Borehole imaging method and system for imaging fractures in shale

Abstract

The application discloses a forward simulation method and system for dual laterolog logging reflecting shale cracks, and comprises the following steps: analyzing crack development characteristics of a target area; determining instrument parameters and wellbore environment measurement parameters of a dual laterolog logging instrument required by current simulation; extracting formation parameters according to the crack development characteristic analysis result, the instrument parameters and the wellbore environment measurement parameters, and establishing a formation model containing crack condition parameters to be analyzed; based on the finite element method, performing forward simulation on electric field distribution information formed by the dual laterolog logging instrument in the formation according to the formation model, and measuring dual laterolog resistivity of the target area. The application can clearly show dual laterolog logging response results under different crack characteristic conditions, form shale crack identification rules, analyze the limits of crack scale identification of the instrument, and lay a theoretical foundation for shale crack identification and evaluation.

Description

Technical Field

[0001] This invention relates to the field of physical geologizing technology, and in particular to a dual-lateral logging forward modeling method and system for reflecting shale fractures. Background Technology

[0002] Existing methods for fracture characteristic research and identification mainly include seismic methods, geological methods, and well logging methods. Seismic methods, primarily using coherent and multi-wave exploration techniques, can comprehensively reflect fracture distribution patterns, offering wide coverage and deep detection. Geological methods are the most direct way to predict fractures, obtaining reliable fracture development characteristics directly through core or outcrop observations. However, this method can only provide qualitative predictions and generally needs to be combined with well logging methods for fracture identification. Geophysical methods can reflect large-scale fracture distribution patterns; for example, using diffraction wave time-of-flight correction multi-point focusing imaging technology to obtain multi-point focused three-dimensional diffraction images to identify fracture development zones. Numerical simulation methods are semi-quantitative to quantitative fracture prediction methods. Well logging methods include acoustic logging, imaging logging, resistivity logging, and nuclear magnetic resonance logging. Acoustic logging mainly includes acoustic time-of-flight, full-waveform, and variable-density acoustic logging. Sonic logging in fractured sections exhibits wave skipping phenomena and generally high transit times. Sonic variable density logging identifies fractures by detecting sawtooth or stripe-like perturbations in the wave train, such as "V"-shaped or "V"-shaped disturbances. Different wave patterns reflect different types of fractures. Imaging logging is a high-resolution formation dip logging method with micro-resistivity scanning imaging, characterized by high vertical resolution and intuitive visualization. It converts differences in formation resistivity near the wellbore into clear images, visually revealing subtle variations in the formation. Nuclear magnetic resonance (NMR) logging results can obtain T2 spectrum distributions reflecting pore throat characteristics, thereby determining the type of reservoir space and the effectiveness of fractures. Resistivity logging is an important method for fracture identification, including micro-lateral, deep lateral, and shallow lateral fractures. Fracture responses can exhibit alternating high and low amplitudes, varying amplitudes, or spikes. Among them, dual lateral logging is currently the most widely used and data-rich electrical logging method. The resistivity measured by it shows that the deep and shallow lateral resistivity values ​​are different in the fracture development section. The more developed the fracture, the greater the difference between the two lateral values ​​is generally.

[0003] Geological methods are affected by core length, core integrity, and subjective factors and identification accuracy. Furthermore, direct visual observation can only reveal surface fractures, failing to observe their extension within the core. Seismic methods can only predict the general location of fractures in a region, lacking a precise description of fracture development. For sonic transit time logging, cycle skipping is prone to occur in fracture-developing sections; for neutron logging, variations in fracture filling materials lead to changes in the hydrogen content index, while density logging provides relatively poor fracture information. These logging methods are low-cost, but their fracture representation is indirect, and the degree to which fractures and logging data reflect each other varies across different regions. Imaging logging is susceptible to the influence of logging resolution. Some small and micro fractures are difficult or impossible to identify, and are often affected by formation interfaces, leading to significant errors in the interpretation of fracture parameters at certain well points (such as wells near faults with a large number of network fractures). In addition, the use of oil-based drilling mud can also interfere with the accuracy of imaging logging data, and is costly and slow to process. Nuclear magnetic resonance logging technology has limitations in identifying non-connected fractures. Radioactive logging can only measure the total content of radioactive elements in the formation, but cannot distinguish the types and contents of radioactive elements contained in the formation.

[0004] Reservoir resistivity is a key geophysical logging parameter for evaluating oil and gas reservoirs. Dual-lateral logging, as a conventional resistivity logging method, is widely used in shale formations. Shale gas reservoirs often have fractures, and the fracture dip angle significantly impacts the permeability of shale gas reservoirs, directly affecting their production efficiency. Furthermore, shale gas reservoirs frequently experience borehole enlargement, leading to localized changes in wellbore dimensions that influence the dual-lateral logging response.

[0005] Therefore, existing technologies need to provide a forward modeling scheme for dual-lateral logging of shale fractures to solve one or more of the above-mentioned technical problems. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for forward modeling dual-lateral logging to reflect shale fractures, comprising: determining the fracture development characteristics of a target area; determining the instrument parameters of the dual-lateral logging instrument required for the current simulation; determining the wellbore environment measurement parameters required for the current simulation; extracting formation parameters based on the fracture development characteristic parameters, instrument parameters, and wellbore environment measurement parameters, and establishing a formation model containing parameters of the fracture conditions to be analyzed; and performing forward modeling of the electric field distribution information formed by the dual-lateral logging instrument in the formation based on the formation model using the finite element method, and measuring the dual-lateral resistivity of the target area.

[0007] Preferably, the step of analyzing the crack development characteristics of the target area includes: analyzing and statistically analyzing the development frequency distribution of cracks at different development angles, crack development scale information, filling material type, filling degree and filling material conductivity within the current target area.

[0008] Preferably, the step of performing forward modeling of the electric field distribution information formed by the dual-lateral logging instrument in the formation based on the formation model using the finite element method to measure the dual-lateral resistivity of the target area includes: establishing an element body matching the current target area based on the finite element method; coupling the formation model containing the fracture condition parameters to be analyzed into the element body; using the finite element simulation method to derive the electric field near each electrode in the dual-lateral logging instrument, forming the electric field distribution information, and further obtaining the dual-lateral resistivity.

[0009] Preferably, the forward modeling method further includes: constructing different data to be analyzed for the fracture condition parameters to be analyzed, establishing fractured formation models containing different data to be analyzed, and then performing corresponding forward modeling for different formation models; and analyzing the influence relationship between different data to be analyzed and the response of dual lateral logging instruments to form a matching relationship between shale fracture conditions and instrument measurement applicability.

[0010] Preferably, the target area is constructed as a cylinder, and the morphological information, including the height, radial section length, and sampling grid size of the cylinder, is determined based on the wellbore environment measurement parameters, thereby establishing the element body with a surface potential of zero.

[0011] Preferably, the wellbore environment measurement parameters include the starting point location of the target area, the simulated sampling interval, the well inclination angle, the mud resistivity, and the wellbore radius, and the formation parameters include the number of formation interfaces, the interface location of each formation, the fracture size, the fracture resistivity, the resistivity of the surrounding rock above and below, and the undisturbed formation resistivity.

[0012] Preferably, the fracture condition parameters to be analyzed are selected from one or more of the following: fracture angle type, fracture scale type, infill type, formation resistivity, and lithological combination.

[0013] Preferably, each step is constructed as a corresponding program block to form an intelligent simulation system.

[0014] On the other hand, the present invention also provides a forward modeling system for reflecting shale fractures using dual lateral logging. The forward modeling system includes: a fracture feature analysis module configured to analyze fracture development characteristics in a target area; an instrument design module configured to determine the instrument parameters of the dual lateral logging instrument required for the current simulation; a wellbore measurement module configured to determine the wellbore environment measurement parameters required for the current simulation; a formation model generation module configured to extract formation parameters and establish a formation model containing fracture condition parameters to be analyzed based on the fracture development feature analysis results, instrument parameters, and wellbore environment measurement parameters; and a forward modeling calculation module configured to perform forward modeling of the electric field distribution information formed by the dual lateral logging instrument in the formation based on the formation model using the finite element method, and to measure the dual lateral resistivity of the target area.

[0015] Preferably, the forward modeling module includes: an element volume construction unit, configured to establish an element volume matching the current target region based on the finite element method; and a dual lateral resistivity generation unit, configured to couple the formation model containing the fracture condition parameters to be analyzed into the element volume, derive the electric field near each electrode in the dual lateral logging instrument using the finite element simulation method, form the electric field distribution information, and further obtain the dual lateral resistivity.

[0016] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0017] This invention proposes a dual-lateral logging forward modeling method and system for reflecting shale fractures. Based on multi-dimensional field-core-logging data, this method and system study the characteristics of typical fracture development in shale reservoirs, extract reasonable shale fracture parameters, establish different shale reservoir fracture models, and complete a dual-lateral logging forward modeling method that can effectively reflect fracture characteristics. Then, it simulates the physical field changes during dual-lateral logging measurements in fractured shale reservoirs. Based on the simulated logging response mechanism, it clarifies the applicability of the dual-lateral logging method under different fracture characteristic conditions, forming shale fracture identification rules. This lays a theoretical foundation for shale fracture identification and evaluation, enabling the selection of the optimal "sweet spot" in the reservoir and comprehensive and accurate reservoir evaluation, providing technical support for increasing oilfield reserves and production.

[0018] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0020] Figure 1 This is a step diagram of a dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0021] Figure 2 This is a schematic diagram of a horizontal fractured formation model in a dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0022] Figure 3 This is a schematic diagram of a vertical fracture formation model in a dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0023] Figure 4 This is a schematic diagram of the unit element volume in the dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0024] Figure 5 This is a specific example diagram illustrating the input-output flow of the forward model in the dual-lateral logging forward modeling simulation method for reflecting shale fractures, as described in this application embodiment.

[0025] Figure 6 This is a schematic diagram of the deep lateral logging response of a horizontal fracture under bitumen-filled conditions in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0026] Figure 7 This is a schematic diagram of the shallow lateral logging response under dip angle in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0027] Figure 8 This is a schematic diagram of the deep lateral logging response under different fracture filling types in the dual lateral logging forward modeling method for reflecting shale fractures, as described in this application embodiment.

[0028] Figure 9 This is a schematic diagram of shallow lateral logging response under different fracture filling types in the dual lateral logging forward modeling method for reflecting shale fractures, as described in this application embodiment.

[0029] Figure 10 This is a schematic diagram of the deep lateral logging response under different shale resistivity conditions in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0030] Figure 11This is a schematic diagram of shallow lateral logging response under different shale resistivity conditions in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0031] Figure 12 This is a schematic diagram of the deep lateral logging response under different lithological combinations in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0032] Figure 13 This is a schematic diagram of shallow lateral logging response under different lithological combinations in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application.

[0033] Figure 14 This is a block diagram of a dual-lateral logging forward modeling system for reflecting shale fractures, according to an embodiment of this application. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, so that the process of how the present invention uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that, as long as there is no conflict, the various embodiments and features in the various embodiments of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0035] Furthermore, the steps illustrated in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Also, although a logical order is shown in the flowcharts, in some cases the steps shown or described may be performed in a different order than that shown here.

[0036] To address the technical problems described in the background section, this application proposes a dual-lateral logging forward modeling method and system for reflecting shale fractures. This method and system utilize a combination of dual-lateral logging and the finite element method to study shale fractures. To achieve low cost, high computational speed, and high accuracy in accurately identifying shale fractures, this invention develops a dual-lateral logging forward modeling method. This method analyzes the physical field variation laws and logging response characteristics to determine the fracture scale that dual-lateral logging can characterize under the influence of the wellbore environment. Based on the method's applicability, it clarifies the conditions for effectively identifying fractures based on dual-lateral logging. Furthermore, it employs programming languages ​​and basic algorithms to fuse large amounts of data, forming an intelligent simulation method, including instrument design, wellbore measurement, formation modeling, and resistivity response calculation modules. In practical applications, by inputting relevant formation model parameters, forward calculations can be directly performed to simulate real formations, thereby converting deep and shallow lateral resistivity values. This achieves true big data fusion and interactive platform processing, with high computational speed and low cost.

[0037] Figure 1 This is a step diagram illustrating the dual-lateral logging forward modeling method for reflecting shale fractures according to an embodiment of this application. See below for reference. Figure 1 The process of the dual-lateral logging forward modeling method for reflecting shale fractures (hereinafter referred to as the "forward modeling method") described in the embodiments of the present invention will be explained.

[0038] Step S110 analyzes the crack development characteristics of the target area. In step S110, the crack development characteristics of the target area to be analyzed (simulated) are analyzed. Specifically, the analysis of the crack development characteristics of the target area includes: analyzing and statistically analyzing the development frequency distribution of cracks at different development angles, crack development scale information, crack surface morphology variation characteristics, and crack filling characteristics (filler type, filling degree, and conductivity of the filling material, etc.) within the current target area.

[0039] Specifically, in step S110, this embodiment of the invention combines outcrops, core samples, and well logging techniques in the target area to statistically analyze the fracture distribution characteristics at different development angles, thereby establishing a development frequency map (e.g., fracture dip angle) of different types of natural fractures in a typical shale reservoir; statistically analyze fracture height and orientation information to determine the fracture development scale characteristics (e.g., scale) within the target area; statistically analyze the fracture density distribution characteristics of multiple wells within the target area to determine whether each fracture surface is flat, smooth, and has morphological variation characteristics, obtaining fracture surface morphological variation characteristics (e.g., fracture width and fracture resistivity); and statistically analyze the fracture filling characteristics such as the type of filling material, degree of filling, and conductivity of filling material at different locations within the target area. Thus, after completing one or more of the above fracture development characteristic analyses, a fracture development characteristic analysis result for all the analysis results is obtained, leading to step S120.

[0040] Step S120 determines the instrument parameters of the dual lateral logging instrument required for the current forward simulation, and step S130 determines the measurement parameters of the wellbore measurement environment required for the current simulation.

[0041] Furthermore, since this embodiment of the invention requires dual-lateral logging simulation of the target area, it is necessary to first determine the instrument parameters of the dual-lateral logging instrument required for the current simulation test in step S120. Specifically, the instrument model is first determined, and then the instrument coefficients Ks and Kd of the shallow and deep lateral logging instruments are determined based on the determined instrument model. Here, Ks represents the shallow lateral logging instrument coefficient of the dual-lateral logging instrument required for the current simulation test, and Kd represents the deep lateral logging instrument coefficient of the dual-lateral logging instrument required for the current simulation test.

[0042] Furthermore, after setting the instrument parameters for the dual-lateral logging instrument, the wellbore environment (measurement) parameters adapted to the current forward modeling need to be set in step S130. Specifically, the wellbore environment parameters matching the current forward modeling test, as well as the following formation parameters, are determined based on the laboratory experimental data obtained from outcrop and core experiments conducted on the target area, geological information about the target area, drilling and logging data of all drilled wells in the target area, and other information.

[0043] In this embodiment of the invention, the wellbore environment measurement parameters include at least: the starting point location of the target area, the simulated sampling interval, the well inclination angle, the mud resistivity, and the radius of the well to be simulated.

[0044] Continue to refer to Figure 1 Step S140 extracts formation parameters based on the fracture development characteristic analysis results obtained in step S110, the instrument parameters obtained in step S120, and the wellbore environment measurement parameters obtained in step S130, thereby establishing a fractured formation model containing the fracture condition parameters to be analyzed. In this embodiment of the invention, the formation parameters include at least: the number of formation interfaces, the location (layer thickness) of each interface, the scale of each fracture within each formation, the resistivity of each fracture within each formation, the resistivity of the surrounding rock above and below each fracture within each formation, and the original formation resistivity (target layer resistivity) of each formation.

[0045] In constructing the formation model, the parameters of the fracture conditions to be analyzed corresponding to the current simulation test are first determined. In this embodiment of the invention, it is necessary to analyze the variation law between one or more fracture conditions and the dual-lateral logging resistivity curve, where the multiple fracture conditions are different parameters to be analyzed. Thus, this invention forms a shale fracture identification law by analyzing the variation law relationship between different fracture conditions and the dual-lateral logging resistivity response curve. Then, after performing actual dual-lateral logging on the wellbore to be analyzed, the development characteristics of peri-well fractures can be quickly identified directly using the fracture identification law formed above based on the dual-lateral resistivity response curve.

[0046] Furthermore, in this embodiment of the invention, the fracture condition parameters to be analyzed are selected from one or more parameters among formation parameters and fracture development characteristics. More specifically, the fracture condition parameters to be analyzed are selected from one or more of the following: fracture angle type (e.g., horizontal fracture, vertical fracture, dip fracture, etc.), fracture scale type, infill type (e.g., unfilled, bitumen-filled, debris-filled, etc.), formation resistivity (resistivity of different target layers), and lithological assemblage (e.g., shale-mudstone assemblage, shale-sandstone assemblage, shale-siltstone assemblage, etc.).

[0047] After determining one or more fracture conditions to be analyzed, in step S140, this invention configures different analytical data for each fracture condition parameter and establishes fractured formation models containing different analytical data. For example, when the current fracture condition parameter to be analyzed is the fracture angle type, corresponding fractured formation models are constructed for horizontal fractures, vertical fractures, dip fractures, etc., respectively. (See [link to relevant documentation]). Figure 2 and Figure 3 .

[0048] Furthermore, when constructing formation models with different analytical data, this invention couples information such as the instrument components and parameters of the dual-lateral logging instrument, formation parameters, fracture development characteristic analysis results, and wellbore environment measurement parameters into the currently constructed fractured formation model.

[0049] Figure 2 This is a schematic diagram of a horizontal fractured formation model in a dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application. Figure 3 This is a schematic diagram of a vertical fracture formation model in a dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application. Figure 2 and Figure 3 The diagrams show the corresponding fractured formation models for horizontal and vertical fracture conditions, respectively. The diagrams show the component distribution characteristics of the dual lateral logging instrument, the well diameter range CAL, the mud resistivity parameter Rm, the number of formation layers, the resistivity of the surrounding rock above and below the current formation Rs, the main fracture scale Rf (fracture width), the formation thickness h, and / or the resistivity of the flushed zone Rxo.

[0050] After constructing the formation model for each fracture condition to be analyzed, proceed to step S150. Step S150 is based on the finite element method. According to the formation model constructed in step S140, forward modeling is performed on the electric field distribution information formed by the dual lateral logging instrument in the formation to measure the dual lateral resistivity of the target area.

[0051] Since step S140 constructs a fractured formation model for each type of analysis data for each fracture condition to be analyzed, it is necessary to perform forward modeling for each fractured formation model under each condition to be analyzed, thereby generating a corresponding dual-direction logging response curve for each type of analysis data.

[0052] Furthermore, for a specific fracture condition to be analyzed, step S140 constructs different data for that fracture condition, thereby establishing fractured formation models containing different data. Then, corresponding forward simulations are performed on each fractured formation model containing different data to obtain dual-lateral logging response curves for each analysis data. Thus, when performing forward simulations based on multiple data for each fracture condition to be analyzed, this invention generates multiple sets of dual-lateral logging response curves for each fracture condition, with each set corresponding to a specific data point. Thus, this invention analyzes the influence relationship between different parameters under analysis and the response of dual-lateral logging instruments to form a shale fracture identification law (that is, a law characterizing the relationship between different fracture conditions and dual-lateral logging responses) that represents the matching relationship between shale fracture conditions and the applicability of instrument measurements. This law is used to identify the fracture development around the wellbore directly based on the dual-lateral logging response curve when performing dual-lateral logging on wellbores in the target area.

[0053] In this embodiment of the invention, since the forward modeling process for each fractured stratum model is similar, this invention will only use the forward modeling process of one stratum model as an example for illustration.

[0054] Specifically, firstly (step S1501, not shown), an element volume matching the current target region is established based on the finite element method. In step S1501, the current target region is constructed as a cylinder. Based on the wellbore environment measurement parameters, the morphological information of the constructed cylinder, including its height, radial subdivision length, and sampling grid size, is determined, thereby establishing an element volume with zero surface potential.

[0055] This invention employs a structured partitioning method, where the target region is represented by a cylinder with a height of D. Z Radius D r This makes the surface potential of the cylinder zero. This requires dividing (subdividing) the cylinder representing the target region according to a preset unit element, where the radial length of the unit element is Δr, the central angle is Δθ, and the axial height is Δz. (See [link to documentation]). Figure 4 .

[0056] Figure 4 This is a schematic diagram of the unit element in the dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application. During partitioning (division), the center of the upper surface of the cylinder is used as the origin, and (r...) i θ j , z kLet ) represent the coordinates of each node within the element, where i represents the index of the radial length subdivision line of the cylinder, and r i This represents the radial length coordinate of the current node (the radial subdivision length of the current node's location is the i-th radial subdivision line), j represents the index of the central angle azimuth subdivision line of the cylinder, and θ j This represents the azimuth coordinates of the central angle of the current node (the azimuth of the central angle at the current node's location is the j-th azimuth subdivision line), k represents the index of the axial height subdivision line of the cylinder, and z represents the azimuth coordinates of the current node. k This represents the axial height coordinate of the current node (the axial height of the current node's location is the k-th axial height subdivision line). Further, using Δr... i , Δθ j Δz k , respectively, represent the segmentation length in the radial direction, the segmentation angle in the azimuth direction, and the segmentation height in the axial direction of each node. Thus, this invention can, according to a preset unit element size, dissect an element body matching the spatial range of the target area into multiple element units that correspond to the azimuth angle, radial length, and axial height of the unit element, respectively (in sequence) along different azimuth directions, along different radial lengths, and along different axial heights.

[0057] Next, after completing the construction of the target area element body, the present invention will (step S1502, not shown) couple a formation model containing the fracture condition parameters to be analyzed into the element body, and use the finite element simulation method to derive the electric field near each electrode in the current dual-lateral logging instrument, so as to simulate the electric field distribution information formed by the real formation, and further obtain the dual-lateral resistivity. In the embodiment of the present invention, the dual-lateral logging instrument has an electrode system, which (refer to...) Figure 6 and Figure 7 It includes: main electrode (A0), monitoring electrode (M1-M2, M1'-M2') and shielding electrode (A1, A1', A2, A2').

[0058] Furthermore, in step S1502, the present invention needs to couple the formation model containing a certain analysis data configured in the fracture condition parameters to be analyzed into the target area element body constructed in step S1501, and use the finite element simulation method to derive the electric field near each electrode in the current dual-lateral logging instrument to form electric field distribution information, and further obtain the dual-lateral resistivity.

[0059] In accordance with Figure 4After the unit grid (unit element volume) divides the target area element volume, each electrode in the current dual-lateral logging instrument will have multiple nodes. Each electrode can be regarded as an equipotential body. Therefore, all nodes on the electrode have the same electromotive force. Similarly, the electromotive force of all nodes on the boundary of the target area is also equal.

[0060] Furthermore, the deep lateral resistivity and shallow lateral resistivity are determined by the ratio of the electromotive forces (EMFs) of the two shielded electrodes A1 and A2 (a pair of symmetrical shielded electrodes) in the logging instrument. The ratio of the EMFs of the two shielded electrodes A1 and A2 in the logging instrument is a constant; the ratio is positive in the deep lateral direction and negative in the shallow lateral direction.

[0061] Figure 5 This is a specific example diagram illustrating the input-output flow of the forward modeling method in the dual-lateral logging forward modeling simulation method for reflecting shale fractures, as described in an embodiment of this application. Figure 5 As shown, the first step is to couple the formation model containing the data to be analyzed into the target area element volume. During coupling, basic data such as the number and starting point of formation interfaces, mud resistivity, simulation sampling interval, well inclination angle, and well radius are input. Then, formation parameters such as interface location (thickness), (main) fracture scale, fracture resistivity, resistivity of the surrounding rock above and below, and resistivity of the undisturbed formation are input sequentially for each formation. When solving for unknowns in the dual lateral response curves, if the ratio of the calculated electromotive forces of the two shielding electrodes is positive, the calculated apparent resistivity is the deep lateral resistivity; if the ratio of the calculated electromotive forces of the two shielding electrodes is negative, the calculated apparent resistivity is the shallow lateral resistivity.

[0062] Thus, based on the constructed elemental volume with zero surface potential, this embodiment of the invention uses the finite element simulation method to derive and calculate the electric field near each electrode in the dual-lateral logging instrument. Furthermore, by calculating the ratio of the two shielded electrodes in the instrument, the dual-lateral resistivity response curve corresponding to the formation model of the current data to be analyzed is solved.

[0063] To obtain a cost-effective, fast, and highly accurate dual-lateral logging method for accurately identifying shale fractures, this invention discloses a dual-lateral forward modeling method. This method analyzes the physical field variation and logging response characteristics to determine the fracture scale that dual-lateral logging can characterize under the influence of the wellbore environment. Based on the method's applicability, it clarifies the conditions and rules for effectively identifying fractures using dual-lateral logging. Furthermore, this invention employs programming languages ​​and basic algorithms to fuse big data into an intelligent forward modeling method. Steps S110 to S150 are respectively formed into corresponding program blocks, generating a fracture feature analysis module (based on step S110), an instrument design module (based on step S120), a wellbore measurement module (based on step S130), a formation model generation module (based on step S140), and a forward modeling module (based on step S150). By inputting relevant stratigraphic model parameters, forward modeling is performed to simulate real stratigraphy, thereby converting deep and shallow lateral resistivity values. This enables the processing of a truly meaningful big data fusion and interactive platform, with fast calculation speed and low cost.

[0064] The following section describes the application of the forward modeling method described in this invention to the fracture characteristics of the Chang 9 section shale reservoir in the Ordos Basin, and analyzes the influence of different fracture condition parameters on the dual lateral logging response mechanism.

[0065] To study the response characteristics of horizontal fractures of different scales under the same filling material conditions, three-layer models of horizontal fractures with asphalt filling material were established under vertical well conditions. The mud resistivity was 1 Ω·m, the resistivity of the upper and lower surrounding rocks was 20 Ω·m, the resistivity of the target layer was 35 Ω·m, and the fracture width varied from 0.5 m to 1 nm. Figure 6 This is a schematic diagram of the deep lateral logging response of a horizontal fracture under bitumen-filled conditions in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application. Figure 7 This is a schematic diagram of the shallow lateral logging response under bitumen-filled conditions in the dual-lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application. Figure 6 and Figure 7 As shown, when the crack width is less than 0.1 to 1 μm, the deep lateral response and the shallow lateral response are in a straight line, and the crack cannot be identified. That is, the smallest identifiable scale of the crack is 0.1 to 1 μm.

[0066] When the fracture filling material is different, the response mechanism of bilateral lateral logging is unclear, making it impossible to effectively extract information about shale fracture filling material and evaluate fracture effectiveness. Therefore, it is necessary to conduct research on the influence mechanism of fracture filling material on bilateral lateral logging response based on the statistical results of fractures in the actual shale reservoirs in the study area. Specifically, when the fracture condition parameters to be analyzed are determined as fracture filling material types, the fracture filling types in the study area are mainly divided into three types: unfilled fractures, bitumen-filled fractures, and calcite-filled fractures. Without considering the influence of mud invasion, fractured (three-layer) formation models with unfilled, bitumen-filled, and plant leaf-filled fractures are established respectively. Figure 8 This is a schematic diagram of the deep lateral logging response under different fracture filling types in the dual lateral logging forward modeling method for reflecting shale fractures, as described in this application embodiment. Figure 9 This diagram illustrates the shallow lateral logging response under different fracture-filling types in the dual lateral logging forward modeling method for reflecting shale fractures, as described in this application embodiment. Figure 8 and Figure 9 As can be seen, the greater the difference between the resistivity after the fracture is filled and the formation resistivity, the greater the difference between the apparent resistivity value and the actual formation resistivity value.

[0067] When fractures develop in different shale reservoirs, the bilateral lateral logging responses differ significantly. This study investigates the case where the resistivity of the shale reservoirs in the research area ranges from 20 to 45 Ω·m. Without considering the influence of mud intrusion, three formation models with different target layer resistivities are established. Under vertical well conditions, with a well diameter of 0.1016 m, a mud resistivity of 1 Ω·m, and surrounding rock resistivities of 50 Ω·m, the target layer resistivities for each formation model are 20 Ω·m, 25 Ω·m, 30 Ω·m, 35 Ω·m, and 40 Ω·m, respectively. Figure 10 This is a schematic diagram of the deep lateral logging response under different shale resistivity conditions in the dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application. Figure 11 This diagram illustrates the shallow lateral logging response under different shale resistivity conditions in a dual lateral logging forward modeling method for reflecting shale fractures, as described in an embodiment of this application. Figure 10 and Figure 11 It can be seen that the resistivity is closest to the actual formation at a depth of 1697.8–1710.4 m. The greater the resistivity of the shale formation itself, the greater the difference between the apparent resistivity value and the actual resistivity value.

[0068] When fractures develop under different lithological combinations, the bilateral lateral logging responses differ significantly. Therefore, it is necessary to explore and analyze the patterns based on the statistical results of fractures in the actual shale reservoirs of the study area. The lithological combinations of the study area are divided into three types: shale-mudstone, shale-sandstone, and shale-siltstone. Under vertical well conditions, three-layer formation models corresponding to the analysis data of the aforementioned three lithological combinations are established respectively. Figure 12 This is a schematic diagram of the deep lateral logging response under different lithological combinations in the dual lateral logging forward modeling method for reflecting shale fractures, as described in this application embodiment. Figure 13 This is a schematic diagram of shallow lateral logging responses under different lithological combinations in a dual lateral logging forward modeling exercise reflecting shale fractures, as described in an embodiment of this application. Figure 12 and Figure 13 It can be seen that the deep lateral response characteristics of the shale and siltstone combination are closest to the actual target layer, while the difference in response characteristics of different lithological combinations reflected in the shallow lateral direction is not as large as that of the deep lateral resistivity.

[0069] On the other hand, based on the above forward modeling model, this embodiment of the invention also provides a dual-lateral logging forward modeling system (hereinafter referred to as "forward modeling system") for reflecting shale fractures. Figure 14 This is a block diagram of a dual-lateral logging forward modeling system for reflecting shale fractures, according to an embodiment of this application. Figure 14 As shown, the forward modeling model described in this embodiment of the invention includes: a fracture feature analysis module 1401, an instrument design module 1402, a wellbore measurement module 1403, a formation model generation module 1404, and a forward modeling module 1405.

[0070] Furthermore, the fracture feature analysis module 1401 is implemented according to the method described in step S110 above, and is configured to analyze the fracture development characteristics of the target area; the instrument design module 1402 is implemented according to the method described in step S120 above, and is configured to determine the instrument parameters of the dual-lateral logging instrument required for the current simulation; the wellbore measurement module 1403 is implemented according to the method described in step S130 above, and is configured to determine the wellbore environment measurement parameters required for the current simulation; the formation model generation module 1404 is implemented according to the method described in step S140 above, and is configured to extract formation parameters based on the fracture development feature analysis results, instrument parameters, and wellbore environment measurement parameters, thereby establishing a formation model containing fracture condition parameters to be analyzed; the forward modeling simulation module 1405 is implemented according to the method described in step S150 above, and is configured to perform forward modeling simulation of the electric field distribution information formed by the dual-lateral logging instrument in the formation based on the finite element method and the formation model above, and measure the dual-lateral resistivity of the current target area.

[0071] The aforementioned forward modeling module 1405 includes an element volume construction unit 1405A and a dual lateral resistivity generation unit 1405B. The element volume construction unit 1405A is configured to establish an element volume matching the current target region based on the finite element method. The dual lateral resistivity generation unit 1405B is configured to couple a formation model containing the fracture condition parameters to be analyzed into the constructed element volume, and use the finite element simulation method to derive the electric field near each electrode in the dual lateral logging instrument, forming electric field distribution information, and further obtaining the dual lateral resistivity.

[0072] This invention discloses a dual-lateral logging forward modeling method and system for reflecting shale fractures. Based on multi-dimensional field-core-logging data, this method and system study the characteristics of typical fracture development in shale reservoirs, extract reasonable shale fracture parameters, establish different shale reservoir fracture models, and complete a dual-lateral logging forward modeling method that can effectively reflect fracture characteristics. Then, it simulates the physical field changes during dual-lateral logging measurements in fractured shale reservoirs. Based on the simulated logging response mechanism, it clarifies the applicable conditions of the dual-lateral logging method under different fracture characteristic conditions, forming shale fracture identification rules. This lays a theoretical foundation for shale fracture identification and evaluation, enabling the selection of the optimal "sweet spot" in the reservoir and comprehensive and accurate evaluation of the reservoir, providing technical support for increasing oilfield reserves and production.

[0073] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0074] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should be extended to equivalent substitutions of these features as understood by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0075] The phrase "an embodiment" or "an embodiment" used in this specification means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Therefore, the phrase "an embodiment" or "an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0076] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection of this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A dual-lateral logging forward modeling method for reflecting shale fractures, characterized in that, include: Determine the crack development characteristics of the target area; Determine the instrument parameters of the dual lateral logging instrument required for the current simulation; Determine the wellbore environment measurement parameters required for the current simulation; Based on fracture development characteristic parameters, instrument parameters, and wellbore environment measurement parameters, formation parameters are extracted, and a formation model containing fracture condition parameters to be analyzed is established. Based on the finite element method and the formation model, a forward modeling simulation is performed on the electric field distribution information generated by the dual lateral logging instrument in the formation to measure the dual lateral resistivity of the target area, including: The target area is constructed as a cylinder. Based on the wellbore environment measurement parameters, the morphological information of the cylinder, including its height, radial subdivision length, and sampling grid size, is determined, thereby establishing a target area element volume with a surface potential of zero that matches the current target area. The target region element volume is divided according to the unit element volume with a ring-shaped sector hexahedron structure. Multiple nodes are set on each electrode in the current dual-lateral logging instrument and each electrode is regarded as an equipotential body, so that all nodes on the electrode have the same electromotive force and all nodes on the boundary of the target region have the same electromotive force. The formation model containing the fracture condition parameters to be analyzed is coupled into the element body. Using the finite element method, the electric field near each electrode in the dual-lateral logging instrument is derived to form the electric field distribution information. The dual-lateral resistivity is then obtained. Specifically, the dual-lateral resistivity response curve corresponding to one of the fracture conditions to be analyzed in the formation model is obtained by calculating the ratio of the two shielded electrodes in the current dual-lateral logging instrument. When the ratio of the calculated electromotive forces of the two shielded electrodes is positive, the apparent resistivity is deep lateral resistivity; when the ratio of the calculated electromotive forces of the two shielded electrodes is negative, the apparent resistivity is shallow lateral resistivity.

2. The dual-lateral logging forward modeling method according to claim 1, characterized in that, The steps for analyzing the crack development characteristics of the target area include: Analyze and statistically analyze the development frequency distribution of cracks at different development angles, crack development scale information, filling material type, filling degree and conductivity of filling material in the current target area.

3. The dual-lateral logging forward modeling method according to claim 1, characterized in that, The forward modeling method further includes: Different data to be analyzed are constructed for the fracture condition parameters to be analyzed, and fractured stratigraphic models containing different data to be analyzed are established respectively, so that corresponding forward modeling is performed for different stratigraphic models. By analyzing the influence relationship between different parameters under different conditions and the response of dual-lateral logging instruments, a matching relationship between shale fracture conditions and the applicability of instrument measurements is established.

4. The dual-lateral logging forward modeling method according to any one of claims 1 to 3, characterized in that, The wellbore environment measurement parameters include the starting point location of the target area, the simulated sampling interval, the well inclination angle, the mud resistivity, and the wellbore radius. The formation parameters include the number of formation interfaces, as well as the interface location, fracture size, fracture resistivity, resistivity of the surrounding rock above and below, and resistivity of the original formation for each formation.

5. The dual-lateral logging forward modeling method according to any one of claims 1 to 3, characterized in that, The fracture condition parameters to be analyzed are selected from one or more of the following: fracture angle type, fracture scale type, infill type, formation resistivity, and lithological combination.

6. The dual-lateral logging forward modeling method according to any one of claims 1 to 3, characterized in that, Each step is constructed into a corresponding program block to form an intelligent simulation system.

7. A dual-lateral logging forward modeling system for reflecting shale fractures, characterized in that, The forward modeling system includes: The crack feature analysis module is configured to analyze the crack development characteristics of the target area; The instrument design module is configured to determine the instrument parameters of the dual-lateral logging instrument required for the current simulation. The wellbore measurement module is configured to determine the wellbore environment measurement parameters required for the current simulation. The formation model generation module is configured to extract formation parameters and establish a formation model containing parameters of the fracture conditions to be analyzed based on the analysis results of fracture development characteristics, instrument parameters and wellbore environment measurement parameters. The forward modeling module is configured to perform forward modeling of the electric field distribution information formed by the dual lateral logging instrument in the formation based on the finite element method and the formation model, and to measure the dual lateral resistivity of the target area. The forward modeling module includes: The element body construction unit is configured to construct the target area as a cylinder, and determine the morphological information of the cylinder, including its height, radial partition length, and sampling grid size, based on the wellbore environment measurement parameters, thereby establishing a target area element body with a surface potential of zero that matches the current target area; The target area element volume division unit is configured to divide the target area element volume according to the unit element volume constructed as a ring-shaped sector hexahedron. Multiple nodes are set on each electrode in the current dual-lateral logging instrument and each electrode is regarded as an equipotential body, so that all nodes on the electrode have the same electromotive force and the electromotive force of all nodes on the boundary of the target area is also equal. A dual lateral resistivity generation unit is configured to couple the formation model containing the fracture condition parameters to be analyzed into the element body, derive the electric field near each electrode in the dual lateral logging instrument using the finite element simulation method, form the electric field distribution information, and further obtain the dual lateral resistivity. Specifically, the dual lateral resistivity response curve corresponding to one of the fracture conditions to be analyzed in the current dual lateral logging instrument is obtained by calculating the ratio of the two shielded electrodes. When the ratio of the calculated electromotive forces of the two shielded electrodes is positive, the solved apparent resistivity is deep lateral resistivity; when the ratio of the calculated electromotive forces of the two shielded electrodes is negative, the solved apparent resistivity is shallow lateral resistivity.

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