Method for optimizing hydraulic fracturing multi-stage fracture global support parameters

Abstract

The present application relates to a kind of hydraulic fracturing multi-stage fracture global support parameter optimization method, comprising the following steps: S1, the support agent particle transport numerical model is established to simulate the transport process of proppant in multi-stage fracture;S2, the transport process of proppant under multiple working conditions is simulated using numerical model, and the corresponding proppant steering into fracture simulation result is obtained;S3, "reynolds number" and "particle size / width ratio of secondary main fracture" are used to construct two-dimensional optimization chart, and the proppant steering into fracture simulation result is substituted into optimization chart, and according to simulation result, optimization chart is divided into different regions;S4, the position of the optimization condition to be optimized in optimization chart is analyzed, the proppant into fracture condition corresponding to the optimization condition to be optimized is judged, and parameter optimization is carried out.The present application can quickly judge whether the specific working condition of proppant can steer into fracture according to optimization chart, and can clearly determine the main influencing factors of proppant steering into fracture and provide parameter optimization direction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas field development engineering, and particularly relates to a hydraulic fracturing multi-stage fracture global support parameter optimization method. BACKGROUND

[0002] Hydraulic fracturing technology is a key means for effective development of unconventional oil and gas reservoirs. At present, it generally presents the characteristics of "large-scale fluid injection at high speed, mixing of multiple proppant particle sizes, and high-strength sanding operation", aiming to increase the effective support range of fractures and improve the flow capacity of supported fractures. Field fracturing test coring observation results show that the reservoir is prone to form the structural characteristics of "main fracture + branch fracture + secondary micro-fracture" after fracturing, but the fracture support volume is limited, and the effective support fracture length and fracture height are greatly different from the hydraulic fracture length and fracture height. The main reasons for this problem are that the proppant particles carried by low-viscosity or high-viscosity gel-breaking fracturing fluid have a high settling rate, and at the same time, due to the narrow fracture width, the proppant is difficult to turn into the secondary fracture, resulting in a lack of effective support at the far end of the fracture. Therefore, under the existing construction method and construction parameters, a large number of artificial hydraulic fractures are wasted, causing the increase in construction scale to be unmatched with the increase in fracturing well production, and it is urgent to improve the development level of unconventional oil and gas reservoirs through hydraulic fracturing technology innovation.

[0003] The "multi-stage fracture global support technology" aims to take the whole unconventional oil and gas reservoir as the target for modification, form multi-scale flow channels in the reservoir through nano-micropore point desorption, nano-pore throat line dredging, micro-fracture plane support, and main fracture three-dimensional support, realize the effective connection of matrix-main fracture-micro-fracture, and achieve the purpose of global support and improved recovery. In view of the problem of insufficient effective support volume of fractures, the global support technology requires introducing micro-proppant (more than 200 mesh) on the basis of the existing main particle size (40 / 70 mesh and 70 / 140 mesh) proppant transport to realize effective support of branch fractures and secondary micro-fractures. Under the background of this technology, the proppant entering the fracture has more distinct and extensive particle size distribution characteristics: particles of different particle sizes are mixed with fracturing fluid to form a complex dense solid-liquid multiphase flow system, which belongs to a typical polydisperse system in fluid mechanics, and the diverse particle size distribution of particles further increases the system complexity and dynamic behavior. Therefore, how to optimize the fracturing construction parameters to improve the support volume of secondary fractures is one of the keys to realizing multi-stage fracture global support. SUMMARY

[0004] In order to overcome the problems in the prior art, the present application provides a hydraulic fracturing multi-stage fracture global support parameter optimization method, system, device and readable storage medium.

[0005] In a first aspect, the present application provides a hydraulic fracturing multi-stage fracture global support parameter optimization method, comprising the following steps:

[0006] S1, a proppant particle transport numerical model is established, the numerical model simulates the transport process of the proppant in the multi-stage fractures;

[0007] S2, the transport process of the proppant in the multi-stage fractures under a plurality of working conditions is simulated by using the numerical model, and corresponding proppant turning into fracture simulation results under the plurality of working conditions are obtained;

[0008] S3, a two-dimensional optimization chart is constructed with "Reynolds number" and "particle size / (secondary fracture width / primary fracture width)", the proppant turning into fracture simulation results in step S2 are substituted into the optimization chart, and the optimization chart is divided into different regions according to the proppant turning into fracture simulation results;

[0009] S4, a position of the working condition to be optimized in the optimization chart is analyzed, a proppant into fracture situation corresponding to the working condition to be optimized is judged according to the position, and parameter optimization is performed according to the judgment result.

[0010] Further technical solutions are that in step S1, a computational fluid dynamics-discrete element coupling method is used to establish a fracturing fluid-proppant particle multiphase coupling transport numerical model.

[0011] Further technical solutions are that in step S2, the proppant particle size includes 40 / 70, 70 / 140, 100 / 200 or 200 / 400 mesh.

[0012] Further technical solutions are that in step S3, the regions of the optimization chart include a first region and a second region, the proppant is located in the first region when the proppant can turn into the secondary fracture, and the proppant is located in the second region when the proppant cannot turn into the secondary fracture.

[0013] Further technical solutions are that in step S3, the determination method of the Reynolds number is:

[0014] Re = p v w / mu

[0015] Wherein, Re is the Reynolds number; p is the density of the fracturing fluid, v is the flow rate of the liquid, w is the width of the primary fracture; mu is the viscosity of the fracturing fluid.

[0016] Further technical solutions are that in step S4, the parameter optimization according to the judgment result further includes:

[0017] The proppant and flow distribution of the primary fracture and the secondary fracture under different parameter conditions are analyzed, the main influencing parameters are determined, and the main influencing parameters are optimized.

[0018] Further technical solutions are that the parameters include the proppant particle size, the fracturing fluid viscosity, and the fracturing fluid speed.

[0019] In another aspect, the present application provides a hydraulic fracturing multi-stage fracture global support parameter optimization system, comprising the following modules:

[0020] A numerical simulation module is configured to simulate the transport process of the proppant in the multi-stage fracture.

[0021] A data storage module is configured to store the proppant turning-in-fracture data corresponding to a plurality of working conditions calculated by the numerical simulation module.

[0022] A graph drawing module is configured to construct a two-dimensional optimization graph with the Reynolds number and the particle size / (secondary fracture width / primary fracture width), and transmit the turning-in-fracture data calculated by the data storage module to the graph drawing module to draw the optimization graph according to the turning-in-fracture data.

[0023] A parameter optimization module is configured to analyze the position of the working condition to be optimized in the optimization graph, judge the proppant turning-in-fracture condition corresponding to the working condition to be optimized according to the position, and perform parameter optimization according to the judgment result.

[0024] In another aspect, the present application provides a computer device comprising a memory, a processor and a computer program stored in the memory and running on the processor, characterized in that the processor implements the steps of the hydraulic fracturing multi-stage fracture global support parameter optimization method of any one of the above claims when executing the computer program.

[0025] In another aspect, the present application provides a computer readable storage medium having a computer program stored thereon, characterized in that the computer program is executed by a processor to implement the steps of the hydraulic fracturing multi-stage fracture global support parameter optimization method of any one of the above claims.

[0026] The present application provides a hydraulic fracturing multi-stage fracture global support parameter optimization method, system, device and readable storage medium, which simulates the turning process of the proppant at the fracture intersection and statistics the proppant turning-in-fracture condition under different working conditions, establishes a proppant turning-in-fracture parameter optimization graph, judges whether there is a proppant turning-in-fracture difficulty problem according to the graph, and determines the main influencing factors of the proppant turning-in-fracture, thereby providing a parameter optimization method for optimizing the main factors as the direction and providing a theoretical basis for realizing the multi-stage fracture global support. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present application, but not limit the present application.

[0028] Figure 1 The method flowchart of the present application is shown in the figure;

[0029] Figure 2 A fracture interaction node grid model diagram in the embodiment of the present application;

[0030] Figure 3 An optimization chart in the embodiment of the present application;

[0031] Figure 4 A parameter optimization flow chart in the embodiment of the present application;

[0032] Figure 5 A main influence parameter optimization schematic diagram in the embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort fall within the scope of protection of the present application.

[0034] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood as the usual meaning understood by those skilled in the art to which the present disclosure belongs. The similar words such as "comprise" or "include" and the like used in the present disclosure mean that the elements or objects before the words cover the elements or objects listed after the words and their equivalents, without excluding other elements or objects.

[0035] In the prior art, in order to improve the supporting effect of the fracture, there are various hydraulic fracturing construction parameter optimization methods, but the optimization method with the multi-stage fracture global support technology implementation as the starting point and the improvement of the secondary fracture support volume as the target has not been established in the prior art.

[0036] As shown in Figure 1 The present application provides a hydraulic fracturing multi-stage fracture global support parameter optimization method, comprising the following steps:

[0037] S1, a proppant particle transport numerical model is established, the numerical model simulates the transport process of the proppant in the multi-stage fracture;

[0038] S2, the transport process of the proppant in the multi-stage fracture under a plurality of working conditions is simulated by using the numerical model, and the corresponding proppant turning into the fracture simulation results under the plurality of working conditions are obtained;

[0039] S3, constructing a two-dimensional optimization chart with "Reynolds number" and "particle size / (secondary fracture width / primary fracture width)", and substituting the proppant diversion into fracture simulation result in step S2 into the optimization chart, and dividing the optimization chart into different regions according to the proppant diversion into fracture simulation result;

[0040] S4, analyzing the position of the to-be-optimized working condition in the optimization chart, judging the proppant diversion into fracture corresponding to the to-be-optimized working condition according to the position, and performing parameter optimization according to the judgment result.

[0041] In step S1, since the Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) coupling method has excellent ability in capturing the fine characteristics of the proppant particle size distribution, can track the movement trajectory of the particles in the complex flow environment, and is suitable for capturing the proppant diversion into fracture process, the Computational Fluid Dynamics-Discrete Element (CFD-DEM) coupling method can be used to establish a proppant particle multiphase coupling transport numerical model.

[0042] Specifically, when establishing the proppant particle multiphase coupling transport numerical model, the Navier-Stokes equation can be used to describe the dynamic behavior of the fracturing fluid in the narrow fracture, Newton's second law and the angular momentum conservation theorem can be used to describe the translation and rotation of the proppant particles, and the Hertz elastic contact theory and the Coulomb friction law can be used to describe the normal contact force and the tangential contact force between the particles and the wall surface.

[0043] Specifically, the Navier-Stokes equation is used to describe the dynamic behavior of the fracturing fluid in the narrow fracture, and its expression is as follows:

[0044]

[0045] In the formula, ρ f is the liquid density; α f is the liquid volume fraction; u f is the liquid velocity; t is the time; p is the flow field pressure; τ f is the liquid shear stress tensor, μ is the liquid dynamic viscosity; g is the gravitational acceleration; S fp is the momentum exchange term between the liquid phase and the solid phase particles.

[0046] The translation and rotation of the proppant particles satisfy Newton's second law and the angular momentum conservation, respectively, and their expressions are as follows:

[0047]

[0048] In the formula, mp is the particle mass; u p is the particle velocity; Fc is the contact force between particles and between particles and wall; F d is the drag force; G is the gravitational force; Fe is other additional forces affecting the particle motion (such as buoyancy, lift, virtual mass force, etc.). I p is the particle moment of inertia; ω p is the particle angular velocity; Mc is the contact moment; M s is the moment caused by fluid shear. Liquid-solid momentum exchange term S fp is the drag force F d Coupling is achieved by two-phase volume fraction calculation and momentum transfer, and the two-phase volume fraction calculation formula is as follows:

[0049]

[0050] α f = 1-α s

[0051] In the formula: α s is the solid volume fraction; N s is the number of particle samples in the calculation grid unit; N t is the total number of samples in the grid unit.

[0052] The Hertz elastic contact theory and the Coulomb friction law are respectively used to describe the normal contact force and the tangential contact force between particles and between particles and the wall, and the expressions are as follows:

[0053]

[0054] F t ≤ μ s F n

[0055] In the formula: E * is the effective Young's modulus; R * is the effective radius; δ is the particle overlap; μ s is the friction coefficient. E * and R * are further expressed as:

[0056]

[0057] In the formula: E1 and E2 are the Young's moduli of the two contact particles respectively; R1 and R2 are the radii of the two contact particles respectively.

[0058] In step S2, as Figure 2As shown, a multi-level fracture interaction node grid model diagram in the numerical model is used for simulation, wherein the horizontal direction fracture is the main fracture, and the inclined direction fracture is the secondary fracture. In the preferred embodiment, the angle between the main fracture and the secondary fracture is set to 60°. The intersection position of the main fracture (i.e. the main crack) and the secondary fracture (i.e. the secondary crack) is set at the position of 2 / 3 of the main crack length. The length of the main fracture and the secondary fracture is 150 mm and 50 mm respectively, and the height is 30 mm.

[0059] In the preferred embodiment, the maximum and minimum values of the main fracture width are 6 and 0.5 mm, and the maximum and minimum values of the secondary fracture width are 3 and 0.125 mm respectively. In the combined embodiment, the combination of the main fracture-secondary fracture width can be set as: 6-3 mm, 1-1 mm, 1-0.5 mm, 1-0.3 mm, 1-0.25 mm, 1-0.15 mm, 0.75-0.375 mm, 0.75-0.1875 mm, 0.5-0.5 mm, 0.5-0.25 mm, 0.5-0.125 mm, wherein the embodiment of 6-3 mm can be used for model verification.

[0060] In the preferred embodiment, the main fracture-secondary fracture width is set to 1-0.5 mm in the fracture interaction node grid model, and the main fracture length direction is set to 500 and 200 grids before and after the intersection of the main fracture and the secondary fracture respectively. The main fracture width direction is set to 10 grids, and the main fracture height direction is set to 120 grids. The secondary fracture length, width and height are set to 250, 5 and 120 grids respectively. When the fracture width is less than 0.5 mm, the grid number is set according to the ratio of 4-5 grids / mm.

[0061] In addition, for the working condition parameters related to the proppant, in the preferred embodiment, the proppant is considered as a spherical particle, and the particle size can be set to 40 / 70, 70 / 140, 100 / 200 and 200 / 400 mesh. The density is 2650 kg / m 3 , the Poisson's ratio is 0.25, the Young's modulus is 1.667×106 Pa, the collision restitution coefficient is 0.2, and the static and dynamic friction coefficients are 0.55 and 0.02 respectively.

[0062] In addition, the variables considered in the proppant transport simulation include transport speed, fracturing fluid viscosity and proppant concentration. The transport speed can be preferably 0.03, 0.05 and 0.08 m / s, the viscosity is set to 2.5, 5, 7.5 and 10 mPa·s, and the proppant concentration is set to 1, 3 and 5%.

[0063] In step S3, as shown in FIG. 3, the fracture width of the main fracture and the secondary fracture is set to 1-0.5 mm, and the intersection position of the main fracture and the secondary fracture is set at the position of 2 / 3 of the main crack length. Figure 3As shown, a chart for optimizing proppant orientation parameters is established by using "Reynolds number" and "particle size / (secondary crack width / primary crack width)" as the ordinate and abscissa, respectively. Figure 3 The paper presents 23 simulated working conditions. Since the fluid dynamics-discrete element method used in this application can directly track the movement trajectory of proppant particles in the crack, the diagrams can be divided according to whether the proppant can be redirected into the crack under these conditions. It can be seen that in working conditions numbered 3, 5, 8, 17, 19, and 21, the proppant cannot enter the secondary crack. Therefore, in... Figure 3 The optimized diagram is divided into a first region and a second region. The working conditions in the first region indicate that the proppant can turn and enter the secondary crack, while the second region indicates that the proppant cannot turn and enter the secondary crack. That is, the first region is the "effective crack entry zone" and the second region is the "crack entry difficulty zone".

[0064] In step S4, it can be based on Figure 4 The flowchart shown illustrates the process of determining operating conditions and optimizing parameters. For a specific operating condition, the flow Reynolds number and the ratio of particle size to (secondary fracture width to primary fracture width) are calculated using parameters such as proppant delivery rate, fracturing fluid viscosity, and fracture width. The calculation results are then input into the optimization chart to quickly determine whether the specific operating condition belongs to the "effective fracture entry zone" or the "difficult fracture entry zone." If the operating condition is in the "difficult fracture entry zone," it is clearly insufficient to meet the support requirements of the secondary fractures, and parameter optimization is required to ensure that the corresponding operating condition falls within the "effective fracture entry zone."

[0065] If the operating condition is within the "effective entry zone," further analysis can be conducted using the relative relationship between the secondary-to-primary joint particle number ratio and the secondary-to-primary joint fluid flow ratio to identify the limiting factors restricting proppant entry. These limiting factors are the parameters to be optimized, i.e., the main influencing parameters restricting proppant entry. Optimizing these main influencing parameters allows the adjusted operating condition to move away from the boundary between the two zones and towards the heart of the "effective entry zone," as shown below. Figure 5 Moving in the direction indicated by the middle arrow provides an improved strategy for parameter optimization.

[0066] like Figure 5As shown, when the primary-secondary fracture width is 1-0.5 mm, under the working condition of No. 12, the migration speed is 0.05 m / s, and the viscosity is 5 mPa·s, the main influencing parameter restricting the diversion of the proppant into the fracture is the particle size (the corresponding short board in the figure); under the working condition of No. 22, the migration speed is 0.05 m / s, and the particle size is 100 / 200 mesh, the short board factor restricting the diversion of the proppant into the fracture is the viscosity; under the working condition of No. 14, the viscosity is 5 mPa·s, and the particle size is 100 / 200 mesh, the short board factor restricting the diversion of the proppant into the fracture is the speed; therefore, the parameter optimization directions of the above three working conditions are to reduce the particle size, increase the liquid viscosity, and increase the conveying speed. Therefore, for the fracture intersection node model with the primary-secondary fracture width of 1-0.5 mm, the staff can conclude that the optimization parameters must ensure that the particle size is less than 70 / 140 mesh, the viscosity is greater than 2.5 mPa·s, and the conveying speed is greater than 0.03 m / s, which can promote the proppant to further smoothly divert into the fracture and improve the effective propped volume of the secondary fracture.

[0067] Therefore, the hydraulic fracturing multi-stage fracture global proppant parameter optimization method provided by the present application can quickly determine whether the proppant can divert into the secondary fracture under a certain working condition, and can quantitatively give a parameter optimization scheme for the proppant to smoothly divert into the fracture, solving the problem of limited single-factor optimization effect in current hydraulic fracturing construction, and providing guidance for the optimization design of the hydraulic fracturing multi-stage fracture global proppant technology.

[0068] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to make equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any simple modification, equivalent change and modification of the above embodiments based on the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A method for optimizing support parameters of hydraulic fracturing multi-stage fractures, comprising the following steps: S1, establishing a support agent particle delivery numerical model, the numerical model simulating the delivery process of the support agent in the multi-stage fractures; S2, using the numerical model to simulate the delivery process of the support agent in the multi-stage fractures under a plurality of working conditions, and obtaining corresponding support agent turning into fracture simulation results under the plurality of working conditions; S3, constructing a two-dimensional optimization chart with "Reynolds number" and "particle size / (secondary fracture width / primary fracture width)", and substituting the support agent turning into fracture simulation results in step S2 into the optimization chart, and dividing the optimization chart into different regions according to the support agent turning into fracture simulation results; the regions of the optimization chart in step S3 include a first region and a second region, the support agent being located in the first region when the support agent can turn into the secondary fracture, and the support agent being located in the second region when the support agent cannot turn into the secondary fracture; S4, analyzing the position of a working condition to be optimized in the optimization chart, judging the support agent turning into fracture condition corresponding to the working condition to be optimized according to the position, and performing parameter optimization according to the judgment result. 2.The method for optimizing support parameters of hydraulic fracturing multi-stage fractures according to claim 1, wherein a computational fluid dynamics-discrete element coupling method is used to establish a fracturing fluid-support agent particle multiphase coupling delivery numerical model in step S1. 3.The method for optimizing support parameters of hydraulic fracturing multi-stage fractures according to claim 1, wherein the support agent particle size in step S2 includes 40 / 70, 70 / 140, 100 / 200 or 200 / 400 mesh. 4.The method for optimizing support parameters of hydraulic fracturing multi-stage fractures according to claim 1, wherein the determination method of the Reynolds number in step S3 is: where v is the velocity of the fracturing fluid, w is the width of the primary fracture, μ is the viscosity of the fracturing fluid, ρ is the density of the fracturing fluid, and g is the acceleration of gravity. 5.The method for optimizing support parameters of hydraulic fracturing multi-stage fractures according to claim 1, wherein the parameter optimization according to the judgment result in step S4 further comprises: analyzing the support agent and flow distribution of the primary fracture and the secondary fracture under different parameter conditions, determining the main influencing parameter, and optimizing the main influencing parameter. 6.The method for optimizing support parameters of hydraulic fracturing multi-stage fractures according to claim 5, wherein the parameters include the support agent particle size, the fracturing fluid viscosity and the fracturing fluid velocity. 7.A system for optimizing support parameters of hydraulic fracturing multi-stage fractures, comprising the following modules: a numerical simulation module for simulating the delivery process of the support agent in the multi-stage fractures; a data storage module for storing the support agent turning into fracture data corresponding to a plurality of working conditions calculated by the numerical simulation module; and a chart drawing module for constructing a two-dimensional optimization chart with "Reynolds number" and "particle size / (secondary fracture width / primary fracture width)", transmitting the turning into fracture data calculated by the data storage module to the chart drawing module, and drawing the optimization chart according to the turning into fracture data; the regions of the optimization chart include a first region and a second region, the support agent being located in the first region when the support agent can turn into the secondary fracture, and the support agent being located in the second region when the support agent cannot turn into the secondary fracture. ​ ​ Re= ​ ​ ​ wherein Re is the Reynolds number; ​ is the fracturing fluid density, v is the liquid flow rate, w is the main fracture width; ​ is the fracturing fluid viscosity. ​ ​ ​ ​ ​ ​ ​ ​ A parameter optimization module is configured to analyze a position of a to-be-optimized working condition in the optimization chart, determine a proppant entry condition corresponding to the to-be-optimized working condition according to the position, and perform parameter optimization according to a result of the determination.

8. A computer device comprising a memory, a processor, and a computer program stored on the memory and running on the processor, characterized in that, The computer program is executed by the processor to implement the steps of the hydraulic fracturing multi-stage fracture global proppant parameter optimization method of any one of claims 1-6.

9. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the hydraulic fracturing multi-stage fracture global proppant parameter optimization method of any one of claims 1-6.

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