Optimization Method for Fracturing Construction Parameters in Shale Gas Formations

Abstract

The present invention discloses a method for optimizing shale gas formation fracturing construction parameters, which includes: obtaining geological parameters, physical property parameters and fracturing design parameters of the reservoir in the shale fracturing block; establishing a dynamic expansion model of a complex fracture network for multi-cluster fracturing in horizontal wells of shale gas; establishing a single-well production calculation model after fracturing and reconstruction of horizontal wells of shale gas; establishing a fracturing transformation cost calculation model for multi-cluster fracturing in horizontal wells of shale gas based on the costs required for various projects of horizontal well fracturing transformation; and combining the fracture network dynamic expansion model, the single-well production calculation model and the fracturing transformation cost calculation model to calculate the net present value of production after fracturing and reconstruction of horizontal wells of shale gas under different fracturing design parameters so as to optimize the fracturing design parameters. The method for optimizing shale gas formation fracturing construction parameters proposed by the present invention has a reliable principle, is operable and accurate, and can optimize the fracturing construction parameters of the entire well section of horizontal wells of shale gas on the premise of given basic parameters.

Description

Technical Field

[0001] The present invention relates to the field of enhanced oil and gas field stimulation, and particularly to a method for optimizing fracturing construction parameters of shale gas formations. Background Art

[0002] Hydraulic fracturing is a key technology for the large-scale development of unconventional oil and gas resources such as shale oil and gas and tight oil and gas. The surface pumping unit injects working fluid into the formation through the wellbore. The reservoir rock fractures under the action of fluid pressure and artificial fractures are generated. Continuing to pump sand-carrying liquid, finally a sand-filled fracture with high conductivity is formed in the reservoir, effectively improving the fluidity of the reservoir, reducing the pressure difference of fluid medium flow in the reservoir and the seepage distance in the porous medium, realizing the transformation of unconventional reservoirs, and increasing the oil and gas production per well.

[0003] The effect of large-scale volume fracturing determines the level of shale gas production. To ensure a high production per well, it is necessary to fully stimulate the shale reservoir. Forming complex fractures with a certain conductivity in the shale reservoir is the key to high production. It is required that multiple fractures can effectively initiate and uniformly expand during multi-cluster fracturing in the horizontal well section, effectively communicate natural fractures to form a complex fracture network, which requires optimizing the design of shale gas horizontal well fracturing construction parameters. Field engineers often increase the amount of fracturing fluid and proppant to increase the fracturing scale in order to obtain high production from shale gas wells, resulting in a mismatch between the degree of reservoir stimulation and reservoir productivity, leading to a large amount of resource waste, increasing the development cost of shale gas, and not conforming to the "cost reduction and efficiency increase" principle of shale gas exploitation, which puts forward higher requirements for optimizing the design of fracturing construction parameters.

[0004] At present, when optimizing the fracturing construction parameters of shale gas horizontal wells in China, it mainly focuses on the fracture propagation of fracturing, emphasizing the effective initiation and effective extension of fractures, aiming at the effective uniform extension of multiple fractures in multi-stage multi-cluster fracturing of horizontal wells and forming fractures with sufficient length and width, optimizing the fracturing construction parameters, without fully considering the post-fracture seepage, lacking the economic evaluation of fracturing construction, that is, optimizing the fracturing construction parameters from the "efficiency increase (i.e., the economic effect of fracturing construction)", weakening the goal of "cost reduction (i.e., reducing the development cost of shale gas)". Summary of the Invention

[0005] The main object of the present invention is to provide a method for optimizing fracturing construction parameters of shale gas formations, aiming at...

[0006] To achieve the above object, the present invention provides a method for optimizing fracturing construction parameters of shale gas formations, which is characterized by including the following steps:

[0007] S1. Obtain the geological parameters, physical properties parameters and fracturing design parameters of the reservoir in the shale fracturing block;

[0008] S2. Establish a dynamic expansion model of complex fracture networks for multi-cluster fracturing in shale gas horizontal wells in segments;

[0009] S3. Based on the geological parameters, fracturing design parameters, and fracture geometry parameters after fracturing obtained from the fracture network dynamic expansion model, establish a single-well production calculation model for shale gas horizontal wells after fracturing transformation;

[0010] S4. Based on the costs required for each project of horizontal well fracturing transformation, establish a cost calculation model for multi-cluster fracturing in segments of shale gas horizontal wells;

[0011] S5. Combine the fracture network dynamic expansion model, single-well production calculation model, and fracturing transformation cost calculation model to calculate the net present value of production after fracturing transformation of shale gas horizontal wells under different fracturing design parameters, and optimize the fracturing design parameters with the maximum net present value.

[0012] Preferably, the geological parameters include: maximum horizontal principal stress, minimum horizontal principal stress, stress difference between reservoir and interlayer, reservoir stress gradient, rock tensile strength, Young's modulus, Poisson's ratio, rock compressibility, rock density, matrix permeability, matrix porosity, gas saturation, reservoir pressure coefficient, reservoir temperature, reservoir thickness, natural fracture length, natural fracture azimuth, natural fracture shear strength, natural fracture wall friction coefficient, natural fracture porosity, natural fracture permeability;

[0013] The fracturing design parameters include: cluster spacing, number of perforation clusters, perforation diameter, number of perforations, construction displacement, fracturing fluid viscosity, construction scale.

[0014] Preferably, the S2 specifically includes:

[0015] S21. Establish the relationship between fracture propagation stress and displacement based on the boundary element method;

[0016] S22. Considering the simultaneous propagation of multiple hydraulic fractures and the induced stress effect between fractures, and then according to the principle of stress superposition, obtain the composite stress field at any point in the reservoir during fracture dynamic expansion, and obtain the induced stress field calculation model;

[0017] S23. Regard the fracturing fluid as an incompressible Newtonian fluid, consider the flow of the fracturing fluid in the horizontal wellbore, perforation holes, and fracturing fractures, as well as the filtration effect of the fracturing fluid, and based on the principle of pressure balance and the principle of mass conservation, use the Newton iteration method to establish a dynamic flow distribution model for multi-cluster fracturing in segments of horizontal wells;

[0018] S24. Considering the composite failure mode of tension and shear of cracks, select the critical energy release rate criterion at the tip as the crack propagation criterion, calculate the crack propagation direction through the maximum tensile stress criterion, consider non-uniform propagation, correct the multi-crack propagation step length, and establish a calculation model for the multi-crack propagation step length and propagation direction;

[0019] S25. Considering the influence of natural cracks developed in shale reservoirs on the propagation of hydraulic fractures, the hydraulic fractures will pass through natural cracks, turn along natural cracks, etc. At the same time, considering the filtration of fracturing fluid into natural cracks, establish an intersection model of hydraulic fractures and natural cracks based on empirical analytical formulas;

[0020] S26. According to the stress-displacement relationship in step S21, the induced stress field calculation model in S22, and the fracturing fluid flow field in S23, couple them to form a fully coupled fluid-solid model for crack propagation. Combine the propagation criterion in step S24 and the intersection criterion in S25 to form a fracture field model. Combine the fully coupled fluid-solid model and the fracture field model to form a dynamic expansion model of complex fracture networks for multi-cluster fracturing in horizontal wells.

[0021] Preferably, when establishing the relationship between crack propagation stress and displacement based on the boundary element method:

[0022]

[0023] In the formula: u i represents the normal displacement of crack element i; v i represents the tangential displacement of crack element i; σ j represents the normal stress of crack element j; τ j represents the tangential stress of crack element j; A ij represents the stress boundary influence coefficient matrix; G ij represents the seam height correction coefficient matrix. When three-dimensional crack propagation occurs, G ij is the identity matrix;

[0024] The induced stress field calculation model is:

[0025]

[0026] In the formula: The subscripts x and y represent directions; represents the induced stress field of crack element j acting on crack element i; G ij represents the seam height correction coefficient. When three-dimensional crack propagation occurs, G ij has a value of 1; C ij represents the displacement boundary influence coefficient; represents the influence coefficient of the normal displacement of crack element j in the x direction on the normal stress of crack element i in the x direction; Denotes the influence coefficient of the tangential displacement of crack element j in the y direction on the normal stress of crack element i in the x direction; Denotes the influence coefficient of the normal displacement of crack element j in the x direction on the normal stress of crack element i in the y direction; Denotes the influence coefficient of the normal displacement of crack element j in the y direction on the normal stress of crack element i in the y direction; Denotes the influence coefficient of the normal displacement of crack element j in the x direction on the tangential stress of crack element i; Denotes the influence coefficient of the normal displacement of crack element j in the y direction on the tangential stress of crack element i ； u j and v j respectively denote the normal displacement and tangential displacement of crack element j;

[0027] The dynamic flow rate allocation model for staged multi-cluster fracturing of horizontal wells is:

[0028]

[0029] In the formula, t represents the fracturing time; x represents the position; A represents the cross-sectional area of the hydraulic fracture; q represents the fracturing fluid flow rate; q leak represents the filtration rate of the fracturing fluid; p Bottom represents the bottom-hole fluid pressure at the heel of the horizontal well; p well,i represents the wellbore friction between the heel of the horizontal well and the i-th perforation cluster; p p,i represents the perforation friction of the i-th perforation cluster; p f,i represents the inlet fluid pressure of the i-th cluster of fractures;

[0030] The calculation model for the multi-fracture propagation step length and propagation direction is:

[0031]

[0032]

[0033]

[0034] In the formula, α represents half of the maximum fracture propagation step length; Δx i represents the propagation step length of the i-th crack tip; G f,i represents the maximum energy release rate of the i-th crack tip; G f represents the maximum energy release rate matrix of the crack tip; G critical represents the critical energy release rate for crack tip propagation; β is the crack propagation deflection angle; K Ι represents the type I stress intensity factor; K ∏ represents the type II stress intensity factor; E represents Young's modulus; v represents Poisson's ratio;

[0035] The model of the intersection between hydraulic fractures and natural fractures is as follows:

[0036]

[0037] In the formula, σ nf and τ nf represent the normal and tangential stress components of the combined stress of in-situ stress and induced stress acting on the natural fracture wall; μ nf represents the friction coefficient of the natural fracture wall; σ h represents the minimum horizontal principal stress; τ0 represents the shear strength of the natural fracture; p nf represents the fluid pressure in the natural fracture; T rock represents the tensile strength of the rock.

[0038] Preferably, the S3 specifically includes:

[0039] S31. Establish a single-well production geological and physical model after the fracturing of a shale gas horizontal well according to the reservoir geological parameters and physical properties parameters of the shale fracturing and reforming block, in combination with the fracture geometric parameters obtained by calculating the dynamic expansion model of the complex fracture network in multi-cluster fracturing of shale gas horizontal wells in segments;

[0040] S32. Import the single-well production geological and physical model after the fracturing of the shale gas horizontal well into the reservoir numerical simulation software CMG to construct a single-well production calculation model after the fracturing of the shale gas horizontal well, and calculate the changes of the shale reservoir pressure and gas saturation with time and the cumulative gas production of a single well under different production systems according to the single-well production calculation model after the fracturing of the shale gas horizontal well.

[0041] Preferably, the S4 specifically includes:

[0042] Consider the material cost, tool cost and construction labor cost required for the fracturing and reforming of horizontal wells, and establish a cost calculation model for multi-cluster fracturing and reforming of shale gas horizontal wells in segments:

[0043]

[0044] In the formula, G all represents the total cost of the fracturing and reforming of a single-well horizontal well of shale gas; m represents the total number of fracturing and reforming sections; g fluid,i represents the fracturing fluid cost of the i-th stage of fracturing; g prop,i represents the proppant cost of the i-th stage of fracturing; g tool,i represents the tool cost of the i-th stage of fracturing; g work,i represents the engineering cost of the i-th stage of fracturing; g else,i represents the other cost of the i-th stage of fracturing.

[0045] Preferably, the S5 specifically includes:

[0046] S51. Based on the fact that the revenue from the fractured shale reservoir comes from the sale of natural gas, establish a calculation model for the sales revenue;

[0047] S52. Use the net present value method to conduct an economic evaluation of the fracturing transformation of shale gas horizontal wells, and establish a calculation model for the net present value of exploitation;

[0048] S53. Combine the fracture network dynamic expansion model, the single-well production calculation model, the fracturing transformation cost calculation model, and the exploitation net present value calculation model to establish the connection between different construction parameters and the exploitation net present value of shale gas. Take obtaining the maximum net present value as the optimization goal, establish an optimization model for the fracturing construction parameters of the shale gas formation, and use the construction parameter combination corresponding to the maximum net present value as the optimization result.

[0049] Preferably, the calculation model for the sales revenue is as follows:

[0050]

[0051] In the formula, G in represents the total annual sales revenue of natural gas; C gas,i represents the natural gas price on the i-th day after the start of production of the shale gas well after fracturing transformation; V gas,i represents the gas production volume on the i-th day after the start of production of the shale gas well after fracturing transformation.

[0052] Preferably, the calculation model for the net present value of exploitation is as follows:

[0053]

[0054] In the formula, NPV represents the net present value; t represents time; (G in -G out ) represents the cash flow in the t-th year; e represents the annual discount rate.

[0055] The optimization method for the fracturing construction parameters of the shale gas formation proposed by the present invention has the following beneficial effects:

[0056] 1. The complex fracture network dynamic expansion model in this optimization method is applicable to two-dimensional, quasi-three-dimensional, and three-dimensional fracture expansion simulations, and can be selected according to requirements;

[0057] 2. The complex fracture network dynamic expansion model in this optimization method can realize multi-fracture induced stress calculation, multi-cluster flow dynamic distribution calculation, and complex fracture network dynamic expansion simulation;

[0058] 3. The single-well production calculation model in this optimization method can calculate the reservoir pressure, stress, and gas saturation under various production systems after fracturing of different shale reservoirs;

[0059] 4. By applying this optimization method and integrating multiple processes such as fracture propagation, post-fracture seepage, and economic evaluation, construction parameters such as pumping rate and fluid volume scale can be optimized to obtain the maximum economic benefits of shale gas development, avoiding the situation where blindly increasing the fracturing scale leads to construction costs higher than the poor fracturing effect.

[0060] 5. This optimization method fully combines fracture propagation and post-fracture seepage, optimizes the fracturing construction parameters through economic evaluation, taking into account both "cost reduction" and "efficiency improvement". The principle of this method is reliable, with operability and accuracy, and can optimize the fracturing construction parameters of the entire well section of shale gas horizontal wells on the premise of given basic parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a schematic flow chart of the method for optimizing the fracturing construction parameters of shale gas formation in the present invention;

[0062] Figure 2 It is a schematic diagram of the complex fracture network propagation trajectory simulated by Scheme 1 in Table 2;

[0063] Figure 3 It is a schematic diagram of the complex fracture network propagation trajectory simulated by Scheme 2 in Table 2;

[0064] Figure 4 It is a schematic diagram of the complex fracture network propagation trajectory simulated by Scheme 3 in Table 2;

[0065] Figure 5 It is a schematic diagram of the complex fracture network propagation trajectory simulated by Scheme 4 in Table 2;

[0066] Figure 6 It is a schematic diagram of the geological and physical model for calculating the production of shale gas wells in the method for optimizing the fracturing construction parameters of shale gas formation in the present invention;

[0067] Figure 7 It is a schematic diagram of the planar fracture model of shale gas hydraulic fracturing in CMG software;

[0068] Figure 8 It is a distribution map of the gas saturation in the reservoir after 3 years of production simulated by Scheme 1;

[0069] Figure 9 It is a distribution map of the gas saturation in the reservoir after 3 years of production simulated by Scheme 2;

[0070] Figure 10 It is a distribution map of the gas saturation in the reservoir after 3 years of production simulated by Scheme 4;

[0071] Figure 11 It is a distribution map of the gas saturation in the reservoir after 3 years of production simulated by Scheme 5;

[0072] Figure 12Schematic diagram of the cumulative gas production change curve of a single well under different scenarios.

[0073] The realization, functional characteristics, and advantages of the object of the present invention will be further described in conjunction with embodiments with reference to the accompanying drawings. Specific embodiments

[0074] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0075] It should be noted that in the description of the present invention, the orientation or positional relationship indicated by the terms "horizontal", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0076] Refer to Figure 1 , the present invention proposes an optimization method for shale gas formation fracturing construction parameters, including the following steps:

[0077] S1. Obtain the geological parameters, physical property parameters, and fracturing design parameters of the reservoir in the shale fracturing block;

[0078] S2. Establish a dynamic expansion model of a complex fracture network for multi-cluster fracturing of horizontal wells in shale gas according to the geological parameters and fracturing design parameters;

[0079] S3. Establish a calculation model for the single-well production after fracturing transformation of horizontal wells in shale gas according to the geological parameters, physical property parameters, fracturing design parameters, and fracture geometry parameters obtained from the fracture network dynamic expansion model;

[0080] S4. Establish a cost calculation model for multi-cluster fracturing transformation of horizontal wells in shale gas based on the costs required for each project of horizontal well fracturing transformation;

[0081] S5. Combine the fracture network dynamic expansion model, single-well production calculation model, and fracturing transformation cost calculation model to calculate the net present value of production after fracturing transformation of horizontal wells in shale gas under different construction parameters, and optimize the fracturing construction parameters with the maximum net present value.

[0082] Specifically, the geological parameters include: maximum horizontal principal stress, minimum horizontal principal stress, stress difference between reservoir and interlayer, reservoir stress gradient, rock tensile strength, Young's modulus, Poisson's ratio, rock compressibility, rock density, matrix permeability, matrix porosity, gas saturation, reservoir pressure coefficient, reservoir temperature, reservoir thickness, natural fracture length, natural fracture azimuth, natural fracture shear strength, natural fracture wall friction coefficient, natural fracture porosity, natural fracture permeability;

[0083] The fracturing design parameters include: cluster spacing, number of perforation clusters, perforation diameter, number of perforations, construction displacement, fracturing fluid viscosity, construction scale.

[0084] Step S2 specifically includes:

[0085] S21. Establish the relationship between fracture propagation stress and displacement based on the boundary element method;

[0086] S22. Considering the simultaneous propagation of multiple hydraulic fractures and the induced stress effect between fractures, and then obtaining the composite stress field at any point in the reservoir during fracture dynamic propagation according to the stress superposition principle, to obtain the induced stress field calculation model;

[0087] S23. Regarding the fracturing fluid as an incompressible Newtonian fluid, considering the flow of the fracturing fluid in the horizontal wellbore, perforation holes, and fracturing fractures as well as the filtration effect of the fracturing fluid, and based on the pressure balance principle and the mass conservation principle, using the Newton iteration method to establish a dynamic flow distribution model for multi-cluster fracturing in horizontal well sections;

[0088] S24. Considering the composite failure mode of fracture tension and shear, selecting the critical energy release rate criterion at the tip as the fracture propagation criterion, calculating the fracture propagation direction through the maximum tensile stress criterion, considering non-uniform propagation, and correcting the propagation step length of multiple fractures to establish a calculation model for the propagation step length and direction of multiple fractures;

[0089] S25. Considering the influence of natural fractures developed in the shale reservoir on the propagation of hydraulic fractures, the hydraulic fractures will pass through natural fractures, turn along natural fractures, etc. At the same time, considering the filtration of the fracturing fluid into natural fractures, based on the empirical analytical formula, establish an intersection model between hydraulic fractures and natural fractures;

[0090] S26. The fracture fluid flow field obtained from the stress-displacement relationship in step S21, the induced stress field calculation model in S22, and the dynamic allocation model of multi-cluster fracturing flow rates for horizontal well segments (the fracture fluid flow field is calculated based on the dynamic allocation model of multi-cluster fracturing flow rates for horizontal well segments) is coupled to form a fully coupled fluid-solid model for fracture propagation. The calculation model of multi-fracture propagation step lengths and propagation directions in step S24 and the model of the intersection of hydraulic fractures and natural fractures in S25 are combined to form a fracture field model. The fully coupled fluid-solid model and the fracture field model are combined to form a dynamic expansion model of complex fracture networks for multi-cluster fracturing of horizontal well segments.

[0091] Specifically, the dynamic allocation model of multi-cluster fracturing flow rates for horizontal well segments is part of the calculation of the fracture fluid flow field. The fully coupled fluid-solid model for fracture propagation = the induced stress field calculation model + the fracture fluid flow field. The fully coupled fluid-solid model for fracture propagation includes the dynamic allocation model of multi-cluster fracturing flow rates for horizontal well segments.

[0092] In S21, when establishing the relationship between fracture propagation stress and displacement based on the boundary element method:

[0093]

[0094] In the formula: u i represents the normal displacement of fracture element i; v i represents the tangential displacement of fracture element i; σ j represents the normal stress of fracture element j; τ j represents the tangential stress of fracture element j; A ij represents the stress boundary influence coefficient matrix; G ij represents the seam height correction coefficient matrix. When three-dimensional fracture propagation occurs, G ij is the identity matrix;

[0095] In S22, the induced stress field calculation model is:

[0096]

[0097] In the formula: The subscripts x and y represent directions; represents the induced stress field of fracture element j acting on fracture element i; G ij represents the seam height correction coefficient. When three-dimensional fracture propagation occurs, G ij has a value of 1; C ij represents the displacement boundary influence coefficient, represents the influence coefficient of the normal displacement of fracture element j in the x direction on the normal stress of fracture element i in the x direction; represents the influence coefficient of the tangential displacement of fracture element j in the y direction on the normal stress of fracture element i in the x direction; Denotes the influence coefficient of the normal displacement of crack element j in the x - direction on the normal stress of crack element i in the y - direction; Denotes the influence coefficient of the normal displacement of crack element j in the y - direction on the normal stress of crack element i in the y - direction; Denotes the influence coefficient of the normal displacement of crack element j in the x - direction on the shear stress of crack element i; Denotes the influence coefficient of the normal displacement of crack element j in the y - direction on the shear stress of crack element i; u j And v j Respectively denote the normal displacement and the shear displacement of crack element j;

[0098] In S23, the dynamic flow - allocation model for staged multi - cluster fracturing of horizontal wells is:

[0099]

[0100] In the formula, t represents the fracturing time; x represents the position; A represents the cross - sectional area of the hydraulic fracture; q represents the fracturing fluid flow rate; q leak Represents the fracturing fluid filtration rate; p Bottom Represents the fluid pressure at the bottom of the horizontal well heel; p well,i Represents the wellbore friction between the horizontal well heel and the i - th perforation cluster; p p,i Represents the perforation friction of the i - th perforation cluster; p f,i Represents the inlet fluid pressure of the i - th cluster of fractures;

[0101] In S24, the calculation model for the propagation step - length and propagation direction of multiple fractures is:

[0102]

[0103]

[0104]

[0105] In the formula, α represents half of the maximum propagation step - length of the fracture; Δx i Represents the propagation step - length of the i - th crack tip; G f,i Represents the maximum energy release rate of the i - th crack tip; G f Represents the matrix of the maximum energy release rate at the crack tip; G critical Represents the critical energy release rate for crack tip propagation; β is the deflection angle of crack propagation; K Ι Represents the type - I stress intensity factor; K ∏ Represents the type - II stress intensity factor; E represents Young's modulus; v represents Poisson's ratio;

[0106] In S25, the model for the intersection of hydraulic fractures and natural fractures is:

[0107]

[0108] In the formula, σ nf and τ nf represent the normal and tangential stress components of the combined stress of in-situ stress and induced stress acting on the natural fracture wall surface; μ nf represents the friction coefficient of the natural fracture wall surface; σ h represents the minimum horizontal principal stress; τ0 represents the shear strength of the natural fracture; p nf represents the fluid pressure in the natural fracture; T rock represents the tensile strength of the rock.

[0109] Step S3 specifically includes:

[0110] S31. According to the reservoir geological parameters and physical property parameters of the shale fracturing and reforming block, and combining the fracture geometric parameters after fracturing calculated by the dynamic expansion model of the complex fracture network for multi-cluster fracturing in horizontal wells of shale gas, establish a single-well production geological and physical model after the fracturing and reforming of the horizontal well of shale gas;

[0111] S32. Import the single-well production geological and physical model after the fracturing and reforming of the horizontal well of shale gas into the reservoir numerical simulation software CMG, construct a single-well production calculation model after the fracturing and reforming of the horizontal well of shale gas, and calculate the changes of the shale reservoir pressure and gas saturation with time and the single-well cumulative gas production under different production systems according to the single-well production calculation model after the fracturing and reforming of the horizontal well of shale gas.

[0112] Step S4 specifically includes:

[0113] Considering the material cost, tool cost and construction labor cost required for the fracturing and reforming of the horizontal well, establish a cost calculation model for multi-cluster fracturing and reforming of the horizontal well of shale gas:

[0114]

[0115] In the formula, G all represents the total cost of the fracturing and reforming of the horizontal well of shale gas per single well; m represents the total number of fracturing and reforming sections; g fluid,i represents the fracturing fluid cost of the i-th stage of fracturing; g prop,i represents the proppant cost of the i-th stage of fracturing; g tool,i represents the tool cost of the i-th stage of fracturing, such as bridge plugs, perforating charges, temporary plugging balls, pump truck groups, etc.; g work,i represents the engineering cost of the i-th stage of fracturing, such as perforating, fracturing, etc.; g else,i represents the other cost of the i-th stage of fracturing, such as workover operations, etc.

[0116] Step S5 specifically includes:

[0117] S51. Based on the fact that the revenue from the fractured shale reservoir comes from the sale of natural gas, establish a calculation model for the sales revenue.

[0118] S52. Use the net present value method to conduct an economic evaluation of the fracturing transformation of shale gas horizontal wells, and establish a calculation model for the net present value of exploitation.

[0119] S53. Combine the fracture network dynamic expansion model, the single-well production calculation model, the fracturing transformation cost calculation model, and the net present value of exploitation calculation model to establish the relationship between different construction parameters and the net present value of shale gas exploitation. Take obtaining the maximum net present value as the optimization goal, establish an optimization model for the fracturing construction parameters of the shale gas formation, and take the construction parameter combination corresponding to the maximum net present value as the optimization result.

[0120] Specifically, the calculation model for the sales revenue is:

[0121]

[0122] In the formula, G in represents the total annual sales revenue of natural gas; C gas,i represents the natural gas price on the i-th day after the start of production of the shale gas well after fracturing transformation; V gas,i represents the gas production volume on the i-th day after the start of production of the shale gas well after fracturing transformation.

[0123] Specifically, the calculation model for the net present value of exploitation is:

[0124]

[0125] In the formula, NPV represents the net present value; t represents time; (G in -G out ) represents the cash flow in the t-th year; e represents the annual discount rate.

[0126] The following is illustrated with a specific embodiment.

[0127] S1. Collect the reservoir geological parameters and fracturing design parameters of the shale fracturing block.

[0128] To make the model results conform to the engineering reality, the basic parameters required for the complex fracture network expansion simulation and the calculation of the single-well production after fracturing need to use field data. In this embodiment, the collected reservoir geological parameters and fracturing design parameters are shown in Table 1. This method can optimize single construction factors or multiple construction factors. In this embodiment, the parameter optimization of the construction displacement is taken as an example for specific illustration, and several preliminary optimization schemes are shown in Table 2.

[0129] Table 1 Reservoir geological parameters and fracturing design parameters

[0130]

[0131] Table 2 Construction Displacement Optimization Plan

[0132] Optimization Plan Plan 1 Plan 2 Plan 3 Plan 4 Construction Displacement <![CDATA[12m 3 / min]]> <![CDATA[14m 3 / min]]> <![CDATA[16m 3 / min]]> <![CDATA[18m 3 / min]]>

[0133] In step S2, substitute the construction displacement parameters in Table 1 and Table 2 into the dynamic expansion model of complex fracture networks for multi-cluster fracturing in horizontal wells. Among them, the fracture fluid volume is 500 m 3 , the total fracturing fluid volume is 2000 m 3 , the number of fracture clusters is 6, and the proppant dosage is 110 t, and the fracture geometric parameters are calculated. Figures 2 to 5 They are the fracture propagation trajectories calculated by Plan 1, Plan 2, Plan 3, and Plan 4 respectively. The average fracture length, average fracture height, and average fracture width of Plan 1 are 188 m, 33.3 m, and 3.1 mm respectively; the average fracture length, average fracture height, and average fracture width of Plan 2 are 208 m, 33.1 m, and 3.0 mm respectively; the average fracture length, average fracture height, and average fracture width of Plan 3 are 228 m, 33.6 m, and 2.4 mm respectively; the average fracture length, average fracture height, and average fracture width of Plan 4 are 202 m, 32.8 m, and 3.3 mm respectively. According to Figures 2 through 5 it can be seen that when the displacement is 16 m 3 / min, the formed fracture network structure is more complex.

[0134] Step S3: Establish a single-well production calculation model after shale gas horizontal well fracturing.

[0135] (1) According to the reservoir geological parameters and physical properties parameters of the shale fracturing block in Table 1, combined with the fracture geometric parameters after fracturing such as Plan 1, Plan 3, Plan 3, and Plan 4 calculated by the dynamic expansion model of complex fracture networks for multi-cluster fracturing in shale gas horizontal wells in step S2, establish a single-well production geological and physical model after shale gas horizontal well fracturing. The schematic diagram of the model is as Figure 6 shown.

[0136] (2) Import the single-well production geological and physical model after shale gas horizontal well fracturing into the IMEX black oil and unconventional simulator in the reservoir numerical simulation software CMG to construct a single-well production calculation model after shale gas horizontal well fracturing. In this embodiment, first, start the IMEX simulator in Buider of the CMG software, select the DUALPERM dual-permeability model, perform grid division on the established single-well production geological and physical model in combination with the reservoir parameters in Table 1, set the component data, relative permeability data, and gas phase adsorption data, and initialize the model. Then, in this embodiment, the horizontal section length of the horizontal well of the shale gas production well is 1200 m, the section length of the fracturing section is 60 m, with a total of 20 sections. Then, establish a shale gas hydraulic fracturing planar fracture model in the IMEX simulator, as Figure 7As shown. Finally, the model established by Buider is imported into the IMEX simulator for calculation to obtain the changes of shale reservoir pressure and gas saturation with time and the cumulative gas production of a single well under different production systems.

[0137] In this embodiment, Figures 8 to 11 They are the gas saturation distribution maps of the reservoir after 3 years of constant-pressure production calculated by Scheme 1, Scheme 2, Scheme 3, and Scheme 4 respectively. Figure 12 It is the change curve of the cumulative gas production of a single well under different schemes. It can be seen that the cumulative production corresponding to Scheme 3 is higher.

[0138] Step S4: Establish a cost calculation model for staged multi-cluster fracturing transformation of shale gas horizontal wells.

[0139] Comprehensively considering the material costs, tool costs, and construction labor costs required for horizontal well fracturing transformation, a cost calculation model for staged multi-cluster fracturing transformation of shale gas horizontal wells is established:

[0140]

[0141] In this embodiment, the length of the horizontal section of Horizontal Well 1 is 1200 m, the length of the fracturing section is 60 m, the liquid consumption per section is 2000 m 3 , the proppant dosage is 110 t, the average cost of liquid per section is 47,000 yuan, the average cost of proppant per section is 1.85 million yuan, the average engineering cost of single-section fracturing construction is 705,000 yuan, the tool cost per section is 155,000 yuan, and the total well testing cost of a single well is about 1.08 million yuan. The total cost of staged multi-cluster fracturing transformation of a single shale gas horizontal well is calculated to be 22.92 million yuan.

[0142] S5: Calculate the production net present value after fracturing transformation of shale gas horizontal wells under different construction parameters, and optimize the fracturing construction parameters with the maximum net present value.

[0143] In this embodiment, according to the simulated calculation, the shale gas production after 2 years of constant-pressure production under different schemes is obtained. For the sake of simplicity in calculation, the average natural gas price per day is adopted as 2.2 yuan / cubic meter. Combining the sales revenue calculation model and the net present value calculation model, the net present value of this shale gas well after 2 years of production under different schemes is calculated, and the results are shown in Table 3.

[0144]

[0145]

[0146] Table 3 Net present value calculation results of different schemes

[0147] Optimization Plan Plan 1 Plan 2 Plan 3 Plan 4 Construction Displacement <![CDATA[12m 3 / min]]> <![CDATA[14m 3 / min]]> <![CDATA[16m 3 / min]]> <![CDATA[18m 3 / min]]> Average Fracture Length 188m 208m 228m 202m Average Fracture Height 33.3m 33.1m 33.6m 32.8m Average Fracture Width 3.1 mm 3.0 mm 2.4 mm 3.3 mm Accumulative Gas Production (2 years) <![CDATA[2097×10 4 m 3 > <![CDATA[2191×10 4 m 3 > <![CDATA[2512×10 4 m 3 > <![CDATA[2210×10 4 m 3 > Natural Gas Sales 46.3437 million yuan 48.4211 million yuan 55.5152 million yuan 48.841 million yuan NPV 23.4237 million yuan 25.5011 million yuan 32.5952 million yuan 25.921 million yuan

[0148] After establishing the connection between different construction parameters and the net present value of shale gas production, it can be seen from the calculation results in Table 3 that different construction displacement affects the complex fracture network structure and fracture geometric parameters, and then affects the production of shale gas wells. In this embodiment, the construction parameters are optimized with the maximum net present value as the optimization goal. The optimized construction displacement plan 3, that is, the construction displacement is 16m 3 / min. At this displacement, the hydraulic fracture can communicate with the natural fracture to the greatest extent, forming a fracture network with a higher complexity, effectively releasing the reservoir productivity and obtaining higher economic benefits.

[0149] The optimization method for shale gas formation fracturing construction parameters proposed in this embodiment has the following beneficial effects:

[0150] 1. The complex fracture network dynamic expansion model in this optimization method is applicable to two-dimensional, quasi-three-dimensional, and three-dimensional fracture expansion simulations and can be selected according to requirements;

[0151] 2. The complex fracture network dynamic expansion model in this optimization method can realize multi-fracture induced stress calculation, multi-cluster flow dynamic distribution calculation, and complex fracture network dynamic expansion simulation;

[0152] 3. The single-well production calculation model in this optimization method can calculate the reservoir pressure, stress, and gas saturation under various production systems after fracturing of different shale reservoirs, and its model accuracy is high;

[0153] 4. Using this optimization method, integrating multiple processes of fracture expansion, post-fracture seepage, and economic evaluation, construction parameters such as pumping displacement and liquid volume scale can be optimized, so as to obtain the maximum economic benefits of shale gas development, and avoid blindly increasing the fracturing scale, resulting in high construction costs and unsatisfactory fracturing effects;

[0154] 5. This optimization method fully combines fracture expansion and post-fracture seepage, optimizes the fracturing construction parameters through economic evaluation, taking into account both "cost reduction" and "efficiency improvement". The principle of this method is reliable, with operability and accuracy, and can optimize the fracturing construction parameters of shale gas horizontal wells in the whole well section on the premise of given basic parameters.

[0155] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A method for optimizing the construction parameters of shale gas formation fracturing, characterized in that, It includes the following steps: S1. Obtain the geological parameters, physical property parameters, and fracturing design parameters of the reservoir in the shale fracturing block; S2. Establish a dynamic expansion model of a complex fracture network for multi-cluster fracturing of horizontal wells in shale gas; S3. Based on the geological parameters, fracturing design parameters, and fracture geometry parameters after fracturing obtained from the fracture network dynamic expansion model, establish a single-well production calculation model for the fracturing transformation of horizontal wells in shale gas; S4. Based on the costs required for each project of the horizontal well fracturing transformation, establish a cost calculation model for multi-cluster fracturing transformation of horizontal wells in shale gas; S5. Combine the fracture network dynamic expansion model, single-well production calculation model, and fracturing transformation cost calculation model to calculate the net present value of production after the fracturing transformation of horizontal wells in shale gas under different fracturing design parameters, and optimize the fracturing design parameters with the maximum net present value; The specific content of S2 includes: S21. Establish the connection between fracture propagation stress and displacement based on the boundary element method; S22. Consider the simultaneous propagation of multiple hydraulic fractures. There is an induced stress effect between the fractures. Then, according to the stress superposition principle, obtain the composite stress field at any point in the reservoir during the dynamic fracture propagation, and obtain the induced stress field calculation model; S23. Regard the fracturing fluid as an incompressible Newtonian fluid. Consider the flow of the fracturing fluid in the horizontal wellbore, perforation holes, and fracturing fractures, as well as the filtration effect of the fracturing fluid. Based on the pressure balance principle and the principle of mass conservation, use the Newton iterative method to establish a dynamic flow distribution model for multi-cluster fracturing of horizontal wells; S24. Consider the combined failure mode of fracture tension and shear. Select the critical energy release rate criterion at the tip as the fracture propagation criterion. Calculate the fracture propagation direction through the maximum tensile stress criterion. Consider non-uniform propagation and correct the propagation step length of multiple fractures to establish a calculation model for the propagation step length and direction of multiple fractures; S25. Consider the influence of natural fractures developed in the shale reservoir on the propagation of hydraulic fractures. The hydraulic fractures will cross natural fractures, turn along natural fractures, etc. At the same time, consider the filtration of the fracturing fluid into natural fractures, and establish an intersection model of hydraulic fractures and natural fractures based on empirical analytical formulas; S26. According to the stress-displacement relationship in step S21, the induced stress field calculation model in step S22, and the fracturing fluid flow field in step S23, couple them to form a fully coupled fluid-solid fracture propagation model. Combine the propagation criterion in step S24 and the intersection criterion in step S25 to form a fracture field model. Combine the fully coupled fluid-solid model and the fracture field model to form a dynamic expansion model of a complex fracture network for multi-cluster fracturing of horizontal wells; 2. The method for optimizing the construction parameters of shale gas formation fracturing according to claim 1, characterized in that, The geological parameters include: maximum horizontal principal stress, minimum horizontal principal stress, stress difference between the reservoir and the interlayer, reservoir stress gradient, rock tensile strength, Young's modulus, Poisson's ratio, rock compressibility, rock density, matrix permeability, matrix porosity, gas saturation, reservoir pressure coefficient, reservoir temperature, reservoir thickness, natural fracture length, natural fracture azimuth, natural fracture shear strength, natural fracture wall friction coefficient, natural fracture porosity, natural fracture permeability; The fracturing design parameters include: cluster spacing, number of perforation clusters, perforation diameter, number of perforations, construction displacement, fracturing fluid viscosity, construction scale.

3. The method for optimizing the construction parameters of shale gas formation fracturing according to claim 1, characterized in that, When establishing the relationship between crack propagation stress and displacement based on the boundary element method: ， In the formula: represents the normal displacement of the crack element ; represents the tangential displacement of the crack element ; represents the normal stress of the crack element ; represents the tangential stress of the crack element ; represents the stress boundary influence coefficient matrix; represents the crack height correction coefficient matrix. When three-dimensional crack propagation occurs, is the identity matrix; The induced stress field calculation model is: ， In the formula: the subscript and represent directions; , , represent fracture elements acting on the fracture element induced stress field; represents the seam height correction coefficient. When three-dimensional fracture propagation occurs, the value of represents the displacement boundary influence coefficient; represents the influence coefficient of the normal displacement of the fracture element along direction on the normal stress of the fracture element along direction; represents the influence coefficient of the tangential displacement of the fracture element along direction on the normal stress of the fracture element along direction; represents the influence coefficient of the normal displacement of the fracture element along direction on the normal stress of the fracture element along direction; represents the influence coefficient of the normal displacement of the fracture element along direction on the normal stress of the fracture element along direction; represents the influence coefficient of the normal displacement of the fracture element along direction on the tangential stress of the fracture element ; represents the influence coefficient of the normal displacement of the fracture element along direction on the tangential stress of the fracture element ; and respectively represent the normal displacement and tangential displacement of the fracture element ; The dynamic flow allocation model for multi-cluster fracturing in horizontal wells by stages is: ， In the formula, represents the fracturing time; represents the position; represents the cross-sectional area of the hydraulic fracture; represents the flow rate of the fracturing fluid; represents the filtration rate of the fracturing fluid; represents the bottom-hole fluid pressure at the heel of the horizontal well; represents the wellbore friction between the heel of the horizontal well and the th perforation cluster; represents the perforation friction of the th perforation cluster; represents the inlet fluid pressure of the cluster of fractures; The calculation model for the propagation step length and direction of multiple cracks is: ， ， ， In the formula, represents half of the maximum crack propagation step length; represents the propagation step length of the th crack tip; represents the maximum energy release rate of the th crack tip; represents the maximum energy release rate matrix of the crack tip; represents the critical energy release rate for crack tip propagation; is the crack propagation deflection angle; represents the mode I stress intensity factor; represents the mode II stress intensity factor; E represents Young's modulus; represents Poisson's ratio; The intersection model of hydraulic fractures and natural fractures is: ， In the formula, represents the normal stress component of the combined in-situ stress and induced stress acting on the natural fracture wall surface; represents the tangential stress component of the combined in-situ stress and induced stress acting on the natural fracture wall surface; represents the friction coefficient of the natural fracture wall surface; represents the minimum horizontal principal stress; represents the shear strength of the natural fracture; represents the fluid pressure in the natural fracture; represents the tensile strength of the rock.

4. The method for optimizing the construction parameters of shale gas formation fracturing according to claim 1, characterized in that, The specific content of S3 includes: S31. Based on the reservoir geological parameters and physical properties of the shale fracturing and reforming block, and combining the fracture geometric parameters after fracturing calculated by the dynamic expansion model of complex fracture networks for multi-cluster fracturing in horizontal wells of shale gas, establish a single-well production geological and physical model after shale gas horizontal well fracturing and reforming; S32. Import the single-well production geological and physical model after shale gas horizontal well fracturing and reforming into the reservoir numerical simulation software CMG to construct a single-well production calculation model after shale gas horizontal well fracturing and reforming. According to the single-well production calculation model after shale gas horizontal well fracturing and reforming, calculate the changes of shale reservoir pressure and gas saturation over time and the cumulative gas production of a single well under different production systems.

5. The optimization method for shale gas formation fracturing construction parameters according to claim 1, wherein, The specific content of S4 includes: Considering the material costs, tool costs, and construction labor costs required for horizontal well fracturing and reforming, establish a cost calculation model for multi-cluster fracturing in horizontal wells of shale gas by stages: ， In the formula, It represents the total cost of fracturing transformation of a single horizontal well of shale gas; Indicates the total number of fracturing stages; Indicates The cost of fracturing fluid for stage fracturing; Indicates Proppant costs for stage fracturing; Indicates Cost of tools for stage fracturing; Indicates The engineering cost of stage fracturing; Indicates Other costs of stage fracturing.

6. The optimization method for shale gas formation fracturing construction parameters according to any one of claims 1 to 5, wherein, The specific content of S5 includes: S51. Based on the fact that the income from the shale reservoir after fracturing and reforming comes from the sale of natural gas, establish a sales revenue calculation model; S52. Use the net present value method to conduct an economic evaluation of the shale gas horizontal well fracturing and reforming, and establish a net present value calculation model for exploitation; S53. Combine the fracture network dynamic expansion model, single-well production calculation model, fracturing and reforming cost calculation model, and net present value calculation model for exploitation to establish the relationship between different construction parameters and the net present value of shale gas exploitation. Taking the maximum net present value as the optimization goal, establish an optimization model for shale gas formation fracturing construction parameters, and take the construction parameter combination corresponding to the maximum net present value as the optimization result.

7. The optimization method for shale gas formation fracturing construction parameters according to claim 6, wherein, The sales revenue calculation model is: ， In the formula, represents the total annual natural gas sales revenue; represents the natural gas price on the th day after the start of production of the shale gas well fracturing transformation; represents the gas production on the th day after the start of production of the shale gas well fracturing transformation.

8. The optimization method for shale gas formation fracturing construction parameters according to claim 6, wherein, The net present value calculation model for exploitation is: ， Wherein, represents the net present value; represents time; ( - ) represents the cash flow in the th year; represents the annual discount rate.

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