A horizontal well segmented multi-cluster fracturing pump pressure simulation method

Abstract

The application discloses a horizontal well segmented multi-cluster fracturing pump-stopping pressure simulation method and relates to the technical field of oil and gas well completion engineering. The application is based on shale gas well conditions and fracturing construction design, obtains key parameters of fracturing pump-stopping pressure simulation, establishes an evolution mathematical model, divides a one-dimensional equal-length unit of a wellbore according to a shale gas fracturing well structure, adopts a characteristic line method to establish a fracturing pump-stopping pressure numerical calculation format, calculates initial fracturing well head and flow distribution according to wellhead head and flow before fracturing pump-stopping, and calculates fracturing well head and flow distribution of a wellhead and a well bottom according to the numerical calculation format and the initial fracturing well head and flow distribution, so as to obtain a wellhead pump-stopping pressure curve changing with time. The application can comprehensively consider the influence of wellbore friction resistance, perforation hole friction resistance and fracturing fracture liquid filtration loss on the fracturing pump-stopping pressure signal, and realizes accurate characterization of the fracturing pump-stopping pressure.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well completion engineering technology, and in particular to a method for simulating the pressure of pump shutdown in multi-cluster fracturing of horizontal wells. Background Technology

[0002] Shale gas reservoirs are tight, characterized by low porosity and extremely low permeability. Horizontal well-stage multi-cluster fracturing is typically employed to stimulate these reservoirs for economical development. Identifying post-fracturing fracture morphology and geometric parameters is crucial for optimizing fracturing techniques and efficiently guiding development. Theory and practice show that surface oscillation pressure characteristics observed after pump shutdown can reflect fracture geometry. However, shutdown pressure is influenced by wellbore structure, casing properties, perforation count, and fracture filtration loss, making accurate simulation and modeling of shutdown pressure difficult. This limits the use of shutdown pressure signals for diagnosing fracture characteristics, impacting fracturing operation decisions and efficient shale gas development.

[0003] There is limited research on the simulation of fracturing shutdown pressure in multi-cluster fracturing in shale gas horizontal wells, both domestically and internationally. Existing studies suggest that the fracturing shutdown pressure signal is mainly affected by wellbore friction, fracture pressure drop, and pre-shutdown pumping pressure and flow rate. This approach equates the fracture pressure drop and elastic reservoir effect to a series-parallel circuit of resistors and capacitors, employing circuit analysis to address the influence of fractures on the shutdown pressure signal and establishing the relationship between circuit parameters and fracture geometric parameters. However, this method does not consider crucial processes such as perforation friction and fluid loss within the fracture, and the physical meaning of parameters like resistance and capacitance in the circuit analysis remains unclear. Summary of the Invention

[0004] To overcome the defects and shortcomings of the existing technologies, this invention provides a simulation method for staged multi-cluster fracturing and pump shutdown in horizontal wells. The purpose of this invention is to overcome the limitations of existing technologies that do not consider important processes such as perforation friction and fluid loss within the fractures. The simulation method of this invention, based on shale gas well conditions and fracturing construction design, obtains key parameters for simulating fracturing and pump shutdown pressure, establishes a mathematical model for the evolution of fracturing and pump shutdown pressure in staged multi-cluster fracturing of shale gas horizontal wells, divides the wellbore into one-dimensional units according to the wellbore structure, and uses the characteristic line method to establish a numerical calculation format for fracturing and pump shutdown pressure, obtaining the wellhead pressure evolution. This invention can comprehensively consider the influence of wellbore friction, perforation friction, and fluid loss within the fractures on the fracturing and pump shutdown pressure signal, achieving accurate characterization of the fracturing and pump shutdown pressure.

[0005] To address the problems existing in the prior art, the present invention is achieved through the following technical solution.

[0006] This invention provides a simulation method for the shutdown pressure of multi-cluster fracturing in horizontal wells, which includes the following steps:

[0007] S1. Based on the well conditions and fracturing construction design of shale gas wells, obtain the key parameters for fracturing pump shutdown pressure simulation. The key parameters include well length, casing cross-sectional area, pipe wall thickness, well inclination angle, friction coefficient, pipe material Young's modulus, fluid density, fluid viscosity, bulk modulus, number of fracturing clusters, fracture size, number of perforations, and perforation diameter.

[0008] S2. Based on the key parameters obtained in step S1, establish a mathematical model for the evolution of pump shutdown pressure in a shale gas well with segmented multi-cluster fracturing. The mathematical model for the evolution of pump shutdown pressure in a shale gas well with segmented multi-cluster fracturing includes the continuity equation and motion equation of fluid flow in the wellbore, the initial wellbore pressure and flow rate conditions, the pump shutdown boundary conditions at the wellhead, and the perforation friction and fluid loss boundary conditions at the fracturing fracture.

[0009] S3. Based on the wellbore structure of shale gas fracturing wells and the simulation accuracy requirements, the wellbore is divided into one-dimensional equal-length units, and the characteristic line method is used to establish a numerical calculation format for fracturing pump shutdown pressure.

[0010] S4. Calculate the initial water head and flow rate distribution in the fracturing well based on the water head and flow rate at the wellhead before pump shutdown.

[0011] S5. Based on the numerical calculation format of the fracturing pump shutdown pressure established in step S3 and the initial water head and flow distribution in the fracturing well calculated in step S4, perform calculations of the water head and flow distribution in the fracturing well, the water head and flow at the wellhead, and the water head and flow at the bottom of the well, respectively, and obtain the curve of the wellhead pump shutdown pressure changing with time.

[0012] Furthermore, in step S2, the continuity equation for fluid flow within the wellbore is as follows:

[0013] In the formula, H is the water head in the well, Q is the flow rate in the well, θ is the inclination angle of the well, a is the pressure wave velocity in the well, g is the acceleration due to gravity, A is the cross-sectional area of ​​the casing, t represents the time step, and x represents the length of the well.

[0014] Furthermore, in step S2, the fluid motion equations within the wellbore are as follows:

[0015] In the formula, H is the water head in the well, Q is the flow rate in the well, g is the acceleration due to gravity, A is the cross-sectional area of ​​the casing, t represents the time step, x represents the length of the well, f is the friction coefficient of the well, and D is the diameter of the well.

[0016] Furthermore, in step S2, the initial wellbore pressure and flow conditions are expressed as follows:

[0017]

[0018] In the formula, Q0 is the fluid flow rate in the wellbore before pump shutdown, H0 is the head at the wellhead before pump shutdown, the superscript 0 indicates the initial time, the subscript 1 indicates the wellhead position, the subscript i indicates any position in the well, f is the friction coefficient along the wellbore, A is the cross-sectional area of ​​the casing, D is the diameter of the wellbore, Q is the flow rate in the wellbore, ΔL is the length of the wellbore section, and ΔH is the head loss of the wellbore section with length ΔL.

[0019] Furthermore, in step S2, the wellhead pump shutdown boundary condition is Q1 = 0.

[0020] Furthermore, in step S2, the boundary conditions for perforation friction and fluid loss at the fracture are as follows:

[0021] In the formula, P w P is the bottom hole pressure. f The pressure inside the fracture, N p Where d is the number of perforations, d is the diameter of the perforation, and C is the diameter of the perfor D Q is the flow coefficient, ρ is the fluid density; in For the flow rate into the fracture, N f h represents the number of pressure fractures. f For the height of the pressure fracture, l f For the half-length of the pressure fracture; w f Δw represents the crack aperture. f Q represents the change in crack aperture caused by pressure variations within the crack; leak This represents the fluid loss rate within the hydraulic fracture.

[0022] Furthermore, in step S3, the established numerical calculation format for the pressure stopping the pump is as follows:

[0023] In the formula, C P C M B P B M For the coefficients in the numerical calculation format; subscripts i-1, i, and i+1 represent sequentially connected wellbore segments; superscripts t and t+Δt represent two adjacent time steps; B is the characteristic impedance of the wellbore; R is the wellbore group coefficient; Δx is the length of the wellbore segment. This represents the head of the (i-1)th well section within time step t; Let represent the flow rate of the (i-1)th well section within time step t, a be the pressure wave velocity inside the well, A be the cross-sectional area of ​​the casing, g be the weight acceleration, and f be the friction coefficient along the well.

[0024] Furthermore, in step S5, the calculation of water head and flow rate distribution within the fracturing well is shown below.

[0025] In the formula, i represents the wellbore section, t+Δt represents the time step, and C P C M B P B M H represents the coefficients in the numerical calculation format. i t+Δt Q represents the head of the i-th well section in time step t+Δt. i t+Δt This represents the flow rate of the i-th well section within the time step t+Δt.

[0026] Furthermore, in step S5, the wellhead head is calculated. Wellhead flow calculation

[0027] Furthermore, in step S5, the bottom head and flow rate are calculated as follows:

[0028] In the formula, n represents the number of the last unit in the wellbore. This indicates the water head of the last unit in the well shaft. This indicates the pressure in the last unit of the wellbore. N represents the flow rate of the last unit in the wellbore. f h represents the number of pressure fractures. f For the height of the pressure fracture, l f For half the length of the pressure crack; Let t be the crack opening at time step t.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0030] This invention establishes a mathematical model for the evolution of fracturing shutdown pressure in shale gas wells based on key parameters such as wellbore length, casing cross-sectional area, pipe wall thickness, wellbore inclination angle, friction coefficient, pipe material Young's modulus, fluid density, fluid viscosity, bulk modulus, number of fracturing clusters, fracture size, number of perforations, and perforation diameter. It comprehensively considers the influence of wellbore friction, perforation orifice friction, and fluid loss within the fracturing fracture on the fracturing shutdown pressure signal, thereby achieving accurate characterization of fracturing shutdown pressure. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a fracturing well simulation model.

[0032] Figure 2 The figure shows the simulation results of the pump shutdown pressure at the wellhead of the fracturing well. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] As a preferred embodiment of the present invention, please refer to the appendix to the specification. Figure 1 and 2 As shown in the figure, this embodiment discloses a simulation method for the shutdown pressure of multi-cluster fracturing in horizontal wells. The simulation method includes the following steps:

[0036] S1. Based on the well conditions and fracturing construction design of shale gas wells, obtain the key parameters for fracturing pump shutdown pressure simulation. The key parameters include well length, casing cross-sectional area, pipe wall thickness, well inclination angle, friction coefficient, pipe material Young's modulus, fluid density, fluid viscosity, bulk modulus, number of fracturing clusters, fracture size, number of perforations, and perforation diameter.

[0037] S2. Based on the key parameters obtained in step S1, establish a mathematical model for the evolution of pump shutdown pressure in a shale gas well with multi-cluster fracturing (e.g., Figure 1 As shown), the mathematical model for the evolution of pump shutdown pressure in a shale gas well segmented multi-cluster fracturing includes the fluid flow continuity equation and motion equation within the wellbore, initial wellbore pressure and flow rate conditions, wellhead pump shutdown boundary conditions, and perforation friction and fluid loss boundary conditions at the fracturing fracture.

[0038] S3. Based on the wellbore structure of shale gas fracturing wells and the simulation accuracy requirements, the wellbore is divided into one-dimensional equal-length units, and the characteristic line method is used to establish a numerical calculation format for fracturing pump shutdown pressure.

[0039] S4. Calculate the initial water head and flow rate distribution in the fracturing well based on the water head and flow rate at the wellhead before pump shutdown.

[0040] S5. Based on the numerical calculation format for fracturing pump shutdown pressure established in step S3 and the initial water head and flow distribution in the fracturing well calculated in step S4, perform calculations for the water head and flow distribution in the fracturing well, the water head and flow at the wellhead, and the water head and flow at the bottom of the well. Obtain the curve of the wellhead pump shutdown pressure changing over time (e.g., ...). Figure 2 (As shown).

[0041] Example 2

[0042] As another preferred embodiment of the present invention, this embodiment discloses a simulation method for the pressure of pump shutdown in a horizontal well segmented multi-cluster fracturing operation. The simulation method includes the following steps:

[0043] (1) Based on the well conditions and fracturing construction design of shale gas wells, obtain the key parameters for fracturing pump shutdown pressure simulation, including well length, casing cross-sectional area, wall thickness, inclination angle, friction coefficient, Young's modulus of pipe material, fluid density, fluid viscosity, bulk modulus, number of fracturing clusters, fracture size, number of perforations and perforation diameter, etc.

[0044] (2) Establish a mathematical model for the evolution of pump shutdown pressure in a multi-cluster fracturing operation of a shale gas horizontal well, including the continuity equation and motion equation of fluid flow in the wellbore, the initial wellbore pressure and flow rate conditions, the pump shutdown boundary conditions at the wellhead, and the perforation friction and fluid loss boundary conditions at the fracturing fracture.

[0045] Continuity equation for fluid flow within the wellbore:

[0046]

[0047] Equations of fluid motion within the wellbore:

[0048]

[0049] Initial wellbore pressure and flow conditions:

[0050]

[0051] Wellhead pump shutdown boundary conditions:

[0052] Q1 = 0 (4)

[0053] Perforation friction and fluid loss boundary conditions at the fracture:

[0054]

[0055] Where: H is the water head in the wellbore; Q is the flow rate in the wellbore; θ is the wellbore inclination angle; a is the pressure wave velocity in the wellbore; g is the gravitational acceleration; A is the casing cross-sectional area; f is the friction coefficient along the wellbore; D is the wellbore diameter; superscript 0 indicates the initial time; subscript 1 indicates the wellhead position; subscript i indicates any position in the well; Q0 is the fluid flow rate in the wellbore before pump shutdown; H0 is the water head at the wellhead before pump shutdown; P w P is the bottom hole pressure; f The pressure inside the fracture; N p d is the number of perforations; d is the diameter of the perforation; C D ρ is the flow coefficient; Q is the fluid density; in N is the flow rate into the crack; f h represents the number of pressure cracks. f The height of the pressure fracture; l f For the half-length of the pressure fracture; w f Δw represents the crack aperture. f Q represents the change in crack aperture caused by pressure variations within the crack;leak ΔL represents the fluid loss rate within the fracture, ΔL is the length of the wellbore section, and ΔH is the head loss of the wellbore section with length ΔL.

[0056] (3) Based on the wellbore structure of shale gas fracturing wells and the simulation accuracy requirements, the wellbore is divided into one-dimensional equal-length units. The characteristic line method is used to establish the numerical calculation format of fracturing pump shutdown pressure, thus forming a simulation method for fracturing pump shutdown pressure.

[0057] Calculation of head and flow distribution in fractured wells (excluding wellhead and bottom):

[0058]

[0059] In the formula: C P C M B P B M For the coefficients in the numerical calculation format; subscripts i-1, i and i+1 represent sequentially connected wellbore segments; superscripts t and t+Δt represent two adjacent time steps; B is the characteristic impedance of the wellbore; R is the wellbore group coefficient; Δx is the length of the wellbore segment; This represents the head of the i-th well section in time step t+Δt. denoted by , where represents the flow rate of the i-th well section within time step t+Δt; a is the pressure wave velocity within the wellbore; A is the cross-sectional area of ​​the casing; g is the weight acceleration; and f is the friction coefficient along the wellbore.

[0060] Wellhead head and flow rate calculation:

[0061]

[0062]

[0063] Well head and flow rate calculation:

[0064]

[0065]

[0066]

[0067] In the formula, n represents the number of the last unit in the wellbore. This indicates the water head of the last unit in the well shaft. This indicates the pressure in the last unit of the wellbore. N represents the flow rate of the last unit in the wellbore. f h represents the number of pressure fractures. f For the height of the pressure fracture, l f For half the length of the pressure crack; Let t be the crack opening at time step t;

[0068] The combined formulas (6)-(9) can be used to calculate the pressure and flow distribution after the pump is shut down in a fracturing well.

[0069] Example 3

[0070] As another preferred embodiment of the present invention, this embodiment discloses a simulation method for the pressure of pump shutdown in a horizontal well segmented multi-cluster fracturing operation. The simulation method includes the following steps:

[0071] S1. Based on the well conditions and fracturing construction design of shale gas wells, obtain the key parameters for fracturing shutdown pressure simulation. The key parameters include well length, casing cross-sectional area, pipe wall thickness, well inclination angle, friction coefficient, pipe material Young's modulus, fluid density, fluid viscosity, bulk modulus, number of fracturing clusters, fracture size, number of perforations, and perforation diameter.

[0072] S2. Based on the key parameters obtained in step S1, establish a mathematical model for the evolution of pump shutdown pressure in a shale gas well with segmented multi-cluster fracturing. The mathematical model for the evolution of pump shutdown pressure in a shale gas well with segmented multi-cluster fracturing includes the continuity equation and motion equation of fluid flow in the wellbore, the initial wellbore pressure and flow rate conditions, the pump shutdown boundary conditions at the wellhead, and the perforation friction and fluid loss boundary conditions at the fracturing fracture.

[0073] The continuity equation for fluid flow within the wellbore is:

[0074] The equation of motion of fluid inside the wellbore is

[0075] The initial wellbore pressure and flow conditions are expressed as follows:

[0076] The wellhead pump shutdown boundary condition is Q1 = 0;

[0077] The boundary conditions for perforation friction and fluid loss at the fracture are as follows:

[0078]

[0079] In the above formula, H is the water head in the wellbore; Q is the flow rate in the wellbore; θ is the wellbore inclination angle; a is the pressure wave velocity in the wellbore; g is the gravitational acceleration; A is the casing cross-sectional area; f is the friction coefficient along the wellbore; D is the wellbore diameter; superscript 0 indicates the initial time; subscript 1 indicates the wellhead position; subscript i indicates any position in the well; Q0 is the fluid flow rate in the wellbore before pump shutdown; H0 is the water head at the wellhead before pump shutdown; P w P is the bottom hole pressure; f The pressure inside the fracture; N p d is the number of perforations; d is the diameter of the perforation; C D ρ is the flow coefficient; Q is the fluid density; in N is the flow rate into the crack;f h represents the number of pressure cracks. f The height of the pressure fracture; l f For the half-length of the pressure fracture; w f Δw represents the crack aperture. f Q represents the change in crack aperture caused by pressure variations within the crack; leak ΔL represents the fluid loss rate within the fracture, ΔL is the length of the wellbore section, and ΔH is the head loss of the wellbore section with length ΔL.

[0080] S3. Based on the wellbore structure of shale gas fracturing wells and the simulation accuracy requirements, the wellbore is divided into one-dimensional equal-length units, and the characteristic line method is used to establish a numerical calculation format for fracturing pump shutdown pressure.

[0081] In the formula, C P C M B P B M For the coefficients in the numerical calculation format; subscripts i-1, i, and i+1 represent sequentially connected wellbore segments; superscripts t and t+Δt represent two adjacent time steps; B is the characteristic impedance of the wellbore; R is the wellbore group coefficient; Δx is the length of the wellbore segment. This represents the head of the (i-1)th well section within time step t; Let represent the flow rate of the (i-1)th well section within time step t, a be the pressure wave velocity inside the well, A be the cross-sectional area of ​​the casing, g be the weight acceleration, and f be the friction coefficient along the well.

[0082] S4. Based on the head and flow rate at the wellhead before pump shutdown and the initial wellbore pressure and flow rate conditions formula in step S2, calculate the initial head and flow rate distribution in the fractured well.

[0083] S5. Based on the numerical calculation format of fracturing pump shutdown pressure established in step S3 and the initial water head and flow distribution in the fracturing well calculated in step S4, perform calculations of water head and flow distribution in the fracturing well, water head and flow at the wellhead, and water head and flow at the bottom of the well, and obtain the curve of wellhead pump shutdown pressure changing with time.

[0084] Among them, the calculation of water head and flow distribution in the fractured well. In the formula, i represents the wellbore section, t+Δt represents the time step, and C P C M B P B M For coefficients in numerical calculation formats, This represents the head of the i-th well section in time step t+Δt. This represents the flow rate of the i-th well section within time step t+Δt;

[0085] Wellhead head calculation Q1t =0; Wellhead flow rate calculation

[0086] The calculation of the bottom head and flow rate is as follows:

[0087] In the formula, n represents the number of the last unit in the wellbore. This indicates the water head of the last unit in the well shaft. This indicates the pressure in the last unit of the wellbore. N represents the flow rate of the last unit in the wellbore. f h represents the number of pressure fractures. f For the height of the pressure fracture, l f For half the length of the pressure crack; Let t be the crack opening at time step t.

[0088] Example 4

[0089] As another preferred embodiment of the present invention, please refer to the appendix to the specification. Figure 1 and attached Figure 2 As shown in the figure, this embodiment discloses a simulation method for the shutdown pressure of multi-cluster fracturing in horizontal wells. The simulation method includes the following steps:

[0090] (1) Based on the well conditions and fracturing construction design of shale gas wells, key parameters for fracturing shutdown pressure simulation were obtained, and a mathematical model for the evolution of fracturing shutdown pressure in a segmented multi-cluster shale gas well was established (e.g., Figure 1 (As shown); the fractured well is divided into a vertical section and a horizontal section. The length of the vertical section is 3180m, and the length of the horizontal section is 2120m. The wellbore inner diameter is 118.6mm, the pipe wall thickness is 10.54mm, the Young's modulus of the pipe material is 206GPa, the Poisson's ratio of the pipe material is 0.3, the pipe wall roughness is 0.015mm, and the fracturing fluid density is 1000kg / m³. 3 The fracturing fluid viscosity was 2 mPa·s, the perforation diameter was 8.128 mm, the fracture half-length was 150 m, the fracture height was 25 m, the number of fractures was 5, and the number of perforations was 20. The well unit length was 100 m, and the fracturing well was divided into 53 well units.

[0091] (2) Based on the head and flow rate at the wellhead before pump shutdown, calculate the initial head and flow rate distribution within the fracturing well; the head at the wellhead before pump shutdown was 5714.3 m, and the flow rate was 2.2 m³ / s. 3 / min. Using the initial wellbore pressure and flow rate condition formulas, the initial water head and flow rate distribution in the fractured well are calculated.

[0092] (3) Based on the mathematical model of the evolution of pump shutdown pressure in a segmented multi-cluster fracturing shale gas well and the initial conditions, simulation calculations of the pump shutdown pressure were carried out to obtain the wellhead pressure evolution. Based on the mathematical model of the evolution of pump shutdown pressure in a segmented multi-cluster fracturing shale gas well established in step (1) and the initial head and flow distribution in step (2), calculations were performed on the head and flow distribution within the fracturing well, the head and flow at the wellhead, and the head and flow at the bottom of the well. The calculated curves of the wellhead pump shutdown pressure changing with time are shown below. Figure 2 As shown.

Claims

1. A method for simulating the pressure at which pumps stop during multi-cluster fracturing in horizontal wells, characterized in that, The simulation method includes the following steps: S1. Based on the well conditions and fracturing construction design of shale gas wells, obtain the key parameters for fracturing pump shutdown pressure simulation. The key parameters include well length, casing cross-sectional area, pipe wall thickness, well inclination angle, friction coefficient, pipe material Young's modulus, fluid density, fluid viscosity, bulk modulus, number of fracturing clusters, fracture size, number of perforations, and perforation diameter. S2. Based on the key parameters obtained in step S1, establish a mathematical model for the evolution of pump shutdown pressure in a shale gas well with segmented multi-cluster fracturing. The mathematical model for the evolution of pump shutdown pressure in a shale gas well with segmented multi-cluster fracturing includes the continuity equation and motion equation of fluid flow in the wellbore, the initial wellbore pressure and flow rate conditions, the pump shutdown boundary conditions at the wellhead, and the perforation friction and fluid loss boundary conditions at the fracturing fracture. S3. Based on the wellbore structure of shale gas fracturing wells and the simulation accuracy requirements, the wellbore is divided into one-dimensional equal-length units, and the characteristic line method is used to establish a numerical calculation format for fracturing pump shutdown pressure. S4. Calculate the initial water head and flow rate distribution in the fracturing well based on the water head and flow rate at the wellhead before the pump is shut down. S5. Based on the numerical calculation format of the fracturing pump shutdown pressure established in step S3 and the initial water head and flow distribution in the fracturing well calculated in step S4, perform calculations of the water head and flow distribution in the fracturing well, the water head and flow at the wellhead, and the water head and flow at the bottom of the well, respectively, and obtain the curve of the wellhead pump shutdown pressure changing with time.

2. The method for simulating the pressure of pump shutdown in a multi-cluster fracturing operation of a horizontal well as described in claim 1, characterized in that: In step S2, the continuity equation for fluid flow within the wellbore is: In the formula, H is the water head inside the well, and Q is the flow rate inside the well. The wellbore inclination angle, Let g be the pressure wave velocity inside the wellbore, g be the acceleration due to gravity, A be the cross-sectional area of ​​the casing, t be the time step, and x be the length of the wellbore.

3. A method for simulating the pressure of pump shutdown in multi-cluster fracturing of a horizontal well as described in claim 1 or 2, characterized in that: In step S2, the fluid motion equations within the wellbore are as follows: In the formula, H is the water head in the well, Q is the flow rate in the well, g is the acceleration due to gravity, A is the cross-sectional area of ​​the casing, t represents the time step, x represents the length of the well, f is the friction coefficient of the well, and D is the diameter of the well.

4. A method for simulating the pressure of pump shutdown in multi-cluster fracturing of a horizontal well as described in claim 1 or 2, characterized in that: In step S2, the initial wellbore pressure and flow conditions are expressed as follows: ； ； In the formula, Q0 is the fluid flow rate in the wellbore before pump shutdown, H0 is the head at the wellhead before pump shutdown, the superscript 0 indicates the initial time, the subscript 1 indicates the wellhead position, the subscript i indicates any position in the well, f is the friction coefficient along the wellbore, A is the cross-sectional area of ​​the casing, D is the diameter of the wellbore, Q is the flow rate in the wellbore, ΔL is the length of the wellbore section, and ΔH is the head loss of the wellbore section with length ΔL.

5. The method for simulating the pressure of pump shutdown in multi-cluster fracturing of a horizontal well as described in claim 1, characterized in that: In step S2, the wellhead pump shutdown boundary condition is: .

6. The method for simulating the pressure of pump shutdown in a multi-cluster fracturing operation of a horizontal well as described in claim 1, characterized in that: In step S2, the boundary conditions for perforation friction and fluid loss at the fracture are as follows: ； ； In the formula, P w P is the bottom hole pressure. f The pressure inside the fracture, N p Where d is the number of perforations, d is the diameter of the perforation, and C is the diameter of the perfor D For flow coefficient, Q is the fluid density; in For the flow rate into the crack, N f h represents the number of pressure fractures. f For the height of the pressure fracture, l f For the half-length of the pressure fracture; w f Δw represents the crack aperture. f Q represents the change in crack aperture caused by pressure variations within the crack; leak This represents the fluid loss rate within the hydraulic fracture.

7. The method for simulating the pressure of pump shutdown in a multi-cluster fracturing operation of a horizontal well as described in claim 1, characterized in that: In step S3, the established format for calculating the pressure at the pump shutdown point is as follows: ； ； ； ； ； ； In the formula, C P C M B P B M These are the coefficients in the numerical calculation format; the subscripts i-1, i, and i+1 represent sequentially connected wellbore segments; the superscripts t and t+Δt represent two adjacent time steps; B is the characteristic impedance of the wellbore; R is the wellbore group coefficient; Δx is the length of the wellbore segment. This represents the head of the (i-1)th well section within time step t; Let represent the flow rate of the (i-1)th well section in time step t, a be the pressure wave velocity in the well, A be the cross-sectional area of ​​the casing, g be the acceleration due to gravity, and f be the friction coefficient along the well.

8. The method for simulating the pressure of pump shutdown in a multi-cluster fracturing operation of a horizontal well as described in claim 7, characterized in that: In step S5, the calculation of water head and flow rate distribution in the fracturing well is shown below. ； ； In the formula, i represents the wellbore section, t+Δt represents the time step, and C P C M B P B M For coefficients in numerical calculation formats, This represents the head of the i-th well section in time step t+Δt. This represents the flow rate of the i-th well section within the time step t+Δt.

9. The method for simulating the pressure of pump shutdown in multi-cluster fracturing of a horizontal well as described in claim 8, characterized in that: In step S5, the wellhead head is calculated. Wellhead flow rate calculation .

10. The method for simulating the pressure of pump shutdown in a multi-cluster fracturing operation of a horizontal well as described in claim 8, characterized in that: In step S5, the bottom head and flow rate are calculated as follows: ； ； ； In the formula, n represents the number of the last unit in the wellbore. This indicates the water head of the last unit in the well shaft. This indicates the pressure in the last unit of the wellbore. N represents the flow rate of the last unit in the wellbore. f h represents the number of pressure fractures. f For the height of the pressure fracture, l f For half the length of the pressure crack; Let t be the crack opening within time step t.

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