Methods and systems for detecting fracture zones in hot dry rock hydraulic fracturing, determining drilling trajectories.

Abstract

This disclosure relates to a method for detecting fracture zones in hot dry rock, a method for determining drilling trajectories, and a system. The detection method includes: determining the fracture length and extension direction of the fracture zone using a surface direct current potential method; determining the top surface of the fracture zone using a variable offset vertical seismic profiling method; determining the three-dimensional dip angle of the fracture surface relative to the fracture initiation point based on the extension direction and the fracture initiation point; and determining the spatial distribution range of the fracture zone based on the top surface, the three-dimensional dip angle, and the fracture length. The technical solution provided by this disclosure can combine the surface direct current potential method and the variable offset vertical seismic profiling method to achieve full-element spatial detection of fracture zones, thereby providing data support for the trajectory design of the second directional well in a hot dry rock geothermal resource development well group, and facilitating the establishment of effective artificial heat exchange channels during the development of hot dry rock geothermal resources.

Description

Technical Field

[0001] This disclosure relates to the field of hot dry rock geothermal resource extraction technology, and in particular to a method and system for detecting fracture zones in hot dry rock, determining drilling trajectories, and related technologies. Background Technology

[0002] Hot dry rock (HDR) is a high-temperature rock mass with little or no internal fluid, a temperature exceeding 150°C, and whose thermal energy can be utilized under current technological and economic conditions. The development and utilization of geothermal energy from hot dry rock primarily employs enhanced geothermal systems. These systems utilize artificially fracturing engineering to create fractures and wellbores, establishing heat exchange channels to economically extract and utilize thermal energy from low-permeability, high-temperature hot rock.

[0003] Currently, the common approach to establishing heat exchange channels is to use a combination of two directional wells and artificial fracturing. However, due to the difficulty and high uncertainty in detecting the spatial morphology and location of the fracture network formed by underground artificial fracturing, there is significant uncertainty in connecting artificially fracturing fracture zones with lower spatial morphology and location accuracy using controllable directional drilling technology. This can lead to the overall failure of geothermal resource development projects in dry hot rock. Summary of the Invention

[0004] To solve the above-mentioned technical problems, or at least partially solve them, this disclosure provides a method for detecting fracture zones in hot dry rock, a method for determining drilling trajectories, and a system.

[0005] This disclosure provides a method for detecting hydraulic fracturing fracture zones in hot dry rock, the method comprising:

[0006] The length and extension direction of the crack zone were determined using the ground direct current potential method.

[0007] The top surface of the fracture zone was determined using the variable offset vertical seismic profiling method;

[0008] Based on the extension direction and the location of the crack initiation point, the solid tilt angle of the crack surface relative to the location of the crack initiation point is determined.

[0009] The spatial distribution range of the crack zone is determined based on the top surface of the crack zone, the three-dimensional tilt angle, and the crack length.

[0010] In some embodiments, determining the fracture length and propagation direction of the fracture zone using the ground direct current potential method includes:

[0011] The distribution data of the crack zone in the horizontal direction were obtained using the ground direct current potential method.

[0012] The horizontal distribution data is projected onto a coordinate system to determine the seam length and the extension direction.

[0013] In some embodiments, determining the top surface of the fracture zone using the variable offset vertical seismic profiling method includes:

[0014] Seismic profile data were obtained using the variable offset vertical seismic profiling method.

[0015] Based on the seismic profile data, time-depth conversion is performed to determine the top surface of the initial fracture zone;

[0016] The position of the top surface of the initial crack zone is corrected to determine the top surface of the crack zone.

[0017] In some embodiments, determining the solid tilt angle of the crack surface relative to the initiation point of the crack zone based on the extension direction and the location of the crack initiation point includes:

[0018] Based on the extension direction and the location of the crack initiation point, determine whether the crack surface is vertical;

[0019] If the crack surface is vertical, then the solid tilt angle is 90°;

[0020] If the crack surface is inclined, the solid tilt angle θ is calculated using θ = arctan(H / k);

[0021] Among them, the intersection of the vertical projection line of the horizontal line passing through the crack initiation point and perpendicular to the extension direction with the top surface of the crack zone is the auxiliary point F. H represents the vertical height of the auxiliary point F to the horizontal plane where the crack initiation point is located, and K represents the distance between the position of the vertical projection point of the auxiliary point F on the horizontal plane where the crack initiation point is located and the position of the crack initiation point.

[0022] In some embodiments, determining the spatial distribution range of the crack zone based on the top surface of the crack zone, the three-dimensional tilt angle, and the crack length includes:

[0023] Project the seam length along the non-horizontal edge of the solid angle onto the top surface of the crack zone, and determine the positions of the first boundary point and the second boundary point on the top surface of the crack zone.

[0024] Based on the top surface of the crack zone, the location of the first boundary point, the location of the second boundary point, and the location of the crack initiation point, the spatial distribution range data of the crack zone is determined.

[0025] In some embodiments, determining the spatial distribution range data of the crack zone based on the top surface of the crack zone, the location of the first boundary point, the location of the second boundary point, and the location of the crack initiation point includes:

[0026] Connect the first boundary point and the crack initiation point to determine the first boundary line;

[0027] Connect the second boundary point and the crack initiation point to determine the second boundary line;

[0028] The line connecting the positions of the first boundary point and the second boundary point defined on the top surface of the crack zone is determined as the third boundary line.

[0029] Boundary data for determining the spatial distribution range of the crack zone by the first boundary line, the second boundary line, and the third boundary line.

[0030] This disclosure also provides a method for determining the drilling trajectory in hot dry rock, the method comprising:

[0031] To detect the spatial distribution range of hydraulic fracturing fracture zones in hot dry rocks;

[0032] Based on the aforementioned spatial distribution range, the reference drilling trajectory for directional wells is determined;

[0033] The spatial distribution range of the hot dry rock fracturing fracture zone is detected using any of the above-mentioned detection methods.

[0034] In some embodiments, determining the reference drilling trajectory of the directional well based on the spatial distribution range includes:

[0035] The reference drilling trajectory of the directional well traverses the spatial distribution range.

[0036] This disclosure also provides a detection system for hydraulically fractured zones in hot dry rock, used to perform any of the above-described detection methods, the detection system comprising:

[0037] A ground-based DC potential method detection device is used to determine the length and extension direction of a crack zone using the ground-based DC potential method.

[0038] A variable offset vertical seismic profiling detection device is used to determine the top surface of a fracture zone using the variable offset vertical seismic profiling method.

[0039] A data processing system is used to determine the three-dimensional tilt angle of the crack surface of the crack zone relative to the crack initiation point position based on the extension direction and the crack initiation point position; and to determine the spatial distribution range of the crack zone based on the top surface of the crack zone, the three-dimensional tilt angle, and the crack length.

[0040] This disclosure also provides a drilling trajectory determination system, including: a detection system for any of the above-mentioned hot dry rock fracturing fracture zones;

[0041] Also includes:

[0042] A drilling trajectory determination device is used to determine a reference drilling trajectory for a directional well based on the spatial distribution range.

[0043] The technical solution provided in this disclosure has the following advantages compared with the prior art:

[0044] The method for detecting fracture zones in hot dry rock provided in this embodiment includes: determining the fracture length and extension direction using a surface direct current potential method; determining the top surface of the fracture zone using a variable offset vertical seismic profiling method; determining the three-dimensional dip angle of the fracture surface relative to the initiation point based on the extension direction and the location of the fracture initiation point; and determining the spatial distribution range of the fracture zone based on the top surface, the three-dimensional dip angle, and the fracture length. Thus, by combining the surface direct current potential method and the variable offset vertical seismic profiling method, a more accurate full-element detection of the fracture zone space can be achieved. This provides data support for the trajectory design of the second directional well in a hot dry rock geothermal resource development well group, which is beneficial for establishing an effective artificial heat exchange channel during the development of hot dry rock geothermal resources and improving the success rate of hot dry rock geothermal resource development projects. Attached Figure Description

[0045] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0046] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A schematic flowchart illustrating a method for detecting fracture zones in hot dry rock according to an embodiment of this disclosure;

[0048] Figure 2 A schematic diagram illustrating the use of the ground-based direct current potential method to detect the spatial orientation of fracturing fracture zones in the detection method provided in this embodiment of the disclosure;

[0049] Figure 3 A schematic diagram illustrating the relative positional relationship between the horizontal projection of the fracturing fracture zone and the location of the fracture initiation point in the detection method provided in this embodiment of the disclosure;

[0050] Figure 4 A schematic diagram illustrating the principle of spatial parameter calculation for inclined fracturing fracture zones in the detection method provided in this embodiment of the disclosure;

[0051] Figure 5 A schematic diagram illustrating the principle of spatial parameter calculation for vertical fracturing fracture zones in the detection method provided in this embodiment of the disclosure;

[0052] Figure 6 A flowchart illustrating a drilling trajectory determination method provided in this embodiment of the disclosure;

[0053] Figure 7 A schematic diagram of the favorable distribution range of the fracturing fracture surface and the drilling trajectory of the second directional well in the detection method provided in this embodiment of the disclosure;

[0054] Figure 8 A schematic diagram of a detection system for hydraulic fracturing fracture zones in hot dry rock provided in this embodiment of the present disclosure;

[0055] Figure 9 This is a schematic diagram of the structure of a drilling trajectory determination system provided in an embodiment of the present disclosure. Detailed Implementation

[0056] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0057] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0058] First, the two detection techniques used in the detection method provided in this embodiment (the ground direct current potential method and the walkaway vertical seismic profiling (Walkaway VSP) method) will be briefly introduced as follows.

[0059] Surface DC potential method: Measuring points are set up on the ground around the fractured well, and power is supplied to the ground through the wellbore. The potential changes between measuring electrodes caused by the entry of fracturing fluid into the formation during fracturing are measured, thus reflecting the extent of the fracturing fracture. The principle of this technology for detecting artificially fractured fracture zones in hot dry rock is as follows: During the formation of artificially fractured fracture zones, when DC power is supplied from the ground to the cemented casing, the low-resistivity fracturing fluid enters the hot dry rock mass along the continuously expanding artificially fractured fracture, causing a change in the potential field of the fractured section. Through a surface observation system, the potential changes during the expansion of underground fractures are measured, and the horizontal extension direction (i.e., extension direction, spatial orientation) and length (i.e., fracture length) of the fracturing fracture are then deduced.

[0060] The technical principle behind this method for detecting fracturing fracture zones reveals that it is limited to acquiring one-dimensional surface potential data. Therefore, it can only accurately retrieve the horizontal projection length and extension direction of the fracturing fracture zone; it cannot retrieve other information regarding the spatial morphology and location of the fracture zone (fracture height, dip angle, and spatial orientation). If this method is used solely for fracturing fracture zone detection, the results will not meet the drilling trajectory design requirements for the second well in the dry hot rock geothermal resource development well group.

[0061] The Walkaway VSP method evolved from the VSP method. Walkaway VSP involves repeatedly generating seismic waves at intervals along a certain direction on the ground, and then deploying a series of geophones at different depths along the wellbore to observe and obtain a vertical seismic profile near the wellbore. The principle of using the Walkaway VSP method for detecting artificially fractured fracture zones in hot dry rock is as follows: after an artificially fractured fracture zone forms within the hot dry rock mass, the fracture zone is filled with fluid, creating a low P-wave velocity zone against a high P-wave velocity background. This results in a three-layered geophysical velocity field: a high P-wave velocity zone, a low P-wave velocity zone, and a high P-wave velocity zone in the longitudinal direction. When multiple artificial seismic sources are used to generate seismic waves at regular intervals along a certain direction on the ground, propagating from the high-P-wave velocity zone to the low-P-wave velocity zone, the seismic waves encounter the upper and lower envelopes of the artificially fractured fracture zone. Due to the seismic reflection impedance surface formed by the change in P-wave velocity at the contact surface, the seismic P-waves are reflected at this interface, forming reflected waves corresponding to the top and bottom interfaces of the fracture. These reflected waves are then received and recorded by a series of geophones deployed in the wellbore, forming seismic recording signals, thus obtaining the Walkaway VSP seismic profile information. By processing the obtained Walkaway VSP seismic profile, the temporal and spatial locations of the top and bottom interfaces of the artificially fractured fracture zone on the seismic profile can be interpreted.

[0062] This technology features high-precision imaging around the wellbore. While it can detect reflected signals from the top and bottom surfaces of artificially fractured zones, limitations in the placement of surface seismic sources and the spacing of downhole geophones result in errors in detecting fracture length and converting time-domain information of the top and bottom interfaces into depth-domain information. Quantifying all spatial elements (fracture length, height, azimuth, and dip) based solely on the detected fracture location would introduce significant errors into the trajectory design of the second connecting well, increasing the risk of failure in establishing an effective artificial heat exchange channel.

[0063] To address the aforementioned issues, this disclosure provides a detection method applicable to hot dry rock development projects, specifically for detecting fracturing fractures in horizontal well sections. This method addresses the limitations of the Walkaway VSP method in quantifying the spatial morphology and location of artificially fractured fracture zones, which suffers from incomplete quantification of all spatial elements and errors during time-depth conversion. This method combines the high-precision fracture length (i.e., fracture length) obtained from the ground-based DC electropotential method with this method. Based on determining the three-dimensional dip angle of the artificially fractured fracture surface, the horizontal fracture length detected by the ground-based DC electropotential method is spatially extended according to the three-dimensional dip angle. This extension intersects with the corrected top surface of the fractured fracture zone to obtain a more accurate range of favorable spatial distribution of the artificially fractured fracture surface, thus achieving quantitative calculation of all spatial elements of the artificially fractured fracture surface. In this way, the accurate spatiotemporal distribution and most favorable distribution range of artificially fractured fracture surfaces can be quantitatively calculated when horizontal wells in hot dry rock masses are multi-stage fractured. This ensures that the second directional well in the hot dry rock geothermal resource development well group penetrates the artificially fractured fracture surface, realizing the establishment of an effective artificial heat exchange channel. This can overcome the problem of establishing effective interconnected fractures in the development of hot dry rock geothermal resources, provide feasible key technologies for the development and utilization of hot dry rock geothermal resources, and facilitate the development and utilization of hot dry rock geothermal resources.

[0064] Below, in conjunction with Figures 1-9 This disclosure provides an exemplary description of the method and system for detecting hydraulic fracturing fractures in hot dry rock, as well as drilling methods and systems based thereon. In the following text, the fracturing fracture zone may be referred to as a fracture zone or an artificially fracturing fracture zone.

[0065] For example, Figure 1 This is a schematic flowchart illustrating a method for detecting fracture zones in hot dry rock, provided as an embodiment of this disclosure. (Refer to...) Figure 1 The detection method may include:

[0066] S110. The length and extension direction of the crack zone are determined by the ground DC potential method.

[0067] This step employs the ground-based direct current potential method, which can accurately measure the length and spatial orientation of the crack zone on the ground, i.e., its direction of extension. This provides highly accurate data support for subsequent data processing.

[0068] In some embodiments, this step may specifically include:

[0069] Step 1: Use the ground direct current potential method to obtain horizontal distribution data of the crack zone.

[0070] In this step, ground distribution data of the crack zone, i.e. ground two-dimensional potential data, can be collected to invert the horizontal projection length of the crack zone on the ground and the extension direction of the crack zone.

[0071] Step 2: Project the horizontal distribution data onto the coordinate system to determine the seam length and extension direction.

[0072] In this step, the data representing the length and extension direction of the crack zone are transformed into a coordinate system, that is, projected into a coordinate system, to determine the extension direction (i.e., spatial orientation) and length of the crack zone in the coordinate system.

[0073] For example, the coordinate system may be a polar coordinate system, a rectangular coordinate system, or an angular coordinate system.

[0074] For example, Figure 2 A schematic diagram illustrating the use of the ground-based direct current potential method to detect the spatial orientation of fracturing fracture zones in the detection method provided in this embodiment of the disclosure. (Refer to...) Figure 2 The measurement results from the ground DC potential method were projected into polar coordinates, with true north (N) as the 0° direction. The spatial azimuth angle of the artificial fracturing fracture zone 01 was determined as α, which is the angle clockwise deviation from the 0° direction. In this way, the orientation element of the artificial fracturing fracture zone was determined.

[0075] In other embodiments, the orientation elements of the crack zone may be represented in other coordinate systems or in other forms, which is not limited to the embodiments disclosed herein.

[0076] S120. The top surface of the fracture zone is determined by the variable offset vertical seismic profile method.

[0077] In this step, the position of the top surface of the fracture zone can be measured using the Walkaway VSP method. In other embodiments, the position of the ground surface of the fracture zone can also be measured simultaneously using the Walkaway VSP method. This can be configured according to the detection requirements of the spatial extent of the fracture zone, and the embodiments disclosed herein are not limited in this regard.

[0078] In some embodiments, this step may specifically include:

[0079] Step 1: Obtain seismic profile data using the variable offset vertical seismic profiling method.

[0080] This step uses the Walkaway VSP method to acquire multiple seismic profile data, which may include, for example, P-wave round-trip time data or other types of data related to the seismic profile.

[0081] Step 2: Perform time-depth conversion based on seismic profile data to determine the top surface of the initial fracture zone.

[0082] Step 3: Correct the position of the top surface of the initial fracture zone to determine the top surface of the fracture zone.

[0083] In steps two and three above, based on multiple seismic profile data, data time-depth conversion and location correction are performed to determine the location of the top surface of the fracture zone.

[0084] The spatial inhomogeneity of formation velocity leads to a certain bias when using the velocity at known locations to infer the velocity at unknown locations. This bias results in an error when converting the time-domain top surface of an artificially fractured fracture zone at an unknown location into its depth-domain top surface. This bias can be determined by fitting the seismic stacking velocity and the time-depth relationship between multiple known points. In this step, the top surface of the artificially fractured fracture zone detected by the Walkaway VSP method is corrected according to m, thereby improving the accuracy of the fracture zone top surface location.

[0085] S130. Based on the extension direction and the location of the crack initiation point, determine the solid dip angle of the crack surface relative to the location of the crack initiation point.

[0086] In this step, the position of the crack surface on the ground can be determined based on the extension direction. By comparing it with the position of the crack initiation point, it can be determined whether the crack surface is vertical. When the crack surface is vertical or inclined, different calculation methods are used to determine the three-dimensional tilt angle, which is detailed below.

[0087] In some embodiments, this step may specifically include:

[0088] Step 1: Determine whether the crack surface is vertical based on the extension direction and the location of the crack initiation point.

[0089] For example, in this step, the spatial position of the horizontal projection of the artificial fracturing fracture zone detected by the ground DC potential method can be compared with the corresponding fracture initiation point. If the fracture initiation point is located within the horizontal projection of the fracture zone, the fracture zone is vertical; if the fracture initiation point is not located within the horizontal projection of the fracture zone, the fracture zone is inclined.

[0090] For example, Figure 3 This diagram illustrates the relative positional relationship between the horizontal projection of the fracturing fracture zone and the location of the fracture initiation point in the detection method provided in this embodiment of the disclosure. (Refer to...) Figure 3 The diagram illustrates three relative spatial relationships between the artificial fracturing fracture zone 01 and the fracture initiation point 02. In cases 011 and 012, the artificial fracturing fracture zone 01 does not cover the fracture initiation point 02, meaning the fracture initiation point 02 is not within the horizontal projection of the artificial fracturing fracture zone 01, and the fracture zone is inclined. In case 013, the artificial fracturing fracture zone 01 covers the fracture initiation point 02, meaning the fracture initiation point 02 is within the horizontal projection of the artificial fracturing fracture zone 01, and the fracture zone is vertical.

[0091] Step 2: If the crack surface is vertical, the solid tilt angle is 90°; if the crack surface is inclined, the solid tilt angle θ is calculated using θ = arctan(H / k).

[0092] Among them, the intersection of the vertical projection line of the horizontal line passing through the crack initiation point and perpendicular to the extension direction with the top surface of the crack zone is the auxiliary point F. H represents the vertical height of the auxiliary point F to the horizontal plane where the crack initiation point is located, and K represents the distance between the position of the vertical projection point of the auxiliary point F on the horizontal plane where the crack initiation point is located and the position of the crack initiation point.

[0093] For example, Figure 4 A schematic diagram illustrating the principle of spatial parameter calculation for inclined fracturing fracture zones in the detection method provided in this embodiment. (Refer to...) Figure 4 Auxiliary point F is the intersection of the vertical projection line passing through the fracture initiation point O and perpendicular to the horizontal line of fracture length L with the corrected top surface 016 of the artificial fracturing fracture zone. H is the vertical height of auxiliary point F from the horizontal plane where the fracture initiation point O is located. K is the distance from the projection point of auxiliary point F on the horizontal plane where the fracture initiation point O is located to the fracture initiation point O. Among them, 015 represents the top surface of the artificial fracturing fracture zone before correction.

[0094] In other embodiments, other inverse trigonometric functions, such as arcsine or arccosine functions, may be used to calculate the solid tilt angle, but this disclosure does not limit this.

[0095] For example, Figure 5 A schematic diagram illustrating the principle of spatial parameter calculation for vertical fracturing fracture zones in the detection method provided in this embodiment. (Refer to...) Figure 5 The crack initiation point O and the auxiliary point F are located in the same vertical plane (or the same vertical line), and the solid tilt angle is 90°.

[0096] In this way, the three-dimensional tilt angle can be determined based on the location of the crack initiation point and the horizontal projection of the crack zone, which prepares for the subsequent determination of the boundary points of the spatial distribution range.

[0097] S140. Based on the top surface of the crack zone, the three-dimensional dip angle, and the crack length, determine the spatial distribution range of the crack zone.

[0098] In this step, the spatial distribution range of the fracture zone can be determined by deduction based on the fracture length determined in S110, the top surface of the fracture zone determined in S120, and the three-dimensional dip angle determined in S130, that is, the favorable development area of ​​each fracture surface in the artificial fracturing fracture zone can be determined.

[0099] In some embodiments, this step may specifically include:

[0100] Step 1: Project the crack length along the non-horizontal edge of the solid angle onto the top surface of the crack zone, and determine the positions of the first boundary point and the second boundary point on the top surface of the crack zone.

[0101] For example, continue to refer to Figure 4When the artificially fractured fracture zone is inclined, after determining the three-dimensional dip angle, the fracture length L obtained by the ground DC electric current method is extended obliquely upward along the three-dimensional dip angle θ and intersects with the top surface 016 of the corrected fracture zone to obtain two intersection points, that is, the positions of the first boundary point B and the second boundary point C are determined.

[0102] Or, continue to refer to Figure 5 When the artificially fractured fracture surface is vertical (i.e., θ = 90°), the fracture length L obtained by ground DC electric current method is extended vertically upward and intersects with the top surface 016 of the corrected fracture zone to obtain intersection points B and C, that is, the positions of the first boundary point B and the second boundary point C are determined.

[0103] Step 2: Determine the spatial distribution range of the crack zone based on the top surface of the crack zone, the location of the first boundary point, the location of the second boundary point, and the location of the crack initiation point.

[0104] In this step, the spatial distribution range data can be defined based on three boundary locations: the first boundary point location B, the second boundary point location C, and the crack initiation point location O; wherein, the line connecting two adjacent boundary points can be a straight line or a curve.

[0105] For example, this step may include: determining three boundary lines based on the locations of the first boundary point, the second boundary point, and the crack initiation point, and defining the boundaries of the spatial distribution range by the boundary lines, specifically including:

[0106] Connect the first boundary point and the fracture initiation point to determine the first boundary line, BO, which is a straight line; connect the second boundary point and the fracture initiation point to determine the second boundary line, CO, which is a straight line; connect the first and second boundary points on the top surface of the fracture zone to determine the third boundary line, BC, which can be a straight line BC or a curve intercepted by BC on the corrected top surface 016 of the fracture zone; the boundary data of the spatial distribution range of the fracture zone are determined by the first boundary line BO, the second boundary line CO, and the third boundary line BC.

[0107] Therefore, the enclosed space defined by the above three boundary lines is the spatial distribution range of the fracture zone. That is, the region OBC is the distribution range of the favorable artificial fracturing fracture zone. The spatial location of the boundary points constituting the region OBC can also be quantified to obtain the spatial coordinates (X, Y, Z) of the favorable artificial fracturing fracture surface distribution range.

[0108] Subsequently, the trajectory of the second directional well in the dry hot rock geothermal resource development well group can be designed within the favorable development area, which is conducive to establishing an effective heat exchange channel.

[0109] It should be noted that in the above steps, S120 may be executed before S110, or the two may be executed in parallel. This embodiment of the present disclosure does not limit this.

[0110] The method for detecting fracture zones in hot dry rock provided in this embodiment can combine the ground DC potential method and the variable offset vertical seismic profile method to accurately detect all elements of the fracture zone space. This provides data support for the trajectory design of the second directional well in the hot dry rock geothermal resource development well group, which is conducive to the establishment of an effective artificial heat exchange channel in the hot dry rock geothermal resource development process and improves the success rate of hot dry rock geothermal resource development projects.

[0111] Specifically, in the detection method provided in this embodiment, the top and bottom interfaces of the artificial fracturing fracture zone detected by the Walkaway VSP method and the horizontal projection of the artificial fracturing fracture zone detected by the ground DC potential method are used as basic data. First, the artificial fracturing fracture zone detected by the ground DC potential method is projected into polar coordinates to obtain the fracture zone orientation elements, and its spatial position is compared with the corresponding fracture initiation point to determine whether the artificial fracturing fracture surface is vertical. Second, after determining whether the artificial fracturing fracture surface is vertical, the solid dip angle of the fracture surface is calculated in two ways (vertical and inclined). Third, the Walkaway VSP method is used to determine the fracture orientation of the artificial fracturing fracture zone. The top surface of the artificially fractured fracture zone detected by the VSP method is corrected according to the error m during time-depth conversion. Then, the fracture length L of the artificially fractured fracture zone detected by the surface DC potential method is spatially extended according to the aforementioned three-dimensional dip angle and intersected with the corrected top surface of the fracture zone. The fracture initiation point is then connected with the boundary point obtained from the intersection to obtain the most favorable development area of ​​the artificially fractured fracture zone. Finally, the spatial location of the boundary point constituting the favorable development area of ​​the artificially fractured fracture surface can be quantified to determine the spatial distribution range of the fracture zone. In this way, accurate and quantitative detection of all spatial elements (fracture length, fracture height, three-dimensional dip angle, and spatial orientation) of the fracture zone is achieved. Subsequently, the trajectory of the second directional well in the dry hot rock geothermal resource development well group can be designed within the favorable development area of ​​the artificially fractured fracture surface, which is conducive to the establishment of an effective artificial heat exchange channel in the dry hot rock geothermal resource development project.

[0112] Based on the above embodiments, this disclosure also provides a method for determining the drilling trajectory of a second directional well in a hot dry rock geothermal resource development and utilization project, in order to establish an effective heat exchange channel. This drilling trajectory determination method is based on the aforementioned detection method; therefore, the trajectory of the second directional well in a hot dry rock geothermal resource development well group can be designed within a favorable area of ​​artificially fractured fracture surfaces, thereby facilitating the establishment of an effective artificial heat exchange channel in the hot dry rock geothermal resource development project.

[0113] For example, Figure 6 This is a flowchart illustrating a drilling trajectory determination method provided in an embodiment of this disclosure. (Refer to...) Figure 6 The drilling trajectory determination method may include:

[0114] S310, Detect the spatial distribution range of hydraulic fracturing fracture zones in hot dry rocks.

[0115] This step can employ any of the aforementioned detection methods. This allows for relatively accurate localization of favorable development areas on each fracture surface within the artificially fractured fracture zone.

[0116] S320. Based on the spatial distribution range, determine the reference drilling trajectory for directional wells.

[0117] In this step, the reference drilling trajectory for the second directional well can be determined based on the favorable development areas of each fracture surface in the artificially fractured fracture zone.

[0118] For example, the reference drilling trajectory of the directional well traverses a spatially distributed area. This facilitates connecting the second directional well to the first directional well via a fracture zone, establishing an effective heat exchange channel.

[0119] For example, Figure 7 A schematic diagram showing the favorable distribution range of the fracturing fracture surface and the drilling trajectory of the second directional well in the detection method provided in this embodiment. (Refer to...) Figure 7 021 represents the trajectory of the first directional well, and 022 represents the reference drilling trajectory of the second directional well; the reference drilling trajectory 022 passes through the favorable development area OBC of each fracture surface in the fracture zone.

[0120] Thus, the drilling trajectory of the second directional well was determined. In subsequent drilling operations, drilling proceeded along the trajectory determined in step S320. Specifically, the second directional well was drilled along the determined drilling trajectory, which served as a reference trajectory, thereby establishing an effective heat exchange channel between the second and first directional wells.

[0121] In the drilling trajectory determination method provided in this embodiment, according to any of the above-mentioned detection methods, the spatial full-element quantitative detection of artificial fracturing fracture surfaces is carried out on each fracturing section of the first directional well in the dry hot rock geothermal resource development well group, and the favorable distribution area of ​​artificial fracturing fracture surfaces in each fracturing section is determined, providing the target point coordinates of artificial fracturing fracture zones for the second directional well in the dry hot rock geothermal resource development well group; based on this, the drilling trajectory (i.e., reference drilling trajectory) of the second directional well is designed, which can realize the effective connection of fracturing fractures by the second directional well, thereby establishing an effective heat exchange channel.

[0122] Based on this, when applying this method to actual drilling operations, drilling can be carried out along the determined drilling trajectory as a reference trajectory. In this way, an effective heat exchange channel can be established between the second directional well and the first directional well.

[0123] Based on the above embodiments, this disclosure also provides a detection system for hydraulic fracturing fracture zones in hot dry rock, which is used to perform any of the above detection methods. Therefore, it also has the beneficial effects of the above detection methods. The similarities can be understood by referring to the explanation of the detection methods above, and will not be repeated below.

[0124] For example, Figure 8 This is a schematic diagram of a detection system for hydraulic fracturing fracture zones in hot dry rock, provided as an embodiment of this disclosure. (Refer to...) Figure 8 The detection system 40 includes:

[0125] Ground DC potential method detection device 410 is used to determine the length and extension direction of the crack zone using the ground DC potential method;

[0126] The variable offset vertical seismic profiling detection device 420 is used to determine the top surface of the fracture zone using the variable offset vertical seismic profiling method.

[0127] The data processing system 430 is used to determine the three-dimensional dip angle of the crack surface of the crack zone relative to the position of the crack initiation point based on the extension direction and the position of the crack initiation point; and to determine the spatial distribution range of the crack zone based on the top surface of the crack zone, the three-dimensional dip angle and the crack length.

[0128] In this way, it is possible to achieve full spatial element detection of artificially fractured fracture zones.

[0129] Based on this, the top surface of the fracture zone can be corrected using the variable offset vertical seismic profile detection device 420, thereby improving the accuracy of all spatial element data.

[0130] Based on the above embodiments, this disclosure also provides a drilling trajectory determination system for executing the above-described drilling trajectory determination method. This drilling trajectory determination system includes any of the aforementioned detection systems. Therefore, this drilling system also possesses the beneficial effects of the aforementioned detection method, detection system, and drilling trajectory determination method. The similarities can be understood with reference to the above description, and will not be repeated below.

[0131] For example, Figure 9 This is a schematic diagram of a drilling trajectory determination system provided in an embodiment of this disclosure. (Refer to...) Figure 9 The drilling trajectory determination system 50 may include: a detection system 40 for hot dry rock fracturing fracture zones; and also includes:

[0132] The drilling trajectory determination device 510 is used to determine the reference drilling trajectory of a directional well based on the spatial distribution range.

[0133] In this way, based on the spatial full-element detection of artificially fractured fracture zones, the drilling trajectory (i.e., reference drilling trajectory) of the second directional well can be designed, thereby realizing the effective connection of the fractured fractures by the second directional well, thus establishing an effective heat exchange channel.

[0134] It should be noted that, in this document, relational terms such as “first” and “second” are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0135] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting hydraulic fracturing fracture zones in hot dry rock, characterized in that, include: The length and extension direction of the crack zone were determined using the ground direct current potential method. The top surface of the fracture zone was determined using the variable offset vertical seismic profiling method. Based on the extension direction and the location of the crack initiation point, the solid tilt angle of the crack surface relative to the location of the crack initiation point is determined. The spatial distribution range of the crack zone is determined based on the top surface of the crack zone, the three-dimensional inclination angle, and the crack length; The method of determining the top surface of the fracture zone using the variable offset vertical seismic profiling method includes: Seismic profile data were obtained using the variable offset vertical seismic profiling method. Based on the seismic profile data, time-depth conversion is performed to determine the top surface of the initial fracture zone; The position of the top surface of the initial crack zone is corrected to determine the top surface of the crack zone.

2. The detection method according to claim 1, characterized in that, The method of determining the length and extension direction of the crack zone using ground-based direct current potential method includes: The distribution data of the crack zone in the horizontal direction were obtained using the ground direct current potential method. The horizontal distribution data is projected onto a coordinate system to determine the seam length and the extension direction.

3. The detection method according to claim 1, characterized in that, Based on the extension direction and the location of the crack initiation point, the solid dip angle of the crack surface relative to the location of the crack initiation point is determined, including: Based on the extension direction and the location of the crack initiation point, determine whether the crack surface is vertical; If the crack surface is vertical, then the solid tilt angle is 90°; If the crack surface is inclined, the solid tilt angle θ is calculated using θ=arctan(H / k); Wherein, the intersection of the vertical projection line of the horizontal line passing through the crack initiation point and perpendicular to the extension direction with the top surface of the crack zone is the auxiliary point F, H represents the vertical height of the auxiliary point F to the horizontal plane where the crack initiation point is located, and K represents the distance between the position of the vertical projection point of the auxiliary point F on the horizontal plane where the crack initiation point is located and the position of the crack initiation point.

4. The detection method according to claim 1, characterized in that, Based on the top surface of the crack zone, the three-dimensional dip angle, and the crack length, the spatial distribution range of the crack zone is determined, including: Project the seam length along the non-horizontal edge of the solid angle onto the top surface of the crack zone, and determine the positions of the first boundary point and the second boundary point on the top surface of the crack zone. Based on the top surface of the crack zone, the location of the first boundary point, the location of the second boundary point, and the location of the crack initiation point, the spatial distribution range data of the crack zone is determined.

5. The detection method according to claim 4, characterized in that, Based on the top surface of the crack zone, the location of the first boundary point, the location of the second boundary point, and the location of the crack initiation point, the spatial distribution range data of the crack zone is determined, including: Connect the first boundary point and the crack initiation point to determine the first boundary line; Connect the second boundary point and the crack initiation point to determine the second boundary line; The line connecting the positions of the first boundary point and the second boundary point defined on the top surface of the crack zone is determined as the third boundary line. Boundary data for determining the spatial distribution range of the crack zone by the first boundary line, the second boundary line, and the third boundary line.

6. A method for determining drilling trajectory in hot dry rock, characterized in that, include: To detect the spatial distribution range of hydraulic fracturing fracture zones in hot dry rocks; Based on the aforementioned spatial distribution range, the reference drilling trajectory for directional wells is determined; The spatial distribution range of the fracturing fracture zone in the dry hot rock is detected using the detection method described in any one of claims 1-5.

7. The drilling trajectory determination method according to claim 6, characterized in that, Based on the aforementioned spatial distribution range, the reference drilling trajectory for directional wells is determined, including: The reference drilling trajectory of the directional well traverses the spatial distribution range.

8. A detection system for hydraulic fracturing fracture zones in hot dry rock, characterized in that, For performing the detection method according to any one of claims 1-5, the detection system comprises: A ground-based DC potential method detection device is used to determine the length and extension direction of a crack zone using the ground-based DC potential method. A variable offset vertical seismic profiling detection device is used to determine the top surface of a fracture zone using the variable offset vertical seismic profiling method. A data processing system is used to determine the three-dimensional tilt angle of the crack surface of the crack zone relative to the crack initiation point position based on the extension direction and the crack initiation point position; and to determine the spatial distribution range of the crack zone based on the top surface of the crack zone, the three-dimensional tilt angle, and the crack length.

9. A drilling trajectory determination system, characterized in that, include: The detection system for hydraulic fracturing fracture zones in hot dry rock as described in claim 8; Also includes: A drilling trajectory determination device is used to determine a reference drilling trajectory for a directional well based on the spatial distribution range.

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