A method and device for simulating water hammer in fracturing

Abstract

The present application discloses a method and device for simulating water hammer in fracturing, which belongs to the technical field of fracturing and exploitation of oil and gas reservoirs. The simulation method includes: determining the simulated wellbore; establishing a water hammer continuity equation and a water hammer motion equation based on water head, flow rate and fluid density; then combining the liquid elasticity equation to establish a water hammer equation group, and solving to obtain the distribution equation of water head, flow rate and density; establishing a relationship between fluid pressure and density and flow rate, and setting up the water hammer equation group in parallel to obtain a water hammer simulation model; setting initial conditions and boundary conditions, and fitting to obtain a curve of water hammer pressure changing with time. 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 can more accurately simulate the water hammer pressure in the fracturing process, help developers use the water hammer pressure in the fracturing process to analyze the fracturing effect, thereby optimizing the fracturing parameters, obtaining a better fracturing effect, and promoting the efficient development of unconventional oil and gas resources.

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 method and device for simulating water hammer during fracturing. Background Art

[0002] In recent years, with the continuous development of the oil industry, my country has achieved great success in the exploitation of unconventional oil and gas resources such as tight oil and gas reservoirs and shale oil and gas reservoirs. However, due to the tightness of tight oil and gas reservoirs and shale oil and gas reservoirs, the exploitation of such oil and gas resources usually requires large-scale hydraulic fracturing to achieve efficient development. By studying the water hammer pressure formed during the fracturing process, it is helpful for developers to effectively evaluate and optimize fracturing operations, improve fracturing effects, and promote the efficient development of unconventional oil and gas resources such as tight oil and gas reservoirs and shale oil and gas reservoirs. Therefore, accurately simulating the water hammer pressure formed during the fracturing process is crucial for effectively evaluating fracture parameters using water hammer pressure.

[0003] There are relatively few studies on the simulation of water hammer pressure during fracturing by domestic and foreign scholars. In the existing research on water hammer pressure during fracturing, the influence of fluid density change on water hammer pressure is not considered. However, in the actual fracturing process, it will affect the accuracy of simulated water hammer pressure. In view of this, it is urgent to propose a simulation method that can more accurately simulate water hammer pressure close to the actual situation. Summary of the invention

[0004] The present application aims to at least to some extent solve the technical problem of inaccurate simulation of water hammer pressure during fracturing. To this end, the present application provides a water hammer simulation method and device for fracturing, which can more accurately simulate the water hammer pressure during fracturing, help developers use the water hammer pressure during fracturing to analyze the fracturing effect, thereby optimizing fracturing parameters, obtaining better fracturing effects, and promoting the efficient development of unconventional oil and gas resources.

[0005] In a first aspect, an embodiment of the present application provides a method for simulating water hammer in fracturing, which comprises:

[0006] determining the wellbore to be simulated;

[0007] The water hammer continuity equation is established according to the corresponding water head, flow rate, wellbore inclination, and fluid density changes of the wellbore;

[0008] According to the changes in water head, flow rate, and fluid density corresponding to the wellbore, the water hammer motion equation is established;

[0009] According to the water hammer continuity equation, water hammer motion equation, combined with the liquid elasticity equation, the water hammer equation group is established, and the water hammer equation group is solved to obtain the distribution equation of water head, flow velocity and density in the middle well section;

[0010] Establish the relationship between the fluid pressure, density and flow rate of the bottom hole fracture, linearly combine the water hammer continuity equation and the water hammer motion equation, and solve the water hammer equations in parallel to obtain the water hammer simulation model;

[0011] The initial conditions and boundary conditions are set, and the curve of water hammer pressure changing with time is obtained by fitting.

[0012] In some embodiments, a water hammer continuity equation is established to satisfy the following conditions at a certain position in the wellbore: the flow velocity changes with time, the head changes caused by the flow velocity change and the gravity component under the inclined wellbore, and the flow velocity and head changes caused by the gravity component under the inclination of the wellbore and the change in fluid density, to achieve a dynamic equilibrium state.

[0013] In some embodiments, a water hammer motion equation is established to satisfy the following conditions at a certain position in the wellbore: changes in gravity component and flow velocity cause changes in water head, changes in water head and density, and changes in pressure caused by wellbore friction, changes in fluid density caused by pressure changes and water head changes, and changes in flow velocity caused by fluid density changes and water head changes, to achieve a dynamic equilibrium state.

[0014] In some embodiments, when the water hammer equations are established, the pressure in the wellbore is equivalent to the water head in the liquid elasticity equation to obtain the relationship between density and water head.

[0015] In some embodiments, when setting the initial conditions, the fluid in the wellbore at the time when fracturing stops is considered to be in steady-state flow, and the flow rate at each location in the wellbore is the same.

[0016] In some embodiments, the boundary conditions include a wellhead flow boundary and a fracture pressure boundary.

[0017] In some embodiments, the pressure boundary of the fracture is established based on the relationship between the perforation friction and the fluid pressure in the fracture.

[0018] In some embodiments, before the fitting process, the water hammer continuity equation and the water hammer motion equation are added together to form a partial differential equation.

[0019] In some embodiments, before setting initial conditions and boundary conditions, a distribution equation of fluid density is added to the water hammer simulation model.

[0020] In a second aspect, an embodiment of the present application provides a water hammer simulation device for fracturing, 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 water hammer simulation method for fracturing as described above.

[0021] It can be seen from the above technical solution that the beneficial effects of this application are:

[0022] 1. The method of the present application introduces water head, flow rate, wellbore inclination and fluid density changes at the same time, establishes water hammer continuity equation and water hammer motion equation, which can comprehensively consider the fluid water hammer phenomenon in the wellbore and more accurately describe the transient hydraulic process. The change of water head is related to the propagation of water hammer pressure wave. Introducing water head to establish equations can study the influence of water head and water hammer pressure. The change of flow rate causes the change of fluid momentum, thereby triggering water hammer phenomenon. Introducing flow rate can determine the generation of water hammer; on the other hand, wellbore inclination will cause the neutral to produce a wellbore axial component of force. By introducing wellbore inclination, the accuracy of water hammer research under long-distance fluid movement is ensured. The compressibility of the fluid causes the density to change. By introducing the change of fluid density, the conservation of mass in the water hammer process can be more accurately described; combined with the liquid elasticity equation, the compressibility of the liquid is considered, so that the water hammer equation group can be determined more accurately. Then, the distribution of water head, flow velocity and density in the middle well section is obtained by solving, which can be used as the intermediate parameters for solving the final water hammer simulation model. By establishing the relationship between fluid pressure, density and flow, the linear combination of the water hammer continuity equation and the water hammer motion equation, and the above-mentioned water hammer equation group, a water hammer simulation model with multi-parameter coupling of water head, flow, well inclination and density can be established. Then, by setting the initial conditions and boundary conditions of the model and adopting the model solving method, the curve of water hammer pressure changing with time can be fitted, and then the water hammer pressure in the fracturing process can be simulated more accurately, helping developers to use the water hammer pressure in the fracturing process to analyze the fracturing effect, thereby optimizing the fracturing parameters, obtaining better fracturing effects, and promoting the efficient development of unconventional oil and gas resources.

[0023] 2. The device of the present application presents the above-mentioned simulation method in the form of a computer program, which corresponds to the execution process of the computer program and is stored in a memory. Through the execution of the computer program by the processor, the simulation structure can be quickly obtained and the results can be output, which simplifies the complex water hammer phenomenon in the fracturing process, improves efficiency, and can quickly simulate the evolving water hammer pressure curve, thereby promoting the efficient development of unconventional oil and gas resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] Figure 1 A schematic diagram of an embodiment of a water hammer simulation method for fracturing according to the present invention is shown;

[0026] Figure 2 A schematic diagram showing the results of an embodiment of the water hammer simulation method for fracturing of the present invention is shown. DETAILED DESCRIPTION

[0027] 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.

[0028] The present application is described below with reference to the accompanying drawings and specific embodiments:

[0029] Please refer to Figure 1 The first embodiment of the present application provides a method for simulating water hammer in fracturing, which includes:

[0030] S1. Determine the simulated wellbore; perform fracturing construction through the wellbore, where the fracturing fluid is located, and the wellbore is divided into a wellhead section, a middle 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 middle 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.

[0031] S2. Establish a water hammer continuity equation based on the corresponding water head, flow rate, wellbore inclination, and fluid density change of the wellbore. The water hammer continuity equation is an equation based on the law of conservation of mass, which describes the relationship between the changes of the fluid in space and time during the flow of the fluid in the wellbore. When considering the influence of the 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.

[0032] S3. Establish the water hammer motion equation according to the changes in the water head, flow rate, and fluid density corresponding to the wellbore; 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. It can determine the changes in parameters such as flow velocity, pressure, and density in the wellbore, thereby analyzing the water hammer phenomenon.

[0033] S4. Based on the water hammer continuity equation and water hammer motion equation, combined with the liquid elasticity equation, a water hammer equation group is established, and the water hammer equation group is solved to obtain the distribution equations of the head, flow velocity and density in the middle section of the wellbore; the liquid elasticity equation describes the elasticity of the liquid, that is, the fluid in the wellbore has a certain compressibility under pressure, and the relationship between pressure and density can be determined. By introducing the liquid elasticity equation, the water head, flow velocity and density distribution of the middle section of the wellbore can be solved, and then used as intermediate parameters to solve the water hammer simulation model.

[0034] S5. Establish the relationship between the fluid pressure, density and flow rate of the bottom hole hydraulic fracture, linearly combine the water hammer continuity equation and the water hammer motion equation, and solve the above water hammer equations in parallel to obtain a water hammer simulation model; there is a certain relationship between the fluid pressure, density and flow rate of the bottom hole hydraulic fracture, and the equation between the bottom hole flow pressure and the fluid density and flow rate of the bottom hole hydraulic fracture is determined by the perforation friction resistance; the water hammer continuity equation and the water hammer motion equation are linearly combined to form an equation, such as ax+by=0, x, y are the equations to be combined, and a, b are linear combination parameters respectively.

[0035] S6. Set initial conditions and boundary conditions. Initial conditions and boundary conditions are the starting point and 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 initial condition is the initial state of water hammer during fracturing, such as the distribution, flow rate, and flow velocity of the pressure in the wellbore at the beginning of the simulation. 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 of the well, such as the pressure or flow rate at the wellhead, and the density or pressure at the bottom of the well. The wellhead parameters can be determined based on existing data such as the construction displacement, and the bottom of the well parameters can be obtained by solving the bottom of the wellbore node parameters using the bottom of the well boundary condition equation. Finally, the established water hammer equation group is coupled with the wellhead and bottom of the well boundary conditions for numerical solution to obtain the water hammer pressure change curve over time.

[0036] The existing simulation of water hammer pressure during fracturing cannot fully and accurately simulate the changes in water hammer pressure during fracturing under real formation environments. This is because the existing research on the fracturing process does not consider the simulation of fluid density changes. In the actual fracturing process, when the flow rate suddenly changes due to pump stop and water hammer occurs, the pressure in the wellbore changes dramatically, which will cause the fluid density to change, thereby affecting the release and attenuation of water hammer pressure. The density of the fluid is affected by its own compressibility, so there is a close correlation between the density of the fluid and the water hammer pressure. Therefore, the current simulation cannot fully and accurately simulate the fracturing process.

[0037] The present application introduces water head, flow rate, wellbore inclination and fluid density changes at the same time, establishes water hammer continuity equation and water hammer motion equation, which can comprehensively consider the fluid water hammer phenomenon in the wellbore and more accurately describe the transient hydraulic process. The change of water head is related to the propagation of water hammer pressure wave. Introducing water head to establish equations can study the influence of water head and water hammer pressure. The change of flow rate causes the change of fluid momentum, thereby triggering water hammer phenomenon. Introducing flow rate can determine the generation of water hammer; on the other hand, wellbore inclination will cause the neutral to produce a wellbore axial component of force on the fluid. By introducing wellbore inclination, the accuracy of water hammer research under long-distance fluid movement is ensured. The compressibility of the fluid causes the density to change. By introducing the change of fluid density, the conservation of mass in the water hammer process can be more accurately described; combined with the liquid elasticity equation, the compressibility of the liquid is considered, so that the water hammer equation group can be determined more accurately. Then, the distribution of water head, flow velocity and density in the middle well section is obtained by solving, which can be used as the intermediate parameters for solving the final water hammer simulation model. By establishing the relationship between fluid pressure, density and flow, the linear combination of the water hammer continuity equation and the water hammer motion equation, and the above-mentioned water hammer equation group, a water hammer simulation model with multi-parameter coupling of water head, flow, well inclination and density can be established. Then, by setting the initial conditions and boundary conditions of the model and adopting the model solving method, the curve of water hammer pressure changing with time can be fitted, and then the water hammer pressure in the fracturing process can be simulated more accurately, helping developers to use the water hammer pressure in the fracturing process to analyze the fracturing effect, thereby optimizing the fracturing parameters, obtaining better fracturing effects, and promoting the efficient development of unconventional oil and gas resources.

[0038] In some embodiments, a water hammer continuity equation is established to meet the following conditions at a certain position in the wellbore: the flow velocity changes with time, the head changes caused by the flow velocity change and the gravity component under the inclined wellbore, the flow velocity and head changes caused by the gravity component under the inclination of the wellbore and the change in fluid density, and a dynamic equilibrium state is achieved. That is, in the above step S2, when establishing the water hammer continuity equation, the head, flow rate, wellbore inclination and fluid density change in the wellbore are considered. The fluid density change is the compressibility of the fluid, and the water hammer continuity equation is established as follows:

[0039]

[0040] 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; t is the fracturing construction time, s; θ—the angle between the wellbore and the horizontal direction; K is the fluid bulk modulus, Pa; A is the wellbore cross-sectional area, m 2 ; E is the Young's modulus of the wellbore casing wall, Pa; e is the thickness of the wellbore casing wall, m; C Mis the intermediate calculation parameter.

[0041] In some embodiments, a water hammer motion equation is established to meet the following conditions at a certain position in the wellbore: the change in gravity component and flow rate causes a change in water head, the change in water head and density, and the change in pressure caused by wellbore friction, the change in fluid density caused by pressure change and water head change, and the change in flow rate caused by fluid density change and water head change, to achieve a dynamic equilibrium state. That is, in the above step S3, when establishing the water hammer motion equation, the water head, flow rate and fluid density are considered, and the water hammer motion equation is:

[0042]

[0043] Where: H is the water head in the wellbore, m; D is the inner diameter of the wellbore, m; ρ is the fluid density, kg / m 3 ; v is the fluid flow rate, m / s; t is the fracturing construction time, s; f is the friction coefficient along the wellbore, dimensionless.

[0044] In some embodiments, the above water hammer continuity equation and water hammer motion equation are combined into a water hammer equation group. When the water hammer equation group is established, the pressure in the wellbore is equivalent to the water head in the liquid elasticity equation to obtain the relationship between density and water head. The liquid elasticity equation is introduced, according to the relationship between liquid density and liquid elastic coefficient K:

[0045]

[0046] Where ρ is the fluid density, kg / m 3 ; p is the pressure in the wellbore, MPa; K is the elastic coefficient; the above formula can be transformed into:

[0047]

[0048] Where t is the fracturing construction time, s.

[0049] The pressure in the wellbore is equivalent to the water head, that is, the pressure p in the above formula (5) is rewritten as the water head H, and the relationship between density and pressure head can be obtained as follows:

[0050]

[0051] Where ρ is the fluid density, kg / m 3 ; t is the fracturing construction time, s; H is the water head in the wellbore, m; s is the wellbore length, m; Z is the reference datum plane, m; K is the elastic coefficient.

[0052] This application considers the influence of fluid compressibility, so that the water hammer continuity equation and water hammer motion equation contain three variable functions of water head, flow velocity and density, while the motion equation and continuity equation only have two equations, and the equation group is not closed. Therefore, the liquid elasticity equation (6) is introduced into the water hammer equation group to make the equation group closed. The complete water hammer equation group considering fluid compressibility is as follows:

[0053]

[0054] 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; f is the friction coefficient along the wellbore, dimensionless; t is the fracturing construction time, s; θ—the angle between the wellbore and the horizontal direction; K is the fluid bulk modulus, Pa; 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; C M is the intermediate calculation parameter.

[0055] The finite difference method is used to solve the above water hammer equations (i.e., Equation 7) to obtain the head, flow rate, and density distribution of the middle well section:

[0056]

[0057] 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, ; Δt is the time step, s; i is the wellbore grid node; j is the time node. In some embodiments, when setting the initial conditions, the fluid in the wellbore at the time of fracturing stopping 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 is stopped at the beginning of the fracturing process is taken as the initial condition. In the initial state, the wellhead head is known, and the head distribution at each location in the wellbore can be calculated based on the friction resistance along the wellbore. The calculation formulas for the flow rate and head distribution at the initial moment are as follows:

[0058]

[0059] Where: Q is the flow rate in the wellbore, m 3 / s;Q 0 is the initial flow rate in the wellbore, m 3 / s; H is the water head in the wellbore, m; H 0 is the initial water head at the wellhead, m.

[0060] The head loss ΔH in the wellbore section is:

[0061]

[0062] Where: ΔL is the length of the variable pipe section, m; Q is the flow rate in the wellbore, m 3 / s; f is the friction coefficient along the wellbore, dimensionless; D is the inner diameter of the wellbore, m; A is the cross-sectional area of ​​the wellbore, m 2 .

[0063] In some embodiments, the boundary conditions include the wellhead flow boundary and the fracture pressure boundary, which are set according to specific needs, such as setting a relationship between the wellhead and the bottom of the well. The wellhead flow boundary condition is set to be the displacement at the wellhead changing with time, and its specific mathematical expression can be expressed by the following formula:

[0064]

[0065] In some embodiments, the pressure boundary of the hydraulic fracture is established based on the relationship between the perforation friction and the fluid pressure in the hydraulic fracture, and the boundary conditions of the bottom hole hydraulic fracture can be obtained as follows:

[0066]

[0067] Where: P w is the bottom hole flowing pressure, Pa; is the average near-wellbore pressure, Pa; P f0 is the average near-wellbore pressure before shut-in, Pa; ρ is the fluid density, kg / m 3 ; Q 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; CD is the flow coefficient, dimensionless; b is the equation fitting coefficient; e is the wellbore casing wall thickness, m; t is the fracturing construction time, s.

[0068] In some embodiments, before setting the initial conditions and boundary conditions, the water hammer continuity equation and the water hammer motion equation are first added to form a partial differential equation, and the addition is linear addition. This processing method is adopted because: for the bottom hole boundary, since the water hammer equation group contains three unknown variables, namely, bottom hole flow, head and density, after adding the bottom hole constraint formula (15), the number of equations is greater than the number of unknowns. Therefore, the continuity equation and the motion equation are combined into a partial differential equation, and the water hammer motion equation is multiplied by v 0 Adding / g to the continuity equation yields:

[0069]

[0070] 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 gravity acceleration, m / s 2 ; ρ is the fluid density, kg / m 3 ; v is the fluid velocity, m / s; v 0 is the initial flow 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.

[0071] In some embodiments, before setting the initial conditions and boundary conditions, the distribution equation of fluid density is added to the water hammer simulation model. After the distribution equation of fluid density is introduced, a complete water hammer simulation model is established. The above equations (7), (15), (16) and (17) are combined and solved by finite difference equations to obtain the bottom hole boundary solution equation format as follows:

[0072]

[0073] Where: H is the water head in the wellbore, m; Z is the reference datum, m; Δt is the time step, s; Δs is the distance step, m; v is the fluid velocity, m / s; v 0 is the initial velocity, 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—the angle between the wellbore and the horizontal direction; 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; C M1 is the intermediate calculation parameter.

[0074] 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 2920m, the horizontal well section length is 2251m, and the fracturing fluid density is 1000kg / m 3 The inner diameter of the wellbore is 114.3 mm, the wall thickness is 15.2 mm, the Young's modulus of the pipe is 206 GPa, the Poisson's ratio of the pipe is 0.3, the viscosity of the fracturing fluid is 2 mPa·s, the perforation diameter is 10 mm, the number of perforations is 25, and the flow rate before the pump is stopped is 2.56 m 3 / min, the flow coefficient is 0.82, and the above parameters are brought into the applied simulation model, and the water hammer pressure is calculated as shown in the figure. According to the figure, the water hammer pressure shows periodic oscillation changes with time and gradually decays with the increase of time.

[0075] The second aspect of the present application provides a water hammer simulation device for 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 steps corresponding to the water hammer simulation method and device for fracturing as described above, and the processor implements the steps in the method embodiment of the present application when executing the computer program; or, the processor implements the functions of each module / unit in the embodiment of the water hammer simulation method and device / terminal device for fracturing when executing the computer program. It should be understood that the devices of each embodiment of the present application can be implemented based on the memory and the processor, each memory is used to store the computer program for executing the above method of the present application, and the processor executes the above computer program, so that the water hammer simulation method and device / terminal device for fracturing implements the methods of the above embodiments. In an optional embodiment, the device further includes a display module, which can be a display, a display screen or other electronic device capable of displaying graphics, and the display module is electrically connected to the processor, and the display module can intuitively display the water hammer pressure curve.

[0076] The above-mentioned device presents the above-mentioned simulation method in the form of a computer program, corresponds to the execution process of the computer program, and is stored in the memory. Through the execution of the computer program by the processor, the simulation structure can be quickly obtained and the results can be output, which simplifies the complex water hammer phenomenon in the fracturing process and improves efficiency. It can quickly simulate the evolving water hammer pressure curve and help developers use the water hammer pressure in the fracturing process to analyze the fracturing effect, thereby promoting the efficient development of unconventional oil and gas resources.

[0077] Regarding the specific implementation of this application, it should be noted that:

[0078] In the description of the present application, the terms "include", "comprise" or any other variant 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 "comprise a ..." do not exclude the presence of additional elements in the process, method, device or readable storage medium including the elements.

[0079] 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.

[0080] 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.

[0081] 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 water hammer simulation method for fracturing, characterized in that: include: determining the wellbore to be simulated; According to the water head, flow rate, wellbore inclination and fluid density change corresponding to the wellbore, a water hammer continuity equation is established; the water hammer continuity equation is as follows: 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; t is the fracturing construction time, s; θ—the angle between the wellbore and the horizontal direction; K is the fluid bulk modulus, Pa; A is the wellbore cross-sectional area, m 2 ; E is the Young's modulus of the wellbore casing wall, Pa; e is the thickness of the wellbore casing wall, m; C M is the intermediate calculation parameter; According to the changes in water head, flow rate, and fluid density corresponding to the wellbore, a water hammer motion equation is established; the water hammer motion equation is: Where: H is the water head in the wellbore, m; D is the inner diameter of the wellbore, m; ρ is the fluid density, kg / m 3 ; v is the fluid velocity, m / s; t is the fracturing construction time, s; f is the friction coefficient along the wellbore, dimensionless; According to the water hammer continuity equation and the water hammer motion equation, combined with the liquid elasticity equation, a water hammer equation group is established, and the water hammer equation group is solved to obtain the distribution equations of the water head, flow velocity and density in the middle well section; a relationship between the fluid pressure and density and flow rate of the bottom hole fracture is established, the water hammer continuity equation and the water hammer motion equation are linearly combined, and the water hammer equation group is solved in parallel to obtain a water hammer simulation model; The initial conditions and boundary conditions are set, and the curve of water hammer pressure changing with time is obtained by fitting.

2. The water hammer simulation method for fracturing according to claim 1, characterized in that: The water hammer continuity equation is established to meet the following conditions at a certain position in the wellbore: the flow velocity changes with time, the head changes caused by the flow velocity change and the gravity component under the inclined wellbore, and the flow velocity and head changes caused by the gravity component under the inclination of the wellbore and the change in fluid density, to achieve a dynamic equilibrium state.

3. The water hammer simulation method for fracturing according to claim 1, characterized in that: The water hammer motion equation is established to meet the following conditions at a certain position in the wellbore: the change in gravity component and flow velocity causes the change in water head, the change in water head and density, the change in pressure caused by wellbore friction, the change in fluid density caused by pressure change and water head change, the change in flow velocity caused by fluid density change and water head change, and a dynamic equilibrium state is achieved.

4. The water hammer simulation method for fracturing according to claim 1, characterized in that: When the combination establishes the water hammer equation group, in the liquid elasticity equation, the pressure in the wellbore is equivalent to the water head to obtain the relationship between the density and the water head.

5. The water hammer simulation method for fracturing according to claim 1, characterized in that: 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.

6. The water hammer simulation method for fracturing according to claim 1, characterized in that: The boundary conditions include a wellhead flow boundary and a fracture pressure boundary.

7. The water hammer simulation method for fracturing according to claim 6, characterized in that: The pressure boundary of the hydraulic fracture is established based on the relationship between the perforation friction and the fluid pressure in the hydraulic fracture.

8. The water hammer simulation method for fracturing according to claim 1, characterized in that: Before the fitting process, the water hammer continuity equation and the water hammer motion equation are added together to form a partial differential equation.

9. The water hammer simulation method for fracturing according to claim 1, characterized in that: Before setting the initial conditions and boundary conditions, the distribution equation of the fluid density is added to the water hammer simulation model.

10. A water hammer simulation device for 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 includes execution steps corresponding to the water hammer simulation method for fracturing as described in any one of claims 1-9.

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