Method, device and equipment for determining brittleness index

Abstract

The embodiment of the present application provides a kind of brittleness index determination method, device and equipment, the method comprises: obtaining the Poisson ratio of target layer;According to the Poisson ratio of target layer, determine the initial brittleness index of target layer;Determine the effective stress of target layer;Construct the geothermal field of target layer;According to the effective stress of target layer and the geothermal field of target layer, the initial brittleness index of target layer is corrected, and the final brittleness index of target layer is obtained.Initial brittleness index expressed as the function of Poisson ratio has better indication effect on favorable brittle zone, has the meaning of geological and engineering double sweet spot;Further, by the correction of effective stress and geothermal field, the change of rock brittleness caused by structural factors (stratum burial depth change) is corrected, so as to improve the prediction accuracy of stratum brittleness in complex structure area, can reflect the real brittleness characteristics of complex structure shale and dense clastic rock reservoir with large burial depth change.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of oil and gas geophysical exploration technology, specifically to a method, apparatus and equipment for determining the brittleness index. Background Technology

[0002] Rock brittleness is a vivid expression of the fracture characteristics of rocks, and the index used to characterize these brittleness characteristics is called the Brittleness Index (BI). Rock brittleness is a key parameter for evaluating rock drillability, compressibility, and wellbore stability, and is a very important evaluation indicator for tight sandstone and shale oil and gas reservoirs. Therefore, improving the prediction accuracy of the Brittleness Index is of great significance.

[0003] Currently, commonly used brittleness indices include the mineral brittleness index and the Rickman mechanical brittleness index. The mineral brittleness index is determined based on the mineral composition of the subsurface medium. Brittle minerals, represented by siliceous minerals, are easily broken under external forces, creating cracks that form pathways for natural gas migration and production. Therefore, formations with high brittle mineral content have a higher brittleness index. The Rickman mechanical brittleness index is determined based on Young's modulus and Poisson's ratio. Young's modulus reflects the ability of shale to retain fractures after being fractured, while Poisson's ratio reflects the ability of shale to fracture under certain pressure. Generally, shale with a low Poisson's ratio and a high Young's modulus exhibits better brittleness.

[0004] As burial depth increases, pressure and temperature rise, causing rocks to undergo a brittle-ductile transition. Even within the same stratum, if the mineral composition is identical (i.e., the brittleness indication based on the mineral brittleness index is consistent), the exhibited brittle characteristics can differ significantly. Therefore, in such cases, the mineral brittleness index cannot accurately reflect the brittleness characteristics of the stratum. At low effective pressure (shallow layers), Young's modulus and Poisson's ratio are significantly affected by effective pressure; at high effective pressure (deep layers), Young's modulus and Poisson's ratio change slowly with effective pressure. Therefore, when the burial depth of the target layer varies considerably, Rickman mechanical brittleness cannot accurately reflect the brittleness characteristics of the stratum.

[0005] In conclusion, for complex shale and tight clastic reservoirs, especially when the reservoir depth varies greatly, neither the mineral brittleness index nor the Rickman mechanical brittleness index can reflect the true brittleness characteristics of the formation. Summary of the Invention

[0006] This invention provides a method, apparatus, and equipment for determining the brittleness index, which solves the problem that existing methods cannot reflect the true brittleness characteristics of complex shale and tight clastic reservoirs with large variations in burial depth.

[0007] In a first aspect, embodiments of the present invention provide a method for determining a fragility index, comprising:

[0008] Obtain the Poisson's ratio of the target layer;

[0009] The initial brittleness index of the target layer is determined based on the Poisson's ratio of the target layer;

[0010] Determine the effective stress of the target layer, which is the difference between the overlying formation pressure and the pore pressure of the target layer;

[0011] Construct the geothermal field of the target layer;

[0012] The initial brittleness index of the target layer is corrected based on the effective stress and geothermal field of the target layer to obtain the final brittleness index of the target layer.

[0013] In one embodiment, determining the initial brittleness index of the target layer based on the Poisson's ratio of the target layer includes:

[0014] The initial brittleness index of the target layer is determined according to the following expression.

[0015]

[0016] Among them, BI initial σ represents the initial brittleness index, and σ represents Poisson's ratio.

[0017] In one embodiment, the overlying formation pressure of the target layer is determined according to the following expression:

[0018]

[0019] Among them, P ov denoted by , z represents the overlying strata pressure, z represents the depth, and g represents the gravitational acceleration.

[0020] In one embodiment, the pore pressure of the target layer in the time domain is determined according to the following expression:

[0021]

[0022] Among them, P p V represents pore pressure, FC represents the Philippians model factor, σ represents Poisson's ratio, and V max V represents the seismic wave velocity when porosity is close to zero. min V represents the seismic wave velocity when rigidity is close to zero. i P represents the velocity of seismic waves. ov The overlying strata pressure is represented by t, time is represented by x, and y is represented by y.

[0023] In one embodiment, correcting the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer includes:

[0024] Determine the effective stress correction factor based on the effective stress of the target layer;

[0025] Determine the geothermal field correction factor based on the geothermal field of the target layer;

[0026] The initial brittleness index of the target layer is corrected based on the effective stress correction factor and the geothermal field correction factor.

[0027] In one embodiment, determining the effective stress correction factor based on the effective stress of the target layer includes:

[0028] The effective stress correction factor is determined according to the following expression:

[0029] f2(P e (x,y,t)=c*P e (x,y,t) p +dp>3,c<0;

[0030] or,

[0031] f2(P e 9x,y,t))=c*P e (x,y,t)+dc<0;

[0032] Where f2 represents the effective stress correction factor, P e d represents the effective stress, and d represents a constant.

[0033] In one embodiment, determining the geothermal field correction factor based on the geothermal field of the target layer includes:

[0034] The geothermal field correction factor is determined according to the following expression:

[0035] f1(T(x,y,t))=a*T(x,y,t) q +bq>3, a<0;

[0036] or,

[0037] f1(T(x,y,t))=a*T(x,y,t)+ba<0;

[0038] Where f1 represents the geothermal field correction factor, T represents the geothermal field, and b represents a constant.

[0039] Secondly, embodiments of the present invention provide an apparatus for determining a brittleness index, comprising:

[0040] The acquisition module is used to obtain the Poisson's ratio of the target layer;

[0041] The processing module is used to determine the initial brittleness index of the target layer based on the Poisson's ratio of the target layer;

[0042] The determination module is used to determine the effective stress of the target layer, which is the difference between the overlying formation pressure and the pore pressure of the target layer.

[0043] The building module is used to construct the geothermal field of the target layer;

[0044] The correction module is used to correct the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer, so as to obtain the final brittleness index of the target layer.

[0045] Thirdly, embodiments of the present invention provide an electronic device, comprising:

[0046] At least one processor and memory;

[0047] The memory stores instructions that the computer executes;

[0048] At least one processor executes computer execution instructions stored in memory, causing the at least one processor to perform the method for determining the fragility index as described in any of the first aspects.

[0049] Fourthly, embodiments of the present invention provide a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, are used to implement the method for determining the fragility index as described in any of the first aspects.

[0050] The method, apparatus, and equipment for determining the brittleness index provided in this invention obtain the Poisson's ratio of the target layer, determine the initial brittleness index of the target layer based on the Poisson's ratio, and finally correct the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer to obtain the final brittleness index of the target layer. The initial brittleness index, expressed as a function of Poisson's ratio, has a good indicative effect on favorable brittleness areas and has significance for both geological and engineering purposes. Furthermore, by correcting the effective stress and geothermal field, the changes in rock brittleness caused by tectonic factors (variations in stratum depth) are corrected, thereby improving the accuracy of stratum brittleness prediction in complex tectonic areas and reflecting the true brittleness characteristics of complex shale and tight clastic reservoirs with large variations in burial depth. Attached Figure Description

[0051] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0052] Figure 1 A flowchart illustrating a method for determining the brittleness index according to an embodiment of the present invention;

[0053] Figure 2 A flowchart of a method for determining the brittleness index provided in another embodiment of the present invention;

[0054] Figure 3 This is a schematic diagram of the intersection of the new elastic brittleness index of well A provided in an embodiment of the present invention;

[0055] Figure 4 This is a schematic diagram of the overlying formation pressure profile of well B, a verified well, according to an embodiment of the present invention.

[0056] Figure 5 A schematic diagram of the structure of a device for determining the brittleness index provided in an embodiment of the present invention;

[0057] Figure 6 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention.

[0058] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0059] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of this application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to this application are not shown or described in the specification. This is to avoid obscuring the core parts of this application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0060] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0061] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0062] The fracturing quality of a reservoir is a key factor in evaluating its "sweet spot," and the brittleness index, used to characterize rock brittleness, is an important indicator for evaluating reservoir fracturing quality. A higher brittleness index indicates a reservoir is more easily fractured and more likely to yield high-yield industrial gas flows. Improving the prediction accuracy of the brittleness index is of significant guiding importance for obtaining both geological and engineering sweet spots.

[0063] Formations with high brittle mineral content generally have a higher brittleness index because brittle minerals, such as siliceous minerals, are easily broken under external forces, creating cracks that form pathways for natural gas migration and production. Therefore, the brittleness index can be determined based on the mineral composition of the subsurface medium. Specifically, the mineral brittleness index BI can be determined using the following expression. min :

[0064]

[0065] Among them, V quartz V indicates the content of quartz minerals. clay V represents the clay mineral content. carbonate This indicates the content of carbonate minerals. The mineral brittleness index and the content of various minerals can both be expressed as a percentage.

[0066] While the brittleness index can be determined based on the mineral composition of the subsurface medium, its accuracy in predicting these mineral components limits its applicability to practical production guidance. Currently, the primary method for guiding practical production is prediction based on seismic data inversion. Pre-stack inversion, specifically using multiple pre-stack data volumes in tandem, yields three parameters: P-wave and S-wave velocities, and density. Elastic parameters are then calculated to evaluate the brittleness of subsurface rock formations. Shales with low Poisson's ratios and high Young's moduli are generally considered to be more brittle. Young's modulus reflects the ability of shale to retain fractures after fracturing, while Poisson's ratio reflects its ability to fracture under pressure. Rickman further proposed a mechanical brittleness index (BI) with proven effectiveness. Specifically, the mechanical brittleness index BI can be determined using the following expression. Rickman :

[0067]

[0068] Among them, E BRIT E represents the normalized Young's modulus. max E represents the maximum Young's modulus. min σ represents the minimum Young's modulus. BRIT σ represents the normalized Poisson's ratio. max σ represents the maximum Poisson's ratio. min BI represents the minimum Poisson's ratio. RickmanThe Rickman brittleness index represents the brittleness index, where E represents the Young's modulus of the formation being tested, and σ represents the Poisson's ratio. The Rickman brittleness index is currently the most widely used brittleness index. The unit for Young's modulus can be GPa.

[0069] Currently, the assessment of shale brittleness is mainly based on experience gained in shale gas exploration and development, using mineralogy or elastic parameter methods for quantitative characterization. These two methods have played a crucial role in evaluating the brittleness of shale gas reservoirs, and researchers have explored numerous improvements to these methods. However, according to fundamental laws of rock mechanics, as burial depth increases, pressure and temperature rise, leading to a brittle-ductile transition in rocks. This means that even within the same formation, if the mineral composition is completely identical (i.e., the brittleness indicators based on brittle minerals are consistent), the exhibited brittle characteristics can differ significantly. Therefore, in such cases, brittleness indicators based on brittle minerals cannot accurately reflect the brittle characteristics of the rock. Furthermore, laboratory experiments and numerical simulations of brittle failure characteristics of shale under different stress conditions show that at low effective pressure Pe (shallow layers), Young's modulus and Poisson's ratio are significantly affected by Pe; however, when Pe > 35 GPa (deep layers), the changes in Young's modulus and Poisson's ratio with Pe become slower. Therefore, for complex shale gas and tight clastic reservoirs, especially in areas where the burial depth of the target layer varies greatly, neither the mineral brittleness index nor the Rickman mechanical brittleness index can objectively reflect the true brittleness characteristics of the formation.

[0070] This application addresses the problem that existing brittleness indices cannot accurately indicate the true brittleness characteristics of strata under complex geological conditions, especially when the target layer has significant variations in burial depth and is affected by changes in temperature and pressure, leading to shifts in the brittle-ductile properties of rocks. It constructs an initial brittleness index that reflects the low-frequency variation trend of brittleness characteristics and corrects this initial brittleness index based on effective stress, thereby improving the prediction accuracy of brittleness indices in complex structural areas. Specific embodiments will be used to illustrate this application in detail below.

[0071] Example 1

[0072] Figure 1 This is a flowchart illustrating a method for determining the fragility index according to an embodiment of the present invention. Figure 1 As shown, the method in this embodiment may include:

[0073] S101. Obtain the Poisson ratio of the target layer.

[0074] In this embodiment, the target layer can be the formation or reservoir to be tested. The Poisson's ratio of the target layer can be obtained, for example, by measuring the target layer sample with an instrument, or by obtaining it from existing literature (such as measurement reports). In this embodiment, there is no limitation on the specific method of obtaining the Poisson's ratio.

[0075] S102. Determine the initial brittleness index of the target layer based on the Poisson's ratio of the target layer.

[0076] As the quartz content in shale increases, Young's modulus increases, but as porosity increases, Young's modulus decreases. Simultaneously, increases in organic matter and gas content in the reservoir also lead to a decrease in Young's modulus. Therefore, while the traditional Rickman mechanical brittleness index can characterize areas with high brittleness, it lacks effective characterization for areas with high porosity, high organic matter content, and high gas content in high-quality shale layers, and cannot simultaneously characterize sweet spots in shale formations.

[0077] To overcome the aforementioned shortcomings, this embodiment employs multidimensional cross-plot analysis to construct an initial brittleness index solely based on Poisson's ratio. The initial brittleness index, a function of Poisson's ratio, effectively distinguishes organic-rich shale reservoirs. Since the initial brittleness index in this embodiment is only related to Poisson's ratio, it effectively avoids the influence of factors such as rock porosity, fluid, and organic matter on the prediction of Young's modulus and Poisson's ratio, achieving a good indication of favorable brittleness zones and possessing both geological and engineering significance.

[0078] In one optional implementation, determining the initial brittleness index of the target layer based on the Poisson's ratio of the target layer may include:

[0079] The initial brittleness index of the target layer is determined according to the following expression.

[0080]

[0081] Among them, BI initial σ represents the initial brittleness index, and σ represents Poisson's ratio.

[0082] Specifically, by substituting the Poisson's ratio of the target layer into the above formula, the initial brittleness index of the target layer can be determined.

[0083] S103. Determine the effective stress of the target layer. The effective stress of the target layer is the difference between the overlying formation pressure and the pore pressure of the target layer.

[0084] As burial depth and effective confining pressure increase, shale undergoes a brittle-plastic transition. When the confining pressure increases from 0 to 80 MPa, the overall brittleness index of shale decreases from 0.8696 to 0.6586, a reduction of 24.3%. Therefore, accurate calculation of effective stress is crucial for the structural correction of the initial brittleness index.

[0085] In one alternative implementation, the effective stress can be determined according to the following expression:

[0086] P e =P ov -P p

[0087] Among them, P e P represents the effective stress. ov P represents the pressure of the overlying strata. p P represents pore pressure. e P ov and P p The unit can be MPa.

[0088] Specifically, by substituting the overlying formation pressure and the pore pressure of the target layer into the above formula, the effective stress of the target layer can be determined.

[0089] S104. Construct the geothermal field of the target layer.

[0090] In this embodiment, the geothermal field (T) of the target layer can be constructed based on the actual well geothermal curve using software such as NEWS and JASON, and the modeling difference algorithm of triangular mesh. Specifically, the time-domain geothermal field can be constructed.

[0091] S105. Correct the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer to obtain the final brittleness index of the target layer.

[0092] While the initial brittleness index can effectively distinguish organic-rich shale reservoirs, it still cannot adequately characterize the changes in rock brittleness and ductility caused by variations in temperature and pressure due to changes in burial depth. Therefore, in this embodiment, the initial brittleness index is further corrected for tectonic (burial depth) conditions based on effective stress and geothermal field.

[0093] As effective stress increases, brittleness gradually decreases; therefore, the final brittleness index is negatively correlated with effective stress. Similarly, as temperature increases, brittleness gradually decreases; therefore, the final brittleness index is negatively correlated with the geothermal field. In other words, the final brittleness index obtained by correcting for effective stress and geothermal field is negatively correlated with both effective stress and geothermal field.

[0094] Under low effective stress, the change in brittleness is not obvious; under high effective stress, the reduction in brittleness is more obvious, so the final brittleness index can decrease exponentially with the increase of effective stress; at a certain temperature critical point, the brittleness of the rock will decrease significantly, showing a more obvious elastoplastic transition, so the final brittleness index can decrease exponentially with the increase of geothermal field.

[0095] In one alternative implementation, the final brittleness index BI of the target layer final It can be determined based on the following expression:

[0096] BI final =BI initial +ΔBI=BI initial+f(P e ,T);

[0097] Where ΔBI represents the correction amount for the initial brittleness index based on the effective stress and geothermal field, f(P) e ,T) represents the correction quantity as a function of effective stress and geothermal field.

[0098] The method for determining the brittleness index provided in this embodiment obtains the Poisson's ratio of the target layer, determines the initial brittleness index based on the Poisson's ratio, and finally corrects the initial brittleness index based on the effective stress and geothermal field of the target layer to obtain the final brittleness index. The initial brittleness index, expressed as a function of Poisson's ratio, has a good indicative effect on areas with favorable brittleness, possessing significance for both geological and engineering purposes. Furthermore, by correcting for changes in rock brittleness caused by tectonic factors (variations in stratum depth), the method corrects for these variations, thereby improving the accuracy of brittleness prediction in complex tectonic areas. The method provided in this embodiment can reflect the true brittleness characteristics of complex tectonic shale and tight clastic reservoirs with significant variations in burial depth.

[0099] Example 2

[0100] Based on the above embodiments, this embodiment further provides a detailed explanation of the calculation of overlying formation pressure and pore pressure.

[0101] Overburden pressure refers to the pressure exerted on a stratum by the total weight of the bedrock and fluids within the pores of the rock above a certain depth. In one optional embodiment, the overburden pressure of the target layer can be determined according to the following expression:

[0102]

[0103] Among them, P ov Let ρ(z) represent the overburden pressure, z represent the depth, g represent the gravitational acceleration (a constant), and ρ(z) represent the density at depth z. Overburden pressure is calculated by integrating from the surface in the depth domain. High-precision overburden pressure calculation is crucial for obtaining formation pressure and effective stress. By matching depth-domain well logging data with time-domain seismic data, the time-domain overburden pressure P is finally obtained. ov (x,y,t), where (x,y) can be coordinates, such as x representing the abscissa and y representing the ordinate, or it can be the abscissa or yscissa line number.

[0104] Overpressure in the formation can lead to a decrease in seismic wave velocity. Under normal compaction conditions, formation velocity increases with depth. When underpressure occurs, the formation velocity is lower than normal. When there is overpressure in the formation, the seismic wave propagation velocity of the formation rocks often decreases significantly, resulting in a low-velocity anomaly. Therefore, seismic velocity prediction methods are currently the primary method used to determine formation pressure. The key issue in pressure prediction is obtaining the formation velocity. Only by obtaining a high-precision, high-resolution velocity field can a relatively accurate pressure field be obtained. The establishment of a high-precision velocity model includes structural modeling, near-surface velocity model establishment, initial velocity modeling, model optimization iteration, and updating. Among these, Discrete Wavelet Transform (DWT)-reflector grid tomography velocity inversion and model optimization iteration are the key and core steps. First, a pre-stack time migration velocity model is used as the initial velocity model for pre-stack depth migration to significantly improve the efficiency of velocity modeling and ensure a certain level of accuracy. Second, the Kirchhoff pre-stack depth migration method is used to generate Common Imaging Point (CIP) gathers for the target line, providing a relatively stable basis for picking up the phase axis of the reflected wave. The optimization and iteration of the velocity model are achieved by solving the mesh tomography equations to obtain the velocity perturbation in the depth domain, and a geologically guided constrained mesh tomography technique is introduced to improve the accuracy of velocity inversion. After multiple iterations, a high-precision velocity model V is finally obtained. i (x,y,t). In obtaining a high-precision velocity model V... i Based on (x,y,t), pre-drilling prediction of formation pressure is performed using an improved Philippian model.

[0105] In one alternative implementation, the pore pressure of the target layer in the time domain can be determined according to the following expression:

[0106]

[0107] Among them, P p Here, FC represents pore pressure, σ represents the Philippian model factor (an improved Philippian pressure prediction model factor can be used), and σ represents Poisson's ratio. Considering that the sensitivity of stress and velocity is related to lithology, and that the Poisson's ratio parameter σ is a comprehensive parameter for inverting the P-wave and S-wave moduli of lithology, this embodiment constructs a parameter correction function FC(σ) using the Poisson's ratio parameter to adjust the overlying formation pressure P. ov Regarding the stress effect on the rock skeleton, FC(σ) can typically be defined as a linear positive function of σ, or it can be defined as a nonlinear positive function of σ. max This represents the seismic wave velocity when porosity is close to zero, approximating the matrix velocity; V min This indicates the seismic wave velocity when rigidity is close to zero, which approximates the pore fluid velocity; V iP represents the seismic wave velocity, which is the velocity obtained by processing seismic data using geologically guided constrained grid tomography. ov The overlying strata pressure is represented by t, time is represented by x, and y is represented by y.

[0108] The method for determining the brittleness index provided in this embodiment, based on the above embodiment, further obtains more accurate effective stress data by calculating the overlying strata pressure and pore pressure with high precision, thereby improving the accuracy of the final brittleness index in predicting the brittleness of strata in complex structural areas.

[0109] Example 3

[0110] Please refer to Figure 2 Based on any of the above embodiments, in order to further improve the accuracy of the final brittleness index in characterizing brittleness, the method for determining the brittleness index provided in this embodiment may include correcting the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer, which may include:

[0111] S1051. Determine the effective stress correction factor based on the effective stress of the target layer.

[0112] As effective stress increases, brittleness gradually decreases. At low effective stress, the change in brittleness is not significant, while at high effective stress, the decrease is more pronounced. Therefore, the effective stress correction factor can be defined as an exponential function of effective stress, or it can be defined as a linear function of effective stress. In this embodiment, the effective stress correction factor is negatively correlated with effective stress.

[0113] In one alternative implementation, when supported by experimental data, the effective stress correction factor can be determined according to the following expression:

[0114] f2(P e (x,u,t))=c*P e (x,y,t0 p +dp>3,c<0;

[0115] Alternatively, when the relationship is uncertain, the effective stress correction factor can be determined according to the following expression:

[0116] f2(P e (x,y,t)=c*P e (x,y,t)+dc<0;

[0117] Where f2 represents the effective stress correction factor, P e d represents the effective stress, and d represents a constant.

[0118] S1052. Determine the geothermal field correction factor based on the geothermal field of the target layer.

[0119] As temperature increases, brittleness gradually decreases, and at a certain critical temperature, rock brittleness significantly decreases, exhibiting a more pronounced elasto-plastic transition. Therefore, the geothermal field correction factor can be defined as an exponential function of the geothermal field, or it can be defined as a linear function of the geothermal field. In this embodiment, the geothermal field correction factor is negatively correlated with the geothermal field.

[0120] In one alternative implementation, when supported by experimental data, the geothermal field correction factor can be determined according to the following expression:

[0121] f1(T(x,y,t))=a*T(x,y,y) q +bq>3, a<0;

[0122] Alternatively, in cases where the relationship is uncertain, the geothermal field correction factor can be determined using the following expression:

[0123] f1(T(x,y,t))=a*T(x,y,t)+ba<0;

[0124] Where f1 represents the geothermal field correction factor, T represents the geothermal field, and b represents a constant.

[0125] S1053. Correct the initial brittleness index of the target layer according to the effective stress correction factor and the geothermal field correction factor.

[0126] After determining the effective stress correction factor and the geothermal field correction factor, the initial brittleness index can be corrected to the sum of the initial brittleness index, the effective stress correction factor, and the geothermal field correction factor. This is the final brittleness index BI. final It can be determined based on the following expression:

[0127] BI final =BI initial +f1(T(x,y,t))+2(P e (x,y,t)).

[0128] The method for determining the brittleness index provided in this embodiment, based on any of the above embodiments, further introduces a geothermal field correction factor and an effective stress correction factor to correct the changes in rock brittleness caused by tectonic factors (changes in stratum depth), thereby further improving the accuracy of stratum brittleness prediction in complex tectonic areas.

[0129] The effectiveness of the method for determining the brittleness index provided by this invention will be illustrated below through specific examples. Please refer to... Figure 3Analysis of the cross-plot of well A in the work area shows that the brittleness index provided by the embodiment of the present invention can effectively distinguish organic-rich shale reservoirs. At the same time, it is only related to Poisson's ratio, avoiding the influence of factors such as rock porosity, fluid, and organic matter on the prediction of Young's modulus and Poisson's ratio. It also has a good indicative effect on favorable brittle zones, and has the significance of both geological and engineering sweet spots.

[0130] Based on the overlying strata pressure profile obtained from well A in this work area, it can be seen that the overlying strata pressure is highly correlated with the burial depth of the target layer, but not entirely affected by stratigraphic structure, which is consistent with geological understanding. The planar diagram of the overlying strata pressure in this work area shows that the target layer has a shallow burial depth in the anticline core, gradually increasing towards the flanks, with significant variations in overlying strata pressure, ranging from 10 to 160 MPa. Verification through blind well B showed that the overlying strata pressure calculated by well logging for the target layer at well B was 81.4 MPa, while the seismic prediction of the overlying strata pressure was 81.9 MPa, with an absolute prediction error of only 0.5 MPa. Figure 4 As shown.

[0131] The pore pressure profile of well A in this work area shows an error of less than 3.5 MPa between the predicted porosity and the measured pore pressure. The planar distribution of pore pressure in the target layer of this work area exhibits significant variations in the pore pressure coefficient, ranging from 0.7 to 1.8. The formation pressure coefficient is relatively low (0.7-1.0) in the core region of the central anticline, gradually increasing in depth from the center towards the slope and the north and south ends. Local variations in the pressure coefficient are substantial, significantly influenced by fractures and fissures.

[0132] In the effective stress plane diagram of the target layer in this work area, the effective stress in the anticline core is 11.38 MPa, while the effective stress in the target layer of well A is 47.72 MPa due to the difference in burial depth. This significant difference in effective stress leads to inaccurate characterization of brittleness based on elasticity, necessitating brittleness correction based on structural features. Secondly, a geothermal field is constructed. Based on the geothermal curves from actual drilled wells, the time-domain geothermal field T(x,y,t) is constructed using the inverse distance weighted modeling difference algorithm in NEWS software.

[0133] Finally, the corrected brittleness index of the block was obtained. Analysis of the prediction results showed that the brittleness distribution in the horizontal section of well A was relatively uniform, with relatively high brittleness. Influenced by the brittleness distribution characteristics, brittleness-induced fractures in sections 1 to 5 developed along a direction of 50° north of east. From the perspective of the ant body, natural fractures developed in section 9, with a high brittleness index and interconnection, leading to the rupture of these natural fractures. The rupture direction was consistent with the brittleness distribution characteristics, along a direction of 75° north of east. The extension direction of the fractures was basically consistent with the brittleness distribution. The microseismic response in sections 26-28 was mainly affected by natural fractures.

[0134] Example 4

[0135] Figure 5 This is a schematic diagram of a device for determining the brittleness index according to an embodiment of the present invention. Figure 5 As shown, the fragility index determination device 30 provided in this embodiment may include: an acquisition module 301, a processing module 302, a determination module 303, a construction module 304, and a correction module 305.

[0136] Module 301 is used to obtain the Poisson's ratio of the target layer;

[0137] Processing module 302 is used to determine the initial brittleness index of the target layer based on the Poisson's ratio of the target layer;

[0138] The determination module 303 is used to determine the effective stress of the target layer, which is the difference between the overlying formation pressure and the pore pressure of the target layer.

[0139] Module 304 is used to construct the geothermal field of the target layer;

[0140] The correction module 305 is used to correct the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer, so as to obtain the final brittleness index of the target layer.

[0141] The apparatus of this embodiment can be used to perform Figure 1 The technical solutions of the method embodiments shown are similar in principle and in effect, and will not be described again here.

[0142] In one optional implementation, the processing module 302 for determining the initial brittleness index of the target layer based on the Poisson's ratio of the target layer may specifically include:

[0143] The initial brittleness index of the target layer is determined according to the following expression.

[0144]

[0145] Among them, BI initial σ represents the initial brittleness index, and σ represents Poisson's ratio.

[0146] In one alternative implementation, the overlying formation pressure of the target layer is determined according to the following expression:

[0147]

[0148] Among them, P ov denoted by , z represents the overlying strata pressure, z represents the depth, and g represents the gravitational acceleration.

[0149] In one alternative implementation, the pore pressure of the target layer in the time domain is determined according to the following expression:

[0150]

[0151] Among them, P p V represents pore pressure, FC represents the Philippians model factor, σ represents Poisson's ratio, and V max V represents the seismic wave velocity when porosity is close to zero. min V represents the seismic wave velocity when rigidity is close to zero. i P represents the velocity of seismic waves. ov The overlying strata pressure is represented by t, time is represented by x, and y is represented by y.

[0152] In one optional implementation, the correction module 305 is used to correct the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer. Specifically, it may include:

[0153] Determine the effective stress correction factor based on the effective stress of the target layer;

[0154] Determine the geothermal field correction factor based on the geothermal field of the target layer;

[0155] The initial brittleness index of the target layer is corrected based on the effective stress correction factor and the geothermal field correction factor.

[0156] In one alternative implementation, the effective stress correction factor can be determined according to the following expression:

[0157] f2(P e (x,y,t)=c*P e (x,y,t) p +dp>3,c<0;

[0158] or,

[0159] f2(P e (x,y,t)=c*P e (x,y,t)+dc<0;

[0160] Where f2 represents the effective stress correction factor, P e d represents the effective stress, and d represents a constant.

[0161] In one alternative implementation, the geothermal field correction factor can be determined according to the following expression:

[0162] f1(T(x,y,t))=a*T(x,y,t) q +bq>3, a<0;

[0163] or,

[0164] f1(T(x,y,t))=a*T9x,y,t)+ba<0;

[0165] Where f1 represents the geothermal field correction factor, T represents the geothermal field, and b represents a constant.

[0166] Example 5

[0167] This invention also provides an electronic device, please refer to [link to relevant documentation]. Figure 6 As shown, the embodiments of the present invention are only used as examples. Figure 6 The examples are provided for illustration only and do not imply that the invention is limited to these examples. Figure 6 This is a schematic diagram of the structure of an electronic device provided according to an embodiment of the present invention. Figure 6 As shown, the electronic device 40 provided in this embodiment includes: a memory 401, a processor 402, and a bus 403. The bus 403 is used to connect the various components.

[0168] The memory 401 stores a computer program, which, when executed by the processor 402, can implement the technical solutions of any of the above method embodiments.

[0169] The memory 401 and the processor 402 are electrically connected directly or indirectly to enable data transmission or interaction. For example, these components can be electrically connected to each other via one or more communication buses or signal lines, such as bus 403. The memory 401 stores a computer program that implements a method for determining the fragility index, including at least one software functional module that can be stored in the memory 401 in the form of software or firmware. The processor 402 executes various functional applications and data processing by running the software program and modules stored in the memory 401.

[0170] The memory 401 may be, but is not limited to, Random Access Memory (RAM), Read Only Memory (ROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), etc. The memory 401 stores programs, and the processor 402 executes the programs after receiving execution instructions. Furthermore, the software programs and modules within the memory 401 may also include an operating system, which may include various software components and / or drivers for managing system tasks (such as memory management, storage device control, power management, etc.) and can communicate with various hardware or software components to provide an operating environment for other software components.

[0171] Processor 402 can be an integrated circuit chip with signal processing capabilities. The aforementioned processor 402 can be a general-purpose processor, including a Central Processing Unit (CPU), a Network Processor (NP), etc. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this invention. The general-purpose processor can be a microprocessor or any conventional processor. It is understood that... Figure 6 The structure shown is for illustrative purposes only and may include more... Figure 6 The more or fewer components shown, or having the same Figure 6 The different configurations shown. Figure 6 The components shown can be implemented in hardware and / or software.

[0172] This invention also provides a computer-readable storage medium storing a computer program thereon, which is executed by a processor to implement the technical solutions of any of the above method embodiments.

[0173] The various embodiments in this disclosure are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0174] The scope of protection of this disclosure is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from its scope and spirit. If such modifications and variations fall within the scope of the claims of this disclosure and their equivalents, then the intent of this disclosure also includes such modifications and variations.

Claims

1. A method for determining the brittleness index, characterized in that, include: Obtain the Poisson's ratio of the target layer; The initial brittleness index of the target layer is determined based on the Poisson's ratio of the target layer; The effective stress of the target layer is determined, wherein the effective stress of the target layer is the difference between the overlying formation pressure and the pore pressure of the target layer; Construct the geothermal field of the target layer; The initial brittleness index of the target layer is corrected based on the effective stress and geothermal field of the target layer to obtain the final brittleness index of the target layer; The step of correcting the initial brittleness index of the target layer based on the effective stress and the geothermal field of the target layer includes: determining an effective stress correction factor based on the effective stress of the target layer; determining a geothermal field correction factor based on the geothermal field of the target layer; and correcting the initial brittleness index of the target layer based on the effective stress correction factor and the geothermal field correction factor.

2. The method according to claim 1, characterized in that, Determining the initial brittleness index of the target layer based on the Poisson's ratio of the target layer includes: The initial brittleness index of the target layer is determined according to the following expression. in, Indicates the initial brittleness index. It represents Poisson's ratio.

3. The method according to claim 1, characterized in that, The overlying formation pressure of the target layer is determined according to the following expression: ； in, Indicates the pressure of the overlying strata. Indicates depth, It represents the acceleration due to gravity.

4. The method according to claim 1, characterized in that, In the time domain, the pore pressure of the target layer is determined according to the following expression: in, Indicates pore pressure, Indicates the factors in the Philippians model. Represents Poisson's ratio. This represents the seismic wave velocity when porosity is close to zero. This indicates the seismic wave velocity when rigidity is close to zero. Indicates the velocity of seismic waves. Indicates the pressure of the overlying strata. Indicates time, Represents the x-axis, Represents the vertical axis.

5. The method according to claim 1, characterized in that, The step of determining the effective stress correction factor based on the effective stress of the target layer includes: The effective stress correction factor is determined according to the following expression: or, in, Indicates the effective stress correction factor. Indicates effective stress. Indicates a constant.

6. The method according to claim 1, characterized in that, The step of determining the geothermal field correction factor based on the geothermal field of the target layer includes: The geothermal field correction factor is determined according to the following expression: or, in, Indicates the geothermal field correction factor. T Indicates the geothermal field. b Indicates a constant.

7. A device for determining the brittleness index, characterized in that, include: The acquisition module is used to obtain the Poisson's ratio of the target layer; The processing module is used to determine the initial brittleness index of the target layer based on the Poisson's ratio of the target layer; The determination module is used to determine the effective stress of the target layer, wherein the effective stress of the target layer is the difference between the overlying formation pressure and the pore pressure of the target layer; The construction module is used to construct the geothermal field of the target layer; The correction module is used to correct the initial brittleness index of the target layer based on the effective stress and geothermal field of the target layer, so as to obtain the final brittleness index of the target layer. The step of correcting the initial brittleness index of the target layer based on the effective stress and the geothermal field of the target layer includes: determining an effective stress correction factor based on the effective stress of the target layer; determining a geothermal field correction factor based on the geothermal field of the target layer; and correcting the initial brittleness index of the target layer based on the effective stress correction factor and the geothermal field correction factor.

8. An electronic device, characterized in that, include: At least one processor and memory; The memory stores computer-executed instructions; The at least one processor executes computer execution instructions stored in the memory, causing the at least one processor to perform the method for determining the fragility index as described in any one of claims 1-6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the method for determining the fragility index as described in any one of claims 1-6.

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