Rock Physics Modeling-Based Methods for Predicting Geostress and its Medium

Abstract

This application discloses a method and medium for predicting geostress based on rock physics modeling. The method may include: calculating pore pressure; calculating rock mechanical parameters; calculating the maximum and minimum effective horizontal principal stresses at wellbore fracture points; inverting tectonic strain coefficients; and obtaining continuous maximum and minimum horizontal principal stress profiles based on pore pressure, rock mechanical parameters, and tectonic strain coefficients. This invention, by modifying the Lade formula rock fracture criterion and using stress polygons for constrained inversion, accurately obtains the maximum and minimum horizontal principal stresses at wellbore fracture points. Based on this, the tectonic strain coefficients are corrected to obtain accurate maximum and minimum horizontal principal stress profiles.

Description

Technical Field

[0001] This invention relates to the field of petroleum engineering technology, and more specifically, to a method and medium for predicting geostress based on rock physics modeling. Background Technology

[0002] In-situ stress research and analysis is a fundamental and crucial research area in shale oil and gas exploration and development. It is widely used to address issues such as the distribution of oil and gas enrichment zones, wellbore stability, reservoir stimulation fracture distribution, hydraulic fracturing initiation and propagation pressures, casing deformation, and engineering design optimization. In petroleum engineering, the orientation of in-situ stress is often determined using imaging logging, dipole fast and slow shear wave data, or multi-arm caliper data, making the study of in-situ stress orientation relatively simple.

[0003] The magnitude of geostress includes overlying formation pressure, maximum horizontal principal stress, and minimum horizontal principal stress. The main methods for measuring the maximum and minimum horizontal principal stresses include hydraulic fracturing, acoustic emission Kaiser effect, and differential strain method. These methods directly measure the geostress magnitude of discrete rocks through core or field tests. In order to obtain geostress profiles, Zobek proposed the effective stress ratio method. This method assumes that the effective stress ratio of the maximum or minimum horizontal principal stress is close to a constant. Using the effective stress ratio method, a continuous stress profile that is basically independent of lithology can be obtained. However, the stress profile calculated using the effective stress ratio method cannot effectively guide fracturing design.

[0004] Scholars have increasingly considered using well logging data and geostress combined spring models to calculate the maximum and minimum horizontal principal stresses. The key to the combined spring model is to obtain the tectonic stress coefficient. Using the LOT (Loop Flow Test) in drilling, the maximum and minimum horizontal principal stresses are obtained by simplifying the formula for the maximum horizontal principal stress and using the conditions for inducing tensile fractures in the wellbore by hydraulic fracturing. Based on this, the tectonic stress coefficient is calculated. However, this method of determining the maximum horizontal principal stress by hydraulic fracturing cannot be used in most environments. Another method is to calculate the maximum horizontal principal stress by combining the ratio of the major and minor semi-axes of the collapsed elliptical wellbore with the minimum horizontal principal stress. Based on this, a comprehensive calculation method is used to calculate the maximum and minimum horizontal principal stresses, and this method has been applied to casing loss prediction. This method uses Mohr-Coulomb criterion measurement and combines the geostress calculation results with the wellbore failure mode to synthesize a wellbore failure image. The synthesized image is compared with electrical imaging logging data. When the wellbore failure conditions reflected by the two are consistent, the horizontal tectonic stress coefficient at this time can be used as the horizontal tectonic stress coefficient of the area. This method is only suitable for formations with relatively brittle strata, and since it does not use stress polygons for constraint, the accuracy is relatively low.

[0005] Therefore, it is necessary to develop a geostress prediction method and medium based on rock physics modeling.

[0006] The information disclosed in the background section of this invention is intended only to enhance the understanding of the general background of this invention, and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] This invention proposes a geostress prediction method and medium based on rock physics modeling, which can modify the Lade formula rock fracture criterion, use stress polygons for constrained inversion, accurately obtain the maximum and minimum horizontal principal stresses at the wellbore fracture point, and correct the tectonic strain coefficient based on this to obtain an accurate maximum and minimum horizontal principal stress profile.

[0008] In a first aspect, embodiments of this disclosure provide a method for predicting geostress based on rock physics modeling, including:

[0009] Calculate pore pressure;

[0010] Calculate rock mechanical parameters;

[0011] Calculate the maximum and minimum effective horizontal principal stresses at the wellbore fracture point;

[0012] Inverted structural strain coefficients;

[0013] Based on the pore pressure, the rock mechanical parameters, and the tectonic strain coefficient, continuous maximum and minimum horizontal principal stress profiles are obtained.

[0014] Preferably, the rock mechanical parameters include Biot coefficient, Poisson's ratio, and Young's modulus.

[0015] Preferably, calculating pore pressure includes:

[0016] Calculate the overlying formation pressure using density logging curves;

[0017] The pore pressure is calculated using the pressure of the overlying formation.

[0018] Preferably, the pore pressure is calculated using formula (1):

[0019]

[0020] Among them, P p S represents the formation pore pressure. v For the overlying formation pressure, P h For normal hydrostatic pressure, Δt n Δt0 represents the time difference of the normal trend line of mudstone and shale at a given depth, Δt0 represents the measured time difference of mudstone and shale formations at a given depth, and N represents the Eaton index, a coefficient related to the formation.

[0021] Preferably, the calculation of the maximum and minimum effective horizontal principal stresses at the wellbore fracture point includes:

[0022] Establish the mathematical relationship between the maximum and minimum effective horizontal principal stresses at the wellbore fracture point and the radial, circumferential, and axial stress components;

[0023] Calculate the maximum and minimum effective horizontal principal stresses at the wellbore fracture point.

[0024] Preferably, the maximum and minimum effective horizontal principal stresses at the wellbore fracture point are calculated using formula (2):

[0025]

[0026] Where, σ θ σ z σ r These represent the radial, circumferential, and axial stress components, respectively, with f1, f2, f3, and m being the calculation parameters. σ CPmax σ CPmin τ represents the maximum and minimum confining pressures, ω represents the wellbore collapse width, υ represents Poisson's ratio, Δp represents the bottom hole pressure differential, and τ represents the maximum and minimum confining pressures. rθ For the shear stress component, σ H σ h These represent the maximum and minimum effective horizontal principal stresses at the wellbore fracture point, σ v This represents the effective vertical stress.

[0027] Preferably, the inverted structural strain coefficients include:

[0028] A spring model is constructed, and the maximum and minimum effective horizontal principal stresses at the wellbore fracture point are substituted into the spring model. The structural strain coefficient is then inverted based on least squares surface fitting.

[0029] Preferably, the spring model is:

[0030]

[0031] Where α is the Biot coefficient, S v S is the overlying formation pressure, E is the static Young's modulus of the rock, and S is the static Young's modulus of the rock. H For the maximum horizontal principal stress, S h For the minimum horizontal principal stress, ε H ε is the structural strain coefficient in the direction of maximum horizontal stress. h The structural strain coefficient is the one in the direction of minimum horizontal stress.

[0032] Preferably, obtaining continuous maximum and minimum horizontal principal stress profiles includes:

[0033] Substituting the inverted structural strain coefficients into the spring model yields continuous maximum and minimum horizontal principal stress profiles.

[0034] As one specific implementation of this disclosure,

[0035] Secondly, embodiments of this disclosure also provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the aforementioned geostress prediction method based on rock physics modeling.

[0036] The methods and apparatus of the present invention have other features and advantages that will be apparent from or will be set forth in detail in the accompanying drawings and following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0037] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same parts.

[0038] Figure 1 A flowchart illustrating the steps of a geostress prediction method based on rock physics modeling according to an embodiment of the present invention is shown.

[0039] Figure 2 A schematic diagram of pore pressure according to an embodiment of the present invention is shown.

[0040] Figure 3 A schematic diagram of rock mechanical parameters according to an embodiment of the present invention is shown.

[0041] Figure 4 A schematic diagram showing the maximum and minimum horizontal principal stresses corresponding to the wellbore fracture point according to an embodiment of the present invention is shown.

[0042] Figure 5 A schematic diagram of the maximum and minimum horizontal principal stresses according to an embodiment of the present invention is shown. Detailed Implementation

[0043] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0044] This invention provides a geostress prediction method based on rock physics modeling, comprising:

[0045] Calculate pore pressure; in one example, calculating pore pressure includes:

[0046] Calculate the overlying formation pressure using density logging curves;

[0047] Pore ​​pressure is calculated using the pressure of the overlying formation.

[0048] In one example, the pore pressure is calculated using formula (1):

[0049]

[0050] Among them, P p S represents the formation pore pressure. v For the overlying formation pressure, P h For normal hydrostatic pressure, Δt n Δt0 represents the time difference of the normal trend line of mudstone and shale at a given depth, Δt0 represents the measured time difference of mudstone and shale formations at a given depth, and N represents the Eaton index, a coefficient related to the formation.

[0051] Specifically, underground rock masses have three principal geostresses that are perpendicular to each other in direction: the pressure of the overlying strata caused by the weight of the rock mass and two principal geostresses in the horizontal direction.

[0052] The overlying formation pressure at a certain point in a formation refers to the pressure exerted by the total weight of the rock matrix and fluids within the pores of the formation above that point. The overlying formation pressure is calculated using density logging curves as follows:

[0053]

[0054] Among them, S v ρ represents the overlying formation pressure at a certain depth, ρ is the density logging curve, g is the gravitational acceleration, and H is the depth of the target layer.

[0055] The Eaton formula is widely used to interpret pore pressure using well logging. The original Eaton method was proposed by Eaton in 1972 as a method for calculating formation pressure based on a normal compaction trend line. It utilizes the power function relationship between pore pressure and parameters such as sonic transit time, which does not change with depth. That is, pore pressure is calculated using formula (1).

[0056] Calculate the rock mechanics parameters; in one example, the rock mechanics parameters include Biot coefficient, Poisson's ratio, and Young's modulus.

[0057] Specifically, rock mechanical parameters are obtained using a rock physics modeling approach. Utilizing the industry-leading Xu-Panye multi-mineral component rock physics modeling method, the framework bulk modulus K is first calculated based on the known moduli of multiple minerals. s and shear modulus μ s Then, pores and fluids are added to obtain the dry rock bulk modulus K. dryand shear modulus μ dry and the bulk modulus K of the saturated fluid sat and shear modulus μ sat Finally, Young's modulus E, Poisson's ratio υ, and Biot coefficient α = 1 - K were calculated. dry / K s This is used for later calculations of the maximum and minimum principal stresses.

[0058] Calculate the maximum and minimum effective horizontal principal stresses at the wellbore fracture point; in one example, calculating the maximum and minimum effective horizontal principal stresses at the wellbore fracture point includes:

[0059] Establish the mathematical relationship between the maximum and minimum effective horizontal principal stresses at the wellbore fracture point and the radial, circumferential, and axial stress components;

[0060] Calculate the maximum and minimum effective horizontal principal stresses at the wellbore fracture point.

[0061] In one example, the maximum and minimum effective horizontal principal stresses at the wellbore fracture point are calculated using formula (2):

[0062]

[0063] Where, σ θ σ z σ r These represent the radial, circumferential, and axial stress components, respectively, with f1, f2, f3, and m being the calculation parameters. Generally, m is between 0 and 0.2, σ CPmax σ CPmin τ represents the maximum and minimum confining pressures, ω represents the wellbore collapse width, υ represents Poisson's ratio, Δp represents the bottom hole pressure differential, and τ represents the maximum and minimum confining pressures. rθ For the shear stress component, σ H σ h These represent the maximum and minimum effective horizontal principal stresses at the wellbore fracture point, σ v This represents the effective vertical stress.

[0064] Specifically, based on the assumption that the crustal stress value cannot exceed the friction strength of the original fault, the horizontal principal stress is inverted by stress polygon constraint. The core idea is to establish a stress polygon based on the fault friction strength theory, then pick the collapse width of the imaging logging image or the tensile crack induced by the drilling process, select an appropriate rock fracture criterion, and constrain the inversion of the horizontal principal stress.

[0065] After the wellbore is formed, if the stress concentration on the wellbore wall exceeds the rock strength, the rock will undergo shear failure, resulting in symmetrical wellbore collapse. Assuming the surrounding rock is porosity elastic and isotropic, and neglecting the effects of wellbore seepage and thermal stress, the stress distribution on the wellbore wall is as follows:

[0066]

[0067] Where θ is the wellbore perimeter angle. If wellbore collapse occurs in the direction of the minimum horizontal principal stress, and if imaging logging observes a wellbore collapse width of ω in a vertical well, then the wellbore perimeter angle at the critical failure location is... The rock fracture criterion adopts a modified form of the Lade criterion, which is Equation (2). That is, the maximum and minimum effective horizontal principal stresses at the wellbore fracture point are calculated using Equation (2). Since the parameters in the mathematical formula of the rock fracture criterion are often fixed, there is a certain deviation when fitting engineering experimental data. Therefore, this method treats the coefficients of the fracture criterion as variables, uses the three-dimensional stress test data of the rock core, and uses the least squares method to fit the data to obtain the three variables f1, f2, and f3 that fit best, that is, to determine the parameters f1, f2, and f3 of the rock fracture criterion.

[0068] Inverted structural strain coefficients; in one example, inverted structural strain coefficients include:

[0069] A spring model was constructed, and the maximum and minimum effective horizontal principal stresses at the wellbore fracture point were substituted into the spring model. The strain coefficients were then constructed by least-squares surface fitting.

[0070] In one example, the spring model is as follows:

[0071]

[0072] Where α is the Biot coefficient, S v S is the overlying formation pressure, E is the static Young's modulus of the rock, and S is the static Young's modulus of the rock. H For the maximum horizontal principal stress, S h For the minimum horizontal principal stress, ε H ε is the structural strain coefficient in the direction of maximum horizontal stress. h The structural strain coefficient is the one in the direction of minimum horizontal stress.

[0073] Specifically, if there are multiple sets of maximum and minimum effective horizontal principal stresses at wellbore fracture points, then the maximum and minimum effective horizontal principal stresses at each set of wellbore fracture points are related to ε. H ε h The function, that is:

[0074]

[0075] The least squares method calculates ε by minimizing the sum of the squares of the differences between the measured value and its corresponding true value. H ε h The model, that is, the main idea of ​​least squares fitting, is to minimize the sum of squares of the errors between the measured data values ​​and their corresponding true values. Therefore, we have...

[0076]

[0077] Where L is the sum of squares of the calculation errors, and to minimize L, the following must be satisfied:

[0078]

[0079] By simplifying formula (8), we can obtain:

[0080]

[0081] make

[0082] Then we have:

[0083]

[0084] The maximum horizontal principal stress structural strain coefficient ε is determined by solving the system of equations (10). H Minimum horizontal principal stress structural strain coefficient ε h .

[0085] Based on pore pressure, rock mechanics parameters, and tectonic strain coefficients, continuous maximum and minimum horizontal principal stress profiles are obtained. In one example, obtaining continuous maximum and minimum horizontal principal stress profiles includes:

[0086] Substituting the inverted structural strain coefficients into the spring model yields continuous maximum and minimum horizontal principal stress profiles.

[0087] The present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method for predicting geostress based on rock physics modeling.

[0088] To facilitate understanding of the solutions and effects of the embodiments of the present invention, two specific application examples are given below. Those skilled in the art should understand that these examples are merely for the purpose of understanding the present invention, and any specific details therein are not intended to limit the present invention in any way.

[0089] Example 1

[0090] Figure 1 A flowchart illustrating the steps of a geostress prediction method based on rock physics modeling according to an embodiment of the present invention is shown.

[0091] like Figure 1As shown, the geostress prediction method based on rock physics modeling includes: step 101, calculating pore pressure; step 102, calculating rock mechanical parameters; step 103, calculating the maximum and minimum effective horizontal principal stresses at the wellbore fracture point; step 104, inverting the tectonic strain coefficient; and step 105, obtaining continuous maximum and minimum horizontal principal stress profiles based on pore pressure, rock mechanical parameters, and tectonic strain coefficients.

[0092] Wells with complete data were selected. Well L69 has measured shear wave data, pore pressure test data, and geostress test data, so it can be used as a test well.

[0093] Figure 2 A schematic diagram of pore pressure according to an embodiment of the present invention is shown.

[0094] Based on the density logging curve, the overlying formation pressure is calculated using formula (4), and the pore pressure is calculated using formula (1), such as... Figure 2 As shown.

[0095] Figure 3 A schematic diagram of rock mechanics parameters according to an embodiment of the present invention is shown, wherein AI: longitudinal wave impedance; SI: transverse wave impedance; K: bulk modulus; G: shear modulus; M: longitudinal wave modulus; Edyn: dynamic Young's modulus; Vdyn: dynamic Poisson's ratio; LaMe: Lamé coefficient.

[0096] Rock mechanics parameters are obtained using a rock physics modeling approach. The mainstream Xu-Panye multi-mineral component rock physics modeling method is used. First, the skeletal bulk modulus and shear modulus are calculated by mixing the known moduli of multiple minerals. Then, pores and fluids are added to obtain the bulk modulus and shear modulus of dry rock and the bulk modulus and shear modulus of saturated fluid. Finally, Young's modulus, Poisson's ratio, and Biot coefficient α are calculated for subsequent calculations of maximum and minimum principal stresses.

[0097] Figure 4 A schematic diagram showing the maximum and minimum horizontal principal stresses corresponding to the wellbore fracture point according to an embodiment of the present invention is shown.

[0098] Establish the mathematical relationship between the maximum and minimum effective horizontal principal stresses at the wellbore fracture point and the radial, circumferential, and axial stress components; the fracture point is located at a depth of 3053m, the collapse width is 45°, and the internal friction coefficient is 0.63. Combined with the static Poisson's ratio, overlying formation pressure, pore pressure, and mud density, the maximum and minimum effective horizontal principal stresses at the wellbore fracture point are calculated using formula (2). The maximum and minimum horizontal principal stresses corresponding to the wellbore fracture point are as follows: Figure 4 As shown.

[0099] The spring model is constructed as formula (3). The maximum and minimum effective horizontal principal stresses at the well wall fracture point are substituted into the spring model. Based on the least squares surface fitting inversion, the structural strain coefficient is calculated. The structural strain coefficient in the direction of maximum horizontal stress is 0.00344675, and the structural strain coefficient in the direction of minimum horizontal stress is 0.00186254.

[0100] Figure 5 A schematic diagram of the maximum and minimum horizontal principal stresses according to an embodiment of the present invention is shown.

[0101] Substituting the inverted structural strain coefficients into the spring model yields continuous maximum and minimum horizontal principal stress profiles, such as... Figure 5 As shown in the figure. This method fully considers the influence of lithology and uses the Lade fracture criterion deformation formula under stress polygon constraints to obtain the maximum and minimum principal stress profiles, thereby improving the accuracy of in-situ stress values ​​and increasing the vertical resolution of reservoirs, providing strong support for subsequent compressibility assessment using seismic data.

[0102] Example 2

[0103] This disclosure provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the described geostress prediction method based on rock physics modeling.

[0104] A computer-readable storage medium according to embodiments of the present disclosure stores non-transitory computer-readable instructions. When these non-transitory computer-readable instructions are executed by a processor, all or part of the steps of the methods described in the foregoing embodiments of the present disclosure are performed.

[0105] The aforementioned computer-readable storage media include, but are not limited to: optical storage media (e.g., CD-ROM and DVD), magneto-optical storage media (e.g., MO), magnetic storage media (e.g., magnetic tape or portable hard drive), media with built-in rewritable non-volatile memory (e.g., memory card), and media with built-in ROM (e.g., ROM cartridge).

[0106] Those skilled in the art should understand that the above description of the embodiments of the present invention is only intended to illustrate the beneficial effects of the embodiments of the present invention, and is not intended to limit the embodiments of the present invention to any of the examples given.

[0107] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for predicting geostress based on rock physics modeling, characterized in that, include: Calculate pore pressure; Calculate rock mechanical parameters; Calculate the maximum and minimum effective horizontal principal stresses at the wellbore fracture point; Inverted structural strain coefficients; Based on the pore pressure, the rock mechanics parameters, and the tectonic strain coefficient, continuous maximum and minimum horizontal principal stress profiles are obtained. The calculation of the maximum and minimum effective horizontal principal stresses at the wellbore fracture point includes: Establish the mathematical relationship between the maximum and minimum effective horizontal principal stresses at the wellbore fracture point and the radial, circumferential, and axial stress components; Calculate the maximum and minimum effective horizontal principal stresses at the wellbore fracture point; The maximum and minimum effective horizontal principal stresses at the wellbore fracture point are calculated using formula (2): （2） in, These represent the radial, circumferential, and axial stress components, respectively, with f1, f2, f3, and m being the calculation parameters. , These are the maximum and minimum values ​​of the confining pressure. This refers to the width of the collapse in the vertical wellbore. Poisson's ratio, For the bottom hole pressure difference, For shear stress components, These represent the maximum and minimum effective horizontal principal stresses at the wellbore fracture point. The effective stress is vertical; The inverted tectonic strain coefficients include: A spring model is constructed, and the maximum and minimum effective horizontal principal stresses at the well wall rupture point are substituted into the spring model. The structural strain coefficient is then inverted based on least squares surface fitting. The spring model is as follows: （3） Where α is the Biot coefficient, S v S is the overlying formation pressure, E is the static Young's modulus of the rock, and S is the static Young's modulus of the rock. H For the maximum horizontal principal stress, S h For the minimum horizontal principal stress, ε H ε is the structural strain coefficient in the direction of maximum horizontal stress. h P is the structural strain coefficient in the direction of minimum horizontal stress. p Formation pore pressure; The least squares method calculates the result by minimizing the sum of the squares of the differences between the measured value and its corresponding true value. The model then has （7） Where L is the sum of squares of the calculation errors, and to minimize L, the following must be satisfied: （8） The simplified version of formula (8) is: （9） make , , Then we have: （10） By solving the system of equations (10), the structural strain coefficient ε of the maximum horizontal principal stress is determined. H Minimum horizontal principal stress structural strain coefficient ε h .

2. The geostress prediction method based on rock physics modeling according to claim 1, wherein, The rock mechanics parameters include Biot coefficient, Poisson's ratio, and Young's modulus.

3. The geostress prediction method based on rock physics modeling according to claim 1, wherein, Calculating pore pressure includes: Calculate the overlying formation pressure using density logging curves; The pore pressure is calculated using the pressure of the overlying formation.

4. The geostress prediction method based on rock physics modeling according to claim 3, wherein, The pore pressure is calculated using formula (1): （1） Among them, S v For the overlying formation pressure, P h For normal hydrostatic pressure, Δt n Δt0 represents the time difference of the normal trend line of mudstone and shale at a given depth, Δt0 represents the measured time difference of mudstone and shale formations at a given depth, and N represents the Eaton index, a coefficient related to the formation.

5. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the geostress prediction method based on rock physics modeling as described in any one of claims 1-4.

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