Method for evaluating fracturing transformation effect through combination of forward modeling and inversion

Abstract

The invention discloses a method for evaluating a fracturing transformation effect through combination of forward modeling and inversion, and the method comprises the following steps: building a single-well fine fracturing model based on the heterogeneity and mechanical difference along a well section according to logging and indoor experiment data; a real fracturing process is simulated according to an actual pump injection program, and a fracture height parameter is obtained through forward modeling; calculating the liquid efficiency and the filtration coefficient of the fractured section through a fracture parameter inversion model according to the fracture height parameter in combination with the pumping stop pressure drop data; based on the process, a boundary element method is used for simulating the fracturing process, fracture length and fracture width parameters are obtained, and the fracturing transformation volume is determined by calculating stress field distribution around the fracture. According to the method for evaluating the fracturing transformation effect through combination of forward modeling and inversion, comprehensive, accurate and real-time evaluation of the fracturing transformation effect is achieved, a scientific basis is provided for optimizing fracturing construction parameters, improving the yield of an oil and gas well and reducing the development cost, and a reference is provided for subsequent fracturing design and construction adjustment.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas development, and particularly to a method for jointly evaluating the fracturing transformation effect by forward and inverse modeling. Background Art

[0002] Nowadays, in the technical field of oil and gas development, the global focus of oil exploration has gradually shifted to unconventional oil and gas with rich reserves. The fracturing transformation effect is affected by various factors, including geological conditions, engineering parameters, fracturing fluid properties, etc. How to accurately evaluate the fracturing transformation effect is of great significance for optimizing fracturing design, improving fracturing efficiency, and reducing development costs.

[0003] Currently, the commonly used methods for evaluating the fracturing transformation effect mainly include: well test analysis, microseismic monitoring, production data analysis, etc. Among them, well test analysis evaluates the impact of fracturing transformation on reservoir permeability and productivity by analyzing well test data before and after fracturing. Microseismic monitoring inversely models the fracture morphology and distribution by monitoring microseismic events generated during fracturing. Production data analysis evaluates the impact of fracturing transformation on oil and gas production by analyzing production data after fracturing. Existing methods have deficiencies such as single evaluation indicators and low evaluation accuracy. There are large differences in the applicability between methods, and even contradictions exist between results, making it difficult to obtain a relatively accurate conclusion.

[0004] The present invention aims to provide a method for jointly evaluating the fracturing transformation effect by forward and inverse modeling, overcoming the deficiencies of the prior art, and providing a scientific basis for fracturing design and construction optimization. Summary of the Invention

[0005] The object of the present invention is to provide a method for jointly evaluating the fracturing transformation effect by forward and inverse modeling, which realizes a comprehensive, accurate, and real-time evaluation of the fracturing transformation effect through forward / inverse joint evaluation of the fracturing transformation effect, provides a scientific basis for optimizing fracturing construction parameters, increasing oil and gas well production, and reducing development costs, and provides a reference for subsequent fracturing design and construction adjustment.

[0006] To achieve the above object, the present invention provides a method for jointly evaluating the fracturing transformation effect by forward and inverse modeling, including the following steps: Step S1: Based on logging and laboratory test data, establish a single-well fine fracturing model according to the in-well section heterogeneity and mechanical differences. Step S2: Simulate the real fracturing process according to the actual pumping program to obtain the fracture height parameter by forward modeling. Step S3: According to the fracture height parameter, combined with the shut-in pressure drop data, calculate the liquid efficiency and filtration coefficient of the fracturing section through the fracture parameter inversion model. Step S4: Based on the above process, use the boundary element method to simulate the fracturing process, obtain the fracture length and width parameters, and determine the fracturing treatment volume by calculating the stress field distribution around the fracture.

[0007] Preferably, in step S1, based on well logging and laboratory test data, and considering the heterogeneity and mechanical differences along the well section, a single-well fine fracturing model is established. The specific process is as follows: Based on well logging, laboratory test and other data, considering the heterogeneity and mechanical differences along the well section, a single-well fine fracturing model that couples the rock solid skeleton deformation and fluid flow control equations is established as follows: ; ; ; In the formula, is the rock control volume; is the effective stress matrix, Pa; is the pore pressure, Pa; is the unit matrix; is the virtual strain rate matrix, S -1 ; is the surface area; is the surface force vector, N / m 2 ; is the virtual velocity vector, m / s; is the body force vector, N / m 3 ; is the rock volume change rate, dimensionless; is the fluid velocity, kg / m 3 ; is the porosity, dimensionless; is the outer normal direction vector of the surface s, dimensionless; is the fluid flow velocity in the rock, m / s; is the rock skeleton permeability tensor, m / s; is the space vector, m; is the acceleration due to gravity, m / s 2 ; represents the partial derivative with respect to time; represents the differential of volume; represents the differential of area.

[0008] Preferably, during the hydraulic fracturing process, coupling the rock solid skeleton deformation and fluid flow control equations is the core algorithm basis of the single-well fine fracturing model; when the established single-well fine fracturing model is simulated by Gohfer, the dynamic interaction between fracture propagation and proppant-carrying fluid flow is considered; While calculating the initiation of a certain grid point according to the stress model, simultaneously calculate the dynamic influence of the pressure change generated after the proppant-carrying fluid enters the fracture on the filtration of the fracturing fluid; and the dynamic filtration of the fracturing fluid will act in the opposite direction on the pressure field in the fracture, thereby real-time correcting the shape and propagation trajectory of the fracture.

[0009] Preferably, in step S2, simulate the real fracturing process according to the actual pumping program to forwardly obtain the fracture height parameter, and the specific process is as follows: First, by setting the actual perforation scheme on site, the performance parameters of the fracturing fluid and the proppant, and using the actual pumping program, simulate the real fracturing process to forwardly obtain the fracture height parameter; then, based on the secondary nominal stress criterion, dynamically determine the initiation and propagation relationship between the hydraulic fracture and the interlayer weak interface; Adopt the element stiffness degradation criterion to describe the fracture propagation process in real time, and simultaneously output the dynamic shape of the fracture and the fracture height parameter, as follows: ; ; ; In the formula, and are the normal and tangential stresses actually borne by the element, Pa; and are the maximum tensile strength and maximum shear strength that the element can bear, respectively, Pa; is the damage factor; and are the stresses calculated according to the undamaged linear elastic criterion for the normal and tangential directions of the element under the current strain, respectively; and are the displacement at the initial damage and the displacement when the element is completely damaged, ; is the maximum displacement value reached during the loading process, .

[0010] Preferably, when the hydraulic fracture intersects with the interlayer weak surface, if the interlayer weak surface fractures first, the hydraulic fracture will be trapped and cannot penetrate the interlayer weak surface; if the rock body on the other side of the interlayer weak surface fractures first, the hydraulic fracture will penetrate the weak surface and continue to propagate.

[0011] Preferably, in step S3, according to the fracture height parameter, combined with the shut-in pressure drop data, calculate the liquid efficiency and filtration coefficient of the fracturing section through the fracture parameter inversion model, and the specific process is as follows: Based on the fracture height parameter obtained from simulating the real fracturing process, combined with the shut-in pressure drop data, calculate the liquid efficiency and filtration coefficient of this fracturing section through the fracture parameter inversion model based on the analysis of the pressure drop curve; By inverting the dynamic data of the synchronous filtration loss and closure process after the pump is stopped for multiple fractures, the model realizes the simultaneous calculation of the fracturing fluid efficiency, filtration coefficient, and fracture geometric parameters, as follows: ; ; ; ; In the formula, is the injection rate, m 3 / s; is the pumping time, s; is the fracture coefficient (for the PKN model, , for the KGD model, ); is the fracture height, m; is the Young's modulus, MPa; δ is the dimensionless time; δ = Δt / t0; Δt is the shut-in time, s; is the bottom-hole pressure corresponding to the dimensionless time δ0, MPa; is the bottom-hole pressure corresponding to the dimensionless time δ, MPa; is the minimum horizontal principal stress, MPa; is the fracture propagation coefficient; is the gamma function of; is the stress interference factor; where, , is the fracture cluster spacing, m; is the half-length of the th fracture, m; is the filtration coefficient of the 0.5 th fracture after the pump is stopped, m / s is the filtration height, m; is the fracturing fluid efficiency, %; is the th fracture volume after the pump is stopped, m 3 ; represents the pressure decay function; represents the differential of the pressure decay function.

[0012] Preferably, the fracture parameter inversion model based on the pressure drop curve analysis satisfies the following conditions: (1) After the pump is stopped, filtration loss and elastic closure occur simultaneously for each fracture; (2) The fracture shape is continuous and symmetric; (3) The reservoir is homogeneous and not interfered by natural fractures; (4) After the pump is stopped, the fracture stops extending and the fracture length is constant.

[0013] Preferably, in step S4, the boundary element method is used to simulate the fracturing process, obtain the fracture length and width parameters, and determine the fracture treatment volume by calculating the stress field distribution around the fracture. The specific process is as follows: Based on the obtained fracture height parameters, liquid efficiency, and filtration coefficient, use the boundary element method to simulate the fracturing process and calculate the fracture length and width parameters; determine the fracture treatment volume by calculating the stress field distribution around the fracture, as follows: ; ; ; In the formula, is the fluid pressure, Pa; is the length of the infinitesimal element of the fracture, m; and are the fluid power-law exponent and consistency exponent; is the fracture height, m; is the fracture width, mm; is the total amount of fracturing fluid, m 3 ; is the normal displacement discontinuity of the th element (the fracture width of the th element), mm; is the length of the th element, m; is the length of the th cluster of fractures at time t, m; is the total number of fractures; is the filtration velocity, m 2 / s; , ,…, and are the number of fracture elements in the 1st, 2nd…Z-1th, and Zth fracturing stages respectively; is the stress correction factor; , , and are the stress influence coefficient matrices; and are the tangential displacement discontinuity and normal displacement discontinuity of the th element respectively, mm; and are the tangential stress and normal stress received by the th element respectively; represents the differential of time; represents the differential of the length of the infinitesimal element of the fracture.

[0014] Preferably, to reduce the solution difficulty and improve the simulation efficiency of multi-fracture propagation within a stage, the following conditions are met: ① The rock is an infinite homogeneous elastic body and obeys linear elastic fracture mechanics; ② The fracturing fluid is an incompressible fluid, and the fluid in the fracture conforms to the Poiseuille laminar flow law; ③ The fluid loss of the fracturing fluid perpendicular to the fracture surface satisfies the Carter model; ④ The wellbore friction is much smaller than the perforation friction and the in-fracture flow friction, so the wellbore flow friction is ignored; ⑤ The proppant migration is not considered, and based on the assumption of high stiffness of the proppant, it is considered that the generation of new fractures will not cause the closure of previous fractures.

[0015] Therefore, the present invention adopts the above method of forward and inverse combined evaluation of fracturing treatment effect. By forward / inverse combined evaluation of the fracturing treatment effect, a comprehensive, accurate, and real-time evaluation of the fracturing treatment effect is achieved, providing a scientific basis for optimizing fracturing construction parameters, increasing the production of oil and gas wells, and reducing development costs, and providing a reference for subsequent fracturing design and construction adjustment.

[0016] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0017] Figure 1 is a flow chart of a method for forward and inverse combined evaluation of fracturing treatment effect of the present invention; Figure 2 is the simulation result of fracture propagation of Well Bai Z21-X2-A9-A10 in the embodiment of the present invention; Figure 3 is the simulation result of the first cluster of fracture propagation of Well Bai Z21-X2-A5-A7 in the embodiment of the present invention; Figure 4 is the simulation result of the second cluster of fracture propagation of Well Bai Z21-X2-A5-A7 in the embodiment of the present invention; Figure 5 is the full-well fracture propagation map of Well Bai Z21-X2 in the embodiment of the present invention; Figure 6 is the forward interpretation result map of Well Bai Z21-X2 in the embodiment of the present invention; Figure 7 is the inverse interpretation result map of Well Bai Z21-X2-A9-A10 in the embodiment of the present invention; wherein, (a) is the fracture morphology map (first-stage fracturing); (b) is the fracture morphology map (top view, first-stage fracturing); Figure 8It is the inversion interpretation result diagram of fracture Z21-X2-A5-A7-2 in the embodiment of the present invention; wherein, (a) is the fracture morphology diagram (the second stage of fracturing); (b) is the fracture morphology diagram (top view, the second stage of fracturing). Figure 9 It is the inversion interpretation result diagram of fracture Z21-X2-A5-A7-1 in the embodiment of the present invention; wherein, (a) is the fracture morphology diagram (the third stage of fracturing); (b) is the fracture morphology diagram (top view, the third stage of fracturing). Figure 10 It is the post-fracture stress field, post-fracture stress interference area and effective fracturing transformation area of Well Z21-X2 in the embodiment of the present invention. Among them, (a) is the post-fracture stress field of the first stage; (b) is the area affected by the post-fracture stress of the first stage; (c) is the effective fracturing transformation area of the first stage; (d) is the post-fracture stress field of the second stage; (e) is the area affected by the post-fracture stress of the second stage; (f) is the effective fracturing transformation area of the first two stages. Specific implementation mode

[0018] The technical solution of the present invention will be further described below with reference to the drawings and embodiments.

[0019] As Figure 1 shown, a method for jointly evaluating the fracturing transformation effect by forward and inverse modeling includes the following steps: Step S1: Based on logging and laboratory test data, and considering the heterogeneity and mechanical differences along the well section, establish a single-well fine fracturing model. Step S2: Simulate the actual fracturing process according to the actual pumping program to obtain the fracture height parameter by forward modeling. Step S3: According to the fracture height parameter, combined with the shut-in pressure drop data, calculate the liquid efficiency and filtration coefficient of the fracturing section through the fracture parameter inversion model. Step S4: Based on the above process, use the boundary element method to simulate the fracturing process, obtain the fracture length and width parameters, and determine the fracturing transformation volume by calculating the stress field distribution around the fracture.

[0020] Embodiment 1 Step S1: Based on logging and laboratory test data, and considering the heterogeneity and mechanical differences along the well section, establish a single-well fine fracturing model.

[0021] Based on data such as logging and laboratory tests, considering the heterogeneity and mechanical differences along the well section, establish a single-well fine fracturing model that couples the rock solid skeleton deformation and fluid flow control equations, as shown below: ; ; ; In the formula, is the rock control volume; is the effective stress matrix, Pa; is the pore pressure, Pa; is the identity matrix; is the virtual strain rate matrix, S -1 ; is the surface area; is the surface force vector, N / m 2 ; is the virtual velocity vector, m / s; is the body force vector, N / m 3 ; is the rock volume change rate, dimensionless; is the fluid velocity, kg / m 3 ; is the porosity, dimensionless; is the outward normal direction vector of surface s, dimensionless; is the fluid flow velocity in the rock, m / s; is the rock matrix permeability tensor, m / s; is the spatial vector, m; is the acceleration due to gravity, m / s 2 ; represents the time partial derivative; represents the volume differential; represents the area differential.

[0022] Among them, in the process of hydraulic fracturing, the coupling of the deformation of the rock solid skeleton and the fluid flow control equation is the core algorithm basis of this model. When the constructed single-well fine fracturing model is simulated by Gohfer, the dynamic interaction between "fracture propagation" and "proppant-carrying fluid flow" can be fully considered.

[0023] When calculating the initiation of a certain grid point according to the stress model, the dynamic influence of the pressure change generated after the proppant-carrying fluid enters the fracture on the dynamic filtration of the fracturing fluid is calculated synchronously. And the dynamic filtration of the fracturing fluid will act on the pressure field in the fracture in the reverse direction, thereby real-time correcting the shape and propagation trajectory of the fracture.

[0024] Step S2, simulate the real fracturing process according to the actual pumping program to obtain the fracture height parameter by forward modeling.

[0025] First, by setting the actual perforation scheme on site, the performance parameters of the fracturing fluid and the proppant, and using the actual pumping program, simulate the real fracturing process to obtain the fracture height parameter by forward modeling. Then, based on the secondary nominal stress criterion, dynamically determine the initiation and propagation relationship between the hydraulic fracture and the interlayer weak interface.

[0026] Adopt the element stiffness degradation criterion to describe the fracture propagation process in real time, and synchronously output the dynamic fracture morphology and fracture height parameters as follows: ; ; ; In the formula, and are the normal and tangential stresses actually borne by the element, in Pa; and are the maximum tensile strength and maximum shear strength that the element can bear, respectively, in Pa; is the damage factor; and are the stresses calculated according to the undamaged linear elastic criterion for the normal and tangential directions of the element under the current strain respectively; and are the displacement at initial damage and the displacement at complete failure of the element, ; is the maximum displacement reached during the loading process, .

[0027] Among them, when the hydraulic fracture intersects with the interlayer weak plane, if the interlayer weak plane fractures first, the hydraulic fracture will be trapped and cannot penetrate the interlayer weak plane; if the rock mass on the other side of the interlayer weak plane fractures first, the hydraulic fracture will penetrate the weak plane and continue to expand.

[0028] Step S3: According to the fracture height parameter, combined with the shut-in pressure drop data, through the fracture parameter inversion model, calculate the liquid efficiency and filtration coefficient of the fracturing stage.

[0029] Based on the fracture height parameter obtained from the simulation of the real fracturing process, combined with the shut-in pressure drop data, through the fracture parameter inversion model based on the analysis of the pressure drop curve, calculate the liquid efficiency and filtration coefficient of the fracturing stage.

[0030] Among them, the fracture parameter inversion model based on the analysis of the pressure drop curve satisfies the following conditions: (1) After the pump is shut off, filtration and elastic closure occur simultaneously for each fracture; (2) The fracture morphology is continuously symmetric; (3) The reservoir is homogeneous and there is no interference from natural fractures; (4) After the pump is shut off, the fracture stops extending and the fracture length is constant.

[0031] This model realizes the simultaneous solution of the fracturing fluid efficiency, filtration coefficient and fracture geometric parameters by inverting the dynamic data of the simultaneous filtration and closure process after the pump is shut off for multiple fractures, as follows: ; ; ; ; In the formula, is the injection displacement, m 3 / s; is the pumping time, s; is the fracture coefficient (for the PKN model, , for the KGD model, ); is the fracture height, m; is the Young's modulus, MPa; δ is the dimensionless time; δ = Δt / t0; Δt is the shut-in time, s; is the bottom-hole pressure corresponding to the dimensionless time δ0, MPa; is the bottom-hole pressure corresponding to the dimensionless time δ, MPa; is the minimum horizontal principal stress, MPa; is the fracture propagation coefficient; is 's gamma function; is the stress interference factor; where, , is the fracture cluster spacing, m; is the th half fracture length, m; is the th filtrate loss coefficient after pump shut-off for the fracture, m / s 0.5 ; is the filtrate loss height, m; is the fracturing fluid efficiency, %; is the th fracture volume after pump shut-off for the fracture, m 3 ; represents the pressure decay function; represents the differential of the pressure decay function.

[0032] Step S4. Based on the above process, use the boundary element method to simulate the fracturing process, obtain the fracture length and width parameters, and determine the fracturing treatment volume by calculating the stress field distribution around the fracture.

[0033] Based on the obtained fracture height parameters, liquid efficiency and filtrate loss coefficient, use the boundary element method to simulate the fracturing process, calculate the fracture length and width parameters; determine the fracturing treatment volume by calculating the stress field distribution around the fracture. The specific process is as follows: ; ; ; In the formula, is the fluid pressure, Pa; is the length of the infinitesimal element of the fracture, m; and are the fluid power-law exponent and consistency exponent; is the fracture height, m; is the fracture width, mm; is the total volume of fracturing fluid, m 3 ; is the normal displacement discontinuity of the th element (the fracture width of the th element), mm; is the length of the th element, m; is the length of the th cluster of fractures at time t, m; is the total number of fractures; is the filtration rate, m 2 / s; , , …, and are the number of fracture elements in the 1st, 2nd, …, Z-1th, and Zth fracturing stages, respectively; is the stress correction factor; , , and are the stress influence coefficient matrices; and are the tangential displacement discontinuity and normal displacement discontinuity of the th element, mm; and are the tangential stress and normal stress on the th element, respectively; represents the time differential; represents the differential of the length of a small fracture element.

[0034] Among them, to reduce the difficulty of solving and improve the simulation efficiency of multi-fracture propagation within a stage, the following conditions are satisfied: ① The rock is an infinite homogeneous elastic body and obeys linear elastic fracture mechanics; ② The fracturing fluid is an incompressible fluid, and the fluid in the fracture conforms to the Poiseuille laminar flow law; ③ The filtration of the fracturing fluid perpendicular to the fracture surface satisfies the Carter model; ④ The wellbore friction is much smaller than the perforation friction and the in-fracture flow friction, so the wellbore flow friction is ignored; ⑤ The proppant transport is not considered, and based on the high stiffness assumption of the proppant, it is assumed that the generation of new fractures will not cause the closure of previous fractures.

[0035] Example 2 This example takes Well BZ21-X2 as an example, and the specific implementation process is as follows: Step S1: Construct a single-well fine fracturing model.

[0036] Based on the reservoir data and logging data of Well Bai Z21-X2, considering the heterogeneity and mechanical differences along the well section, a single-well fine model is constructed.

[0037] Among them, the reservoir data includes burial depth, thickness, porosity, permeability, formation pressure, rock mechanical parameters (Young's modulus, Poisson's ratio, compressive strength, etc.); the logging data interprets the in-situ stress data, constructs a three-dimensional grid structure model, and realizes formation division, such as Figure 2 , Figure 3 , Figure 4 and Figure 5 as well as shown in Table 1.

[0038] Table 1 Fracture parameters of each section of the whole well.

[0039]

[0040] Step S2: Replicate the real fracturing process to obtain the fracture height parameter by forward modeling.

[0041] According to the fracturing design of Well Bai Z21-X2, clarify the target fracturing horizon, fracturing stage clusters, and perforation scheme. Determine the properties and types of fracturing fluid and proppant. According to the required fracturing fluid and proppant in the fracturing design, select the corresponding matching fracturing fluid and proppant from the GOHFER fracturing fluid and proppant database. Use the actual pumping program to simulate the real fracturing process, dynamic fracture propagation simulation, and calculate the fracture height parameter based on the shear-slip elastic mechanics model, as shown in Table 2 and Figure 6 .

[0042] Table 2 Forward modeling interpretation results.

[0043]

[0044] Step S3: Invert the liquid efficiency and filtration coefficient based on the shut-in pressure drop data.

[0045] Use the shut-in pressure drop data, based on the fracture height parameter obtained in Step S2, and calculate the liquid efficiency and filtration coefficient of this fracturing stage through the fracture parameter inversion model.

[0046] By establishing the mathematical relationship between the pressure drop curve and the fracture dynamics, the model can simultaneously invert the dynamic data of the multi-fracture synchronous filtration and closure process during the shut-in stage, and realize the coupled solution of the fracturing fluid efficiency, filtration coefficient, and fracture geometric parameters (including the spatial distribution of fracture length and width), such as Figure 7 , Figure 8 , Figure 9 and shown in Table 2, Table 3, and Table 4.

[0047] Table 3 Inversion Interpretation Results of Z21-X2-A9-A10 in Bai

[0048]

[0049] Table 4 Inversion Interpretation Results of Z21-X2-A5-A7-Fracture 2 in Bai

[0050]

[0051] Table 5 Inversion Interpretation Results of Z21-X2-A5-A7-Fracture 1 in Bai

[0052]

[0053] This inversion process particularly emphasizes the dynamic simulation of the actual fracturing process, inputs the fracture height parameter as a known boundary condition into the model, and effectively improves the engineering reliability of the calculation results.

[0054] Step S4: Obtain fracture parameters and treatment volume through forward fracturing.

[0055] Based on the obtained fracture height, liquid efficiency, and filtration coefficient, use the boundary element method to simulate the fracturing process, calculate and obtain the fracture length and width parameters; calculate the stress field distribution around the fracture. Among them, it is stipulated that the area where the additional stress rises by 0.5 MPa is the stress-affected area after fracturing; the area where the additional stress rises by 1 MPa is the effective fracturing treatment area. Determine the fracturing treatment volume based on the area of the effective fracturing treatment area and the fracture height data, as shown in Table 6 and Figure 10 as shown.

[0056] Table 6 Summary of Results of Different Interpretation Methods.

[0057]

[0058] Therefore, the present invention adopts the above method of jointly evaluating the fracturing treatment effect by forward and inversion, realizes the comprehensive, accurate, and real-time evaluation of the fracturing treatment effect through the joint evaluation of forward / inversion, provides a scientific basis for optimizing fracturing construction parameters, increasing the oil and gas well production, and reducing the development cost, and provides a reference for subsequent fracturing design and construction adjustment.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for jointly evaluating the fracturing transformation effect by forward and inverse modeling, characterized in that, It includes the following steps: Step S1: Based on logging and laboratory test data, and on the heterogeneity and mechanical differences along the well section, establish a single-well fine fracturing model; Step S2: According to the actual pumping program, simulate the real fracturing process to forward model the fracture height parameter; Step S3: According to the fracture height parameter, combined with the shut-in pressure drop data, through the fracture parameter inversion model, calculate the liquid efficiency and filtration coefficient of the fracturing section; Step S4: Based on the above process, use the boundary element method to simulate the fracturing process, obtain the fracture length and width parameters, and determine the fracturing treatment volume by calculating the stress field distribution around the fracture.

2. The method for jointly evaluating the fracturing transformation effect by forward and inverse modeling according to claim 1, wherein In step S1, based on logging and laboratory test data, and on the heterogeneity and mechanical differences along the well section, establish a single-well fine fracturing model. The specific process is as follows: Based on data such as logging and laboratory tests, combined with the heterogeneity and mechanical differences along the well section, establish a single-well fine fracturing model that couples the control equations of rock solid skeleton deformation and fluid flow, as follows: ； ； ； In the formula, is the rock control volume; is the effective stress matrix, Pa; is the pore pressure, Pa; is the unit matrix; is the virtual strain rate matrix, S -1 ; is the surface area; is the surface force vector, N / m 2 ; is the virtual velocity vector, m / s; is the body force vector, N / m 3 ; is the rock volume change rate, dimensionless; is the fluid velocity, kg / m 3 ; is the porosity, dimensionless; is the outer normal direction vector of the surface s, dimensionless; is the fluid flow velocity in the rock, m / s; is the rock skeleton permeability tensor, m / s; is the space vector, m; is the gravitational acceleration, m / s 2 ; represents the time partial derivative; represents the volume differential; represents the area differential.

3. The method for jointly evaluating the fracturing transformation effect by forward and inverse modeling according to claim 2, wherein During the hydraulic fracturing process, coupling the control equations of rock solid skeleton deformation and fluid flow is the core algorithm basis of the single-well fine fracturing model; when the constructed single-well fine fracturing model is simulated by Gohfer, according to the dynamic interaction between fracture propagation and the flow of proppant-carrying fluid; When calculating the initiation of a certain grid point according to the stress model, simultaneously calculate the dynamic influence of the pressure change generated after the proppant-carrying fluid enters the fracture on the filtration of the fracturing fluid; and the dynamic filtration of the fracturing fluid will act in reverse on the pressure field in the fracture, thereby real-time correcting the fracture morphology and propagation trajectory.

4. A method for jointly evaluating the effect of fracturing reconstruction by forward and inverse modeling according to claim 1, characterized in that In step S2, according to the actual pumping program, simulate the real fracturing process to forward model the fracture height parameter. The specific process is as follows: First, by setting the actual perforation scheme on site, the performance parameters of the fracturing fluid and proppant, and using the actual pumping program, simulate the real fracturing process to forward model the fracture height parameter; then, based on the secondary nominal stress criterion, dynamically determine the initiation and propagation relationship between the hydraulic fracture and the weak interface between layers; Adopt the element stiffness degradation criterion to describe the fracture propagation process in real time, and simultaneously output the dynamic fracture morphology and fracture height parameter, as follows: ； ； ； In the formula, and are the normal and tangential stresses actually borne by the element, in Pa; and are respectively the maximum tensile strength and the maximum shear strength that the element can bear, in Pa; is the damage factor; and are respectively the stresses calculated according to the undamaged linear elastic criterion for the normal and tangential directions of the element under the current strain; and are the displacement at the initial damage and the displacement at the complete failure of the element, ; is the maximum displacement reached during the loading process, .

5. The method for jointly evaluating the fracturing transformation effect by forward and inverse modeling according to claim 4, wherein When the hydraulic fracture intersects the weak interface between layers, if the weak interface between layers fractures first, the hydraulic fracture will be trapped and cannot penetrate the weak interface between layers; if the rock body on the other side of the weak interface between layers fractures first, the hydraulic fracture will penetrate the weak interface and continue to propagate.

6. The method for jointly evaluating the fracturing transformation effect by forward and inverse modeling according to claim 1, characterized in that, In step S3, according to the fracture height parameter, combined with the shut-in pressure drop data, through the fracture parameter inversion model, calculate the liquid efficiency and filtration coefficient of the fracturing section. The specific process is as follows: Based on the fracture height parameter obtained from simulating the real fracturing process, combined with the shut-in pressure drop data, through the fracture parameter inversion model based on the analysis of the pressure drop curve, calculate the liquid efficiency and filtration coefficient of this fracturing section; This model realizes the simultaneous solution of the fracturing fluid efficiency, filtration coefficient and fracture geometric parameters by inverting the dynamic data of the synchronous filtration and closure process after shutting in multiple fractures, as follows: ； ； ； ； In the formula, is the injection displacement, m 3 / s; is the pumping time, s; is the fracture coefficient (for the PKN model, , for the KGD model, ); is the fracture height, m; is the Young's modulus, MPa; δ is the dimensionless time; δ = Δt / t0; Δt is the shut-in time, s; is the bottom-hole pressure corresponding to the dimensionless time δ0, MPa; is the bottom-hole pressure corresponding to the dimensionless time δ, MPa; is the minimum horizontal principal stress, MPa; is the fracture propagation coefficient; is the gamma function of; is the stress interference factor; where , is the fracture cluster spacing, m; is the half-length of the th fracture, m; is the filtration coefficient of the 0.5 th fracture after pump shut-off, m / s is the filtration height, m; is the fracturing fluid efficiency, %; is the th fracture volume after pump shut-off, m 3 ; represents the pressure decay function; represents the differential of the pressure decay function.

7. A method for jointly evaluating the fracturing transformation effect by forward and inverse modeling according to claim 6, characterized in that The fracture parameter inversion model based on the analysis of the pressure drop curve meets the following conditions: (1) After shutting in, each fracture undergoes synchronous filtration and elastic closure; (2) The fracture morphology is continuous and symmetric; (3) The reservoir is homogeneous and there is no interference from natural fractures; After the pump is stopped, the crack stops extending and the crack length remains constant.

8. A method for jointly evaluating the fracturing transformation effect by forward and inverse modeling according to claim 1, characterized in that, In step S4, the fracturing process is simulated using the boundary element method to obtain the crack length and crack width parameters, and the fracturing treatment volume is determined by calculating the stress field distribution around the crack. The specific process is as follows: Based on the obtained fracture height parameters, liquid efficiency, and filtration coefficient, the fracturing process is simulated using the boundary element method to calculate the crack length and crack width parameters; the fracturing treatment volume is determined by calculating the stress field distribution around the crack, as follows: ； ； ； In the formula, is the fluid pressure, in Pa; is the length of the infinitesimal element of the fracture, in m; and are the fluid power-law exponent and consistency exponent; is the fracture height, in m; is the fracture width, in mm; is the total amount of fracturing fluid, in m 3 ; is the normal displacement discontinuity of the th element (the fracture width of the th element), in mm; is the length of the th element, in m; is the length of the th cluster of fractures at time t, in m; is the total number of fractures; is the filtration rate, in m 2 / s; , , …, and are the numbers of fracture elements in the 1st, 2nd, …, (Z - 1)th, and Zth fracturing stages respectively; is the stress correction factor; , , and are the stress influence coefficient matrices; and are the tangential displacement discontinuity and normal displacement discontinuity of the th element respectively, in mm; and are the tangential stress and normal stress on the th element respectively; represents the time differential; represents the differential of the length of the infinitesimal element of the fracture.

9. The method for jointly evaluating the fracturing transformation effect by forward and inverse modeling according to claim 8, characterized in that, To reduce the solution difficulty and improve the simulation efficiency of multi-crack propagation within a stage, the following conditions are met: ① The rock is an infinite homogeneous elastic body and obeys linear elastic fracture mechanics. ② The fracturing fluid is an incompressible fluid, and the fluid in the crack conforms to the Poiseuille laminar flow law. ③ The filtration of the fracturing fluid perpendicular to the crack surface satisfies the Carter model. ④ The wellbore friction is much smaller than the perforation friction and the in-crack flow friction, so the wellbore flow friction is ignored. ⑤ The proppant migration is ignored, and based on the high stiffness assumption of the proppant, it is considered that the generation of new cracks will not cause the closure of previous cracks.

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