Shale reservoir geostress interpretation method, device, system and storage medium

Abstract

The application discloses a shale reservoir ground stress interpretation method and device, system and storage medium, and comprises the following steps: S1, a shale rheological constitutive model is acquired; S2, the shale rheological constitutive model is introduced into finite element simulation, a stress evolution process of the shale reservoir under different sedimentary evolution conditions is reconstructed, and influences of a strong extrusion dominant path and a lifting and denudation dominant path on present ground stress distribution are compared; and S3, in combination with in-situ testing and logging data, the simulation result is constrained and checked, and a shale reservoir ground stress solution considering sedimentary evolution and rock rheology is formed. The application can realize promotion from "static elastic estimation" to "sedimentary evolution-rheological coupling interpretation".

Description

Technical Field

[0001] This invention belongs to the field of information processing technology, specifically relating to a method, apparatus, system, and storage medium for interpreting geostress in shale reservoirs. Background Technology

[0002] Deep shale gas reservoirs exhibit significant vertical heterogeneity, with frequent interbedded layers of siliceous shale and clay-rich soft rock. Under complex sedimentary evolution, inaccurate interpretation of current geostress makes it difficult to effectively predict fracture propagation paths, fracture height evolution, and stress disturbance ranges during fracturing, potentially inducing engineering disasters such as fault slip and casing deformation. Fracture height is controlled by multiple factors, including the distribution of minimum principal stress, bedding, and natural fractures. When the stress variation characteristics between different layers are unclear, cross-layer propagation is more likely to occur, increasing the difficulty of fracture height control. In deep shale gas development, the combined effects of high temperature and pressure conditions and complex sedimentary evolution processes make current geostress more likely to reflect the combined influence of historical processes and time-dependent deformation. Simply relying on static elastic estimations often fails to reliably explain the fracture height response across different layers. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method, apparatus, system, and storage medium for interpreting geostress in shale reservoirs.

[0004] To achieve the above objectives, the present invention provides the following solution: A method for interpreting in-situ stress in shale reservoirs includes: Step S1: Obtain the shale rheological constitutive model; Step S2: Introduce the shale rheological constitutive model into the finite element simulation to reconstruct the stress evolution process of shale reservoirs under different sedimentary evolution conditions, and compare the influence of the strong compression-dominated path and the uplift-erosion-dominated path on the current geostress distribution. Step S3: Combine in-situ testing and well logging data to constrain and verify the simulation results, forming a geostress interpretation of shale reservoirs that considers sedimentary evolution and rock rheology.

[0005] As a preferred option, in step S1, triaxial creep and relaxation tests are carried out under near-in-situ temperature and pressure conditions to establish a shale rheological constitutive model that considers the influence of clay mineral content and temperature.

[0006] As a preferred option, in step S2, different sedimentary evolution scenarios are parameterized into input boundary conditions, combined with shale rheological constitutive models, to conduct numerical simulations of geostress evolution on geological timescales, and to compare the influence of strong compression-dominated pathways and uplift-erosion-dominated pathways on the current geostress distribution.

[0007] The present invention also provides a shale reservoir in-situ stress interpretation device, comprising: The first processing module is used to obtain the shale rheological constitutive model; The second processing module is used to introduce the shale rheological constitutive model into the finite element simulation, reconstruct the stress evolution process of shale reservoirs under different sedimentary evolution conditions, and compare the influence of the strong compression-dominated path and the uplift-erosion-dominated path on the current geostress distribution. The third processing module is used to combine in-situ testing and well logging data to constrain and verify the simulation results, forming a geostress interpretation of shale reservoirs that takes into account sedimentary evolution and rock rheology.

[0008] As a preferred option, the first processing module conducts triaxial creep and relaxation tests under near-in-situ temperature and pressure conditions to establish a shale rheological constitutive model that considers the influence of clay mineral content and temperature.

[0009] As a preferred approach, the second processing module parameterizes different sedimentary evolution scenarios into input boundary conditions, combines them with shale rheological constitutive models, and conducts numerical simulations of geostress evolution on geological timescales to compare the impact of strong compression-dominated pathways and uplift-erosion-dominated pathways on the current geostress distribution.

[0010] The present invention also provides a shale reservoir in-situ stress interpretation system, comprising: a memory and a processor, wherein the memory stores a computer program executed by the processor, and the computer program executes a shale reservoir in-situ stress interpretation method when executed by the processor.

[0011] The present invention also provides a storage medium storing a computer program that executes a shale reservoir in-situ stress interpretation method when running.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention takes "lithological composition and structure characterization - rheological tests and constitutive calibration - numerical simulation of sedimentary evolution - in-situ constraint interpretation" as the main line. By setting different sedimentary evolution scenarios such as strong compression-dominated path and uplift-erosion-dominated path, it compares and analyzes the differences in the current geostress distribution response, quantitatively identifies the main controlling role of sedimentary evolution stage, lithological combination and rheological parameters on the geostress distribution law, thereby realizing the method improvement from "static elastic estimation" to "sedimentary evolution-rheological coupling interpretation".

[0013] 2. This invention emphasizes the methodological approach of "in-situ evidence constraint". It utilizes in-situ stress constraint points such as closure pressure or ISIP, as well as well-drilled observation information such as imaging logging, to perform inversion calibration and consistency verification of key model parameters. On this basis, it establishes a method for interpreting geostress in shale reservoirs that considers sedimentary evolution and rock rheological effects. Attached Figure Description

[0014] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart of the shale reservoir in-situ stress interpretation method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the construction path and boundary conditions; Figure 3 A schematic diagram illustrating the continuous geostress interpretation of shale reservoirs coupled with sedimentary evolution. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] Example 1 like Figure 1 As shown, the present invention provides a method for interpreting in-situ stress in shale reservoirs, comprising: Step S1: Obtain the shale rheological constitutive model; Step S2: Introduce the shale rheological constitutive model into the finite element simulation to reconstruct the stress evolution process of shale reservoirs under different sedimentary evolution conditions, and compare the influence of the strong compression-dominated path and the uplift-erosion-dominated path on the current geostress distribution. Step S3: Combine in-situ testing and well logging data to constrain and verify the simulation results, forming a geostress interpretation of shale reservoirs that considers sedimentary evolution and rock rheology.

[0019] As one embodiment of the present invention, step S1 includes: Step S11: Using a high-temperature and high-pressure rock mechanics testing system, multi-level deviatoric triaxial creep and stress relaxation tests were conducted on Longmaxi Formation shale cores with different clay mineral contents (siliceous hard rock and clay-rich soft rock) under near-in-situ temperature and pressure conditions to accurately obtain the instantaneous elastic deformation and long-term rheological deformation characteristics of different lithological components. Step S12: Based on the long-term rheological deformation characteristics of shale, key rheological parameters such as creep compliance and viscosity coefficient are extracted. Combined with mineral composition analysis, the relationship between static elastic modulus, clay mineral content, and rheological parameters is clarified. Based on this, a nonlinear viscoelastic-plastic rheological constitutive model for deep shale, comprehensively considering the influence of temperature conditions and deviatoric stress levels, is established.

[0020] As one embodiment of the present invention, step S21 includes: Step S21: Based on the lithological profile obtained by fine interpretation of well logging data, establish a finite element numerical model of interbedded rock mass containing clay-rich soft rock layer and siliceous hard rock layer, and assign the aforementioned nonlinear rheological constitutive model to the corresponding stratigraphic unit.

[0021] Step S22: Set up two representative sedimentary evolution scenarios for comparative simulation: one is a sedimentary evolution path dominated by strong compression, and the other is a sedimentary evolution path dominated by uplift and erosion. By parametrically inputting evolution stages such as burial, compaction, tectonic compression, and uplift and erosion, conduct geostress evolution simulation on a geological timescale to reveal the influence of different sedimentary evolution processes on the current geostress distribution and clarify the role of rock rheology in it.

[0022] As one embodiment of the present invention, step S3 includes: Step S31: Based on the numerical simulation revealing the dynamic distribution mechanism of interlayer stress, and based on the theory of porous viscoelastic media, a geostress correction calculation model considering the cumulative effect of geological time is established by introducing the tectonic loading and unloading history and rock rheological effect into the traditional geostress calculation framework.

[0023] Step S32: Obtain continuous lithology and static parameters using logging curves from the entire well section. Combine these with in-situ hydraulic fracturing response, microseismic characteristics, and in-situ test results as constraints to invert and calibrate the theoretical calculation results, determining key rheological time parameters and structural boundary parameters. Based on this, establish a high-precision continuous geostress interpretation method for deep, complex interbedded strata.

[0024] Example: Sampling was conducted using core samples from deep shale gas wells in a specific location. Based on core observations, conventional logging responses, and bedding characteristics, representative shale samples were screened and classified according to lithology, with the selection of typical samples reflecting different lithological combinations being prioritized. XRD analysis was used to obtain the mineral composition and relative content of the shale samples, focusing on identifying major components such as quartz, feldspar, calcite, and clay minerals, providing mineralogical basis for lithological end-member classification and interpretation of rheological parameter differences. Combined with SEM and other testing methods, the bedding structure, grain contact relationships, pore and fracture development characteristics, and clay mineral occurrence states of the shale samples were characterized, analyzing the differences in microstructure among different lithological intervals and their potential impact on rheological deformation characteristics. Based on this, classification criteria for shale samples of different lithologies were established, determining the representative sample groups required for subsequent high-temperature and high-pressure rheological tests and constitutive parameter calibration. The specific process is as follows: Step 1: In-situ multi-stage deviatoric stress triaxial rheological experiments and establishment of a nonlinear rheological constitutive model under in-situ thermo-baric conditions This invention proposes to utilize the GCTS high-temperature, high-pressure fluid-structure interaction experimental machine to conduct triaxial creep tests on Longmaxi Formation shale core samples with different clay mineral contents. Existing research indicates that when the creep duration exceeds 24 hours, the experimental results show good consistency. Considering both the reliability of the experimental results and the time cost, this invention proposes to set the single-stage creep duration to 24–72 hours. The confining pressure in the test is determined based on the measured minimum horizontal principal stress, and the axial load is determined based on the calculated vertical stress. The creep test yields the time-dependent deformation curve of the rock under constant load, and key rheological parameters such as creep compliance and viscosity coefficient of different lithological samples are extracted by fitting the experimental data.

[0025] Based on time-dependent deformation curves obtained from rheological experiments, the instantaneous elastic strain and rheological strain components of shale are decomposed. Through curve fitting, creep compliance and viscosity coefficients of different lithological samples under different deviatoric stress levels are extracted. Combined with mineral content data obtained from XRD, quantitative relationships between static elastic parameters, clay mineral content, and key rheological parameters are established, constructing a nonlinear rheological constitutive model capable of characterizing the time-dependent deformation and viscoplastic relaxation features of the deep Longmaxi Formation shale.

[0026] Step 2: Numerical simulation of shale reservoir geostress evolution under different sedimentary evolution scenarios A three-dimensional geometric model reflecting the characteristics of the Longmaxi Formation shale reservoir was established using Rhino. The model explicitly considers key elements such as layer thickness ratio and zonal assignment of mechanical parameters. To ensure the stability and accuracy of the numerical calculations, a combined strategy of intra-layer refinement, inter-layer transition, and loading-face refinement was adopted for mesh generation, with a focus on refining high-stress gradient regions to reduce the impact of numerical diffusion on the calculation results. In the material property settings, the aforementioned nonlinear rheological constitutive model was assigned to the corresponding stratigraphic units through a user-defined material subroutine (UMAT), thereby achieving material response simulation considering time-dependent effects.

[0027] The amplitude and rate parameters of the sedimentary evolution process will be constrained by research findings on the sedimentary evolution of the Sichuan Basin and regional geological data, and reasonable value ranges will be determined through sensitivity analysis. The macroscopic evolution process is input with three-stage boundary conditions (such as...). Figure 2 (As shown). The first stage is the deep burial stage, where vertical self-weight is applied and lateral constraints are set. Initial pore pressure and overlying pressure are assigned according to depth distribution to make the model reach an initial stress state consistent with deep burial conditions. The second stage is the tectonic modification stage, where horizontal strain is applied while maintaining overlying pressure to simulate the influence of tectonic compression on the formation stress state. Two representative sedimentary evolution scenarios are set up for comparative study in this stage: one is the strong compression-dominated scenario, which focuses on reflecting the evolution process of strong tectonic activity after early deep burial; the other is the uplift and erosion-dominated scenario, which focuses on the evolution process dominated by burial compaction and later uplift and unloading. The third stage is the later uplift and adjustment stage, which uses the method of slowly unloading overlying pressure and adjusting boundary constraints to simulate the influence of uplift, erosion and later adjustment on the current stress state. The unloading process is also input using a time integration method, and together with the rheological constitutive model, it controls the evolution of stress over time.

[0028] For the strain rate and duration of each evolution stage, this embodiment of the invention uses a magnitude constraint under a geological timescale. Specifically, based on the deformation magnitude and duration given by regional sedimentary evolution and tectonic restoration studies, the total deformation is converted into an equivalent strain rate and input into the model. Sensitivity analysis is used to examine the impact of strain rate changes on the current geostress distribution. A staged loading and time step control strategy is adopted in the numerical solution process. Each stage first performs elastic equilibrium calculations, followed by rheological time integration calculations; the time step is adaptive to ensure sufficient time resolution for stages with rapid stress changes. To ensure that the model results can be used for subsequent geostress interpretation and mechanism analysis, the numerical output includes: the magnitude and direction of the principal stresses at the end of each stage, the stress evolution curve over time, stress gradient changes, and the degree of stress adjustment in different layers.

[0029] Two methods were used for model verification. First, consistency was checked with in-situ constraint data, for example, by using the minimum principal stress to constrain the closed pressure and verifying the principal stress direction using wellbore failure information. Second, the model was compared with existing analytical or semi-analytical results under simplified conditions to verify the correctness of the UMAT material realization and time integration process.

[0030] Step 3: Analysis of the distribution law of in-situ stress in shale reservoirs and its main controlling factors Based on finite element numerical simulation results, data on the evolution of stress and strain in various rock strata over time at geological timescales are extracted, and an analytical framework of "sedimentary evolution input—material rheological response—current stress distribution output" is constructed. The focus is on analyzing the formation and evolution of geostress in shale reservoirs under different sedimentary evolution scenarios, quantitatively statistically analyzing the accumulation of viscoplastic strain, stress adjustment amplitude, and characteristic timescales of different strata, identifying the differences in rheological dissipation characteristics among different lithological strata, and analyzing which strata are more likely to retain higher stress levels.

[0031] Based on this, a comparative analysis framework is constructed for the results of purely elastic calculations and rheological evolution calculations. Under the same geometric model and boundary conditions, purely elastic calculations and evolution calculations considering rheological effects are carried out respectively, and the differences between the two types of results in terms of principal stress magnitude, stress gradient, and characteristics of variation with depth are compared. This analysis examines the main sources and controlling factors of deviations in traditional static elastic interpretation in shale reservoirs, such as lithological assemblage, rheological parameters, sedimentary evolution duration, and loading rate. Furthermore, the deviation range of the static elastic model under different parameter combinations is given, achieving a quantitative characterization of the sources of error.

[0032] Based on the above analysis, this study aims to elucidate from a rock mechanics perspective that under different sedimentary evolution scenarios, rock rheology in shale reservoirs alters the adjustment mode and distribution characteristics of present-day in-situ stress, thereby causing it to deviate from the predictions of static elastic models. This understanding will provide a mechanistic basis for the subsequent construction of in-situ stress interpretation methods for shale reservoirs, and will enable the model results to be verified and cross-validated with field observation data.

[0033] Step 4: Interpretation of continuous geostress in shale reservoirs coupled with sedimentary evolution Based on the aforementioned analysis of geostress evolution and controlling factors, a geostress interpretation method for shale reservoirs combining "sedimentary evolution parameters, rheological parameters, continuous well logging input, and in-situ constraint calibration" is established. First, based on the stress decomposition approach of porous media, the horizontal principal stress is expressed as a combination of overlying pressure, pore pressure, elastic response term, and sedimentary evolution effect term. Rheological effect corrections are introduced into the traditional elastic response framework to reflect the influence of stress evolution on the current geostress distribution over geological timescales. This interpretation model includes two types of key parameters: one is the equivalent boundary parameter characterizing the sedimentary evolution process, and the other is the rheological parameter obtained from experimental calibration, used to jointly constrain the stress evolution characteristics of different layers over time, such as... Figure 3 As shown.

[0034] This invention has the following characteristics: (1) At the level of rheological constitutive model: obtain the nonlinear rheological parameters of deep interbedded shale (siliceous hard rock and clay-rich soft rock), and establish a viscoelastic-plastic rheological constitutive model of deep shale that comprehensively considers the influence of temperature and pressure conditions and mineral composition. (2) At the level of geostress occurrence mechanism: clarify the long-term evolution characteristics of geostress in shale reservoirs under different sedimentary evolution conditions, and focus on revealing the different effects of strong compression-dominated path and uplift-erosion-dominated path on the current geostress distribution pattern, as well as the controlling role of rock rheology in it; (3) At the engineering evaluation level: Establish a shale reservoir geostress interpretation model that considers sedimentary evolution and rock rheological effects, and form a continuous geostress interpretation based on well logging data and in-situ measured constraints.

[0035] Example 2 The present invention also provides a shale reservoir in-situ stress interpretation device, comprising: The first processing module is used to obtain the shale rheological constitutive model; The second processing module is used to introduce the shale rheological constitutive model into the finite element simulation, reconstruct the stress evolution process of shale reservoirs under different sedimentary evolution conditions, and compare the influence of the strong compression-dominated path and the uplift-erosion-dominated path on the current geostress distribution. The third processing module is used to combine in-situ testing and well logging data to constrain and verify the simulation results, forming a geostress interpretation of shale reservoirs that takes into account sedimentary evolution and rock rheology.

[0036] As one embodiment of the present invention, the first processing module conducts triaxial creep and relaxation tests under near-in-situ temperature and pressure conditions to establish a shale rheological constitutive model that considers the influence of clay mineral content and temperature.

[0037] In one embodiment of the present invention, the second processing module parameterizes different sedimentary evolution scenarios into inputtable boundary conditions, combines them with shale rheological constitutive models, and conducts numerical simulations of geostress evolution on geological timescales to compare the influence of strong compression-dominated pathways and uplift-erosion-dominated pathways on the current geostress distribution. Example 3 The present invention also provides a shale reservoir in-situ stress interpretation system, comprising: a memory and a processor, wherein the memory stores a computer program executed by the processor, and the computer program executes a shale reservoir in-situ stress interpretation method when executed by the processor.

[0038] Example 4 The present invention also provides a storage medium storing a computer program that executes a shale reservoir in-situ stress interpretation method when running.

[0039] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for interpreting in-situ stresses in a shale reservoir, characterized in that, include: Step S1: Obtain the shale rheological constitutive model; Step S2: Introduce the shale rheological constitutive model into the finite element simulation to reconstruct the stress evolution process of shale reservoirs under different sedimentary evolution conditions, and compare the influence of the strong compression-dominated path and the uplift-erosion-dominated path on the current geostress distribution. Step S3: Combine in-situ testing and well logging data to constrain and verify the simulation results, forming a geostress interpretation of shale reservoirs that considers sedimentary evolution and rock rheology.

2. The method for shale reservoir geostress interpretation of claim 1, wherein, In step S1, triaxial creep and relaxation tests are carried out under near-in-situ temperature and pressure conditions to establish a shale rheological constitutive model that considers the influence of clay mineral content and temperature.

3. The method for shale reservoir geostress interpretation of claim 2, wherein, In step S2, different sedimentary evolution scenarios are parameterized into input boundary conditions and combined with shale rheological constitutive models to conduct numerical simulations of geostress evolution on geological timescales, comparing the impact of strong compression-dominated pathways and uplift-erosion-dominated pathways on the current geostress distribution.

4. A shale reservoir geostress interpretation apparatus, characterized in that, include: The first processing module is used to obtain the shale rheological constitutive model; The second processing module is used to introduce the shale rheological constitutive model into the finite element simulation, reconstruct the stress evolution process of shale reservoirs under different sedimentary evolution conditions, and compare the influence of the strong compression-dominated path and the uplift-erosion-dominated path on the current geostress distribution. The third processing module is used to combine in-situ testing and well logging data to constrain and verify the simulation results, forming a geostress interpretation of shale reservoirs that takes into account sedimentary evolution and rock rheology.

5. The shale reservoir geostress interpretation device of claim 4, wherein, The first processing module conducts triaxial creep and relaxation tests under near-in-situ temperature and pressure conditions to establish a shale rheological constitutive model that considers the influence of clay mineral content and temperature.

6. The shale reservoir geostress interpretation device of claim 5, wherein, The second processing module parameterizes different sedimentary evolution scenarios into input boundary conditions, combines them with shale rheological constitutive models, and conducts numerical simulations of geostress evolution on geological timescales to compare the impact of strong compression-dominated pathways and uplift-erosion-dominated pathways on the current geostress distribution.

7. A shale reservoir geostress interpretation system characterized by, include: A memory and a processor, wherein the memory stores a computer program executed by the processor, the computer program, when executed by the processor, performs the shale reservoir in-situ stress interpretation method as described in any one of claims 1-3.

8. A storage medium, characterized by The storage medium stores a computer program that, when executed, performs the shale reservoir in-situ stress interpretation method as described in any one of claims 1-3.

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