Carbonate rock pore pressure measuring and calculating method based on crustal stress inversion

Abstract

The invention discloses a carbonate rock pore pressure measuring and calculating method based on crustal stress inversion, and relates to the technical field of geological exploration. The method comprises the following steps: firstly, analyzing carbonate rock stratum reservoir characteristics and fracture-cavity secondary changes, and selecting important parameters of a related pore pressure cause mechanism; the method comprises the following steps: dividing a target block reservoir space into four carbonate rock geologic structure models according to the reservoir body scale, amplifying a small-scale reservoir body to enhance seismic response, correcting by combining seismic data and logging data, mutually overlapping and fusing the four models, and depicting a macroscopic geologic model of the block; a unit body boundary displacement combinatorial theory is introduced into the geologic model, a crustal stress field of a simulation area is established, root mean square error analysis calculation is added, a crustal stress inversion calibration calculation formula is exported, and crustal stress distribution under the inversion condition is calculated; and finally, on the basis of a crustal stress inversion result, analyzing and calculating the vertical effective stress of the carbonate-containing rock stratum section, and establishing a crustal stress inversion-based carbonate rock stratum pore pressure measuring and calculating model.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration, and more specifically to a carbonate rock pore pressure measurement method based on ground stress inversion. Background Art

[0002] Carbonate rocks generally refer to dolomite or limestone composed of carbonate minerals such as calcite and dolomite. They are mainly formed in marine environments, and a few are formed in terrestrial environments. Their physical properties vary depending on the distribution area. Carbonate reservoirs are prone to forming large oil and gas fields, which account for about 50% of the world's total oil and gas reserves. my country's carbonate rocks are mainly distributed in the Sinian and Cambrian formations, among which the deep formations in the southwest are the most developed, such as the Zhongjiang-Penglai block in central Sichuan. Carbonate rocks are the key development targets for deep and ultra-deep oil and gas resources in the central Sichuan region. Pre-monitoring of pore pressure in the Zhongjiang-Penglai block is a key factor restricting on-site well control safety. However, due to the complexity of diagenesis and the large differences in the properties of limestone and dolomite, pre-monitoring of pore pressure in carbonate rocks has become a problem. Traditional pressure measurement methods are often based on single well drilling geological data and clastic rock sedimentary phase theory, which does not fully conform to the formation mechanism of carbonate pore pressure, making it impossible to accurately apply it to pre-monitoring of carbonate pore pressure in southwest my country. Summary of the invention

[0003] In order to overcome the defects existing in the above-mentioned prior art, the present invention discloses a carbonate rock pore pressure measurement method based on geostress inversion. The purpose of the present invention is to solve the problem that the traditional pressure measurement method in the prior art cannot be accurately applied to the carbonate rock pore pressure pre-monitoring in the southwest region of my country. The present invention first analyzes the reservoir characteristics of carbonate rock formations and secondary changes in fractures and caves, and proposes to select important parameters of the related pore pressure genesis mechanism; divides the reservoir space of the target block into four carbonate rock geological structure models of "large caves, dissolved cavities, large-scale fractures, and small-scale fractures" according to the scale of the reservoir body, amplifies and enhances the seismic response of the small-scale reservoir body, combines seismic data with well logging data correction, and superimposes and merges the four models to depict the macro geological model of the block; introduces the unit body boundary displacement combination theory into the geological model, establishes the geostress field of the simulation area, adds the root mean square error analysis and calculation, derives the geostress inversion calibration calculation formula, and calculates the geostress distribution under the inversion condition; finally, based on the geostress inversion result, analyzes and calculates the vertical effective stress of the carbonate rock section, and establishes a carbonate rock formation pore pressure measurement model based on geostress inversion, which is convenient for accurately calculating the numerical value of carbonate rock pore pressure.

[0004] In order to achieve the above objectives, the technical solution adopted by the present invention is: A method for calculating carbonate rock pore pressure based on geostress inversion comprises the following steps: 1. Summarize and analyze the characteristics of carbonate reservoirs and select important parameters of pore pressure formation mechanism; S1. Analyze the reservoir characteristics and secondary changes of fractures and caves in carbonate formations, and select important parameters of the related pore pressure formation mechanism; The reservoir space of carbonate formations is usually divided into three categories: primary pores, caves and fractures. The secondary changes are large, and the oil and gas accumulation principle is different from that of sedimentary strata such as clastic rocks. The porosity of medium and shallow carbonate rocks decreases with increasing burial depth, while the porosity of deep and ultra-deep carbonate rocks tends to increase with burial depth. This indicates that the compaction of the overburden fails at a certain burial depth, so the traditional pore pressure algorithm related to the overburden pressure is not suitable.

[0005] The formation of pore pressure in carbonate formations is mainly affected by the process of pressurization, and locally by the process of depressurization. The main causes of pressurization are structural extrusion, crude oil cracking, and natural gas injection, while the main causes of depressurization are fluid dissolution, uplift erosion, and other effects.

[0006] In the present invention, taking sandstone, a common type of clastic rock, as an example, carbonate rock and sandstone reservoirs differ in the following aspects: porosity, permeability, reservoir space, diagenesis, fracture action, reservoir-forming environment, lithology, and porosity-permeability relationship.

[0007] In the present invention, after the ultra-deep carbonate rock core is taken out and reaches the surface, the stress field, seepage field, etc. have changed and are irreversible, so the experimental results are difficult to restore the pore pressure response characteristics under deep burial. The existing analytical equations for the change of carbonate rock pore volume show multiple solutions, indicating that the cause of carbonate rock pore pressure is associated with multiple parameters.

[0008] Preferably, in the step S1, the important parameters of the pore pressure genesis mechanism include the volume ratio of deep and ultra-deep fractures and caves, the gradient of secondary porosity change, and the fracture conductivity.

[0009] The reservoir space of carbonate formations is usually divided into three categories: primary pores, caves and fractures. The secondary changes are large, and the oil and gas accumulation principle is different from that of sedimentary strata such as clastic rocks. The porosity of medium-shallow carbonate rocks decreases with increasing burial depth, while the porosity of deep and ultra-deep carbonate rocks tends to increase with burial depth. This shows that the traditional method of calculating the pore pressure of overlying rock layers based on compaction sedimentation theory is not suitable for carbonate rocks.

[0010] The entire carbonate rock pore pressure calculation is actually mainly affected by the dynamic changes of three types of reservoir spaces: primary pores, caves and fractures at the rock physics level.

[0011] We want to extract the key physical parameters that can represent the dynamic changes of carbonate rock formations over time based on the diagenetic process of carbonate rocks and their various physical and chemical reactions, and invert and infer their changing characteristics, laying the foundation for further deriving a calculation method for the pore pressure of carbonate rocks.

[0012] In the present invention, the deep and ultra-deep fracture-cavity volume ratio is selected as an important parameter of the pore pressure genesis mechanism because: the pores in the carbonate formation are in dynamic change due to the effects of pressurization and decompression, and microcracks are developed; large-scale cracks are easily generated during coring operations; the static porosity data of the core experiment cannot be used simply to indicate the entire pore dynamic change process, so we start directly from the macroscopic point and consider the macroscopic changes of pores, fractures, and caves in the entire deep formation at any time of coring to characterize the dynamic change response of the carbonate formation reservoir space.

[0013] The secondary porosity gradient is selected as an important parameter of the pore pressure formation mechanism because: during the entire carbonate oil and gas development process, human operations such as oil drilling and completion, reservoir production increase and transformation can easily induce changes in pores, fractures and holes, forming artificial fracture networks, inducing the generation and connection of secondary pores and microcracks. Therefore, attention should be paid to the change of secondary porosity, and corresponding parameters of dynamic changes are selected to characterize it.

[0014] The proposed selection of fracture conductivity as an important parameter of the pore pressure formation mechanism is because: it has been explained above that carbonate formations are in dynamic change during oil and gas operations, and there are many related influencing factors. The single-point permeability data of traditional core experiments are not sufficient to indicate the oil and gas seepage process under such dynamic changes. The pore pressure we often refer to is actually the pressure exhibited when fluid seeps in pores and other reservoir spaces. Fracture conductivity can better characterize the actual dynamic change process of carbonate oil and gas seepage. Many literatures have also made calculation analysis and examples to illustrate this point. There is no problem in selecting fracture conductivity as an important parameter of the pore pressure formation mechanism.

[0015] Preferably, in step S1, the volume ratio of the deep and ultra-deep fractures and caves is: The secondary porosity variation gradient is: The fracture conductivity is: Where: is the volume ratio of deep and ultra-deep fractures and caves, dimensionless; is the volume of deep and ultra-deep fractures and caves, cm 3 ; is time, min; is the formation fluid viscosity, mPa •s; is the formation fluid density, g / cm 3 ; is the angular frequency of seismic waves, dimensionless; represents secondary porosity, %; They represent the total rock reflectivity, rock skeleton reflectivity, and reservoir fluid reflectivity, respectively, and are dimensionless; It represents the phase parameters of two seismic reflection waves, which can be displayed by the instrument and is dimensionless. It represents the gradient of secondary porosity change, which is a dimensionless value. It represents the phase frequency of seismic reflection wave, dimensionless; is the fracture conductivity, dimensionless; The pressure measured at the abnormal point by the formation reflection wave, MPa; is the apparent volume of the reservoir in the target block, m 3 ; is the conductivity factor, which can be obtained experimentally and is dimensionless; is the crack length, obtained from experiments, cm.

[0016] 2. Construct a carbonate geological model for the target area and calibrate it using the well logging data of a single well in the area; S2. Combined with the important parameters of the pore pressure genesis mechanism, a variety of carbonate geological structure models are constructed for the target block according to the reservoir body scale, and the constructed models are superimposed and integrated with each other. At the same time, the model is corrected by combining seismic data and well logging data to construct a macro geological model of the block; Preferably, in step S2, the multiple different carbonate rock geological structure models include four carbonate rock geological structure models: large caves, dissolution cavities, large-scale fractures, and small-scale fractures.

[0017] In the present invention, there are many types of carbonate oil and gas reservoir storage spaces, with large scales and random distribution, making it difficult to accurately understand them. It is not practical to apply the clastic rock geological modeling method to this. According to the characteristics of carbonate reservoirs, there should be four basic carbonate geological structure models of "large caves, dissolution cavities, large-scale fractures, and small-scale fractures" according to the scale of the reservoir. According to the composite basin and geological evolution, the four basic models are superimposed and integrated to depict a macroscopic geological model close to reality.

[0018] Preferably, in the modeling of step S2, an operating block containing carbonate rocks is selected as a preset area for geological modeling, and the multi-scale classification and multi-constraint geological modeling thinking is followed to describe the morphological characteristics of fractures and caves in detail, establish an overall model of the preset area, divide the finite element small areas in the overall model according to the positions of the ground stress test points, and then establish the finite element optimization boundary conditions so that the boundary conditions can correspond to the ground stress test points.

[0019] Preferably, in the modeling of step S2, seismic reflection structure analysis detects large-scale caves, seismic geometric attribute analysis detects large-scale fracture zones, and reservoir enhanced seismic response detects small-scale dissolution cavities and small-scale fractures.

[0020] In the present invention, petrel software can be used to establish a preset regional geological model, and of course the specific establishment tool can also be 3DEC, ABAQUS, ANSYS and other software. At the same time, in the above modeling process, seismic reflection structure analysis detects large-scale caves, seismic geometric attribute analysis detects large-scale fracture zones, and small-scale dissolved cavities and small-scale fractures need to be detected through reservoir enhanced seismic response.

[0021] Preferably, in step S2, the reservoir is enhanced in seismic response by: based on amplitude spectrum gradient processing, according to the correlation between secondary porosity and deep and ultra-deep fracture-cavern volumes, considering the power operation of small-scale reservoir frequencies, broadening the bandwidth of seismic data, and thereby amplifying and enhancing the seismic response of the reservoir.

[0022] In the present invention, based on the amplitude spectrum gradient processing, according to the correlation between secondary porosity and deep and ultra-deep fracture-cavern volume (the numerical relationship is expressed by the abstract function ), consider the frequency square operation of small-scale reservoirs, broaden the bandwidth of seismic data, and then amplify and enhance the seismic response of reservoirs. It uses the two parameters of deep and ultra-deep fracture-cavity volume ratio and secondary porosity change gradient among the important parameters of the relevant pore pressure genesis mechanism selected in step S1.

[0023] According to the calculation results of the above formula, the frequency display is amplified to capture the signal characteristics of small-scale caves and small-scale fractures, and the initial geological model of carbonate reservoirs is constructed. At the same time, the single well logging data near the ground stress test point is used as the genus optimization boundary condition to further calibrate and constrain the characteristic display of reservoirs of different scales.

[0024] 3. By applying geostress inversion to the geological model, the geostress field is simulated and the geostress distribution is obtained; S3. Using the boundary displacement combination theory, the geostress inversion is performed on the macro geological model, the geostress field of the simulation area is established and the theoretical stress distribution is obtained; then the error analysis of the theoretical stress distribution is performed, the geostress inversion calibration model is obtained using the error root mean square, and the calibration model is used to obtain the optimized geostress distribution under the inversion conditions; In the present invention, the geological model is regarded as composed of many geological units. The finite element method is used for the corrected macroscopic geological model. Through the boundary displacement combination theory, the boundary displacement loading conditions are continuously adjusted until the internal unit stress components are consistent with the measured values ​​of the ground stress measuring points, thereby simulating the ground stress field matching the target block.

[0025] Preferably, in step S3, the use of boundary displacement combination theory to perform geostress inversion on the macro geological model, establish the geostress field of the simulation area and obtain the theoretical stress distribution specifically includes: Where: is the stress component, 1, 2, and 3 correspond to any three orthogonal directions of the ground stress at a certain point; It represents the mass of the reservoir at the measurement point of a single well in the geological model, kg; Indicates Displacement speed of the unit cell boundary, m / min; Indicates The constant term is calculated for each unit body and is assigned a value according to the geological model. represents the relative horizontal displacement of the boundaries of two unit cells, m; represents the relative shear displacement between the two unit cell boundaries, m; represents the relative strike-slip displacement between the two unit cells, m; In form, it is a 6-dimensional vector, called a computational particle, representing the The boundary displacement combination of each unit cell.

[0026] In the present invention, They represent the relative displacement of one unit body boundary surface relative to another unit body boundary surface, and the displacement combination is expressed as: Where: represents the relative horizontal displacement of the boundaries of two unit cells, m; represents the relative shear displacement between the two unit cell boundaries, m; represents the relative strike-slip displacement between the two unit cells, m; In form, it is a 6-dimensional vector, called a computational particle, representing the The boundary displacement combination of each unit cell.

[0027] The computing particles form a computing matrix, forming the vector space of the target search. The displacement velocity of the unit cell boundary is: Considering the causes of geostress, it is mainly due to the effects of compression, collision, and overlay between rock layers. Therefore, there is a relative displacement movement trend between rock layers under the action of geostress. According to the calculation of geostress components, we have: Where: is the stress component, 1, 2, and 3 correspond to any three orthogonal directions of the ground stress at a certain point; It represents the mass of the reservoir at the measurement point of a single well in the geological model, kg; Indicates Displacement speed of the unit cell boundary, m / min; Indicates The constant term is calculated for each unit body and is assigned a value according to the geological model.

[0028] On the basis of geological model, the geomechanical characteristics are analyzed, and then by continuously changing the mode of action of unit boundary force (including the magnitude and direction of force), the relative displacement of unit is calculated, the ground stress field of the simulation area is established, and the stress components are solved to represent the theoretical stress distribution of a certain point on the geological model.

[0029] Preferably, in step S3, the root mean square error is: Where: is the root mean square, %; Relative error between theoretical value and measured value of principal stress component, %.

[0030] Preferably, in step S3, the in-situ stress inversion calibration model is: Where: Represents the optimized inverse geostress vector form, including magnitude and direction; Represents the optimization dependent variable. The smaller the value, the smaller the error between the theoretical value of the stress distribution of the geological model and the measured value.

[0031] In the present invention, different The theoretical stress distribution under the calculation should also be subjected to error analysis before it can represent the template of the ground stress field under different boundary displacement loading conditions. The root mean square of the relative error between the calculated value and the measured value under each set of boundary displacement loading conditions is defined as the dependent variable, and its calculation formula is: Where: is the root mean square, %; Relative error between theoretical value and measured value of principal stress component, %.

[0032] In the present invention, matching different With dependent variable The error between them is shown in the following table: In this invention, regression technology is used to screen and optimize variables, analyze the mathematical relationship between the root mean square of relative error and boundary displacement, make the change trend of regional reservoir internal stress consistent with the measured results of ground stress and source mechanism data, and achieve the best fitting regression. Under the optimized dependent variable conditions, that is, "under the premise of the optimal theoretical and measured error that can be achieved", the closer the value is to the optimized error value, the better the result will be. The closer the theoretical stress distribution under calculation is to the real regional ground stress distribution, the more the force direction is considered and brought into vector form. The ground stress inversion calibration calculation formula here is: Where: Represents the optimized inverse geostress vector form, including magnitude and direction; Represents the optimization dependent variable. The smaller the value, the smaller the error between the theoretical value of the stress distribution of the geological model and the measured value.

[0033] 4. Based on the inversion results of geostress, calculate the numerical value of carbonate rock pore pressure.

[0034] S4. Based on the inversion results of geostress, the vertical effective stress of carbonate rock sections is calculated in combination with the important parameters of pore pressure genesis mechanism. A carbonate rock formation pore pressure calculation model based on geostress inversion is established using the vertical effective stress, and the numerical value of carbonate rock pore pressure is calculated using the calculation model.

[0035] Preferably, in the step S4, according to the distribution of carbonate reservoirs, similar cores are taken out, and the fracture conductivity of each group of taken cores is calculated. , use this data to replace the permeability changes of carbonate reservoirs and their surrounding areas, organize the fracture conductivity data according to the format requirements of the geological modeling software, and then load it into the geological model after the inversion of ground stress; according to the fracture conductivity data display of the geological model, under the premise that the fractures can conduct flow, determine the flowable reservoir and its nearby strata, and calculate the vertical effective stress there. , formation resistivity and compensation density data are introduced to establish a calculation model suitable for the pore pressure of carbonate formations.

[0036] In the above method, the fracture conductivity parameter among the important parameters of the relevant pore pressure formation mechanism to be selected in step S1 is used.

[0037] Preferably, in step S4, the carbonate formation pore pressure calculation model is: Where: is the formation pore pressure, MPa; is the vertical in-situ stress, MPa; is the vertical effective stress, MPa; Biot coefficient, which is iteratively calculated according to the drilling conditions and has no dimension. Represents the optimized inverse geostress vector form; represents the vertical coordinate unit vector, dimensionless; It represents the angle between the ground stress direction at a certain point and the vertical direction, °; The pressure coefficient is calculated for the fit, dimensionless; is the formation resistivity, Ω·m; To compensate for density, g / cm 3 ; is the longitudinal wave time difference, s.

[0038] The calculation principle of the above carbonate formation pore pressure calculation model is as follows: Vertical effective stress: Where: is the vertical effective stress, MPa; is a multivariate abstract function, and the independent variables are in brackets; is the formation resistivity, Ω·m; To compensate for density, g / cm 3 ; is the longitudinal wave time difference, s; is the vertical in-situ stress, MPa; is the formation pore pressure, MPa; It is the Biot coefficient, which is iteratively calculated according to the drilling conditions and has no dimension.

[0039] Here the fracture conductivity T is T i , T max There are two symbols. The former represents the single-point fracture conductivity value of any geological unit in the S2 geological model. Among all the N geological units, there must be a maximum value T of the single-point fracture conductivity value. max The multivariate fitting calculation model of vertical effective stress of carbonate rock formations based on logging data must be constrained in the above-mentioned geological model. If the calculation results of the effective stress multivariate fitting cannot match the distribution of geological model attribute data well, it proves that the calculation process of the effective stress multivariate fitting is incorrect, and it is necessary to re-extract the calculation coefficients for calculation and analysis until it matches the geological model.

[0040] For the above vertical effective stress According to the optimal linear regression, the fitting relationship between it and the P-wave time difference, compensation density and formation resistivity can be obtained: On the basis of geostress inversion, the inverted geostress is introduced to calculate the vertical geostress. The formula is: Where: represents the vertical coordinate unit vector, dimensionless; It represents the angle between the ground stress direction at a certain point and the vertical direction, °; Calculate the pressure coefficient for the fit, dimensionless.

[0041] According to the above formula, a carbonate formation pore pressure calculation model is established, and the calculation formula is as follows: Beneficial effects of the present invention: The carbonate rock pore pressure calculation method based on geostress inversion provided by the present invention first establishes a more practical macroscopic carbonate rock geological model based on carbonate reservoir conditions and relevant data of the target block and its reasonable interpretation, and quotes the unit body boundary displacement combination theory to complete the theoretical practice of geostress inversion, which is convenient for performing relevant software operations of geostress inversion, calculates the vertical effective stress of carbonate rock layer sections by inverting geostress field analysis, and establishes a carbonate rock formation pore pressure calculation model based on geostress inversion, which is convenient for accurately calculating the numerical value of carbonate rock pore pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a macroscopic geological model diagram of carbonate rocks; Figure 2 It is a schematic diagram of unit body boundary displacement; Figure 3 Orthogonal decomposition diagram of inverse geostress (vertical, orthogonal horizontal); Figure 4 This is the three pressure prediction profiles of the carbonate rock interval in Pengtan 1 Well. DETAILED DESCRIPTION

[0043] The concept, specific structure and technical effects of the present invention will be clearly and completely described below in combination with the embodiments and drawings to fully understand the purpose, characteristics and effects of the present invention.

[0044] Example 1 A method for calculating carbonate rock pore pressure based on geostress inversion comprises the following steps: S1. Analyze the reservoir characteristics and secondary changes of fractures and caves in carbonate formations, and select important parameters of the related pore pressure formation mechanism; S2. Combined with the important parameters of the pore pressure genesis mechanism, a variety of carbonate geological structure models are constructed for the target block according to the reservoir body scale, and the constructed models are superimposed and integrated with each other. At the same time, the model is corrected by combining seismic data and well logging data to construct a macro geological model of the block; S3. Using the boundary displacement combination theory, the geostress inversion is performed on the macro geological model, the geostress field of the simulation area is established and the theoretical stress distribution is obtained; then the error analysis of the theoretical stress distribution is performed, the geostress inversion calibration model is obtained using the error root mean square, and the calibration model is used to obtain the optimized geostress distribution under the inversion conditions; S4. Based on the inversion results of geostress, the vertical effective stress of carbonate rock sections is calculated in combination with the important parameters of pore pressure genesis mechanism. A carbonate rock formation pore pressure calculation model based on geostress inversion is established using the vertical effective stress, and the numerical value of carbonate rock pore pressure is calculated using the calculation model.

[0045] In this embodiment, the reservoir characteristics are summarized and analyzed, the important parameters of the pore pressure formation mechanism are selected, and a carbonate rock geological model based on the correction of seismic data and logging data is constructed. Through the relevant theory of geostress inversion, the inverted geostress field of the target block is simulated, and the vertical effective stress of the carbonate rock section is calculated based on the geostress inversion results to establish a carbonate rock formation pore pressure measurement model.

[0046] Example 2 This embodiment further elaborates on step S1 based on embodiment 1. The reservoir space of carbonate formations is generally divided into three categories: primary pores, caves and fractures. The secondary changes are large, and the principle of oil and gas accumulation is different from that of sedimentary strata such as clastic rocks. The porosity of medium and shallow carbonate rocks decreases with increasing burial depth, and the porosity of deep and ultra-deep carbonate rocks tends to increase with burial depth. This shows that the compaction of the overburden fails at a certain burial depth, so the traditional pore pressure algorithm related to the overburden pressure is not suitable.

[0047] The formation of pore pressure in carbonate formations is mainly affected by the process of pressurization, and locally by the process of depressurization. The main causes of pressurization are structural extrusion, crude oil cracking, and natural gas injection, while the main causes of depressurization are fluid dissolution, uplift erosion, and other effects.

[0048] This example takes sandstone, a common type of clastic rock, as an example to illustrate the differences in reservoir characteristics between carbonate rock and sandstone. The table is as follows: Table 1 Comparison of carbonate and sandstone reservoir characteristics Combined with the information in the table, after the ultra-deep carbonate rock core is taken out and reaches the surface, the stress field and seepage field have changed and are irreversible, so the experimental results are difficult to restore the pore pressure response characteristics of the deep burial. The existing analytical equations for the change of carbonate rock pore volume show multiple solutions, indicating that the cause of carbonate rock pore pressure is related to multiple parameters.

[0049] In the step S1, the important parameters of the pore pressure formation mechanism include the volume ratio of deep and ultra-deep fractures and caves, the gradient of secondary porosity change, and the fracture conductivity.

[0050] In the step S1, the volume ratio of the deep and ultra-deep fracture-caves is: The secondary porosity variation gradient is: The fracture conductivity is: Where: is the volume ratio of deep and ultra-deep fractures and caves, dimensionless; is the volume of deep and ultra-deep fractures and caves, cm 3 ; is time, min; is the formation fluid viscosity, mPa •s; is the formation fluid density, g / cm 3 ; is the angular frequency of seismic waves, dimensionless; represents secondary porosity, %; They represent the total rock reflectivity, rock skeleton reflectivity, and reservoir fluid reflectivity, respectively, and are dimensionless; It represents the phase parameters of two seismic reflection waves, which can be displayed by the instrument and is dimensionless. It represents the gradient of secondary porosity change, which is a dimensionless value. It represents the phase frequency of seismic reflection wave, dimensionless; is the fracture conductivity, dimensionless; The pressure measured at the abnormal point by the formation reflection wave, MPa; is the apparent volume of the reservoir in the target block, m 3 ; is the conductivity factor, which can be obtained experimentally and is dimensionless; is the crack length, obtained from experiments, cm.

[0051] Example 3 This embodiment further elaborates on step S2 on the basis of embodiment 2. There are many types of carbonate oil and gas reservoir storage spaces, with large scales and random distribution, which are difficult to accurately understand. It is not practical to apply the clastic rock geological modeling method to this. According to the characteristics of carbonate reservoirs, there should be four basic carbonate geological structure models of "large caves, dissolution cavities, large-scale fractures, and small-scale fractures" according to the scale of the reservoir body. According to the composite basin and geological evolution, the four basic models are superimposed and integrated to depict a macroscopic geological model close to reality.

[0052] A further technical solution is to select an operating block containing carbonate rocks as the preset area for geological modeling, follow the multi-scale classification and multi-constraint geological modeling thinking, carefully describe the morphological characteristics of fractures and caves, establish an overall model of the preset area, divide the finite element small areas in the overall model according to the positions of the ground stress test points, and then establish the finite element optimization boundary conditions so that the boundary conditions can correspond to the ground stress test points.

[0053] It should be noted that, in the embodiment of the present invention, the preset regional geological model can be established by using petrel software, and of course, the specific establishment tool can also be 3DEC, ABAQUS, ANSYS and other software. At the same time, in the above modeling process, seismic reflection structure analysis detects large-scale caves, seismic geometric attribute analysis detects large-scale fracture zones, and small-scale dissolution cavities and small-scale fractures need to be detected by enhancing the seismic response of the reservoir.

[0054] A further technical solution is to process the amplitude spectrum gradient and calculate the correlation between the secondary porosity and the volume of deep and ultra-deep fractures and caves (the numerical relationship is expressed by the abstract function ), taking into account the frequency square operation of small-scale reservoirs, the bandwidth of seismic data is broadened, thereby amplifying and enhancing the seismic response of the reservoir.

[0055] According to the calculation results of the above formula, the frequency display is amplified to capture the signal characteristics of small-scale caves and small-scale fractures, and the initial geological model of carbonate reservoirs is constructed. At the same time, the single well logging data near the ground stress test point is used as the attribute optimization boundary condition to further calibrate and constrain the characteristic display of reservoirs of different scales. The corrected macroscopic geological model is as follows Figure 1 shown.

[0056] Example 4 This embodiment further elaborates on step S3 based on embodiment 3. The geological model is regarded as composed of many geological units, and the finite element method is used for the corrected macroscopic geological model. The boundary displacement loading conditions are continuously adjusted through the boundary displacement combination theory until the internal unit stress component is consistent with the measured value of the ground stress measuring point, so as to simulate the ground stress field matching the target block.

[0057] like Figure 2 As shown, use They represent the relative displacement of one unit body boundary surface relative to another unit body boundary surface, and the displacement combination is expressed as: Where: represents the relative horizontal displacement of the boundaries of two unit cells, m; represents the relative shear displacement between the two unit cell boundaries, m; represents the relative strike-slip displacement between the two unit cells, m; In form, it is a 6-dimensional vector, called a computational particle, representing the The boundary displacement combination of each unit cell.

[0058] The computing particles form a computing matrix, forming the vector space of the target search. The displacement velocity of the unit cell boundary is: Considering the causes of geostress, it is mainly due to the effects of compression, collision, and overlay between rock layers. Therefore, there is a relative displacement movement trend between rock layers under the action of geostress. According to the calculation of geostress components, we have: Where: is the stress component, 1, 2, and 3 correspond to any three orthogonal directions of the ground stress at a certain point; It represents the mass of the reservoir at the measurement point of a single well in the geological model, kg; Indicates Displacement speed of the unit cell boundary, m / min; Indicates The constant term is calculated for each unit body and is assigned a value according to the geological model.

[0059] On the basis of geological model, the geomechanical characteristics are analyzed, and then by continuously changing the mode of action of unit boundary force (including the magnitude and direction of force), the relative displacement of unit is calculated, the ground stress field of the simulation area is established, and the stress components are solved to represent the theoretical stress distribution of a certain point on the geological model.

[0060] Different The theoretical stress distribution under the calculation should also be subjected to error analysis before it can represent the template of the ground stress field under different boundary displacement loading conditions. The root mean square of the relative error between the calculated value and the measured value under each set of boundary displacement loading conditions is defined as the dependent variable, and its calculation formula is: Where: is the root mean square, %; Relative error between theoretical value and measured value of principal stress component, %.

[0061] In the present invention, matching different With dependent variable The error between them is shown in the following table: A further technical solution is to use regression technology to screen and optimize variables, analyze the mathematical relationship between the root mean square of relative error and boundary displacement, make the change trend of regional reservoir internal stress consistent with the measured results of ground stress and source mechanism data, and achieve the best fitting regression. Under the optimized dependent variable conditions, that is, "under the premise of the optimal theoretical and measured error that can be achieved", the closer the value is to the optimized error, the better the result will be. The closer the theoretical stress distribution under calculation is to the real regional ground stress distribution, the more the force direction is considered and brought into vector form. The ground stress inversion calibration calculation formula here is: Where: Represents the optimized inverse geostress vector form, including magnitude and direction; Represents the optimization dependent variable. The smaller the value, the smaller the error between the theoretical value of the stress distribution of the geological model and the measured value.

[0062] Example 5 This embodiment further describes step S4 based on embodiment 4. In step S4, similar cores are taken out according to the distribution of carbonate reservoirs, and the fracture conductivity of each group of taken cores is calculated. , use this data to replace the permeability changes of carbonate reservoirs and their surrounding areas, organize the fracture conductivity data according to the format requirements of the geological modeling software, and then load it into the geological model after the inversion of ground stress; according to the fracture conductivity data display of the geological model, under the premise that the fractures can conduct flow, determine the flowable reservoir and its nearby strata, and calculate the vertical effective stress there. , introduce formation resistivity and compensation density data, and establish a calculation model suitable for carbonate formation pore pressure. The calculation principle is as follows: Vertical effective stress: Where: is the vertical effective stress, MPa; is a multivariate abstract function, and the independent variables are in brackets; is the formation resistivity, Ω·m; To compensate for density, g / cm 3 ; is the longitudinal wave time difference, s; is the vertical in-situ stress, MPa; is the formation pore pressure, MPa; It is the Biot coefficient, which is iteratively calculated according to the drilling conditions and has no dimension.

[0063] For the above vertical effective stress According to the optimal linear regression, the fitting relationship between it and the P-wave time difference, compensation density and formation resistivity can be obtained: On the basis of geostress inversion, the inverted geostress is introduced to calculate the vertical geostress. The formula is: Where: represents the vertical coordinate unit vector, dimensionless, such as Figure 3 As shown; It represents the angle between the ground stress direction at a certain point and the vertical direction, °; Calculate the pressure coefficient for the fit, dimensionless.

[0064] According to the above formula, a carbonate formation pore pressure calculation model is established, and the calculation formula is as follows: like Figure 4 As shown, they are the three pressure prediction profiles of the carbonate rock layer in Well Pengtan 1.

[0065] The above is a specific description of the implementation mode of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention, and these equivalents or substitutions are all included in the scope defined by the claims of the present invention.

Claims

1. A method for calculating carbonate rock pore pressure based on geostress inversion, characterized in that: The following steps are involved: S1. Analyze the reservoir characteristics and secondary changes of fractures and caves in carbonate formations, and select important parameters of the related pore pressure formation mechanism; S2. Combined with the important parameters of the pore pressure genesis mechanism, a variety of carbonate geological structure models are constructed for the target block according to the reservoir body scale, and the constructed models are superimposed and integrated with each other. At the same time, the model is corrected by combining seismic data and well logging data to construct a macro geological model of the block; S3. Using the boundary displacement combination theory, the geostress inversion is performed on the macro geological model, the geostress field of the simulation area is established and the theoretical stress distribution is obtained; then the error analysis of the theoretical stress distribution is performed, the geostress inversion calibration model is obtained using the error root mean square, and the calibration model is used to obtain the optimized geostress distribution under the inversion conditions; S4. Based on the inversion results of geostress, the vertical effective stress of carbonate rock sections is calculated in combination with the important parameters of pore pressure genesis mechanism. A carbonate rock formation pore pressure calculation model based on geostress inversion is established using the vertical effective stress, and the numerical value of carbonate rock pore pressure is calculated using the calculation model.

2. The carbonate rock pore pressure calculation method according to claim 1, characterized in that: In the step S1, the important parameters of the pore pressure formation mechanism include the volume ratio of deep and ultra-deep fractures and caves, the gradient of secondary porosity change, and the fracture conductivity.

3. The carbonate rock pore pressure calculation method according to claim 2, characterized in that: In the step S1, the volume ratio of the deep and ultra-deep fracture-caves is: The secondary porosity variation gradient is: The fracture conductivity is: Where: is the volume ratio of deep and ultra-deep fractures and caves, dimensionless; is the volume of deep and ultra-deep fractures and caves, cm 3 ; is time, min; is the formation fluid viscosity, mPa •s; is the formation fluid density, g / cm 3 ; is the angular frequency of seismic waves, dimensionless; represents secondary porosity, %; They represent the total rock reflectivity, rock skeleton reflectivity, and reservoir fluid reflectivity, respectively, and are dimensionless; It represents the phase parameters of two seismic reflection waves, which can be displayed by the instrument and is dimensionless. It represents the gradient of secondary porosity change, which is a dimensionless value. It represents the phase frequency of seismic reflection wave, dimensionless; is the fracture conductivity, dimensionless; The pressure measured at the abnormal point by the formation reflection wave, MPa; is the apparent volume of the reservoir in the target block, m 3 ; is the conductivity factor coefficient, which can be obtained experimentally and is dimensionless; is the crack length, obtained from experiments, cm.

4. The carbonate rock pore pressure calculation method according to claim 1, characterized in that: In the modeling of step S2, an operating block containing carbonate rocks is selected as the preset area for geological modeling. Following the multi-scale classification and multi-constraint geological modeling thinking, the morphological characteristics of fractures and caves are described in detail, and an overall model of the preset area is established. The finite element small areas in the overall model are divided according to the positions of the ground stress test points, and then the finite element optimization boundary conditions are established so that the boundary conditions can correspond to the ground stress test points.

5. The carbonate rock pore pressure calculation method according to claim 1, characterized in that: In the step S2, the multiple different carbonate rock geological structure models include four carbonate rock geological structure models: large karst caves, karst cavities, large-scale fractures, and small-scale fractures; In the modeling of step S2, seismic reflection structure analysis detects large-scale caves, seismic geometric attribute analysis detects large-scale fracture zones, and reservoir enhanced seismic response detects small-scale dissolution cavities and small-scale fractures; The reservoir enhanced seismic response is: based on amplitude spectrum gradient processing, according to the correlation between secondary porosity and deep and ultra-deep fracture-cavern volume, considering the square operation of small-scale reservoir frequency, broadening the bandwidth of seismic data, and then amplifying and enhancing the seismic response of the reservoir.

6. The carbonate rock pore pressure measurement method according to claim 1, characterized in that: In the step S3, the in-situ stress inversion of the macro geological model is performed by using the boundary displacement combination theory, the in-situ stress field of the simulation area is established and the theoretical stress distribution is obtained, which specifically includes: Where: is the stress component, 1, 2, and 3 correspond to any three orthogonal directions of the ground stress at a certain point; It represents the mass of the reservoir at the measurement point of a single well in the geological model, kg; Indicates Displacement speed of the unit cell boundary, m / min; Indicates The constant term is calculated for each unit body and is assigned a value according to the geological model. represents the relative horizontal displacement of the boundaries of two unit cells, m; represents the relative shear displacement between the two unit cell boundaries, m; represents the relative strike-slip displacement between the two unit cells, m; In form, it is a 6-dimensional vector, called a computational particle, representing the The boundary displacement combination of each unit cell.

7. The carbonate rock pore pressure calculation method according to claim 6, characterized in that: In the step S3, the root mean square error is: Where: is the root mean square, %; Relative error between theoretical value and measured value of principal stress component, %.

8. The carbonate rock pore pressure calculation method according to claim 7, characterized in that: In the step S3, the inverse calibration model of the geostress is: Where: Represents the optimized inverse geostress vector form, including magnitude and direction; Represents the optimization dependent variable. The smaller the value, the smaller the error between the theoretical value of the stress distribution of the geological model and the measured value.

9. The carbonate rock pore pressure calculation method according to claim 1, characterized in that: In the step S4, similar cores are taken out according to the distribution of carbonate reservoirs, and the fracture conductivity of each group of taken cores is calculated. , use this data to replace the permeability changes of carbonate reservoirs and their surrounding areas, organize the fracture conductivity data according to the format requirements of the geological modeling software, and then load it into the geological model after the inversion of ground stress; according to the fracture conductivity data display of the geological model, under the premise that the fractures can conduct flow, determine the flowable reservoir and its nearby strata, and calculate the vertical effective stress there. , formation resistivity and compensation density data are introduced to establish a calculation model suitable for the pore pressure of carbonate formations.

10. The carbonate rock pore pressure measurement method according to claim 1, characterized in that: In the step S4, the carbonate formation pore pressure calculation model is: Where: is the formation pore pressure, MPa; is the vertical in-situ stress, MPa; is the vertical effective stress, MPa; Biot coefficient, which is iteratively calculated according to the drilling conditions and has no dimension. Represents the optimized inverse geostress vector form; represents the vertical coordinate unit vector, dimensionless; It represents the angle between the ground stress direction at a certain point and the vertical direction, °; The pressure coefficient is calculated for the fit, dimensionless; is the formation resistivity, Ω·m; To compensate for density, g / cm 3 ; is the longitudinal wave time difference, s.

Images