A method for identifying internal structure of fault-controlled fracture-cave type reservoirs

Abstract

The present application belongs to the technical field of oil exploration and development, and relates to a method for identifying the internal structure of fault-controlled fracture-cave type reservoirs. The present application divides the fault-controlled fracture-cave type reservoirs into different internal structures, and uses a numerical simulation method to construct a variation chart of stress-strain curves in rock mechanics properties based on different internal structures of the fault-controlled fracture-cave type reservoirs. By monitoring the stress-strain curves of the reservoirs and projecting them into the chart, the internal structure of the reservoirs can be determined. The present application draws a limit range chart based on the variation of stress-strain curves in rock mechanics properties, and provides a new method for identifying the internal structure of the fault-controlled fracture-cave type reservoirs. The method can effectively characterize the heterogeneity of the reservoirs, reduce the errors caused by technical detection, and is highly targeted, simple to operate and convenient.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration and development technology, specifically to a method for identifying the internal structure of fault-controlled fracture-vuggy reservoirs. Background Technology

[0002] Fault-controlled fracture-vuggy reservoirs are an important type of carbonate oil and gas reservoir. Their reservoir space is dominated by a network of dissolution pores and fractures controlled by fault zones, exhibiting strong heterogeneity and complex spatial structure. Under the multi-stage tectonic fracturing of large faults, fault-controlled fracture-vuggy reservoirs have formed numerous dissolution-expanded branch and secondary faults, constituting a vast fracture network system, which has become a dominant channel for oil and gas migration, charging, and accumulation.

[0003] With the acquisition of high-precision seismic data and the development of computer technology, the accuracy requirements for identifying the internal structure of fractured-vuggy reservoirs are becoming increasingly stringent. In fault-controlled fractured-vuggy reservoirs, rocks can be divided according to the location of the fracture zone into a central fracture zone (fault core), a surrounding fracture zone (fault breccia zone and fractured reservoir), and an external matrix rock zone (surrounding rock zone). Due to the unique geomechanical characteristics of fault-controlled fractured-vuggy reservoirs, the rocks in the fracture zone exhibit significant discontinuity, and the mechanical properties of rocks in different zones transitioning from the fracture zone to the matrix zone differ markedly.

[0004] Currently, the identification of internal structures is mostly based on seismic and well logging data. However, due to the limited accuracy of seismic and well logging technologies, certain measurement accuracy errors occur.

[0005] Chinese patent CN116931070A, entitled "A Method for Characterizing Fracture-Cavity Reservoirs with Inversion," discloses a method for characterizing fracture-cavity reservoirs with inversion. This method, starting from inversion, introduces constraint terms to effectively improve the spatial heterogeneity of the inversion results. It also provides optimization methods for background trend suppression and anomalous response enhancement, thereby improving the identification accuracy of dissolution cavities and fracture zones.

[0006] Chinese patent CN119272461A, entitled "Prediction Method, System, and Electronic Equipment for Fault-Controlled Fracture-Void High-Quality Reservoirs in Carbonate Rocks," provides a method, system, and electronic equipment for predicting fault-controlled fracture-void high-quality reservoirs in carbonate rocks. Based on an introduced mathematical probability model, it combines geophysical exploration techniques with mathematical analysis to achieve quantitative characterization and prediction of fault-controlled fracture-void high-quality reservoirs. The process is simple and rapid, enabling accurate prediction of cave-type fracture-void high-quality reservoirs.

[0007] Chinese patent CN116299664A, entitled "Method, Apparatus, and Equipment for Determining Fault-Controlled Fracture-Void Reservoirs," provides a method, apparatus, and equipment for determining fault-controlled fracture-void reservoirs. This method utilizes a self-organizing neural network model to comprehensively characterize different seismic attribute information reflecting seismic facies in fault-developed areas into an effective attribute data volume representing the reservoir structure, and achieves quantitative characterization of different types of reservoirs using seismic facies.

[0008] The aforementioned patents target a relatively limited range of types for identifying the internal structure of fractured-vuggy reservoirs, and do not consider using rock mechanical properties as a breakthrough point for research. Summary of the Invention

[0009] This invention aims to provide a method for identifying the internal structure of fault-controlled fracture-vuggy reservoirs. Starting from rock mechanical properties, it seeks to solve the problem of identifying the types of internal structures in these reservoirs. This invention will use numerical simulation to construct a chart depicting the changes in stress-strain curves of different internal structures in fault-controlled fracture-vuggy reservoirs within rock mechanical properties. By monitoring the stress-strain curves of the reservoir and projecting them onto the chart, the internal structure of the reservoir can be determined, providing a new method for identifying the internal structure of fault-controlled fracture-vuggy reservoirs.

[0010] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method and system for identifying the internal structure of fractured-vuggy reservoirs, comprising the following steps:

[0011] (1) Obtain geological and physical property data of the target fault-controlled fracture-vuggy reservoir, including parameters such as reservoir pressure, Young's modulus of rock, and Poisson's ratio of rock.

[0012] (2) Based on the spatial characteristics of fault-controlled fracture-vuggy reservoirs, the internal structure of fault-controlled fracture-vuggy reservoirs is divided into three types of internal structure, including: fracture type, fracture-vuggy type and pore-fracture type.

[0013] (3) Based on the three types of internal structure, construct the mechanism model of the three internal structure, namely, construct the numerical simulation mechanism model of the fault-controlled fracture-vuggy reservoir with internal structure of fracture-type, fracture-vuggy and pore-type.

[0014] (4) Based on the established mechanism models of different internal structures, the stress-strain curves of the mechanism models of different internal structures under different pressure levels are simulated and calculated under the action of the solid mechanics physical field.

[0015] The constitutive equations for the physical fields of solid mechanics in the three-dimensional case can be expressed as:

[0016] σ xx =λe+2με xx ,σ yy =λe+2μεyy ,σ zz =λe+2με zz

[0017] τ xy =μγ xy , τ yz =μγ yz ,τ zx =μγ zx

[0018]

[0019] In the formula, σ xx σ yy σ zz It is the normal stress component, Pa; τ xy τ yz τ zx It is the shear stress component, Pa; ε xx ε yy ε zz It is a normal strain component, dimensionless; γ xy γ yz γ zx These are shear strain components, dimensionless; λ is the first Lamé constant, GPa; μ is the second Lamé constant, GPa; e = ε xx +ε yy +ε zz σ is stress, Pa; ε is strain, dimensionless.

[0020] The relationships between the first and second Lamé constants and Young's modulus and Poisson's ratio are as follows:

[0021]

[0022] In the formula, E is Young's modulus, GPa; ν is Poisson's ratio, dimensionless.

[0023] (5) Plot the stress-strain curve results of different internal structure mechanism models and the stress-strain limit range in the same coordinate system;

[0024] (6) Perform stress-strain monitoring on the target reservoir and obtain the stress-strain curve of the target reservoir;

[0025] (7) Compare the stress-strain curve of the target reservoir in step (6) with the stress-strain limit range chart to determine the corresponding type of the internal structure of the target reservoir.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) Existing technologies often rely on a single attribute (such as seismic amplitude) or a general classification (such as the cave / fracture dichotomy), resulting in insufficient description of heterogeneity. This invention proposes three classifications of the internal structure of fault-controlled fracture-cavity oil and gas reservoirs, which can effectively characterize reservoir heterogeneity and provide a reference for clarifying reservoir structure and optimizing oil and gas field well network deployment.

[0028] (2) This invention proposes a new method to reflect the internal structure of fault-controlled fracture-vuggy reservoirs by using the stress-strain variation curve in rock mechanical parameters. The internal structure type of fault-controlled fracture-vuggy reservoirs can be determined by the difference in rock mechanical properties of different internal structures. Starting from the properties of the reservoir rock itself, it can effectively reduce the error caused by technical detection, and is highly targeted and easy to operate.

[0029] (3) Compared with the prior art, the present invention is more convenient. By constructing a map once for the target fault-controlled fracture-vuggy oil and gas reservoir, the internal structure of the strata at different depths and pressures can be identified. Attached Figure Description

[0030] Figure 1 This invention provides numerical simulation models for reservoirs with interrupted fracture, fracture-vault, and pore-fracture internal structures.

[0031] Figure 2 The stress-strain curve of reservoir G at 6200m is shown in the example.

[0032] Figure 3 This is a diagram showing the stress-strain limit range in the embodiments.

[0033] Figure 4 Core samples were taken from reservoir G at 6200m in the example.

[0034] Figure 5 The stress-strain curves of some models in the embodiments are shown under a certain pressure level. Detailed Implementation

[0035] Taking the G oil and gas reservoir as an example, geological data and well logging analysis indicate that it is a carbonate fault-controlled fracture-vuggy reservoir with a burial depth of 6000m–6500m. The reservoir space is dominated by a network of dissolution pores and fractures controlled by fault zones, exhibiting strong heterogeneity and a complex spatial structure. Based on well logging data and rock mechanics testing, the pressure at 6200m in the study area is 85MPa, the Young's modulus is 28GPa, and the Poisson's ratio is 0.27.

[0036] Based on the above analysis results, the internal structure of the G-fault-controlled fracture-vuggy oil and gas reservoir was identified. The specific operation steps are as follows:

[0037] Step 1: Obtain geological and physical property data of the target fault-controlled fracture-vuggy reservoir. The reservoir pressure is 85 MPa, Young's modulus is 28 GPa, and Poisson's ratio is 0.27.

[0038] Step 2: Based on the spatial characteristics of fault-controlled fracture-vuggy reservoirs, the internal structure of fault-controlled fracture-vuggy reservoirs is divided into three categories: fault-fracturing type, fracture-vuggy type, and pore-fracture type.

[0039] Among them, the internal structure of fracture-vuggy reservoirs is classified into three categories, mainly based on the genetic mechanisms and spatial characteristics of fracture-dominated (fracture-type), dissolution-fracture composite (fracture-vuggy), and pore-fracture type (pore-fracture type) reservoirs. By classifying the internal structure, reservoir heterogeneity can be quantified, guiding differentiated development strategies (e.g., deploying horizontal wells along fracture zones for fracture-type reservoirs, optimizing gas injection and gravity drive for fracture-vuggy reservoirs, and implementing acid fracturing for pore-fracture type reservoirs), significantly improving reservoir prediction accuracy and supporting precise tapping of remaining oil potential.

[0040] Step 3: Based on the three types of internal structures, construct numerical simulation models of fault-controlled fracture-vuggy reservoirs with corresponding internal structures of fracture-type, fracture-vuggy, and pore-type internal structures.

[0041] The three types of internal structure fracture-vuggy reservoir models all employ discrete fracture networks for more realistic fracture characterization. The discrete fracture networks are programmed using MATLAB software to obtain discrete fracture models within a given range. Specifically, the fracture-vuggy type includes both fractures and cracks, with fracture generation lengths set to 200m–250m and a maximum of 4 fractures, crack generation lengths set to 40m–60m, and a maximum of 36 cracks. The fracture-vuggy type includes both cracks and cavities, with crack generation lengths set to 40m–60m, a maximum of 32 cracks, and cavities constructed using an artificial geometric model, with diameters set to 20m–70m and a maximum of 5 cavities. The porous-fracture type includes a porous matrix and fractures, with the matrix set as a porous medium and a porosity of 0.3, crack generation lengths set to 40m–60m, and a maximum of 45 fractures. Based on the given range of crack length, range of cave diameter, and number of generated cracks, three crack models were obtained for each model, thus constructing three types of numerical simulation models for internal structures.

[0042] Step 4: Based on the constructed numerical simulation models of different internal structures, under the action of a solid mechanics physical field, simulate and calculate the stress-strain curves of the numerical simulation models under pressure levels ranging from 60 MPa to 100 MPa, as shown below. Figure 5 .

[0043] The constitutive equations for the physical fields of solid mechanics in the three-dimensional case can be expressed as:

[0044] σ xx =λe+2με xx ,σ yy =λe+2με yy ,σ zz =λe+2με zz

[0045] τ xy =μγ xy , τ yz =μγ yz ,τ zx =μγ zx

[0046]

[0047] In the formula, σ xx σ yy σ zz It is the normal stress component, Pa; τ xy τ yz τ zx It is the shear stress component, Pa; ε xx ε yy ε zz It is a normal strain component, dimensionless; γ xy γ yz γ zx These are shear strain components, dimensionless; λ is the first Lamé constant, GPa; μ is the second Lamé constant, GPa; e = ε xx +ε yy +ε zz σ is stress, Pa; ε is strain, dimensionless.

[0048] The relationships between the first and second Lamé constants and Young's modulus and Poisson's ratio are as follows:

[0049]

[0050] In the formula, E is Young's modulus, taken as 28 GPa; ν is Poisson's ratio, taken as 0.27. Calculations show that λ is 12.941 GPa and μ is 11.024 GPa.

[0051] Step 5: Under the influence of the solid mechanics physical field, simulate the stress-strain curves of the numerical simulation model at pressure levels ranging from 60 MPa to 100 MPa. Plot the stress-strain limits of the fault-controlled fracture-vuggy reservoir with fracture-type, fracture-vuggy, and pore-fracture-type internal structures in the same coordinate system. Figure 3 .

[0052] Step Six: Import the stress-strain curve chart into the reservoir stress-strain monitoring system, and use the reservoir stress-strain monitoring system to monitor the stress and strain at 6200m in the G oil and gas reservoir to obtain the reservoir stress-strain curve. Figure 2 ).

[0053] The reservoir stress-strain monitoring system described in this invention can employ commonly used monitoring systems in the field.

[0054] Step 7: Compare the stress-strain curve of the monitored target reservoir with the imported stress-strain curve charts of fracture-vuggy reservoirs with different internal structures to determine that the corresponding type of internal structure at 6200m in the monitored target block reservoir is a porosity-fracture reservoir. Figure 3 ).

[0055] To verify the correctness of the above invention, core samples were taken at a depth of 6200m from the G oil and gas reservoir. Figure 4 ).

[0056] Core sampling clearly revealed fractures in the carbonate rock, and the intact core indicates the absence of fractures or cavities. Furthermore, the carbonate rock itself is porous, suggesting that the reservoir at 6200m is a fractured-pore type. This result is consistent with that obtained in step seven, demonstrating the correctness of the proposed method.

[0057] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. The implementation steps and related parameters may vary. All equivalent changes and modifications made without departing from the technical solution of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for identifying the internal structure of fractured-vuggy reservoirs, characterized in that, The fault-controlled fracture-vuggy reservoir is divided into different internal structures. A numerical simulation method is used to construct a chart showing the changes in stress-strain curves in rock mechanical properties based on different internal structures of the fault-controlled fracture-vuggy reservoir. By monitoring the stress-strain curves of the reservoir and projecting them onto the chart, the internal structure of the reservoir can be determined. Includes the following steps: (1) Obtain geological and physical property data of the target fault-controlled fracture-vuggy reservoir; (2) Based on the spatial characteristics of fault-controlled fracture-vuggy reservoirs, the internal structure of fault-controlled fracture-vuggy reservoirs is divided into three types of internal structure. (3) Based on the three types of internal structure, construct numerical simulation models for the three internal structures; (4) Based on the constructed numerical simulation models of different internal structures, under the action of the solid mechanics physical field, the stress-strain curves of the numerical simulation models of different internal structures under different pressure levels are simulated and calculated. (5) Plot the stress-strain curves of numerical simulation models of different internal structures in the same coordinate system and plot the stress-strain limit range. (6) Perform stress-strain monitoring on the target reservoir and obtain the stress-strain curve of the target reservoir; (7) Compare the stress-strain curve of the target reservoir in step (6) with the stress-strain limit range chart to determine the corresponding type of the internal structure of the target reservoir; In step (2), the three types of internal structures include the fracture type, the hole type, and the pore type.

2. The method for identifying the internal structure of fractured-vuggy reservoirs according to claim 1, characterized in that, In step (4), the constitutive equation of the solid mechanics physical field in the three-dimensional case can be expressed as: ； ； ； In the formula, It is the normal stress component, Pa; It is the shear stress component, Pa; It is a normal strain component, dimensionless; It is a shear strain component, dimensionless; μ is the first Lamé constant, GPa; μ is the second Lamé constant, GPa; σ is stress, in Pa; ε is strain, which is dimensionless.

3. The method for identifying the internal structure of fractured-vuggy reservoirs according to claim 2, characterized in that, In step (4), the relationship between the first Lamé constant and the second Lamé constant and Young's modulus and Poisson's ratio is as follows: ； ； In the formula, E is Young's modulus, GPa; It is Poisson's ratio, dimensionless.

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