Oil reservoir numerical simulation method based on stress steering mechanism

Abstract

The invention provides an oil reservoir numerical simulation method based on a stress steering mechanism, and belongs to the technical field of oil-gas field development, and the method comprises the following steps: building a mathematical characterization model of interference stress between fractures in a reservoir fracturing process; compiling a stress steering calculation and drawing module; establishing a fluid-solid coupling model based on stress steering; establishing a reservoir hydraulic fracturing crack propagation simulation model by using a mesoscopic damage finite element method, and performing reservoir coupling numerical simulation; and simulating and analyzing the induced stress steering mechanism under different conditions, and simulating and analyzing the influence of the induced stress steering mechanism on the hydraulic fracture propagation of the reservoir. According to the method, the induced stress steering mechanism and the influence of the induced stress steering mechanism on fracture propagation are researched, the hydraulic fracturing fracture propagation rule and the final fracture form are defined, the conglomerate oil reservoir yield increase transformation mechanism is understood, the horizontal well volume fracturing engineering design is guided, the horizontal well fracturing effect is improved, and the recovery efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and in particular relates to a reservoir numerical simulation method based on stress diversion mechanism. Background Art

[0002] Tight gravel reservoirs have poor porosity and permeability, high gravel content, large gravel diameter differences, and strong heterogeneity. Compared with traditional fracturing methods, new fracturing technologies such as dense cutting make the interference between fractures and sections more significant. Clarifying the changing laws of the stress field in gravel reservoirs, the mechanism of fracture initiation and expansion, and reasonably demonstrating the fracturing construction parameters to achieve efficient production under the scale of fracturing construction are the key to rational exploitation and one of the main problems currently faced by the development of tight gravel reservoirs.

[0003] Through the study of inter-fracture interference and stress deflection mechanism, it is an important next step in the development of tight conglomerate reservoirs to clarify the control role of heterogeneity of parameters such as stress and permeability and stress shadow effect on the non-equilibrium expansion process of fractures.

[0004] Multi-cluster fracturing will cause stress direction deflection, and the stress in the fracture area may become a reverse fault state. Reducing the cluster spacing makes it more difficult for the inter-fracture stress to be converted to a vertical minimum, and the inter-fracture stress mainly rotates horizontally. When the net pressure in the fracture is large enough, the stress state around the fracture changes, and strike-slip faults and reverse fault areas may appear at the same time. The angles of induced tensile fractures and artificial fractures are also different under different stress states. Therefore, the stress deflection and steering during fracturing in the development of unconventional oil reservoirs cannot be ignored.

[0005] Chinese invention patent CN104727798B discloses a low permeability gas reservoir redirection re-fracturing process method, and its specific process method is implemented according to the following steps: analysis of the reasons for failure or inefficiency of the initial fracturing of the gas well, reservoir evaluation before redirection re-fracturing, decision-making on well and layer selection for redirection re-fracturing, rock mechanics parameters and geostress testing, simulation of geostress field changes for redirection re-fracturing, optimization of fracture geometry parameters and conductivity, optimization of redirection re-fracturing process, research on fracturing fluid and redirection agent, re-fracturing construction, and evaluation after re-fracturing. Among them, the decision-making on well and layer selection and residual gas detection, fracturing design and fracture detection are mutually verified systems, and a low permeability gas well redirection re-fracturing process method using a new fracture redirection agent is used. The present invention realizes the "integrated" design of low permeability gas reservoir redirection re-fracturing, and has the characteristics of macroscopic integration of design links, local innovation, close connection, mutual verification, advanced design, and obvious technical advantages. Among them, the decision-making on well and layer selection and residual gas detection, fracturing design and fracture detection are mutually verified systems, and a low permeability gas well redirection re-fracturing process method using a new fracture redirection agent is used. However, this method cannot achieve the optimal simulation of construction parameters and achieve efficient production under the scale of fracturing construction.

[0006] Chinese invention patent CN202011040126 discloses a directional fracturing method and application for deep oil and gas reservoirs, which includes: changing the stress direction by using the induced stress field and mutual superposition principle of the formed fractures through multiple temporary plugging and steering, and then controlling the steering angle to make the fractures extend in the desired direction, increase the complexity of the fractures, and expand the transformation volume of the fractures. However, this method cannot achieve the optimization simulation of construction parameters and achieve efficient production under the scale of fracturing construction. Summary of the invention

[0007] In view of the problems existing in the above-mentioned prior art, the present invention provides a reservoir numerical simulation method based on the stress steering mechanism. The technical problem to be solved by the present invention is to study the interference between fractures and the stress deflection mechanism, clarify the expansion law of hydraulic fracturing fractures and the final shape of the fractures, guide the design of horizontal well volume fracturing engineering, improve the horizontal well fracturing effect, and increase the recovery rate.

[0008] In order to solve the above technical problems, the present invention provides a reservoir numerical simulation method based on stress diversion mechanism, comprising the following steps:

[0009] Step S1: Based on complex function analysis and fracture mechanics theory, and according to the variation law of inter-fracture induced stress field under multi-well interference conditions, a mathematical characterization model of inter-fracture interference stress during reservoir fracturing is established;

[0010] Step S2: Based on the mathematical characterization model in step S1, compile a stress steering calculation and drawing module;

[0011] Step S3: Based on the stress steering calculation and drawing module, the stress deflection and stress magnitude variation during the fracturing process are analyzed, and a fluid-solid coupling model based on stress steering is established;

[0012] Step S4: Based on the mathematical characterization model of inter-fracture interference stress, a reservoir hydraulic fracturing fracture propagation simulation model is established by using the mesoscopic damage finite element method, the reservoir hydraulic fracturing fracture propagation simulation model is combined with the fluid-solid coupling model, and a reservoir coupling numerical simulation is performed;

[0013] Step S5: simulate and analyze the induced stress diversion mechanism under different conditions, simulate and analyze the influence of the induced stress diversion mechanism on the expansion of hydraulic fractures in conglomerate reservoirs, and clarify the expansion law of hydraulic fracturing fractures and the final shape of the fractures.

[0014] Furthermore, the mathematical characterization model of the inter-fracture interference stress during the reservoir fracturing process in step S1 is expressed as follows:

[0015]

[0016]

[0017] σ yy =μ(σ xx +σ zz )(3)

[0018]

[0019] τ xy =0(5)

[0020] Among them, σ xx is the induced stress in the direction of the minimum horizontal principal stress, MPa; σ yy is the induced stress in the direction of the maximum horizontal principal stress, MPa; σzz is the induced stress in the direction of the vertical stress, MPa; P is the formation pressure, MPa; L is the distance from any point to the center of the fracture, m; L1 and L2 are the distances from any two different points different from L to the center of the fracture, m; θ, θ1, θ2 are the angles between the straight lines from the middle, top and bottom of the fracture to the particle and the fracture surface, degrees; a-half fracture height, m; μ-Poisson's ratio; τ xy - Shear stress component, MPa.

[0021] Furthermore, in the step S2, the MATLAB scientific computing software platform is used to compile a stress interference calculation and drawing module based on a mathematical characterization model of inter-fracture interference stress during the reservoir fracturing process.

[0022] Furthermore, in step S3, a fluid-solid coupling model based on stress diversion is established, which takes into account the mutual influence of reservoir seepage field, stress field, rock matrix and gravel deformation and fracturing.

[0023] Furthermore, in step S3, based on the stress steering calculation and drawing module, the induced stress field is calculated and combined with the fluid seepage equation to establish a fluid-solid coupling model in which the stress field and the seepage field interact and influence each other.

[0024] Furthermore, in step S4, the theories of damage mechanics and fracture mechanics are combined, and the mesoscopic damage finite element method is used to establish a reservoir hydraulic fracturing fracture propagation simulation model, and perform reservoir coupling numerical simulation.

[0025] Furthermore, based on the stress steering calculation and drawing module, the magnitude and direction of pore pressure and induced stress are calculated, and the mesoscopic damage finite element method is used to establish a simulation model of reservoir hydraulic fracturing crack propagation.

[0026] Furthermore, in step S5, the induced stress diversion mechanism under different fracturing fluid properties, principal stress differences, cementation surface strengths and gravel strength conditions is simulated and analyzed, and the influence of the induced stress diversion mechanism on the expansion of reservoir hydraulic fractures is simulated and analyzed, thereby realizing numerical simulation of oil reservoirs based on the stress diversion mechanism.

[0027] The invention discloses a reservoir numerical simulation method based on stress diversion mechanism, which aims at the influence of stress diversion mechanism on the expansion path of hydraulic fractures, takes fracture mechanics as a theoretical basis, analyzes the stress field; aims at the interference problem of multiple fractures in staged fracturing of horizontal wells, takes boundary element method, linear elastic fracture mechanics and fluid mechanics as theoretical basis, studies the distribution of stress field of multiple fractures and the flow law of fracturing fluid inside the fractures, establishes a fluid-solid coupled horizontal well hydraulic fracture expansion mechanical model, weaves it into a calculation module by using MATLAB, embeds the module into the reservoir numerical simulation model, considers the influence of stress diversion on fracture expansion in the reservoir numerical simulation model, and thus studies its influence on the horizontal well production capacity, reservoir seepage law and ultimate recovery rate of the reservoir.

[0028] The present invention studies the mechanism of induced stress diversion and its influence on fracture propagation, clarifies the law of hydraulic fracturing fracture propagation and the final form of fracture, understands the mechanism of production increase and transformation of conglomerate reservoirs, guides the design of horizontal well volume fracturing engineering, improves the effect of horizontal well fracturing, and increases the recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a flow chart of a method for numerical simulation of oil reservoirs based on stress diversion mechanism.

[0030] Figure 2 It is a schematic diagram of a reservoir hydraulic fracturing fracture expansion simulation model based on a stress steering mechanism reservoir numerical simulation method of the present invention.

[0031] Figure 3 (a) is a schematic diagram of interference stress between wells of staggered seams based on a numerical simulation method of oil reservoirs according to the stress steering mechanism of the present invention, wherein the half seam length is 3 / 4 of the well spacing (strong interference); Figure 3 (b) is a schematic diagram of interference stress between wells with staggered seams according to a numerical simulation method for oil reservoirs based on stress steering mechanism of the present invention, wherein the half-seam length is 2 / 3 of the well spacing (interference is weak). DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0035] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In order to better understand the purpose, structure and function of the present invention, a reservoir numerical simulation method based on stress diversion mechanism of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0037] Embodiment 1:

[0038] like Figure 1 As shown, the present invention provides a reservoir numerical simulation method based on stress diversion mechanism, comprising the following steps:

[0039] Step S1: Based on complex function analysis and fracture mechanics theory, and according to the variation law of inter-fracture induced stress field under multi-well interference conditions, a mathematical characterization model of inter-fracture interference stress during reservoir fracturing is established;

[0040] Step S2: Based on the mathematical characterization model in step S1, compile a stress steering calculation and drawing module;

[0041] Step S3: Based on the stress steering calculation and drawing module, the stress deflection and stress magnitude variation during the fracturing process are analyzed, and a fluid-solid coupling model based on stress steering is established;

[0042] Step S4: Based on the mathematical characterization model of inter-fracture interference stress, a reservoir hydraulic fracturing fracture propagation simulation model is established by using the mesoscopic damage finite element method, the reservoir hydraulic fracturing fracture propagation simulation model is combined with the fluid-solid coupling model, and a reservoir coupling numerical simulation is performed;

[0043] Step S5: simulate and analyze the induced stress diversion mechanism under different conditions, simulate and analyze the influence of the induced stress diversion mechanism on the expansion of hydraulic fractures in conglomerate reservoirs, and clarify the expansion law of hydraulic fracturing fractures and the final shape of the fractures.

[0044] Embodiment 2:

[0045] like Figure 1 As shown, the present invention provides a reservoir numerical simulation method based on stress diversion mechanism, comprising the following steps:

[0046] Step S1: Based on complex function analysis and fracture mechanics theory, and according to the variation law of inter-fracture induced stress field under multi-well interference conditions, a mathematical characterization model of inter-fracture interference stress during reservoir fracturing is established;

[0047] Step S2: Based on the mathematical characterization model in step S1, compile a stress steering calculation and drawing module;

[0048] Step S3: Based on the stress steering calculation and drawing module, the stress deflection and stress magnitude variation during the fracturing process are analyzed, and a fluid-solid coupling model based on stress steering is established;

[0049] Step S4: Based on the mathematical characterization model of inter-fracture interference stress, a reservoir hydraulic fracturing fracture propagation simulation model is established by using the mesoscopic damage finite element method, the reservoir hydraulic fracturing fracture propagation simulation model is combined with the fluid-solid coupling model, and a reservoir coupling numerical simulation is performed;

[0050] Step S5: simulate and analyze the induced stress diversion mechanism under different conditions, simulate and analyze the influence of the induced stress diversion mechanism on the expansion of hydraulic fractures in conglomerate reservoirs, and clarify the expansion law of hydraulic fracturing fractures and the final shape of the fractures.

[0051] The difference between this embodiment and the first embodiment is that:

[0052] The mathematical characterization model of the inter-fracture interference stress during the reservoir fracturing process in step S1 is expressed as follows:

[0053]

[0054]

[0055] σ yy =μ(σ xx +σ zz ) (3)

[0056]

[0057] τ xy =0 (5)

[0058] Among them, σxx is the induced stress in the direction of the minimum horizontal principal stress, MPa; σ yy is the induced stress in the direction of the maximum horizontal principal stress, MPa; σ zz is the induced stress in the vertical stress direction, MPa; P is the formation pressure, MPa; L is the distance from any point to the center of the fracture, m; L1 and L2 are the distances from any two different points different from L to the center of the fracture; θ, θ1, θ2 are the angles between the straight lines from the middle, top and bottom of the fracture to the particle and the fracture surface, degrees; a is the half fracture height, m; μ is Poisson's ratio; τ xy - Shear stress component, MPa.

[0059] In the step S2, a stress interference calculation and drawing module is compiled using the MATLAB scientific computing software platform based on the mathematical characterization model of inter-fracture interference stress in the reservoir fracturing process;

[0060] In step S3, based on the stress steering calculation and drawing module, the induced stress field and fluid seepage equation calculated are used to establish a fluid-solid coupling model in which the stress field and the seepage field interact and influence each other;

[0061] In the step S3, a fluid-solid coupling model based on stress diversion is established, which takes into account the mutual influence of reservoir seepage field, stress field, rock matrix and gravel deformation and fracturing;

[0062] In step S4, Figure 2 As shown, combining the theories of damage mechanics and fracture mechanics, based on the stress steering calculation and drawing module, the magnitude and direction of pore pressure and induced stress are calculated, and the micro-damage finite element method is used to establish a reservoir hydraulic fracturing crack expansion simulation model.

[0063] Step S5: Figure 3 As shown, the induced stress diversion mechanism under different fracturing fluid properties, principal stress difference, cementation surface strength and gravel strength conditions is simulated and analyzed, and the influence of the induced stress diversion mechanism on the expansion of hydraulic fractures in conglomerate reservoirs is simulated and analyzed, thereby realizing the numerical simulation of tight conglomerate reservoirs based on the stress diversion mechanism.

[0064] The influence of stress diversion mechanism on the expansion of hydraulic fractures in conglomerate reservoirs: From the perspective of fracture expansion length, the greater the horizontal stress difference, the narrower the fracture width after diversion; the greater the displacement and viscosity of the fracturing fluid, the greater the residual energy after the fracture diversion, and the larger the fracture width; when the approach angle between hydraulic fractures and natural fractures is about 30°, it is most likely to divert along the natural fracture; after the hydraulic fracture diversion, the apparent morphology changes greatly, and the fracture expands in the direction away from the maximum principal stress, causing the fracture width to narrow. When two adjacent horizontal wells in the well platform are fracturing simultaneously, the injection of fracturing working fluid and rock fracture will cause formation deformation and stress changes, forming stress shadows, which in turn affect the fracture expansion path and fracturing effect. Stress shadows are directly related to the elastic parameters of the formation, the length and width of the existing fracture network, and the positional relationship between the expanding fractures and the existing fractures.

[0065] In view of the influence of stress steering mechanism on the expansion path of hydraulic fractures, the stress field is analyzed based on fracture mechanics. In view of the interference problem of multiple fractures in staged fracturing of horizontal wells, the stress field distribution of multiple fractures and the flow law of fracturing fluid inside the fractures are studied based on boundary element method, linear elastic fracture mechanics and fluid mechanics. A fluid-solid coupled mechanical model of hydraulic fracture expansion in horizontal wells is established, which is woven into a calculation module using MATLAB and embedded in the numerical simulation model of the reservoir. The influence of stress steering on fracture expansion is considered in the numerical simulation model of the reservoir, so as to study its influence on the horizontal well production capacity, reservoir seepage law and ultimate recovery of the reservoir.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A reservoir numerical simulation method based on stress diversion mechanism, characterized in that: The following steps are involved: Step S1: Based on complex function analysis and fracture mechanics theory, and according to the variation law of inter-fracture induced stress field under multi-well interference conditions, a mathematical characterization model of inter-fracture interference stress during reservoir fracturing is established; Step S2: Based on the mathematical characterization model in step S1, compile a stress steering calculation and drawing module; Step S3: Based on the stress steering calculation and drawing module, the stress deflection and stress magnitude variation during the fracturing process are analyzed, and a fluid-solid coupling model based on stress steering is established; Step S4: Based on the mathematical characterization model of inter-fracture interference stress, a reservoir hydraulic fracturing fracture propagation simulation model is established by using the mesoscopic damage finite element method, the reservoir hydraulic fracturing fracture propagation simulation model is combined with the fluid-solid coupling model, and a reservoir coupling numerical simulation is performed; Step S5: simulate and analyze the induced stress diversion mechanism under different conditions, simulate and analyze the influence of the induced stress diversion mechanism on the expansion of hydraulic fractures in conglomerate reservoirs, and clarify the expansion law of hydraulic fracturing fractures and the final shape of the fractures.

2. The reservoir numerical simulation method based on stress diversion mechanism according to claim 1, characterized in that: The mathematical characterization model of the inter-fracture interference stress during the reservoir fracturing process in step S1 is expressed as follows: s yy =μ(σ xx +s zz (3) t xy =0(5) Among them, σ xx is the induced stress in the direction of the minimum horizontal principal stress, MPa; σ yy is the induced stress in the direction of the maximum horizontal principal stress, MPa; σzz is the induced stress in the direction of the vertical stress, MPa; P is the formation pressure, MPa; L is the distance from any point to the center of the fracture, m; L1 and L2 are the distances from any two different points different from L to the center of the fracture, m; θ, θ1, θ2- are the angles between the straight lines from the middle, top and bottom of the fracture to the particle and the fracture surface, degrees; a is the half fracture height, m; μ is the Poisson's ratio; τ xy is the shear stress component, MPa.

3. The reservoir numerical simulation method based on stress diversion mechanism according to claim 1, characterized in that: In the step S2, a stress interference calculation and drawing module is compiled using the MATLAB scientific computing software platform based on a mathematical characterization model of inter-fracture interference stress during the reservoir fracturing process.

4. The reservoir numerical simulation method based on stress diversion mechanism according to claim 1, characterized in that: In step S3, a fluid-solid coupling model based on stress diversion is established, which takes into account the mutual influence of reservoir seepage field, stress field, rock matrix and gravel deformation and fracturing.

5. The reservoir numerical simulation method based on stress diversion mechanism according to claim 1, characterized in that: In step S3, based on the stress steering calculation and drawing module, the induced stress field is calculated and combined with the fluid seepage equation to establish a fluid-solid coupling model in which the stress field and the seepage field interact and influence each other.

6. The reservoir numerical simulation method based on stress diversion mechanism according to claim 1, characterized in that: In step S4, a reservoir hydraulic fracturing fracture propagation simulation model is established by combining theories of damage mechanics and fracture mechanics and using a microscopic damage finite element method, and a reservoir coupling numerical simulation is performed.

7. The reservoir numerical simulation method based on stress diversion mechanism according to claim 1, characterized in that: In step S4, based on the stress steering calculation and drawing module, the pore pressure, the magnitude and direction of the induced stress are calculated, and a reservoir hydraulic fracturing fracture propagation simulation model is established using the mesoscopic damage finite element method.

8. The reservoir numerical simulation method based on stress diversion mechanism according to claim 1, characterized in that: In step S5, the induced stress diversion mechanism under different fracturing fluid properties, principal stress difference, cementation surface strength and gravel strength conditions is simulated and analyzed, and the influence of the induced stress diversion mechanism on the expansion of reservoir hydraulic fractures is simulated and analyzed to realize the numerical simulation of the reservoir based on the stress diversion mechanism.

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