Method for evaluating stress sensitivity of strata-containing shale reservoir

Abstract

The invention relates to a stress sensitivity evaluation method for a shale reservoir with a lamina, which comprises the following steps of: 1, establishing a two-dimensional standard rock core column geometric model with different lamina angles and different lamina thicknesses on the basis of a pore elastic-plastic seepage model; 2, based on geophysical interpretation, literature investigation and laboratory experiments, obtaining geomechanical parameters such as reservoir crustal stress, pore pressure, elastic modulus and Poisson's ratio; 3, different effective confining pressures are applied to the rock core in finite element software, and the change process of ground stress borne by the stratum is simulated; 4, applying seepage pressure difference to the upper end face and the lower end face of the rock core column, and monitoring the total flow flowing out of the end face of the rock core, 5, calculating to obtain the equivalent permeability of the strata-containing shale according to the Darcy law, and 6, drawing a stress sensitivity curve according to the obtained data, and evaluating the stress sensitivity of the strata-containing shale reservoir. And quantitative and accurate evaluation on the reservoir permeability sensitivity of the simulated strata shale reservoir under different effective stress conditions is realized.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development technology, specifically relating to a method for evaluating the stress sensitivity of layered shale reservoirs using finite element software, applicable to stress sensitivity studies and practical engineering applications of layered shale. Background Technology

[0002] With the rapid growth of global energy demand and the continued advancement of unconventional oil and gas exploration and development, shale oil and gas are playing an increasingly important role in the world's energy structure. my country's shale oil and gas reservoirs are generally characterized by deep burial, complex geological structures, low organic matter maturity, strong rock heterogeneity, and high extraction difficulty. Furthermore, shale reservoirs have a very dense structure; shale cores extracted from deep underground show almost no fractures but exhibit obvious laminar structures, with abundant laminar shale bedding. The assessment of the stress sensitivity of laminar shale directly affects the accuracy of in-situ shale oil and gas reserve calculations. Only by clarifying the reservoir stress sensitivity patterns can the conversion standards from conventional reservoir physical properties to in-situ physical properties be determined, thereby calculating the true reserves. Moreover, stress sensitivity is a core parameter for determining the reasonable production pressure differential in oilfields. Only by quantitatively clarifying the reservoir stress sensitivity characteristics can the safe and efficient extraction of shale oil be achieved; that is, the accuracy of stress sensitivity understanding directly affects the recovery rate improvement. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for evaluating the stress sensitivity of layered shale reservoirs, which enables a quantitative and accurate evaluation of the permeability sensitivity of simulated layered shale reservoirs under different effective stress conditions.

[0004] A method for evaluating the stress sensitivity of layered shale reservoirs, characterized by comprising the following steps:

[0005] Step 1: Based on the pore elastoplastic flow model, establish two-dimensional standard core column geometric models with different lamellar angles and thicknesses; the lamellar thicknesses are X1, X2, X3, X4, X5, and the lamellar angles are A1, A2, A3, A4, A5, A6, A7; the lamellar shale reservoir is assumed to be a pore elastoplastic medium, and the rock deformation under external load and the pore fluid seepage process satisfy stress balance and seepage mass conservation. The rock deformation mechanical equilibrium equation is:

[0006]

[0007] The fluid flow continuity equation is:

[0008]

[0009] Step 2: Based on geophysical interpretation, literature review, and laboratory experiments, obtain geomechanical parameters such as reservoir stress, pore pressure, elastic modulus, and Poisson's ratio. Input the elastic modulus E1 and Poisson's ratio 1 of the laminae, and the relationship between the permeability coefficient and porosity of the laminae in the finite element software; and the elastic modulus E2 and Poisson's ratio 2 of the shale layers, and the relationship between the permeability coefficient and porosity of the shale layers.

[0010] Step 3: Apply different effective confining pressures to the rock core in the finite element software to simulate the change process of the in-situ stress on the formation. The effective confining pressures are F1, F2, F3, F4, F5, F6, F7, and F8, respectively. At the same time, apply boundary conditions that meet the experimental conditions.

[0011] Step 4: Apply a seepage pressure difference of x to the upper and lower ends of the core column, and monitor the total flow rate y flowing out of the core end face.

[0012] Step 5: Calculate the equivalent permeability of the layered shale according to Darcy's law.

[0013] Darcy's law describes the linear relationship between the seepage velocity of water in saturated soil and the hydraulic gradient. It is also known as the linear seepage law. Through experimental studies on saturated sand, it was found that the seepage flow rate Q is directly proportional to the difference in water head between upstream and downstream (h2-h1) and the cross-sectional area A perpendicular to the direction of water flow, and inversely proportional to the seepage length L, that is: Q=K*A*(h2-h1) / L;

[0014] Step 6: Plot stress sensitivity curves based on the obtained data to evaluate the stress sensitivity of lamellar shale reservoirs.

[0015] The beneficial effects of this invention are:

[0016] This study enabled a quantitative and accurate evaluation of the permeability sensitivity of simulated layered shale reservoirs under different effective stress conditions. Attached Figure Description

[0017] Figure 1 Core model diagrams with different lamellar angles;

[0018] Figure 2 Core model diagrams for different shale / lamella thickness ratios;

[0019] Figure 3 Stress-sensitive curves of laminated shale under different angles of lamination;

[0020] Figure 4 The figures show the stress sensitivity curves of layered shale at different thickness ratios. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] A method for evaluating the stress sensitivity of layered shale reservoirs, characterized by comprising the following steps:

[0023] Step 1: Based on the pore elastoplastic seepage model, establish a two-dimensional standard core column geometric model with different laminar angles and thicknesses; such as... Figure 2 As shown, the lamellar thicknesses are X1, X2, X3, X4, and X5, respectively. From left to right, the shale / lamellar thickness ratios are 1.5, 2.5, 5, and 7.5, respectively. Figure 1 As shown, the lamellar angles are A1, A2, A3, A4, A5, A6, and A7; from left to right, the lamellar angles are 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The lamellar shale reservoir is assumed to be a porous elastoplastic medium. The rock deformation under external load and the seepage process of pore fluid satisfy stress equilibrium and seepage mass conservation. The rock deformation mechanical equilibrium equation is:

[0024]

[0025] The fluid flow continuity equation is:

[0026]

[0027] Step 2: Based on geophysical interpretation, literature review, and laboratory experiments, obtain geomechanical parameters such as reservoir stress, pore pressure, elastic modulus, and Poisson's ratio. Input the elastic modulus E1 and Poisson's ratio 1 of the laminae, and the relationship between the permeability coefficient and porosity of the laminae in the finite element software; and the elastic modulus E2 and Poisson's ratio 2 of the shale layers, and the relationship between the permeability coefficient and porosity of the shale layers.

[0028] Step 3: Apply different effective confining pressures to the rock core in the finite element software to simulate the change process of the in-situ stress on the formation. The effective confining pressures are F1, F2, F3, F4, F5, F6, F7, and F8, respectively. At the same time, apply boundary conditions that meet the experimental conditions.

[0029] Step 4: Apply a seepage pressure difference of x to the upper and lower ends of the core column, and monitor the total flow rate y flowing out of the core end face.

[0030] Step 5: Calculate the equivalent permeability of the layered shale according to Darcy's law.

[0031] Darcy's law describes the linear relationship between the seepage velocity of water in saturated soil and the hydraulic gradient. It is also known as the linear seepage law. Through experimental studies on saturated sand, it was found that the seepage flow rate Q is directly proportional to the difference in water head between upstream and downstream (h2-h1) and the cross-sectional area A perpendicular to the direction of water flow, and inversely proportional to the seepage length L, that is: Q=K*A*(h2-h1) / L;

[0032] Step Six: Plot stress sensitivity curves based on the obtained data to evaluate the stress sensitivity of lamellar shale reservoirs. For example... Figure 3 As shown, a stress-sensitivity curve was plotted based on the obtained data. The smaller the laminar angle, the greater the damage to permeability. When the laminar angle is 0°, the permeability decreases by 20%. Figure 4 Note: The shale / layer thickness ratio has a relatively small impact on permeability stress sensitivity.

Claims

1. A method for evaluating the stress sensitivity of layered shale reservoirs, characterized in that, Includes the following steps: Step 1: Based on the pore elastoplastic flow model, establish two-dimensional standard core column geometric models with different lamellar angles and thicknesses; the lamellar thicknesses are X1, X2, X3, X4, X5, and the lamellar angles are A1, A2, A3, A4, A5, A6, A7; the lamellar shale reservoir is assumed to be a pore elastoplastic medium, and the rock deformation under external load and the pore fluid seepage process satisfy stress balance and seepage mass conservation. The rock deformation mechanical equilibrium equation is: The fluid flow continuity equation is: Step 2: Based on geophysical interpretation, literature review, and laboratory experiments, obtain geomechanical parameters such as reservoir stress, pore pressure, elastic modulus, and Poisson's ratio. Input the elastic modulus E1 and Poisson's ratio 1 of the laminae, and the relationship between the permeability coefficient and porosity of the laminae in the finite element software; and the elastic modulus E2 and Poisson's ratio 2 of the shale layers, and the relationship between the permeability coefficient and porosity of the shale layers. Step 3: Apply different effective confining pressures to the rock core in the finite element software to simulate the change process of the in-situ stress on the formation. The effective confining pressures are F1, F2, F3, F4, F5, F6, F7, and F8, respectively. At the same time, apply boundary conditions that meet the experimental conditions. Step 4: Apply a seepage pressure difference of x to the upper and lower ends of the core column, and monitor the total flow rate y flowing out of the core end face. Step 5: Calculate the equivalent permeability of the layered shale according to Darcy's law. Darcy's law describes the linear relationship between the seepage velocity of water in saturated soil and the hydraulic gradient. It is also known as the linear seepage law. Through experimental studies on saturated sand, it was found that the seepage flow rate Q is directly proportional to the difference in water head between upstream and downstream (h2-h1) and the cross-sectional area A perpendicular to the direction of water flow, and inversely proportional to the seepage length L, that is: Q=K*A*(h2-h1) / L; Step 6: Plot stress sensitivity curves based on the obtained data to evaluate the stress sensitivity of lamellar shale reservoirs.

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