influence the ability for fluids to flow in the subsurface, particularly in low- permeability geologic settings that include, for example, shale gas, shale oil, oil shale, and geothermal formations.

[0049] The location, geometry, and extent of wellbores can have a strong influence on the pattern of fluid flow through the subsurface because the wellbore controls the fluid entry and exit points as well as the pressure perturbations that drive flow. Therefore, in formations where a portion of the flow occurs through fractures, it is important to consider the role of stress fracture interactions in the wellbore design process.

[0050] Mixed-mechanism fracturing can be used to describe situations when natural fractures and new tensile fractures interact. As natural fractures that are oriented oblique to the principal stress are pressurized and slip, local stress concentrations are generated near the fracture tips. In regions of decreased compression, splay fractures are encouraged to initiate. If the fracture remains pressurized at pressure equal to or above the magnitude of the minimum principal stress, the splay fractures may propagate outside of the stress concentration zones. As splay fractures intersect with other natural fractures, they may terminate or propagate through. In either case, the natural fracture intersected by the splay may become pressurized, potentially triggering slip and causing another splay fracture to form off its tip. This complex interaction between natural fractures and newly formed tensile splay fractures can result in growth of the stimulated reservoir volume that depends on the properties of the natural fractures, the newly formed splay fractures, and the stress state.

[0051] The present invention presumes that the state of stress in the reservoir has been determined and the preexisting fractures have been characterized. Based on the measured, extrapolated, or expected distribution of preexisting fractures in the reservoir, fractures are grouped into sets that share similar characteristics; the most prevalent set or the set that contains the most fractures will be identified as the primary preexisting (natural) fracture set.

[0052] In one example of the invention relevant to strike-slip stress regimes and where a flow connection is desired, the critical orientation is calculated as the average of the predominant fracture set orientation and the orientation of the maximum horizontal stress; two or more horizontal wells are drilled in the orientation of the minimum horizontal stress, where the heel and toe of the wells are offset by a distance equal to the well spacing divided by the tangent of the critical orientation.

[0053] In one example relevant to normal faulting stress regimes and where a flow connection between one or more wells is desired, the critical orientation is effectively equal to the orientation of the vertical stress; two or more horizontal wells are drilled in the orientation of the minimum horizontal stress, and the wells are stacked directly above or below each other.

[0054] In one example relevant to transitional strike-slip/normal faulting stress regimes and where a flow connection between one or more wells is desired, two critical angles are calculated based on pure normal faulting and pure strike-slip regimes. The relative wellbore placement is offset vertically and horizontally based on the two critical orientations.

[0055] FIG. 1 A shows an example 100 of a natural resource system 102 in accordance with examples described herein. For example, the natural resource system 102 may pump fluid or gas from one or more geothermal energy sources. As illustrated in FIG. 1A, the natural resource system 102 can inject a fluid or a gas through a subsurface 104 via an injection well 108 to fractures 110a, 110b, 110c. The fractures 110a, 110b, 110c can be part of an enhanced geothermal system, which can be a man-made reservoir created where there is hot rock but insufficient or little natural permeability or fluid saturation. In some instances, fluid or gas can be injected through the injection well 108 to cause the fractures 110a, 110b, 110c to open or re-open to creating permeability. In some instances, fluid or gas can be injected through the injection well 108 as part of a flow through the fractures 110a, 110b, 110c. The flow through the fractures 110a, 110b, 110c can be enhanced through reservoir stimulation. Here, stimulation of multiple fractures, such as the fractures 110a, 110b, 110c, allows for an area to be stimulated in a series of smaller stimulations, minimizing local stress perturbations. The stimulation of multiple fractures provides for access to significantly more of the reservoir and provides additional flow opportunities, increasing overall flow rate. Thus, the present invention provides for various advantages over conventional approaches, which face challenges with respect to generating flow. For example, through multizone stimulation flow rates of 40-80 kg/s for commercial production may be achieved where stimulation of a single fracture may fail to achieve a flow greater than 25 kg/s.

As illustrated in FIG. 1 A, fluid or gas can flow from the fractures 110a, 110b, 110c to the natural resource system 102 through the subsurface 104 via a production well 106. The natural resource system 102 can extract energy (e.g., heat, thermal energy) from the fluid or the gas from the fractures 110a, 110b, 110c. As illustrated in FIG. 1A, the injection well 108 and the production well 106 can be horizontal wells. The injection well 108 and the production well 106 can have limited entry completion designs to maximize thermal sustainability. In general, limited entry completion designs refer to well stimulation techniques that effectively treat multiple zones simultaneously. Through limited entry completion designs, even stimulation and uniform flow can be achieved. Thus, the present invention provides for various advantages over conventional approaches, including improved productivity, increased pay zone, reduced seismicity risk, and lower induced thermal drawdown.

[0056] FIG. IB illustrates an example 150 of multizone stimulation in accordance with examples described herein. For example, multizone stimulation of zones 162a, 162b, 162c can be achieved through steps 152, 154, 156, 158, 16. As illustrated in step 152, a first flow rate 166 can be applied to an injection well 164 with access to zones 162a, 162b, 162c. The first flow rate 166 can apply a hydrostatic pressure that does not cause breaks in the zones 162a, 162b, 162c. As illustrated in step 154, a second flow rate 168 can be applied to the injection well 164. The second flow rate 168 can be larger than the first flow rate 166 and apply increased pressure with respect to the first flow rate 166. The second flow rate 168 can cause a break 176 in zone 162b. As illustrated in step 156, a third flow rate 170 can be applied to the injection well 164. The third flow rate 170 can be larger than the second flow rate 168 and apply increased pressure with respect to the second flow rate 168. The third flow rate 170 can cause a fracture 178 in zone 162b and a break 180 in zone 162c. As illustrated in step 158, a fourth flow rate 172 can be applied to the injection well 164. The fourth flow rate 172 can be larger than the third flow rate 170 and apply increased pressure with respect to the third flow rate 170. The fourth flow rate 172 can cause a fracture 184 in zone 162b and a fracture 186 in zone 162c. The fourth flow rate 172 can cause a break 182 in zone 162a. As illustrated in step 160, zones 162a, 162b, 162c are fractured with fractures 188, 190, 192 respectively. A fifth flow rate 174 can be applied to the injection well 164 to maintain flow through the fractures 188, 190, 192. The fifth flow rate 174 can apply, for example, a hydrostatic pressure. As illustrated in FIG. IB, multizone stimulation advantageously increases potential flow over conventional approaches. Furthermore, an area can be stimulated in a series of smaller stimulations, minimizing local stress perturbations.

[0057] FIG. 2A illustrates an example technique 200 for a wellbore engineering design for a strike-slip stress regime in accordance with examples described herein. The steps of the example technique 200 are illustrative, and the example technique 200 can be performed with additional or fewer steps. The steps of the example technique 200 can be performed in sequence, in parallel, or in various orders.

[0058] In a strike-slip stress regime, the maximum and minimum horizontal stresses can be the largest and smallest principal stresses, respectively. The vertical stress can be the intermediate stress. The maximum horizontal stress can be oriented perpendicular to the fault plane. The minimum horizontal stress can be oriented parallel to the fault plane. [0059] At step 202, the example technique 200 calculates a first orientation as an average of a fracture set orientation and a second orientation of a maximum horizontal stress. For example, a critical orientation for a wellbore can be calculated as an average of a predominant fracture set orientation and an orientation of a maximum horizontal stress. Here, the critical orientation can refer to the specific direction and angle for a wellbore relative to the in-situ stress state in the subsurface.

[0060] At step 204, the example technique 200 drills two or more horizontal wells in a third orientation of a minimum horizontal stress, wherein heels of the two or more horizontal wells and toes of the two or more horizontal wells are offset by a distance equal to a well spacing divided by a tangent of the first orientation.

[0061] FIG. 2B illustrates an example technique 230 for a wellbore engineering design for a normal faulting stress regime in accordance with examples described herein. The steps of the example technique 230 are illustrative, and the example technique 230 can be performed with additional or fewer steps. The steps of the example technique 230 can be performed in sequence, in parallel, or in various orders.

[0062] In a normal faulting stress regime, the vertical stress is the maximum principal stress. The horizontal stresses can be the minimum and the intermediate principal stresses.

[0063] At step 232, the example technique 230 calculates a first orientation as equal to a second orientation of a vertical stress. For example, a critical orientation can be calculated as effectively equal to an orientation of a vertical stress. Here, the critical orientation can refer to the specific direction and angle for a wellbore relative to the in- situ stress state in the subsurface.

[0064] At step 234, the example technique 230 drills two or more horizontal wells in a third orientation of a minimum horizontal stress, wherein the two or more horizontal wells are stacked above or below each other.

[0065] FIG. 2C illustrates an example technique 260 for a wellbore engineering design for a transitional strike-slip/normal faulting stress regime in accordance with examples described herein. The steps of the example technique 260 are illustrative, and the example technique 260 can be performed with additional or fewer steps. The steps of the example technique 260 can be performed in sequence, in parallel, or in various orders. [0066] In a transitional strike-slip/normal faulting stress regime, the vertical stress and the maximum horizontal stress can be close in magnitude. The minimum horizontal stress can be the smallest in magnitude. The transitional strike-slip/normal faulting stress regime shows characteristics of both the strike-slip faulting stress regime and the normal faulting stress regime.

[0067] At step 262, the example technique 260 calculates two angles based on a normal faulting regime and a strike-slip regime. For example, two critical angles can be calculated based on pure normal faulting and pure strike-slip regimes. Here, the two critical angles can be an azimuth angle (e.g., horizontal angle) for determining the horizontal orientation of a wellbore and a vertical angle for determining the vertical orientation of the wellbore.

[0068] At step 264, the example technique 260 places a wellbore offset vertically and horizontally based on the two angles.

[0069] FIG. 3 illustrates generally an example of a block diagram of a machine 300 upon which any one or more of the techniques (e.g., methodologies) discussed herein may perform in accordance with some examples. In alternative examples, the machine 300 may operate as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine 300 may operate in the capacity of a server machine, a client machine, or both in server-client network environments. In an example, the machine 300 may act as a peer machine in peer-to-peer (P2P) (or other distributed) network environment. The machine 300 may be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile telephone, a web appliance, a network router, switch or bridge, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.

[0070] Examples, as described herein, may include, or may operate on, logic or a number of components, modules, or mechanisms. Modules are tangible entities (e.g., hardware) capable of performing specified operations when operating. A module includes hardware. In an example, the hardware may be specifically configured to carry out a specific operation (e.g., hardwired). In an example, the hardware may include configurable execution units (e.g., transistors, circuits, etc.) and a computer readable medium containing instructions, where the instructions configure the execution units to carry out a specific operation when in operation. The configuring may occur under the direction of the execution units or a loading mechanism. Accordingly, the execution units are communicatively coupled to the computer readable medium when the device is operating. In this example, the execution units may be a member of more than one module. For example, under operation, the execution units may be configured by a first set of instructions to implement a first module at one point in time and reconfigured by a second set of instructions to implement a second module.

[0071] Machine (e.g., computer system) 300 may include a hardware processor 302 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 304 and a static memory 306, some or all of which may communicate with each other via an interlink (e.g., bus) 308. The machine 300 may further include a display unit 310, an alphanumeric input device 312 (e.g., a keyboard), and a user interface (UI) navigation device 314 (e.g., a mouse). In an example, the display unit 310, alphanumeric input device 312 and UI navigation device 314 may be a touch screen display. The machine 300 may additionally include a storage device (e.g., drive unit) 316, a signal generation device 318 (e.g., a speaker), a network interface device 320, and one or more sensors 321, such as a global positioning system (GPS) sensor, compass, accelerometer, or other sensor. The machine 300 may include an output controller 328, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).

[0072] The storage device 316 may include a machine readable medium 322 that is non- transitory on which is stored one or more sets of data structures or instructions 324 (e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions 324 may also reside, completely or at least partially, within the main memory 304, within static memory 306, or within the hardware processor 302 during execution thereof by the machine 300. In an example, one or any combination of the hardware processor 302, the main memory 304, the static memory 306, or the storage device 316 may constitute machine readable media.

[0073] While the machine readable medium 322 is illustrated as a single medium, the term “machine readable medium” may include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) configured to store the one or more instructions 324.

[0074] The term “machine readable medium” may include any medium that is capable of storing, encoding, or carrying instructions for execution by the machine 300 and that cause the machine 300 to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting machine-readable medium examples may include solid-state memories, and optical and magnetic media. Specific examples of machine-readable media may include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magnetooptical disks; and CD-ROM and DVD-ROM disks.

[0075] The instructions 324 may further be transmitted or received over a communications network 326 using a transmission medium via the network interface device 320 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks may include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), and wireless data networks (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as Wi-Fi®, IEEE 802.16 family of standards known as WiMax®), IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks, among others. In an example, the network interface device 320 may include one or more physical jacks (e.g., Ethernet, coaxial, or phonejacks) or one or more antennas to connect to the communications network 326. In an example, the network interface device 320 may include a plurality of antennas to wirelessly communicate using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. The term “transmission medium” shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the machine 300, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.

[0076] The various examples of systems, compositions, articles, uses, applications, equipment, methods, activities, and operations set forth in this specification may be used for various other fields and for various other activities, uses and examples. Additionally, these examples may be used with: existing systems, compositions, articles, uses, applications, equipment, methods, activities, and operations; may be used with systems, compositions, articles, uses, applications, equipment, methods, activities, and operations that may be developed in the future; and with such systems, compositions, articles, uses, applications, equipment, methods, activities, and operations that may be modified, inpart, based on the teachings of this specification. Further, the various examples set forth in this specification may be used with each other, in whole or in part, and in different and various combinations. Thus, for example, the configurations provided in the various examples of this specification may be used with each other; and the scope of protection afforded the present inventions should not be limited to a particular example, configuration or arrangement that is set forth in a particular example, or in an example in a particular figure.

[0077] The invention may be embodied in other forms than those specifically disclosed herein without departing from its spirit or essential characteristics. The described examples are to be considered in all respects only as illustrative and not restrictive.

Claims

CLAIMS What is claimed is:

1. A method for a wellbore engineering design for a strike-slip stress regime, the method comprising: calculating a first orientation as an average of a fracture set orientation and a second orientation of a maximum horizontal stress; and drilling two or more horizontal wells in a third orientation of a minimum horizontal stress, wherein heels of the two or more horizontal wells and toes of the two or more horizontal wells are offset by a distance equal to a well spacing divided by a tangent of the first orientation.

2. The method of claim 1, further comprising: recovering a natural resource from a borehole based on the wellbore engineering design.

3. The method of claim 1, further comprising: determining a lateral offset between the two or more horizontal wells based on strike-slip faulting stress conditions.

4. The method of claim 1, further comprising: isolating a first wellbore from communicating hydraulically from a second wellbore based on subsurface fluid flow affected by stress and fractures.

5. The method of claim 1, further comprising: encouraging hydraulic communication between a first wellbore and a second wellbore based on subsurface fluid flow affected by stress and fractures.

6. A method for a wellbore engineering design for a normal faulting stress regime, the method comprising: calculating a first orientation as equal to a second orientation of a vertical stress; and drilling two or more horizontal wells in a third orientation of a minimum horizontal stress, wherein the two or more horizontal wells are stacked above or below each other.

7. The method of claim 6, further comprising: recovering a natural resource from a borehole based on the wellbore engineering design.

8. The method of claim 6, further comprising: determining a vertical offset between the two or more horizontal wells based on normal faulting stress conditions.

9. The method of claim 6, further comprising: isolating a first wellbore from communicating hydraulically from a second wellbore based on subsurface fluid flow affected by stress and fractures.

10. The method of claim 6, further comprising: encouraging hydraulic communication between a first wellbore and a second wellbore based on subsurface fluid flow affected by stress and fractures.

11. A method for a wellbore engineering design for a transitional strike-slip/normal faulting stress regime, the method comprising: calculating two angles based on a normal faulting regime and a strike-slip regime; and placing a wellbore offset vertically and horizontally based on the two angles.

12. The method of claim 11, further comprising: recovering a natural resource from a borehole based on the wellbore engineering design.

13. The method of claim 11, further comprising: determining a vertical offset and a lateral offset between two horizontal wells based on transitional strike-slip/normal faulting stress conditions.

14. The method of claim 11, further comprising: isolating the wellbore from communicating hydraulically from another wellbore based on subsurface fluid flow affected by stress and fractures.

15. The method of claim 11, further comprising: encouraging hydraulic communication between the wellbore and another wellbore based on subsurface fluid flow affected by stress and fractures.