Horizontal well fracturing productivity numerical simulation method and system considering pressure fluctuation

Abstract

The invention provides a horizontal well fracturing productivity numerical simulation method and system considering pressure fluctuation, and the method comprises the steps: firstly dividing an oil reservoir matrix of a whole physical property and a pressure field attribute into a limited number of oil reservoir units according to the geological feature data of a target oil reservoir in combination with a structured grid technology; determining each target spot of the fluctuating horizontal well, setting a well track based on the oil reservoir unit through an interpolation method, and dividing along the well track to obtain a complete flow unit correspondingly presented by the oil reservoir unit and the shaft unit; then determining hydraulic fracture parameters along a wellbore track, coupling the hydraulic fracture parameters with the flow units, constructing an oil-gas flow numerical value operation model of a fracture coupling oil reservoir matrix and a wellbore in a set time period, performing discrete operation to obtain oil-gas flow velocity and content of each flow unit, and analyzing and simulating productivity. By adopting the scheme, operation and analysis are carried out based on the coupling unit division and the mixed numerical simulation program of the discrete fracture and the discrete well, and the pressure distribution and fluctuation of the fluctuating horizontal well can be effectively reflected.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development and optimization, and in particular to a method and system for numerically simulating the production capacity of horizontal well fracturing considering pressure fluctuations. Background Art

[0002] Horizontal well fracturing is one of the important means for the oil and gas industry to efficiently develop oil and gas resources. It is widely used in the exploitation of unconventional resources such as tight oil and gas, shale oil and gas, and coalbed methane. The technology for calculating reservoir productivity based on horizontal well fracturing can analyze the relationship between reservoir pressure and saturation over time and space, and derive the relationship between the target well productivity and time. In actual operations, it is a key guide for guiding the design and optimization of horizontal well drilling, completion and oil production processes in oil fields, and an important reference for maximizing oil and gas production productivity and ensuring economic efficiency.

[0003] The calculation method of horizontal well fracturing capacity mainly considers the capacity of the reservoir and the wellbore. The reservoir part mainly considers the flow law of fluid in and between media such as pores and fractures, and couples the calculation of the relationship between the rock reservoir and the physical properties of the fluid and the environmental variables, and then obtains the fluid flow field within the entire reservoir. The wellbore part mainly considers the pipe flow law after the reservoir fluid converges in the wellbore, and calculates the relationship between the well pressure and the flow rate of the fluid flowing into the reservoir by calculating the pressure drop along the way and the local pressure drop. In summary, in order to achieve accurate horizontal well fracturing capacity calculation, it is necessary to couple the reservoir and the wellbore with high quality.

[0004] At present, in the research on horizontal well fracturing capacity calculation, a relatively systematic simulation method has been formed for the reservoir part, such as the numerical simulation method represented by the finite element method and the discrete fracture method. By dividing the reservoir into a finite number of units and coupling the fracture flow with the matrix flow, the flow control equation is solved by numerical methods; for the horizontal wellbore part, some researchers construct theories and models about the pressure distribution and the cause of pressure drop in the pipeline, analyze the data of different gas-liquid distribution and flow states in the pipeline and establish models, and then study the state of the wellbore fluid and verify it through experimental environment.

[0005] However, in the numerical simulation calculation of reservoir productivity, the horizontal well is generally assumed to be completely horizontal, and the internal pressure loss is ignored, that is, the wellbore is regarded as the source term. In fact, the wellbore of a horizontal well is not literally completely "horizontal". Due to the influence of factors such as geology and drilling and completion, the wellbore trajectory of the horizontal well will have certain ups and downs, resulting in fluid potential energy-pressure conversion. At the same time, there may be complex multiphase flow conditions of liquid and gas in the horizontal well, resulting in fluid kinetic energy-pressure conversion. Therefore, the existing reservoir-wellbore coupling method is essentially a simplified theoretical calculation model. Although it reduces the difficulty of the algorithm and can analyze different productivity data in different situations to a certain extent, it also introduces significant errors in the calculation of horizontal well fracturing productivity. Therefore, there is an urgent need for a numerical simulation method for horizontal well fracturing productivity that takes into account the pressure fluctuations in the horizontal well.

[0006] The information disclosed in the background technology section of the present invention is only intended to deepen the understanding of the general background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0007] To solve the above problems, the present invention provides a method and system for numerical simulation of horizontal well fracturing productivity taking into account pressure fluctuations. In one embodiment, the method includes:

[0008] Reservoir unit model generation step: according to the geological characteristic data of the target reservoir, the entire reservoir matrix is ​​divided in combination with the structured grid technology to obtain a reservoir unit model with a limited number of reservoir units, and the initial physical properties and pressure field data of each reservoir unit are set;

[0009] The flow unit formation step is to determine the target point of the undulating horizontal well, set the wellbore trajectory in the reservoir unit model by interpolation, divide along the wellbore trajectory to obtain a finite number of wellbore units corresponding to the reservoir unit and set the wellbore physical properties to form a complete flow unit;

[0010] Fracture coupling step, determining shape parameters of each hydraulic fracture along the wellbore trajectory, coupling it with the flow unit and determining the physical properties of each fracture;

[0011] Discrete calculation steps: Based on the reservoir pressure field data and the physical property data of the reservoir, wellbore and fractures, a numerical calculation model of oil and gas flow in the fracture-coupled reservoir matrix and wellbore within a set time period is constructed, and discrete calculations are performed on different flow units to obtain the oil and gas flow velocity and content data of a single flow unit, and then the corresponding production capacity is calculated.

[0012] Preferably, in one embodiment, in the reservoir matrix division step, the initial physical properties of the reservoir include: the porosity, permeability, initial saturation of phases and rock volume compressibility of the matrix; the density, viscosity, solution gas-oil ratio, oil-gas ratio, relative permeability and volume coefficient of each phase of the reservoir fluid.

[0013] Further, in one embodiment, reservoir pressure field data is determined according to rock compressibility based on the following logic:

[0014]

[0015] Among them, c r is the rock compression coefficient, φ m is the reservoir matrix porosity, and p is the reservoir pressure.

[0016] On the other hand, in one embodiment, in the flow unit forming step, after determining the heel endpoint coordinates and toe endpoint coordinates of the horizontal well, several points on the measured horizontal well trajectory are selected between the two as target points.

[0017] In an optional embodiment, in the reservoir matrix division step, the reservoir is divided into a number of cubic reservoir units with equal length, width and height, which serve as geometric units of the reservoir matrix and storage units of reservoir physical properties.

[0018] Furthermore, in one embodiment, the fracture coupling step includes determining the hydraulic fracture initiation point, boundary and spacing along the wellbore trajectory, coupling with the matrix unit through a discrete fracture method, and determining the fracture properties.

[0019] As a further improvement of the present invention, in one embodiment, the discrete operation step further includes reducing the dimension of the hydraulic fractures using an embedded discrete fracture method to implicitly express the fractures in the reservoir matrix grid.

[0020] Optionally, in one embodiment, a numerical calculation model of oil and gas flow is constructed as shown in the following formula:

[0021]

[0022]

[0023]

[0024] The oil, gas and water saturations in each flow unit satisfy: S g +S o +S w =1

[0025] Wherein, subscripts o, g and w correspond to oil phase, gas phase and water phase respectively, v represents the fluid velocity, q is the source term calculated by embedded discrete fracture method, V is the unit cell volume, S represents the initial saturation of phase state, ρ α Indicates the density of each phase in the fluid, α represents the phase state, α=o,g,s, represents the Darcy velocity of the fluid, K represents the absolute permeability, k rα represents the relative permeability of the fluid, μ α Indicates viscosity.

[0026] Furthermore, in an optional embodiment, the MATLAB Reservoir Simulation Toolbox (MRST) sequential implicit coupling framework is used to discretize the relevant equations of the coupled oil and gas flow numerical calculation model to obtain a nonlinear calculation matrix, and the nonlinear calculation matrix is ​​solved using the Newton-Raphson method to obtain converged pressure and saturation solutions, and then the pressure and saturation solutions are combined with the changing relationship between the time and space parameters to analyze the production capacity status within the set period of different flow units.

[0027] Based on other aspects of the method described in any one or more of the above embodiments, the present invention also provides a horizontal well fracturing productivity numerical simulation system taking into account pressure fluctuations, which executes the method described in any one or more of the above embodiments.

[0028] Compared with the closest prior art, the present invention also has the following beneficial effects:

[0029] The present invention provides a method and system for numerically simulating the production capacity of horizontal well fracturing considering pressure fluctuations. The method first divides the reservoir matrix of the entire physical property and pressure field attribute into a finite number of reservoir units according to the geological characteristic data of the target reservoir in combination with the structured grid technology; then determines each target point of the fluctuating horizontal well, sets the wellbore trajectory based on the reservoir unit by the interpolation method, and divides along the wellbore trajectory to obtain a complete flow unit corresponding to the reservoir unit and the wellbore unit; then determines each hydraulic fracture parameter along the wellbore trajectory and couples it with the flow unit; based on the division of the structured grid reservoir matrix, the present invention further couples and sets the wellbore and fractures of different sections of the fluctuating horizontal well, divides the comprehensive fluid unit, and lays a physical model foundation for the subsequent production capacity analysis of multi-stage fracturing horizontal wells under the influence of the fluctuating horizontal wells;

[0030] Furthermore, a numerical calculation model of oil and gas flow in fracture-coupled reservoir matrix and wellbore within a set time period is constructed, and discrete calculations are performed to obtain the oil and gas flow velocity and content of each flow unit and analyze the simulated production capacity. At the same time, considering the cross-scale flow of oil-gas-water multiphase flow in the reservoir matrix, fractures and wellbore, calculations and analysis are performed based on a hybrid numerical simulation program of discrete fractures and discrete wells to solve the temporal and spatial variation characteristics of reservoir pressure and saturation in different flow units, which can effectively reflect the pressure distribution and fluctuation of undulating horizontal wells.

[0031] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 It is a flow chart of a method for numerically simulating the production capacity of horizontal well fracturing considering pressure fluctuations provided by one embodiment of the present invention;

[0034] Figure 2 It is a detailed operation diagram of a method for numerically simulating the production capacity of horizontal well fracturing considering pressure fluctuations provided in an embodiment of the present invention;

[0035] Figure 3 This is an example diagram of the division result of the three-dimensional structured grid of the reservoir matrix of the numerical simulation method of horizontal well fracturing productivity considering pressure fluctuation provided by the embodiment of the present invention;

[0036] Figure 4 It is a schematic diagram of a front view perspective of a concave undulating horizontal well in an oil reservoir grid provided by another embodiment of the present invention;

[0037] Figure 5 This is an example diagram of determining the position of a single hydraulic fracture in a method for numerically simulating the productivity of horizontal well fracturing considering pressure fluctuations provided in an embodiment of the present invention;

[0038] Figure 6 This is an example diagram of the distribution positions of multiple hydraulic fractures in a numerical simulation method for horizontal well fracturing productivity taking into account pressure fluctuations provided in an embodiment of the present invention;

[0039] Figure 7 It is a comparison diagram of bottom hole pressures of various well nodes calculated using the model of the present invention and a conventional well model provided by an embodiment of the present invention;

[0040] Figure 8 This is an example diagram of the relationship between oil production and time calculated using the model of the present invention and a conventional well model provided in an embodiment of the present invention;

[0041] Fig. 9 This is an example diagram of the distribution positions of multiple hydraulic fractures in a numerical simulation method for horizontal well fracturing productivity taking into account pressure fluctuations provided in an embodiment of the present invention;

[0042] Fig.10 It is a structural schematic diagram of a horizontal well fracturing productivity numerical simulation system considering pressure fluctuations provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following will describe the implementation methods of the present invention in detail in conjunction with the accompanying drawings and embodiments, so that the implementers of the present invention can fully understand how the present invention applies technical means to solve technical problems and achieve the implementation process of technical effects and implement the present invention specifically according to the above implementation process. It should be noted that as long as there is no conflict, the various embodiments and various features of the embodiments in the present invention can be combined with each other, and the technical solutions formed are all within the protection scope of the present invention.

[0044] Although the flowcharts describe the operations as sequential processes, many of the operations may be performed in parallel, concurrently, or simultaneously. The order of the operations may be rearranged. A process may be terminated when its operations are completed, but may also have additional steps not included in the accompanying drawings. A process may correspond to a method, function, procedure, subroutine, subprogram, etc.

[0045] Computer devices include user devices and network devices. Among them, user devices or clients include but are not limited to computers, smart phones, PDAs, etc.; network devices include but are not limited to a single network server, a server group consisting of multiple network servers, or a cloud composed of a large number of computers or network servers based on cloud computing. Computer devices can be operated alone to implement the present invention, or they can be connected to the network and implement the present invention through interactive operations with other computer devices in the network. The network where the computer device is located includes but is not limited to the Internet, wide area network, metropolitan area network, local area network, VPN network, etc.

[0046] The terms "first", "second", etc. may be used herein to describe various units, but these units should not be limited by these terms, and these terms are used only to distinguish one unit from another unit. The term "and / or" used herein includes any and all combinations of one or more of the listed associated items. When a unit is referred to as being "connected" or "coupled" to another unit, it can be directly connected or coupled to the other unit, or there can be intermediate units.

[0047] The terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "one", "one" and "item" used herein are also intended to include plural numbers. It should also be understood that the terms "include" and / or "comprise" used herein specify the existence of stated features, integers, steps, operations, units and / or components, without excluding the existence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0048] Horizontal well fracturing is a conventional means for the oil and gas industry to efficiently develop oil and gas resources. It is widely used in the exploitation of unconventional resources such as tight oil and gas, shale oil and gas, and coalbed methane. The reservoir capacity calculation based on horizontal well fracturing can analyze the relationship between reservoir pressure and saturation over time and space, and derive the relationship between well capacity and time. Therefore, it is a key guide for guiding oil fields to carry out horizontal well drilling and completion and oil production process design and optimization, and is an important reference for maximizing oil and gas production capacity.

[0049] The calculation method of horizontal well fracturing capacity mainly includes two parts: reservoir and wellbore. The reservoir part mainly considers the flow law of fluid in and between media such as pores and fractures, and couples the calculation of the relationship between the physical properties of rocks and fluids and environmental variables, and then obtains the fluid flow field within the entire reservoir. The wellbore part mainly considers the pipe flow law after the reservoir fluid converges in the wellbore, and calculates the relationship between the well pressure and the flow rate of the fluid flowing into the reservoir by calculating the pressure drop along the way and the local pressure drop. In summary, the reservoir and wellbore parts need to be well coupled to achieve accurate horizontal well fracturing capacity calculation.

[0050] Among the current mainstream horizontal well fracturing productivity calculation methods, a relatively systematic simulation method has been formed for the reservoir part, especially the numerical simulation methods represented by the finite element method and the discrete fracture method. It divides the reservoir into a finite number of units, couples the fracture flow with the matrix flow, and solves the flow control equation through numerical methods. For the horizontal wellbore part, scholars have constructed relatively complete theories and models on the pressure distribution and pressure drop causes in the pipeline. Models have been established for different gas-liquid distributions and flow states in the pipeline, and have been verified experimentally. However, in the numerical simulation calculation of reservoir productivity, the horizontal well is generally assumed to be completely horizontal, and the internal pressure loss is ignored, that is, the wellbore is regarded as a source term.

[0051] In fact, the wellbore of a horizontal well is not literally "horizontal". Due to factors such as geology and drilling and completion, the wellbore trajectory of a horizontal well will have certain ups and downs, resulting in fluid potential energy-pressure conversion. At the same time, there may be complex multiphase flow conditions of liquid and gas in the horizontal well, resulting in fluid kinetic energy-pressure conversion. Therefore, although the simplified reservoir-wellbore coupling method effectively reduces the difficulty of the algorithm, it also introduces significant errors in the calculation of horizontal well fracturing capacity. Therefore, a numerical simulation method for horizontal well fracturing capacity that takes into account the pressure fluctuations in the horizontal well is urgently needed.

[0052] In order to solve the problems existing in the prior art, the present invention provides a horizontal well fracturing productivity numerical simulation method taking into account the fluctuation of wellbore pressure, so as to better describe the production situation of the horizontal well and improve the accuracy of the numerical simulation. In the reservoir numerical simulation method of the present invention, the reservoir is first divided into finite units and the initial physical properties and pressure fields are assigned; the fluctuating horizontal well target points are determined, and the wellbore trajectory is determined by interpolation; the position of the hydraulic fracture is confirmed along the wellbore trajectory and coupled with the matrix unit; after the oil and gas flow equations of the reservoir and wellbore at different time steps are discretized and iteratively calculated, the oil and gas flow rate and content of each reservoir and wellbore unit can be obtained, and then the productivity is determined.

[0053] Next, the detailed process of the method of the embodiment of the present invention is described in detail based on the accompanying drawings. The steps shown in the flowchart of the accompanying drawings can be executed in a computer system including a set of computer executable instructions. Although the logical order of each step is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0054] Embodiment 1

[0055] Figure 1 FIG. 1 shows a flow chart of a method for numerically simulating the horizontal well fracturing productivity taking into account pressure fluctuations provided in the first embodiment of the present invention, referring to FIG. Figure 1 It can be seen that the method includes the following steps.

[0056] Reservoir unit model generation step: according to the geological characteristic data of the target reservoir, the entire reservoir matrix is ​​divided in combination with the structured grid technology to obtain a reservoir unit model with a limited number of reservoir units, and the initial physical properties and pressure field data of each reservoir unit are set;

[0057] The flow unit formation step is to determine the target point of the undulating horizontal well, set the wellbore trajectory in the reservoir unit model by interpolation, divide along the wellbore trajectory to obtain a finite number of wellbore units corresponding to the reservoir unit and set the wellbore physical properties to form a complete flow unit;

[0058] Fracture coupling step, determining shape parameters of each hydraulic fracture along the wellbore trajectory, coupling it with the flow unit and determining the physical properties of each fracture;

[0059] Discrete calculation steps, build a numerical calculation model of oil and gas flow of fracture-coupled reservoir matrix and wellbore within a set time period based on reservoir pressure field data and physical property data of reservoir, wellbore and fracture, and perform discrete calculations according to different flow units to obtain oil and gas flow velocity and content data of a single flow unit, and then calculate the corresponding production capacity. The horizontal well fracturing production capacity numerical simulation method considering pressure fluctuations provided by the present invention can realize reliable production capacity numerical calculation on the basis of considering the pressure change factor of the horizontal well fluctuating wellbore trajectory, so as to more accurately characterize the impact of flow under different fluctuating conditions in the horizontal wellbore on production capacity, further clarify the principle of wellbore pressure drop, and provide a basis for formulating oil and gas well production system.

[0060] In actual application, in the process of dividing the reservoir into finite elements, the initial physical properties and pressure field of the reservoir matrix are set. Specifically, in a preferred embodiment, the initial physical properties of the reservoir include: porosity, permeability, initial saturation of phase state and rock volume compression coefficient of the reservoir matrix; density, viscosity, solution gas-oil ratio, oil-gas ratio, relative permeability and volume coefficient of each phase of the reservoir fluid.

[0061] Record the reservoir physical property data and pressure field data within the required time period, where the time period is constrained by the end time and time interval, and the specific value can be set according to the actual analysis requirements. The reservoir matrix data within the period is usually recorded as: reservoir matrix porosity ф m , permeability k m , initial phase saturation S, rock volume compressibility, etc., density of each phase in the fluid ρ α , viscosity μ α , dissolved gas-oil ratio R s , oil-gas ratio R v , relative permeability K rα and volume factor B α wait.

[0062] In a preferred embodiment, the reservoir pressure field data is determined according to the rock compressibility coefficient based on the following logic:

[0063]

[0064] Among them, c r is the rock compression coefficient, φ m is the reservoir matrix porosity, p is the reservoir pressure, and the above formula characterizes the relationship between the rock compressibility and the reservoir pressure.

[0065] Based on the above methods, the initial physical properties and pressure field data of each reservoir unit are set to provide boundaries and restriction conditions for subsequent pressure propagation and fluid inflow into the reservoir.

[0066] Preferably, the boundary condition of the reservoir is a closed boundary or a constant pressure boundary; the initial condition of the reservoir is the pressure corresponding to the reservoir depth with or without considering gravity;

[0067] Specifically, it should be noted that in the reservoir matrix division step, the present invention divides the reservoir into a number of cubic reservoir units with equal length, width and height, which serve as geometric units of the reservoir matrix and storage units of reservoir physical properties, and are not only a geometric division of the reservoir.

[0068] Further, the target point of the undulating horizontal well is determined by executing the flow unit forming step, the wellbore trajectory is set in the reservoir unit model by the interpolation method, and a finite number of wellbore units corresponding to the reservoir unit are obtained by dividing along the wellbore trajectory to form a complete flow unit;

[0069] Among them, in the flow unit formation step, after determining the heel endpoint coordinates and toe endpoint coordinates of the horizontal well, several points on the measured horizontal well trajectory are selected between the two as target points, and the hydraulic fracture initiation point, boundary and spacing are determined along the wellbore trajectory, and coupled with the matrix unit through the discrete fracture method, and the fracture properties are determined.

[0070] In actual application, the horizontal well target points are several points on the measured horizontal well trajectory, expressed as:

[0071] a=x 0 ,x 1 ,...,x i ,x i+1 ,...,x n (1)

[0072] where x 0 Represents the coordinates of the end point of the horizontal well, x n Represents the toe point coordinates of the horizontal well.

[0073] Furthermore, the interpolation curve according to the horizontal well target point can be expressed as:

[0074] [X,Y,Z]=spline(x) (2)

[0075] Among them, spline represents cubic spline data interpolation.

[0076] Preferably, the wellbore unit division refers to dividing the wellbore into m small sections, each of which corresponds to a reservoir cell one by one; Figure 4As shown in the figure, the example undulating horizontal well passes through 11 reservoir matrix grids, so the undulating horizontal well is divided into 11 units numbered 1-11, corresponding to matrix grids 3, 13, 14, 24, 35, 36, 37, 26, 16, and 7 from small to large. Each unit cell is not only a geometric division of the wellbore, but also changes with different numbers of grids. It also defines the length L of the flow unit. w,m , diameter D w,m , volume V w,m , depth Z w,m , wellbore damage w,m and the unit centroid position x w,m Furthermore, multiple wells are divided into flow units according to this step.

[0077] Further, a fracture coupling step is performed, shape parameters of each hydraulic fracture are determined along the wellbore trajectory, and coupled to the flow unit;

[0078] Specifically, the hydraulic fracture initiation point, boundary and spacing are determined along the wellbore trajectory, and coupled with the matrix unit through the discrete fracture method. Among them, based on the horizontal well target point difference calculation (Formula 3), a certain point is selected as the fracture initiation point, set as [X i ,Y i ,Z i ];

[0079] Furthermore, in practical applications, the hydraulic fracture can be regarded as a plane facing the vertical direction. When the horizontal wells are distributed along the Y axis, the four endpoints of the hydraulic fracture can be expressed as:

[0080]

[0081] Specifically, the hydraulic fracture locations are determined according to the segment spacing and cluster spacing distribution. Each fracture unit stores the fracture porosity and permeability k f , length L f , height H f and width W f parameter.

[0082] Furthermore, by executing discrete calculation steps, a numerical calculation model of oil and gas flow in the fracture-coupled reservoir matrix and wellbore within a set time period is constructed based on the reservoir pressure field data and the physical property data of the reservoir, wellbore and fracture, and discrete calculations are performed according to different flow units to obtain the oil and gas flow velocity and content data of a single flow unit, and then the corresponding production capacity is calculated.

[0083] The discrete operation step also includes reducing the dimension of hydraulic fractures by using an embedded discrete fracture method to implicitly express fractures in the reservoir matrix grid.

[0084] Specifically, in one embodiment, the MATLAB Reservoir Simulation Toolbox (MRST) sequential implicit coupling framework is used to discretize the relevant equations of the coupled oil and gas flow numerical calculation model to obtain a nonlinear calculation matrix, and the nonlinear calculation matrix is ​​solved using the Newton-Raphson method to obtain converged pressure and saturation solutions, and then the pressure and saturation solutions are combined with the changing relationship between the time and space parameters to analyze the production capacity status within the set period of different flow units.

[0085] The oil and gas flow equations of the reservoir and wellbore from time t to t+Δt are coupled and calculated, and discretized and iteratively solved according to finite elements. The oil and gas flow velocity and corresponding content of each reservoir and wellbore unit from time t to t+Δt are calculated, and the well production capacity is obtained to determine the impact of the pressure fluctuation in the horizontal wellbore on the oil and gas production capacity of the reservoir at different times. On this basis, the fluid flow field and oil and gas production in the reservoir at different times are accurately simulated and calculated.

[0086] In the actual operation process, the embedded discrete fracture method (EDFM) can be used to reduce the dimension of the hydraulic fractures, so as to implicitly express the fractures in the reservoir matrix grid. Specifically, the flow of the fluid in the fracture that satisfies the Navier-Stokes equation is equivalent to that obeying the Darcy seepage law, which is expressed in source terms as:

[0087]

[0088] Where N nnc Represents the number of non-adjacent connected units in a specific matrix unit, and m represents the unit from 1 to N nnc nnc means the marked unit belongs to a non-adjacent connected unit, x means the marked unit belongs to a specific phase of oil, gas and water, ρ means density, μ means viscosity, k r represents the relative permeability, d represents the distance from the centroid of the fracture surface to the collection of non-adjacent connected units, P x represents the crack pressure, represents the matrix pressure.

[0089] and They represent the area, permeability and spacing of the mth non-adjacent connected unit respectively. The values ​​of the three under matrix-crack coupling are expressed as:

[0090]

[0091]

[0092]

[0093] Among them, Af represents the cross-sectional crack area, k m represents the matrix unit permeability, k f represents the fracture permeability, x n represents the cross-section normal vector, v represents the microvolume unit, and V represents the total volume of the unit.

[0094] In an optional embodiment, the oil-gas-water flow equation is composed of a mass conservation equation and a Darcy velocity-pressure relationship equation, the former of which can be expressed as:

[0095]

[0096] Wherein, subscripts o, g and w correspond to the oil phase, gas phase and water phase respectively, ρ represents density, v represents fluid flow velocity, q is the source term, and V is the unit cell volume.

[0097] Furthermore, the oil-gas velocity-pressure relationship is expressed as:

[0098]

[0099] Where α represents the phase state, subscripts o, g and w correspond to the oil phase, gas phase and water phase respectively; μ α Indicates viscosity, k rα represents the relative permeability, is the Laplace operator, Φ is the potential energy, and K is the absolute permeability.

[0100] Furthermore, the oil, gas and water saturations in each flow unit satisfy the following relationship:

[0101] S g +S o +S w =1 (10)

[0102] In a preferred embodiment, the oil and gas flow equation in the wellbore can be expressed as a mass conservation equation and a pipe flow velocity-pressure equation. The mass conservation equation can be expressed as:

[0103]

[0104] In the formula, the coupling term q α represents the phase flow rate flowing into or out of the wellbore flow unit, q α It can be expressed as:

[0105]

[0106] Where δ is the Dirac function defined at the geometric center of the wellbore flow unit, i.e., the centroid, B is the volume coefficient, and P is bhis the pressure of the wellbore flow unit, WI is the well index corresponding to the wellbore flow unit, Z is the depth of the matrix unit corresponding to the wellbore flow unit, μ α Indicates viscosity, k rα Represents relative permeability.

[0107] Preferably, the oil and gas flow equation in the wellbore can be expressed as a mass conservation equation and a pipe flow velocity-pressure equation. The pipe flow velocity-pressure equation can be expressed as:

[0108]

[0109] Where g represents the acceleration due to gravity (not a subscript), u c and u represent the flow rate in the nozzle and horizontal wellbore respectively, C v represents the nozzle flow coefficient, f represents the friction coefficient; all fluid parameters in the formula are the physical properties parameters of the oil-gas-water mixed fluid.

[0110] Preferably, the discrete phase velocity of the relevant equation (taking the oil phase as an example) is expressed by the two-point flux approximation format (TPFA) as follows:

[0111]

[0112] Where v represents the fluid velocity, q is the source term calculated by the embedded discrete fracture method, V is the unit cell volume, S represents the initial saturation of the phase, and ρ α Indicates the density of each phase in the fluid, α represents the phase state, α=o,g,s, represents the Darcy velocity of the fluid, k rα represents the relative permeability of the fluid, μ α Indicates viscosity, T ik represents the transmission coefficient of two adjacent reservoir units i and k, λ o is the fluidity of the oil phase.

[0113] Preferably, the MATLAB Reservoir Simulation Toolbox (MRST) sequential implicit coupling framework is used to discretize equations (5)-(14);

[0114] Furthermore, the Newton-Raphson iteration method is used as follows:

[0115]

[0116] The left term of the equal sign in the formula is the Jacobian matrix, and X is the initial variable.

[0117] Furthermore, after each time step (cycle) calculation, the reservoir will update the pressure and saturation distribution, and then obtain the corresponding well production capacity.

[0118] Based on the above embodiments, the present invention establishes a structured reservoir matrix grid according to the actual geological structure of the target reservoir, and determines the positions of wells and hydraulic fractures accordingly, thereby implicitly characterizing the hydraulic fractures, dividing the wellbore according to the matrix grid to form a complete reservoir flow unit, collecting and recording the physical parameters of the reservoir, hydraulic fractures and wells of the reservoir, and assigning them to the reservoir flow unit; then, the parameters collected by the parameter collection and assignment module are brought into the fluid flow equation, and discretized based on the reservoir flow unit to form a discrete equation group, that is, a nonlinear calculation matrix; further solve the nonlinear calculation matrix in the physical model module and solve the nonlinear calculation matrix using the Newton-Raphson method to obtain converged pressure and saturation solutions; finally, the well production is obtained according to the pressure and saturation solutions for each time period solved by the calculation module, and the production dynamics of the well are analyzed to achieve controllable fluctuating well production capacity prediction, which is applied to optimize production capacity.

[0119] Implementation Cases:

[0120] In order to facilitate understanding of the scheme and effect of the embodiment of the present invention, a specific application example is given below. Those skilled in the art should understand that this example is only for the purpose of facilitating understanding of the present invention, and any specific details thereof are not intended to limit the present invention in any way. Taking a certain undulating horizontal well reservoir area as an example, the process of realizing the numerical simulation of horizontal well fracturing capacity considering the undulating wellbore is as follows:

[0121] S101: setting the initial physical properties and pressure field of the reservoir, and performing finite element division of the reservoir, the end time and the time interval Δt;

[0122] S102: Determine the target point of the fluctuating horizontal well, determine the wellbore trajectory by interpolation method, divide the wellbore unit with reference to the reservoir unit, and determine the physical properties of the wellbore;

[0123] S103: Determine the hydraulic fracture initiation point, boundary and spacing along the wellbore trajectory, couple with the matrix unit through the discrete fracture method, and determine the fracture physical properties;

[0124] S104: coupling and calculating the oil and gas flow equations of the reservoir and the wellbore from time t to t+Δt, and discretizing and iteratively solving them according to finite elements;

[0125] S105: Calculate the oil and gas flow rate and corresponding content of each reservoir and wellbore unit from time t to t+Δt, and obtain the well productivity;

[0126] S106: Enter the next time period and repeat steps 4)-5). The detailed process of the above operation is as follows: Figure 2 shown.

[0127] The operation process of this implementation case is further described below.

[0128] 1) Basic process of reservoir, fracture and wellbore unit division

[0129] The present invention first needs to divide the entire oil reservoir into grids. The present invention mainly uses structured grids to divide the entire oil reservoir matrix. The structured grid is used for matrix division because it is suitable for oil reservoirs of various shapes, has high calculation accuracy, and occupies less resources. Figure 3 The division result of the three-dimensional structured grid of the reservoir matrix in the embodiment is shown;

[0130] After the reservoir matrix grid is determined, the present invention further determines the division of the wellbore grid according to the undulating horizontal well trajectory. Figure 4 The figure shows a front view of a concave undulating horizontal well in the reservoir grid, where the undulating horizontal well passes through 11 reservoir matrix grids, so the undulating horizontal well is divided into 11 units numbered 1-11, which correspond to matrix grids 3, 13, 14, 24, 35, 36, 37, 26, 16, and 7 from small to large. Under different numbers of grids, the one-to-one correspondence will also change.

[0131] After the wellbore units are divided, the present invention further inserts hydraulic fractures on the horizontal well trajectory. Figure 5 The schematic diagram of the position determination of a single hydraulic fracture in the embodiment is shown. The fracture direction is vertical and rectangular. The center of the fracture coincides with the center of the undulating horizontal well, and the fracture boundary is further determined based on points 1-4. After the geometric shape of a single fracture is confirmed, the hydraulic fracture is inserted at a specific spacing, such as Figure 6 In the illustrated embodiment, 1 to 5 hydraulic fractures are distributed at various locations of the undulating horizontal well at specific intervals.

[0132] 2) Taking the parameters of a condensate gas reservoir as an example, the reservoir parameter settings are shown in Table 1. The reservoir fluid flow unit is divided into equal-sized rectangular blocks with a length of 100 m, a width of 100 m, and a height of 30 m. The horizontal well and hydraulic fracture parameters are shown in Table 2.

[0133] A concave undulating horizontal well is arranged in the oil reservoir. The undulating horizontal well is a straight line in the horizontal direction, and the highest point and the lowest point differ by 300m.

[0134] The reservoir is set as a constant pressure boundary, a single production well, and a constant pressure of 5MPa. The production performance of the reservoir in the previous three years is calculated by replacing the node well model in this method with a conventional well model. Including reservoir pressure distribution, oil production, gas production rate, and cumulative oil / gas production.

[0135] Figure 7The bottom hole pressure of each well node calculated using the node well model and the conventional well model is shown. The undulating horizontal well is divided into 25 segments. Under the constant flow production mode, the bottom hole pressure of both models decreases with time. Under the same bottom hole pressure, the bottom hole pressure of the conventional well model only changes with time and does not change with the position of the well. The use of the node well model can obviously better reflect the actual bottom hole pressure distribution. At the middle node 16, the bottom hole pressure reaches the maximum value because it is close to the lowest point of the example horizontal well. At the same time, for nodes with the same height, the node pressure near the heel is lower, which is caused by friction along the way.

[0136] Figure 8 The reservoir pressure distribution under the node well model is demonstrated. The calculation method using the node well model can effectively reflect the pressure distribution and fluctuation of the undulating horizontal well, while the conventional well model has a consistent pressure distribution along the well and cannot reflect the changes in wellbore pressure caused by the height difference.

[0137] Fig. 9 The relationship between oil production and time calculated by the two models is shown. Due to the introduction of more pressure loss, the production capacity of the node well model is slightly lower than that of the conventional well model, which is closer to reality.

[0138] Table 1 Reservoir parameters

[0139]

[0140]

[0141] Table 2 Horizontal well and hydraulic fracture parameters

[0142] parameter Value parameter Value Horizontal well length, km 1 Seam half length, m 150 Horizontal well diameter, mm 150 Seam height, m 10 Horizontal well shape Concave type Seam width, cm 0.5 Horizontal well height difference, m 300 Slit porosity, % 0.8 Number of cracks, 6 Slit permeability, D <![CDATA[10 4 ]]> Seam half length, m 150 Slit permeability, D <![CDATA[10 4 ]]>

[0143] Compared with the traditional capacity analysis and calculation technology, the present invention carries out a numerical simulation study on the capacity of horizontal well fracturing considering the undulating wellbore based on the reservoir matrix and fracture grid division tools, and develops a hybrid numerical simulation program based on structured grids, discrete fractures and discrete wells for horizontal well reservoirs with undulating wellbore containing oil, in which hydraulic fractures and wellbore are implicitly processed. The program will simultaneously consider the cross-scale flow of oil-gas-water multiphase flow in the reservoir matrix, fractures and wellbore, and then solve the spatiotemporal variation characteristics of reservoir pressure and saturation, derive the corresponding capacity of the oil well, and analyze the influence of factors such as undulating horizontal wells on the capacity. The influence of the undulating wellbore trajectory on the pressure distribution in the wellbore is added to reveal the influence of the undulating horizontal well on the capacity, so that the capacity calculation results after the horizontal well fracturing are more accurate. The simulation method can effectively reflect the pressure distribution and fluctuation of the undulating horizontal well, further clarify the principle of wellbore pressure drop, and provide a basis for formulating the production system of oil and gas wells.

[0144] In addition, the calculation principle of the present invention can also be applied to the productivity analysis of multi-stage fracturing operations of ordinary horizontal wells and undulating horizontal wells, and to provide productivity prediction support for the optimization of fracturing layout schemes.

[0145] For the above-mentioned method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the order of the actions described, because according to the present invention, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0146] It should be pointed out that in other embodiments of the present invention, the method can also obtain a new horizontal well fracturing capacity numerical simulation method by combining one or several of the above embodiments to achieve comprehensive capacity analysis and high-quality optimization of oil reservoir exploitation.

[0147] It should be noted that, based on the method in any one or more of the above-mentioned embodiments of the present invention, the present invention also provides a storage medium, on which is stored a program code that can implement the method as described in any one or more of the above-mentioned embodiments, and when the code is executed by the operating system, it can implement the numerical simulation method of horizontal well fracturing capacity considering pressure fluctuations as described above.

[0148] Embodiment 2

[0149] The method is described in detail in the embodiments disclosed in the present invention. The method of the present invention can be implemented by various devices or systems. Therefore, based on other aspects of the method described in any one or more embodiments, the present invention also provides a horizontal well fracturing capacity numerical simulation system considering pressure fluctuations. The system is used to execute the horizontal well fracturing capacity numerical simulation method considering pressure fluctuations described in any one or more embodiments. Specific embodiments are given below for detailed description.

[0150] Specifically, Fig.10 FIG. 4 is a schematic diagram showing a structure of a numerical simulation system for horizontal well fracturing productivity considering pressure fluctuations provided in an embodiment of the present invention. Fig.10 As shown, the system includes:

[0151] A reservoir unit model generation module is configured to divide the entire reservoir matrix according to the geological characteristic data of the target reservoir in combination with the structured grid technology, obtain a reservoir unit model with a limited number of reservoir units, and set the initial physical property and pressure field data of each reservoir unit;

[0152] A flow unit forming module is configured to determine the target point of the undulating horizontal well, set the wellbore trajectory in the reservoir unit model by interpolation, divide along the wellbore trajectory to obtain a finite number of wellbore units corresponding to the reservoir unit and set the wellbore physical properties to form a complete flow unit;

[0153] a fracture coupling module configured to determine shape parameters of each hydraulic fracture along the wellbore trajectory, couple it with the flow unit and determine the physical properties of each fracture;

[0154] The discrete operation module is configured to construct a numerical operation model of oil and gas flow in the fracture-coupled reservoir matrix and wellbore within a set time period based on the reservoir pressure field data and the physical property data of the reservoir, wellbore and fracture, and to perform discrete operations on different flow units to obtain the oil and gas flow velocity and content data of a single flow unit, thereby calculating the corresponding production capacity.

[0155] Preferably, in one embodiment, the reservoir matrix partitioning module sets the following initial physical properties of the reservoir: porosity, permeability, initial phase saturation and rock volume compressibility of the matrix; density, viscosity, solution gas-oil ratio, oil-gas ratio, relative permeability and volume coefficient of each phase of the reservoir fluid.

[0156] Further, in one embodiment, the reservoir matrix partitioning module is configured to determine the reservoir pressure field data according to the rock compressibility coefficient based on the following logic:

[0157]

[0158] Among them, c r is the rock compression coefficient, φ m is the reservoir matrix porosity, and p is the reservoir pressure.

[0159] Furthermore, in one embodiment, the reservoir matrix division module is configured to divide the reservoir into a number of cubic reservoir units with equal length, width and height, which serve as geometric units of the reservoir matrix and storage units of reservoir physical properties.

[0160] In a preferred embodiment, the flow unit forming module determines the target point of the horizontal well by the following operations:

[0161] After determining the heel point coordinates and toe point coordinates of the horizontal well, several points on the measured horizontal well trajectory are selected between the two as target points.

[0162] Specifically, in one embodiment, the fracture coupling module is configured to: determine the hydraulic fracture initiation point, boundary and spacing along the wellbore trajectory, couple with the matrix unit through the discrete fracture method, and determine the fracture properties.

[0163] Furthermore, in one embodiment, the discrete operation module is configured to reduce the dimension of the hydraulic fractures using an embedded discrete fracture method to implicitly express the fractures in the reservoir matrix grid.

[0164] In a preferred embodiment, the discrete computing module constructs an oil and gas flow numerical computing model as shown in the following formula:

[0165]

[0166]

[0167]

[0168] Among them, the oil, gas and water saturations in each flow unit satisfy: S g +S o +S w =1

[0169] Wherein, subscripts o, g and w correspond to oil phase, gas phase and water phase respectively, v represents the fluid velocity, q is the source term calculated by embedded discrete fracture method, V is the unit cell volume, S represents the initial saturation of phase state, ρ α Indicates the density of each phase in the fluid, α represents the phase state, α=o,g,s, represents the Darcy velocity of the fluid, K represents the absolute permeability, k rα represents the relative permeability of the fluid, μ α Indicates viscosity.

[0170] Furthermore, in one embodiment, the discrete operation module is configured as follows: using the MATLAB ReservoirSimulation Toolbox (MRST) sequential implicit coupling framework to discretize the relevant equations of the coupled oil and gas flow numerical operation model to obtain a nonlinear calculation matrix, using the Newton-Raphson method to solve the nonlinear calculation matrix to obtain converged pressure and saturation solutions, and then combining the pressure and saturation solutions with the changing relationship between the time and space parameters to analyze the production capacity status within the set period of different flow units.

[0171] In the numerical simulation of horizontal well fracturing productivity considering pressure fluctuations provided by the embodiment of the present invention, each module or unit structure can be operated independently or in combination according to actual unit setting requirements and calculation requirements to achieve corresponding technical effects.

[0172] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0173] The "one embodiment" mentioned in the specification means that a particular feature, structure or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Therefore, the phrase "one embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0174] Although the embodiments disclosed in the present invention are as above, the above contents are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for numerical simulation of horizontal well fracturing productivity considering pressure fluctuations, characterized in that: The method comprises: Reservoir unit model generation step: according to the geological characteristic data of the target reservoir, the entire reservoir matrix is ​​divided in combination with the structured grid technology to obtain a reservoir unit model with a limited number of reservoir units, and the initial physical properties and pressure field data of each reservoir unit are set; The flow unit formation step is to determine the target point of the undulating horizontal well, set the wellbore trajectory in the reservoir unit model by interpolation, divide along the wellbore trajectory to obtain a finite number of wellbore units corresponding to the reservoir unit and set the wellbore physical properties to form a complete flow unit; Fracture coupling step, determining the shape parameters of each hydraulic fracture along the wellbore trajectory, coupling it with the flow unit and determining the physical properties of each fracture; Discrete calculation steps: Based on the reservoir pressure field data and the physical property data of the reservoir, wellbore and fractures, a numerical calculation model of oil and gas flow in the fracture-coupled reservoir matrix and wellbore within a set time period is constructed, and discrete calculations are performed on different flow units to obtain the oil and gas flow velocity and content data of a single flow unit, and then the corresponding production capacity is calculated.

2. The method according to claim 1, characterized in that In the reservoir matrix division step, the initial physical properties of the reservoir include: the porosity, permeability, initial saturation of phases and rock volume compressibility of the reservoir matrix; the density, viscosity, solution gas-oil ratio, oil-gas ratio, relative permeability and volume coefficient of each phase of the reservoir fluid.

3. The method according to claim 1, characterized in that The reservoir pressure field data is determined based on the rock compressibility coefficient based on the following logic: Among them, c r is the rock compression coefficient, φ m is the reservoir matrix porosity, and p is the reservoir pressure.

4. The method according to claim 1, characterized in that: In the flow unit forming step, after the heel end point coordinates and the toe end point coordinates of the horizontal well are determined, several points on the measured horizontal well trajectory are selected between the two as target points.

5. The method according to claim 1, characterized in that In the reservoir matrix division step, the reservoir is divided into a number of cubic reservoir units with equal length, width and height, which serve as geometric units of the reservoir matrix and storage units of reservoir physical properties.

6. The method according to claim 1, characterized in that In the fracture coupling step, it includes determining the hydraulic fracture initiation point, boundary and spacing along the wellbore trajectory, coupling with the matrix unit through the discrete fracture method, and determining the fracture physical properties.

7. The method according to claim 1, characterized in that The discrete operation step also includes reducing the dimension of hydraulic fractures by using an embedded discrete fracture method to implicitly express the fractures in the reservoir matrix grid.

8. The method according to claim 1, characterized in that Construct a numerical calculation model of oil and gas flow as shown below: The oil, gas and water saturations in each flow unit satisfy: S g +S o +S w =1 Wherein, subscripts o, g and w correspond to oil phase, gas phase and water phase respectively, v represents the fluid velocity, q is the source term calculated by embedded discrete fracture method, V is the unit cell volume, S represents the initial saturation of phase state, ρ α Indicates the density of each phase in the fluid, α represents the phase state, α=o,g,s, represents the Darcy velocity of the fluid, K represents the absolute permeability, k rα represents the relative permeability of the fluid, μ α Indicates viscosity.

9. The method according to claim 1, characterized in that: The MATLAB Reservoir Simulation Toolbox (MRST) sequential implicit coupling framework is used to discretize the relevant equations of the coupled oil and gas flow numerical calculation model to obtain the nonlinear calculation matrix. The nonlinear calculation matrix is ​​solved using the Newton-Raphson method to obtain convergent pressure and saturation solutions. Then, the pressure and saturation solutions are combined with the changing relationship between the time and space parameters to analyze the production capacity status within the set period of different flow units.

10. A horizontal well fracturing productivity numerical simulation system considering pressure fluctuations, characterized in that: The system executes the method according to any one of claims 1 to 9.

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