A fracture diagnosis method and device for fracturing

Abstract

The present application discloses a fracture diagnosis method and device for fracturing, which belongs to the technical field of fracturing and exploitation of oil and gas reservoirs. The diagnostic method establishes a water hammer equation group through the water hammer continuity equation, the water hammer motion equation and the liquid elasticity equation; solves the water hammer equation group to obtain the distribution equations of the head, flow velocity and density in the middle well section; determines the initial conditions in the studied wellbore, and obtains the expressions of the head, flow rate and density distribution in combination with the distribution equation; couples the water hammer equation group with the wellhead flow boundary conditions and the bottom hole fracture boundary conditions to calculate and obtain the water hammer pressure curve; and determines the fracture parameters by adjusting the fracture related parameters in the bottom hole fracture boundary conditions. The device includes a memory and a processor for storing a computer program, and the program includes the steps corresponding to the above method. The present application quickly diagnoses the fracture related parameters after fracturing based on the water hammer pressure during fracturing, and provides a basis for the design and modification of the oil and gas resource reservoir transformation plan, thereby improving the fracturing transformation effect.

Description

Technical Field

[0001] The present application belongs to the technical field of oil and gas reservoir fracturing and exploitation, and in particular, relates to a fracturing crack diagnosis method and device. Background Art

[0002] In recent years, with the continuous development of fracturing technology, it has greatly contributed to the efficient development of unconventional oil and gas resources such as shale oil and gas reservoirs. The final recovery rate of unconventional oil and gas resources such as shale oil and gas reservoirs is significantly affected by the geometry of fractures. Real-time and efficient hydraulic fracturing diagnostic methods are crucial to improving the effect of fracturing transformation and improving the efficiency of unconventional oil and gas resource development.

[0003] However, existing fracturing diagnostic methods, such as microseismic, drilling coring observation, and perforation imaging monitoring, have problems such as limited observation range, high precision of required equipment, and high construction cost.

[0004] The above-mentioned fracturing diagnosis problems limit the promotion of these methods in practical applications. Therefore, there is an urgent need to develop more economical fracture diagnosis technologies with relatively simple usage conditions, so as to optimize the construction design plan in real time, improve construction results and reduce costs. Summary of the invention

[0005] The present application aims to solve, at least to a certain extent, the technical problem of how to economically diagnose fracture parameters. To this end, the present application provides a fracture diagnosis method and device for hydraulic fracturing, which can quickly diagnose fracture-related parameters after hydraulic fracturing based on the water hammer pressure during the hydraulic fracturing process, provide a basis for the design and modification of oil and gas resource reservoir transformation plans, and thus improve the hydraulic fracturing transformation effect.

[0006] In a first aspect, an embodiment of the present application provides a fracture diagnosis method for hydraulic fracturing, which comprises:

[0007] Through the water hammer continuity equation, water hammer motion equation and liquid elasticity equation, a water hammer equation group based on water head, flow velocity and fluid density is established;

[0008] The finite difference method is used to solve the water hammer equations to obtain the distribution equations of the water head, flow velocity and density in the middle well section;

[0009] Determine the initial conditions in the wellbore under study and combine the distribution equations to obtain expressions for the head, flow rate, and density distribution;

[0010] The water hammer equations are coupled with the wellhead flow boundary conditions and the bottom hole fracture boundary conditions to calculate and obtain the water hammer pressure curve;

[0011] The fracture parameters are determined by adjusting the fracture half-length, fracture height, effective perforation number, and effective cluster number in the bottom hole fracture boundary conditions and fitting them with the measured water hammer pressure curve.

[0012] In some embodiments, the water hammer equations are established as:

[0013]

[0014] Where: g is the acceleration due to gravity, m / s 2 ; H is the water head in the wellbore, m ; S is the wellbore length, m ; Z is the reference plane, m ; ρ is the fluid density, kg / m 3 ; v is the fluid flow rate, m / s ; D is the inner diameter of the wellbore, m ; f is the friction coefficient along the wellbore, dimensionless; t is the fracturing construction time, s ; θ is the angle between the wellbore and the horizontal direction; K is the bulk modulus of the fluid, Pa ; C M is the intermediate calculation parameter, ; A is the cross-sectional area of ​​the wellbore, m 2 ; E is the Young's modulus of the wellbore casing wall, Pa ; e is the wall thickness of the wellbore casing, m .

[0015] In some embodiments, solving the water hammer equations using a finite difference method includes:

[0016] Establish the first finite difference scheme of partial differentials of hydraulic head, flow velocity and fluid density with respect to time;

[0017] A second finite difference scheme is established for the partial differentials of hydraulic head, flow velocity and fluid density with respect to distance along the wellbore;

[0018] The water hammer equations are solved using the finite difference format to obtain the distribution equations of the hydraulic head, flow velocity and density in the middle well section.

[0019] In some embodiments, the first finite difference format and the second finite difference format are:

[0020]

[0021]

[0022] Where: Y Represents water head, flow velocity, and density; represent j Time Layer i The function value of the cross section, i represents the wellbore grid node, j Indicates a time node; S is the wellbore length, m ; α Represents the weighting coefficient of the difference format, which has been verified to be α =0.1, the stability condition is met; is the time step, s; is the distance step, m.

[0023] In some embodiments, the distribution equations of the hydraulic head, flow rate and density in the middle well section are:

[0024]

[0025] Where: C A1 is the intermediate calculation parameter, ; C A2 is the intermediate calculation parameter, ; C B1 is the intermediate calculation parameter, ; C B2 is the intermediate calculation parameter, ; C E1 is the intermediate calculation parameter, ; C E2 is the intermediate calculation parameter, ; C M is the intermediate calculation parameter, ; C N is the intermediate calculation parameter, ; R is the intermediate calculation parameter, ; is the time step, s; i is the wellbore grid node; j is the time node; represent j Time Layer i The water head value of the cross section; represent j Time Layer i The velocity value of the cross section; represent j Time Layer i Density value of the section.

[0026] In some embodiments, the boundary conditions between the wellhead and the bottom of the well are the wellhead flow boundary condition and the bottom of the well fracture boundary condition. The wellhead flow boundary condition is:

[0027]

[0028] Where: For Change Wellhead flow rate at time, m 3 / s; For Change Wellhead flow rate at time, m 3 / s; is the time step, s; t is the fracturing construction time, s .

[0029] In some embodiments, the bottom hole fracture boundary condition is:

[0030]

[0031]

[0032] Where: p w is the bottom hole flowing pressure, Pa ; p f is the fluid pressure in the fracture, Pa ; ρ is the fluid density, kg / m 3 ; is the flow rate in the wellbore, m 3 / s ; N p is the number of open perforations, dimensionless; d is the perforation hole diameter, m ; C D is the flow coefficient, dimensionless; N f is the number of open clusters, dimensionless; h f is the crack height, m ; l f For half the length of the crack,m ; w f is the crack opening, m ; is the fluid loss in the fracture, m 3 / s .

[0033] In some embodiments, the crack opening w f The fluid pressure in the fracture p f Crack height h f The relevant relationship is:

[0034]

[0035] Where: σ min is the minimum horizontal ground stress, Pa ; is the rock Poisson's ratio, dimensionless; G is the rock shear modulus, Pa ; α s is the crack shape factor, dimensionless.

[0036] In some embodiments, when the water hammer equations are coupled to the wellhead flow boundary condition and the bottom hole fracture boundary condition, the water hammer continuity equation and the water hammer motion equation in the water hammer equations are linearly combined, and the water hammer motion equation is multiplied by v 0 / g Adding it to the water hammer continuity equation gives:

[0037]

[0038] Where: H is the water head in the wellbore, m ; t is the fracturing construction time, s ; S is the wellbore length, m ; Z is the reference plane, m ; g is the acceleration due to gravity, m / s 2 ; ρ is the fluid density, kg / m 3 ; v is the fluid flow rate, m / s ; v 0 is the initial flow rate,m / s ; θ is the angle between the wellbore and the horizontal direction; f is the friction coefficient along the wellbore, dimensionless; D is the inner diameter of the wellbore, m ; C M is the intermediate calculation parameter.

[0039] In a second aspect, an embodiment of the present application provides a hydraulic fracture diagnosis device, comprising a memory, a processor, and a computer program stored in the memory and executable in the processor, wherein the computer program comprises execution steps corresponding to the hydraulic fracture diagnosis method described above.

[0040] It can be seen from the above technical solution that the beneficial effects of this application are:

[0041] 1. The method of the present application can avoid increasing construction time and the cost of fracturing diagnosis by modeling. By combining the water hammer continuity equation, the water hammer motion equation and the liquid elasticity equation, a water hammer equation group with multiple parameters of water head, flow velocity and fluid density is obtained, which can accurately describe the flow state of the fluid in the wellbore, obtain the distribution of water head, flow rate and density, and accurately describe the state and behavior of the fluid in the wellbore. In combination with the initial conditions and the coupled wellhead flow boundary conditions and bottom hole fracture boundary conditions, the fracture related parameters are introduced, so that the relationship between the fracture related parameters and the water hammer pressure can be determined. In this way, the fracture related parameters after fracturing can be quickly diagnosed based on the water hammer pressure during the fracturing process, which provides a basis for the design and modification of oil and gas resource reservoir transformation plans, thereby improving the fracturing transformation effect.

[0042] 2. The device of the present application presents the above-mentioned fracture parameter diagnosis method in the form of a computer program, which corresponds to the execution process of the computer program and is stored in a memory. By executing the computer program by the processor, the fracture parameters can be quickly obtained and the results can be output, which simplifies the fracture judgment and analysis process during the fracturing process and improves efficiency. It can quickly determine the fracture half-length, fracture height, number of open clusters, and number of open perforations, thereby judging the formation fracturing effect, and use it as a basis for optimization to improve the fracturing transformation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other embodiments and drawings can be obtained based on these drawings without creative work. The block diagrams shown in the drawings are only functional entities, which do not necessarily correspond to physically independent entities, that is, these functional entities can be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices. The flowcharts shown in the drawings are only exemplary illustrations, and do not necessarily include all the contents and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can also be decomposed, and some operations / steps can be merged or partially merged, so the actual execution order may change according to the actual situation.

[0044] Figure 1 A schematic diagram of an embodiment of a water hammer simulation method for fracturing according to the present invention is shown;

[0045] Figure 2 A schematic diagram showing the results of an embodiment of the water hammer simulation method for fracturing according to the present invention; DETAILED DESCRIPTION

[0046] The following will be combined with the accompanying drawings corresponding to the specific implementation methods of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. The following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection. The described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, various different configurations can be used to arrange and design. All other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0047] The present application is described below with reference to the accompanying drawings and specific embodiments:

[0048] Please refer to Figure 1 The first embodiment of the present application provides a method for diagnosing fractures in a hydraulic fracturing process, which comprises:

[0049] S1. A group of water hammer equations based on water head, flow velocity and fluid density is established through the water hammer continuity equation, water hammer motion equation and liquid elasticity equation. The water hammer continuity equation is an equation established based on the law of conservation of mass, which describes the relationship between the changes of fluid in space and time during the flow of fluid in the wellbore. When considering the influence of water head, a plane is selected along the wellbore direction as a reference datum plane. When establishing the water hammer continuity equation, the changes in water head, flow rate, well inclination and fluid density are all used as parameters to establish a polynomial equation. The water hammer motion equation is an equation that describes the changes in parameters such as flow velocity and pressure in the wellbore of the water hammer phenomenon, and can determine the changes in parameters such as flow velocity, pressure, density in the wellbore, thereby analyzing the water hammer phenomenon. The liquid elasticity equation describes the elasticity of the liquid, that is, the fluid in the wellbore has a certain compressibility under the action of pressure, and can determine the relationship between pressure and density.

[0050] S2. Use the finite difference method to solve the water hammer equations and obtain the distribution equations of the head, velocity and density in the middle well section; when using the finite difference method to solve, establish the partial differential equations of the head, velocity and density. The finite difference method is a numerical method used to solve partial differential equations by discretizing the continuous space and time domains into a series of discrete points of head, velocity and density, and approximating the solution of the equations at these points.

[0051] S3. Determine the initial conditions in the wellbore under study, and combine the distribution equation to obtain the expressions of the head, flow rate and density distribution; wherein the fracturing construction is carried out through the wellbore, the fracturing fluid is located in the wellbore, and the wellbore is divided into a wellhead section, an intermediate section and a bottom section, the wellhead section is the first section of the tubing from top to bottom of the wellbore, the bottom section is the last section of the tubing from top to bottom of the wellbore, and the intermediate section is the part between the wellhead section and the bottom section, wherein the wellbore may be vertical or may have a certain well inclination angle. The initial condition is the starting point for calculating the water hammer simulation model. The initial condition is the initial state of the water hammer during the fracturing process, such as the distribution of pressure, flow rate, flow velocity, etc. in the wellbore at the beginning of the simulation, which can be determined based on existing data such as the construction displacement. In an optional embodiment, the operation sequence for determining the initial condition is after step S1 and before step S2, and then the state parameters of the fluid are determined. In actual operation, the sequence can be adjusted as needed.

[0052] S4. Couple the water hammer equation group with the wellhead flow boundary conditions and the bottom hole fracture boundary conditions, use the finite difference method to solve the equation group, and calculate the water hammer pressure curve; the boundary conditions are the constraint range for calculating the water hammer simulation model. After setting, the state and parameter changes at the beginning of the water hammer simulation can be determined. The boundary conditions limit the solution range. The boundary conditions can be set to the state parameters of the fluid at the wellhead or bottom hole, such as the pressure or flow at the wellhead, the density or pressure at the bottom hole. The fluid parameters at the wellhead can be determined based on the construction displacement data, and the bottom hole fluid parameters can be obtained by solving the finite difference equations based on the bottom hole boundary conditions, as shown in the following formula (20).

[0053] S5. The fracture parameters are determined by adjusting the fracture half-length, fracture height, effective perforation number, and effective cluster number in the bottom hole fracture boundary conditions and fitting them with the measured water hammer pressure curve. Specifically, the above fracture-related parameters are adjusted so that the bottom hole fracture boundary is compared with the measured water hammer pressure curve for fitting, and the fracture parameters are determined by the fracture boundary conditions corresponding to the water hammer pressure curve; the relationship between the fracture aperture and the fluid pressure in the fracture, the fracture half-length, the fracture height, the number of open clusters, the number of open perforations, etc. is established, and the relationship between the water hammer pressure and the fracture is obtained, thereby determining the fracture-related parameters.

[0054] Existing fracturing diagnostic methods, such as microseismic, drilling coring observation, perforation imaging monitoring and other methods, have limited observation range, high precision equipment and high construction costs. Therefore, how to economically diagnose fracture parameters has become the basis for optimizing fracturing construction and indirectly reflects the fracturing effect. The cost of fracturing diagnosis is high. This is because fracturing is to inject fracturing fluid into the reservoir through the wellbore, and the reservoir is located in the formation. It is impossible to obtain data intuitively and can only be done by indirect means. However, the current fracturing diagnostic methods all require tool detection, and the construction takes a long time and increases the cost of fracturing.

[0055] The present application can avoid increasing construction time and the cost of fracturing diagnosis by modeling. By combining the water hammer continuity equation, the water hammer motion equation and the liquid elasticity equation, a group of water hammer equations with multiple parameters such as head, flow velocity and fluid density are obtained. The flow state of the fluid in the wellbore can be accurately described, and the distribution of head, flow rate and density can be obtained. The state and behavior of the fluid in the wellbore can be accurately described. By combining the initial conditions and the coupled wellhead flow boundary conditions and bottom hole fracture boundary conditions, the fracture-related parameters are introduced, so that the relationship between the fracture-related parameters and the water hammer pressure can be determined. In this way, the fracture-related parameters after fracturing can be quickly diagnosed based on the water hammer pressure during the fracturing process, which provides a basis for the design and modification of oil and gas resource reservoir transformation plans, thereby improving the fracturing transformation effect.

[0056] In some embodiments, the water hammer equations are established as:

[0057] (1)

[0058] Where: g is the acceleration due to gravity, m / s 2 ; H is the water head in the wellbore, m ; S is the wellbore length, m ; Z is the reference plane, m ; ρ is the fluid density, kg / m 3 ; v is the fluid flow rate, m / s ; D is the inner diameter of the wellbore, m ; f is the friction coefficient along the wellbore, dimensionless; t is the fracturing construction time, s ; θ is the angle between the wellbore and the horizontal direction; K is the bulk modulus of the fluid, Pa ; , C M is the intermediate calculation parameter; A is the cross-sectional area of ​​the wellbore, m 2 ; E is the Young's modulus of the wellbore casing wall, Pa ; e is the wall thickness of the wellbore casing, m .

[0059] In some embodiments, since the water hammer equations include multiple variables such as fluid density, water head, flow rate, etc., the finite difference method is used to solve the equations, that is, the equation solution area is subdivided into a network consisting of a finite number of grid points, and the finite difference formula is used for approximation solution. Using the finite difference method to solve the water hammer equations includes:

[0060] Establish the first finite difference scheme of partial differentials of hydraulic head, flow velocity and fluid density with respect to time;

[0061] A second finite difference scheme is established for the partial differentials of hydraulic head, flow velocity and fluid density with respect to distance along the wellbore;

[0062] The water hammer equations are solved using the finite difference format to obtain the distribution equations of the hydraulic head, flow velocity and density in the middle well section.

[0063] In some embodiments, the first finite difference format and the second finite difference format are the following finite difference format for partial differential of time (Equation (2)) and finite difference format for partial differential of distance (Equation (3)):

[0064] (2)

[0065] (3)

[0066] Where: Y Represents water head, flow velocity, and density; represent j Time Layer i The function value of the cross section, i represents the wellbore grid node, j Indicates a time node; S is the wellbore length, m ; α Represents the weighting coefficient of the difference format, which has been verified to be α =0.1, the stability condition is met; is the time step, s; is the distance step, m.

[0067] In some embodiments, the water hammer equations (Equation (1)) are solved using a finite difference format to obtain the distribution equations of the water head, flow velocity and density in the middle well section:

[0068]

[0069] Where: C A1 is the intermediate calculation parameter, ; C A2 is the intermediate calculation parameter, ; C B1 is the intermediate calculation parameter, ; C B2 is the intermediate calculation parameter, ; C E1 is the intermediate calculation parameter, ; C E2 is the intermediate calculation parameter, ; C M is the intermediate calculation parameter, ; C N is the intermediate calculation parameter, ; R is the intermediate calculation parameter, ; is the time step, s; i is the wellbore grid node; j is the time node; represent j Time Layer i The water head value of the cross section; represent j Time Layer i The velocity value of the cross section; represent j Time Layer i Density value of the section.

[0070] In some embodiments, when setting the initial conditions, the fluid in the wellbore at the time when fracturing stops is regarded as steady-state flow, and the flow rate at each location in the wellbore is the same. That is, the flow state of the fluid in the wellbore when the pump stops at the beginning of the fracturing process is taken as the initial condition. In the initial state, the wellhead water head is known, and the water head distribution at each location in the wellbore can be calculated based on the friction along the wellbore. The initial conditions in the wellbore under study are determined as the water head, flow rate, fluid density and pressure distribution at the wellhead, where the water head and flow rate distribution at the initial moment are:

[0071] (7)

[0072] (8)

[0073] (9)

[0074] Where: is the initial flow rate in the wellbore, ; H 1 0 is the initial water head at the wellhead, ; is the head loss in the wellbore section, .

[0075] The fluid density and pressure distribution are:

[0076]

[0077] Where: H is the water head in the wellbore, m ; Z is the reference plane, m ; ρ is the fluid density, kg / m 3 ; K is the bulk modulus of the fluid, Pa ; p is the wellhead pressure, MPa .

[0078] In some embodiments, the boundary conditions of the water hammer equations are set, and the boundary conditions of the wellhead and the bottom of the well are the wellhead flow boundary conditions and the bottom of the well fracture boundary conditions. During the fracturing process, in order to avoid the pressure wave caused by the instantaneous pump stop causing damage to the pipeline and equipment, a step-by-step reduction in displacement is usually used to stop the pump, that is, gradually reducing the displacement until the pump is completely stopped. The wellhead flow boundary condition is the change of the flow at the wellhead over time:

[0079] (12)

[0080] Where: For Change Wellhead flow rate at time, m 3 / s; For Change Wellhead flow rate at time, m 3 / s; is the time step, s; t is the fracturing construction time, s ;

[0081] In fracturing, it is usually considered that a fracturing cluster will produce a main fracture, or no fracture will be opened. Based on the mass conservation relationship, the bottom hole fracture boundary condition can be expressed as follows:

[0082] (13)

[0083] (14)

[0084] Where: p w is the bottom hole flowing pressure, Pa ; P f is the pressure inside the crack, Pa ; ρ is the fluid density, kg / m 3 ; is the flow rate in the wellbore, m 3 / s ; N p is the number of open perforations, dimensionless; d is the perforation hole diameter, m ; C D is the flow coefficient, dimensionless; N f is the number of open clusters, dimensionless; h f is the crack height, m ; lf For half the length of the crack, m ; w f is the crack opening, m ; is the filtration loss in the cracks, m 3 / s .

[0085] In some embodiments, the bottom hole fracture boundary condition is:

[0086] (15)

[0087] (16)

[0088] Where: p w is the bottom hole flowing pressure, Pa ; p f is the fluid pressure in the fracture, Pa ; ρ is the fluid density, kg / m 3 ; is the flow rate in the wellbore, m 3 / s ; N p is the number of open perforations, dimensionless; d is the perforation hole diameter, m ; C D is the flow coefficient, dimensionless; N f is the number of open clusters, dimensionless; h f is the crack height, m ; l f For half the length of the crack, m ; w f is the crack opening, m ; is the fluid loss in the fracture, m 3 / s .

[0089] In some embodiments, the crack opening w f The fluid pressure in the fracture p f Crack height h f The relevant relationship is:

[0090]

[0091] Where: σ min is the minimum horizontal ground stress, Pa ; is the rock Poisson's ratio, dimensionless; G is the rock shear modulus, Pa ; α s is the crack shape factor, dimensionless.

[0092] In some embodiments, the fluid loss effect is taken into account, and the fracture parameters are introduced into the formula at the bottom hole fracture boundary, so as to establish the fracture parameters that comprehensively consider the fluid density change, wellbore friction, perforation friction, and fluid loss effect. The fluid loss amount in the above fracture is determined by the following formula:

[0093] (18)

[0094] Where: is the fluid loss in the fracture, m 3 / s ; N f is the number of open clusters, dimensionless; h f is the crack height, m ; l f For half the length of the crack, m ; C L is the filtration coefficient, m / s 0.5 ; t f is the filtration loss reference time, s.

[0095] In some implementations, for the solution of the bottom hole boundary water head, flow rate and density, since the water hammer equation group already contains three equations, after adding two bottom hole constraints (Equation (15) and Equation (16), the bottom hole solution equation group contains five equations, while the unknowns are only four unknown parameters, namely water head, flow rate, density and pressure in the fracture, resulting in the contradiction that the number of equations is greater than the number of unknowns. Therefore, the continuity equation and the motion equation in the water hammer equation group are combined into one partial differential equation, which is then solved by the finite difference method.

[0096] When coupling the water hammer equations with the wellhead flow boundary conditions and the bottom hole fracture boundary conditions, the water hammer continuity equation and the water hammer motion equation in the water hammer equations are linearly combined, and the water hammer motion equation is multiplied by v0 / g Adding it to the water hammer continuity equation gives:

[0097] (19)

[0098] Where: H is the water head in the wellbore, m ; t is the fracturing construction time, s ; S is the wellbore length, m ; Z is the reference plane, m ; g is the acceleration due to gravity, m / s 2 ; ρ is the fluid density, kg / m 3 ; v is the fluid flow rate, m / s ; v 0 is the initial flow rate, m / s ; θ is the angle between the wellbore and the horizontal direction; f is the friction coefficient along the wellbore, dimensionless; D is the inner diameter of the wellbore, m ; C M is the intermediate calculation parameter.

[0099] Finally, the water hammer equations (Equation (1)) and the bottom hole fracture constraint equations (12) to (18) and (19) are combined and solved using finite difference equations to obtain the bottom hole head, flow rate and density distribution. The solution format is as follows:

[0100] (20)

[0101] In the formula: In the formula: H is the water head in the wellbore, m ; Z is the reference plane, m ; is the time step, s; is the distance step, m; v is the fluid flow rate, m / s ; v 0 is the initial flow rate, m / s ; g is the acceleration due to gravity, m / s 2 ; S is the wellbore length, m; ρ is the fluid density, kg / m 3 ; f is the friction coefficient along the wellbore, dimensionless; t is the fracturing construction time, s ; θ is the angle between the wellbore and the horizontal direction; N p is the number of open perforations, dimensionless; d is the perforation hole diameter, m ; C D is the flow coefficient, dimensionless; N f is the number of open clusters, dimensionless; h f is the crack height, m ; l f For half the length of the crack, m ; C N is the intermediate calculation parameter, m / s 0.5 ; w f is the crack opening, m ; is the fluid loss in the fracture, m 3 / s ; , C M1 is the intermediate calculation parameter.

[0102] Please refer to Figure 2 The method of the present application is described by taking a fracturing well in the Sichuan Basin as an example. The vertical well section length of the well is 3180 m , the horizontal well section length is 2120 m , the inner diameter of the wellbore is 118.6mm, the wall thickness is 10.54mm, the rock modulus is 42GPa, and the rock Poisson's ratio is 0.22. The above-mentioned relevant parameters are brought into the water hammer equation group of this application, and the water hammer pressure is calculated as shown in the figure. According to the figure, it can be seen that the calculated water hammer pressure curve has a high degree of fit with the measured curve. The calculated crack length is 160m, the crack height is 19m, the number of open clusters is 4 clusters, and the number of open perforations is 14.

[0103] The second embodiment of the present application provides a fracture diagnosis device for hydraulic fracturing, including a memory, a processor, and a computer program stored in the memory and executable in the processor, wherein the computer program includes the execution steps corresponding to the fracture diagnosis method for hydraulic fracturing described above, and the processor implements the steps in the above method embodiment when executing the computer program; or, the processor implements the functions of each module / unit in the above fracture diagnosis method and device embodiment when executing the computer program. It should be understood that the devices of each embodiment of the present application can be implemented based on a memory and a processor, each memory is used to store a computer program for executing the above method of the present application, and the processor executes the above computer program so that the fracture diagnosis method and device for hydraulic fracturing implement the methods of each of the above embodiments.

[0104] Regarding the specific implementation of this application, it should be noted that:

[0105] In the description of the present application, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, device or readable storage medium including a series of elements includes not only those elements, but also includes other elements that are not explicitly listed and are consistent with the concept of the present application, or also includes elements inherent to such process, method, device or readable storage medium. In the absence of further restrictions, the elements defined by the sentence "comprises a ..." do not exclude the presence of additional elements in the process, method, device or readable storage medium including the elements.

[0106] In the description of the present application, the descriptions of reference terms such as "some embodiments", "optional embodiments", "examples", "specific examples", "optional examples" or "optional embodiments" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application, but do not mean that these embodiments illustrate and describe all possible forms of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0107] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in the field to implement. Although the embodiments of the present application have been shown and described, these embodiments can be changed, modified, replaced and modified in various ways without departing from the principles and purpose of the present application. Ordinary technicians in the field can understand that according to the technical inspirations disclosed in the present application, various other specific changes and combinations of embodiments that do not depart from the essence of the present application are made, which are still within the scope of protection defined by the claims of the present invention and their equivalent technical solutions.

[0108] At the same time, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

Claims

1. A fracture diagnosis method for hydraulic fracturing, characterized in that: include: Through the water hammer continuity equation, water hammer motion equation and liquid elasticity equation, a water hammer equation group based on water head, flow velocity and fluid density is established; the water hammer equation group is: Where: g is the acceleration due to gravity, m / s 2 ; H is the water head in the wellbore, m; S is the length of the wellbore, m; Z is the reference plane, m; ρ is the fluid density, kg / m 3 ; v is the fluid velocity, m / s; D is the inner diameter of the wellbore, m; f is the friction coefficient along the wellbore, dimensionless; t is the fracturing construction time, s; θ is the angle between the wellbore and the horizontal direction; K is the fluid bulk modulus, Pa; C M is the intermediate calculation parameter, ; A is the cross-sectional area of ​​the wellbore, m 2 ; E is the Young's modulus of the wellbore casing wall, Pa; e is the thickness of the wellbore casing wall, m; The water hammer equations are solved by using a finite difference method to obtain distribution equations of water head, flow velocity and density in the middle well section; Determine the initial conditions in the wellbore under study and obtain expressions for the head, flow rate and density distribution in combination with the distribution equations; The water hammer equation group is coupled with the wellhead flow boundary condition and the bottom hole fracture boundary condition to calculate and obtain the water hammer pressure curve; The fracture parameters are determined by adjusting the fracture half-length, fracture height, effective perforation number, and effective cluster number in the bottom hole fracture boundary conditions and fitting them with the measured water hammer pressure curve.

2. The fracture diagnosis method of hydraulic fracturing according to claim 1, characterized in that: The method of solving the water hammer equations by using the finite difference method includes: Establish the first finite difference scheme of partial differentials of hydraulic head, flow velocity and fluid density with respect to time; A second finite difference scheme is established for the partial differentials of hydraulic head, flow velocity and fluid density with respect to distance along the wellbore; The water hammer equations are solved using a finite difference format to obtain distribution equations of water head, flow velocity and density in the middle well section.

3. The fracture diagnosis method of hydraulic fracturing according to claim 2, characterized in that: The first finite difference scheme and the second finite difference scheme are: Where: Y represents water head, flow velocity, and density; represents the function value of the section i at time j, i represents the wellbore grid node, j represents the time node; S is the wellbore length, m; α represents the weighting coefficient of the difference format. After verification, when α=0.1, the stability condition is met; is the time step, s; is the distance step, m.

4. The fracture diagnosis method of hydraulic fracturing according to claim 2, characterized in that: The distribution equations of the water head, flow velocity and density in the middle well section are: Where: C A1 is the intermediate calculation parameter, ; C A2 is the intermediate calculation parameter, ; C B1 is the intermediate calculation parameter, ; C B2 is the intermediate calculation parameter, ; C E1 is the intermediate calculation parameter, ; C E2 is the intermediate calculation parameter, ; C M is the intermediate calculation parameter, ; C N is the intermediate calculation parameter, ; R is the intermediate calculation parameter, ; is the time step, s; i is the wellbore grid node; j is the time node; represents the hydraulic head value of section i at time j; represents the velocity value of section i at time j; Represents the density value of section i at time j.

5. The fracture diagnosis method of hydraulic fracturing according to claim 1, characterized in that: The boundary conditions of the wellhead and the bottom of the well are the wellhead flow boundary condition and the bottom of the well fracture boundary condition. The wellhead flow boundary condition is: Where: For Change Wellhead flow rate at time, m 3 / s; For Change Wellhead flow rate at time, m 3 / s; is the time step, s; t is the fracturing construction time, s.

6. The fracture diagnosis method of hydraulic fracturing according to claim 5, characterized in that: The bottom hole fracture boundary condition is: Where: p w is the bottom hole pressure, Pa; p f is the fluid pressure in the fracture, Pa; ρ is the fluid density, kg / m 3 ; is the flow rate in the wellbore, m 3 / s; N p is the number of perforations opened, dimensionless; d is the diameter of the perforation hole, m; C D is the flow coefficient, dimensionless; N f is the number of open clusters, dimensionless; h f is the crack height, m; l f is the half length of the crack, m; w f is the crack opening, m; is the fluid loss in the fracture, m 3 / s.

7. The fracture diagnosis method of hydraulic fracturing according to claim 6, characterized in that: The crack opening w f The fluid pressure p in the fracture f and crack height h f The relevant relationship is: Where: min is the minimum horizontal in-situ stress, Pa; is the rock Poisson's ratio, dimensionless; G is the rock shear modulus, Pa; α s is the crack shape factor, dimensionless.

8. The fracture diagnosis method of hydraulic fracturing according to claim 1, characterized in that: When the water hammer equation group is coupled with the wellhead flow boundary condition and the bottom hole fracture boundary condition, the water hammer continuity equation and the water hammer motion equation in the water hammer equation group are linearly combined, and the water hammer motion equation is multiplied by v0 / g and added to the water hammer continuity equation to obtain: Where: H is the water head in the wellbore, m; t is the fracturing construction time, s; S is the wellbore length, m; Z is the reference datum plane, m; g is the gravitational acceleration, m / s 2 ; ρ is the fluid density, kg / m 3 ; v is the fluid velocity, m / s; v0 is the initial velocity, m / s; θ is the angle between the wellbore and the horizontal direction; f is the friction coefficient along the wellbore, dimensionless; D is the inner diameter of the wellbore, m; C M is the intermediate calculation parameter.

9. A fracture diagnosis device for hydraulic fracturing, comprising a memory, a processor, and a computer program stored in the memory and executable in the processor, characterized in that: The computer program comprises execution steps corresponding to the method for diagnosing fractures in hydraulic fracturing according to any one of claims 1 to 8.

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