Hydraulic fracturing multistage fracture global support parameter optimization method

Abstract

The invention relates to a hydraulic fracturing multi-stage fracture global support parameter optimization method. The method comprises the steps that S1, a propping agent particle conveying numerical model is established to simulate the conveying process of a propping agent in a multi-stage fracture; s2, the numerical model is used for simulating the conveying process of the propping agent under multiple working conditions, and a corresponding propping agent steering and seam entering simulation result is obtained; s3, constructing a two-dimensional optimization plate according to the Reynolds number and the particle size / secondary main fracture width ratio, substituting the simulation result of turning the propping agent into the fracture into the optimization plate, and dividing the optimization plate into different areas according to the simulation result; and S4, analyzing the position of the to-be-optimized working condition in the optimization plate, judging the propping agent crack entering condition corresponding to the to-be-optimized working condition, and performing parameter optimization. Whether the proppant can be steered into the seam or not under the specific working condition can be quickly judged according to the optimization plate, main influence factors for restricting the proppant to steer into the seam can be clearly defined, and a parameter optimization direction is provided.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas field development engineering, and particularly to an optimization method for the whole-region support parameters of multi-stage fractures in hydraulic fracturing. Background Art

[0002] The hydraulic fracturing technology is a key means for the effective development of unconventional oil and gas reservoirs. Currently, it generally presents characteristics such as "large-scale fluid high-speed injection, mixing of various proppant particle sizes, and high-intensity sand addition operations", aiming to increase the effective support range of fractures and enhance the flow capacity of the supported fractures. The results of on-site fracturing test coring observations show that the post-fracture reservoir is prone to form a structural feature of "main fracture + branch fracture + secondary micro-fracture", but the fracture support volume is limited, and there is a large gap between the effective supported fracture length and height of the fracture and the hydraulic fracture length and height. The main reasons for this problem are that the settlement rate of proppant particles is fast under the carrying of low-viscosity or high-viscosity gel-breaking fracturing fluid, and at the same time, due to the narrow fracture width, it is difficult for the proppant to turn and enter the secondary fractures, resulting in a lack of effective support at the far end of the fracture. Therefore, under the existing construction methods and construction parameters, a large number of artificial hydraulic fractures are wasted, resulting in a mismatch between the increase in construction scale and the increase in the production of fractured wells. It is urgent to improve the development level of unconventional oil and gas reservoirs through hydraulic fracturing technology innovation.

[0003] The "multi-stage fracture whole-region support technology" aims to take the whole unconventional oil and gas reservoir as the transformation target, and form multi-scale flow channels in the reservoir through nano-micro pore desorption, nano-pore throat line dredging, micro-fracture plane support, and main fracture three-dimensional support, so as to achieve the effective connection of matrix-main fracture-micro fracture, and achieve the purpose of whole-region support and enhanced oil recovery. Aiming at the problem of insufficient effective support volume of fractures, the whole-region support technology requires the introduction of micro-proppant (above 200 mesh) on the basis of the existing main particle size (40 / 70 mesh and 70 / 140 mesh) proppant transportation to achieve effective support for branch fractures and secondary micro-fractures. Under this technical background, the proppant entering the fracture has a more distinct and extensive particle size distribution characteristic: particles of different particle sizes are closely mixed with the fracturing fluid, jointly constituting a complex dense solid-liquid multiphase flow system, which belongs to a typical polydisperse system in fluid mechanics. The diverse particle size distribution of particles further increases the system complexity and dynamic behavior. Therefore, how to improve the support volume of secondary fractures by optimizing fracturing construction parameters is one of the keys to achieving multi-stage fracture whole-region support. Summary of the Invention

[0004] In order to overcome the problems in the prior art, the present invention provides an optimization method, system, device and readable storage medium for the whole-region support parameters of multi-stage fractures in hydraulic fracturing.

[0005] In the first aspect, the present invention provides an optimization method for the whole-region support parameters of multi-stage fractures in hydraulic fracturing, including the following steps:

[0006] S1. Establish a numerical model for the transport of proppant particles, which simulates the transport process of proppant in multi-stage fractures;

[0007] S2. Use the numerical model to simulate the transport process of proppant in multi-stage fractures under multiple working conditions, and obtain the simulation results of proppant diversion into fractures corresponding to the multiple working conditions;

[0008] S3. Construct a two-dimensional optimization chart with "Reynolds number" and "particle size / (secondary fracture width / principal fracture width)", substitute the simulation results of proppant diversion into fractures in step S2 into the optimization chart, and divide the optimization chart into different regions according to the simulation results of proppant diversion into fractures;

[0009] S4. Analyze the position of the working condition to be optimized in the optimization chart, judge the proppant entry into fractures corresponding to the working condition to be optimized according to the position, and optimize the parameters according to the judgment result.

[0010] A further technical solution is that in step S1, a multi-phase coupled transport numerical model of fracturing fluid-proppant particles is established by using the computational fluid dynamics-discrete element coupling method.

[0011] A further technical solution is that in step S2, the proppant particle sizes include 40 / 70, 70 / 140, 100 / 200 or 200 / 400 mesh.

[0012] A further technical solution is that in step S3, the regions of the optimization chart include a first region and a second region. When the proppant can divert into the secondary fracture, it is in the first region, and when the proppant cannot divert into the secondary fracture, it is in the second region.

[0013] A further technical solution is that the method for determining the Reynolds number in step S3 is:

[0014] Re = ρvw / μ

[0015] where Re is the Reynolds number; ρ is the density of the fracturing fluid, v is the liquid flow velocity, w is the width of the principal fracture; μ is the viscosity of the fracturing fluid.

[0016] A further technical solution is that in step S4, optimizing the parameters according to the judgment result further includes:

[0017] Analyze the proppant and flow rate distribution between the principal fracture and the secondary fracture under different parameter conditions, determine the main influencing parameters, and optimize the main influencing parameters.

[0018] A further technical solution is that the parameters include proppant particle size, fracturing fluid viscosity, and fracturing fluid velocity.

[0019] On the other hand, the present invention provides a system for optimizing the full-domain support parameters of multi-stage fractures in hydraulic fracturing, including the following modules:

[0020] A numerical simulation module for simulating the transportation process of proppants in multi-stage fractures;

[0021] A data storage module for storing the proppant diversion and entry data corresponding to multiple working conditions calculated by the numerical simulation module;

[0022] A chart drawing module that constructs a two-dimensional optimization chart with "Reynolds number" and "particle size / (secondary fracture width / primary fracture width)", transfers the entry data calculated by the data storage module to the chart drawing module, and draws an optimization chart based on the diversion and entry data;

[0023] A parameter optimization module for analyzing the position of the working condition to be optimized in the optimization chart, judging the proppant entry situation corresponding to the working condition to be optimized according to the position, and performing parameter optimization according to the judgment result.

[0024] On the other hand, the present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and running on the processor, wherein the processor implements the steps of the method for optimizing the full-domain support parameters of multi-stage fractures in hydraulic fracturing according to any one of the above claims when executing the computer program.

[0025] On the other hand, the present invention provides a computer-readable storage medium, on which a computer program is stored, wherein the computer program implements the steps of the method for optimizing the full-domain support parameters of multi-stage fractures in hydraulic fracturing according to any one of the above claims when executed by a processor.

[0026] The present invention provides a method, a system, a device, and a readable storage medium for optimizing the full-domain support parameters of multi-stage fractures in hydraulic fracturing. By simulating the diversion process of proppants at the fracture intersections and counting the proppant diversion and entry situations under different working conditions, an optimization chart of proppant diversion and entry parameters is established. According to the chart, it is judged whether there is a problem with difficult proppant diversion and entry in a specific working condition, and the main influencing factors restricting proppant diversion and entry are clarified. Thus, a parameter optimization method with the direction of optimizing the main factors is proposed, providing a theoretical basis for realizing the full-domain support of multi-stage fractures. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0028] Figure 1 It is a schematic flow chart of the method of the present invention;

[0029] Figure 2 It is a grid model diagram of a crack interaction node in an embodiment of the present invention;

[0030] Figure 3 It is an optimized chart in an embodiment of the present invention;

[0031] Figure 4 It is a flow chart of parameter optimization in an embodiment of the present invention;

[0032] Figure 5 It is a schematic diagram of the optimization of main influencing parameters in an embodiment of the present invention. Specific implementation manners

[0033] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Unless otherwise defined, the technical terms or scientific terms used in this disclosure shall have the ordinary meanings understood by those of ordinary skill in the art to which this disclosure pertains. The words such as "including" or "comprising" used in this disclosure mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0035] In the prior art, in order to improve the support effect of cracks, there are various optimization methods for hydraulic fracturing construction parameters. However, in the prior art, an optimization method starting from the realization of the multi-stage crack global support technology and aiming at increasing the support volume of secondary cracks has not been established.

[0036] As Figure 1 shown, the present invention provides a method for optimizing parameters of multi-stage crack global support for hydraulic fracturing, including the following steps:

[0037] S1. Establish a numerical model for proppant particle transportation, and the numerical model simulates the transportation process of proppants in multi-stage cracks;

[0038] S2. Use the numerical model to simulate the transportation process of proppants in multi-stage cracks under multiple working conditions, and obtain the simulation results of proppant turning into the cracks corresponding to the multiple working conditions;

[0039] S3. Construct a two-dimensional optimization chart using the "Reynolds number" and "particle size / (secondary fracture width / primary fracture width)", substitute the simulation results of proppant diversion into the fracture in step S2 into the optimization chart, and divide the optimization chart into different regions according to the simulation results of proppant diversion into the fracture;

[0040] S4. Analyze the position of the working condition to be optimized in the optimization chart, judge the proppant entry situation corresponding to the working condition to be optimized according to the position, and optimize the parameters according to the judgment result.

[0041] In step S1, since the computational fluid dynamics (CFD)-discrete element method (DEM) coupling method has shown excellent capabilities in capturing the fine characteristics of proppant particle size distribution, can track the movement trajectories of particles in complex flow environments, and is suitable for capturing the process of particles entering the fracture, the CFD-DEM coupling method can be used to establish a numerical model for multiphase coupled transportation of fracturing fluid-proppant particles.

[0042] Specifically, when establishing the numerical model for multiphase coupled transportation of fracturing fluid-proppant particles, the Navier-Stokes equation can be used to describe the dynamic behavior of fracturing fluid in narrow fractures, the Newton's second law and the law of conservation of angular momentum can be used to describe the translational and rotational motions of proppant particles, and the Hertz elastic contact theory and the Coulomb friction law can be used to describe the normal and tangential contact forces between particles and between particles and the wall surface.

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

[0044]

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

[0046] The translational and rotational motions of proppant particles respectively satisfy Newton's second law and the law of conservation of angular momentum, 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 the wall; F d is the drag force; G is the gravity; Fe is the additional force affecting particle motion (such as buoyancy force, lift force, virtual mass force, etc.). I p is the moment of inertia of the particle; ω p is the angular velocity of the particle; Mc is the contact moment; M s is the moment caused by fluid shear. The liquid-solid momentum exchange term S fp and the drag force F d are coupled through two-phase volume fraction calculation and momentum transfer. 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-phase volume fraction; N s is the number of particle samples in the calculation grid cell; N t is the total number of samples in the grid cell.

[0052] The Hertz elastic contact theory and Coulomb friction law are respectively used to describe the normal contact force and tangential contact force between particles and between particles and the wall. Their 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 contacting particles respectively; R1 and R2 are the radii of the two contacting particles respectively.

[0058] In step S2, if Figure 2As shown, a multi-level fracture interaction node grid model diagram in a numerical model is used for simulation. Among them, the horizontal fractures are the main fractures, and the inclined fractures are the secondary fractures. In a preferred embodiment, the included angle between the main fracture and the secondary fracture is set at 60°. The intersection position of the main fracture (i.e., the main seam) and the secondary fracture (i.e., the secondary seam) is set at the 2 / 3 position of the main seam length. The lengths of the main fracture and the secondary fracture are 150 mm and 50 mm respectively, and the heights are both 30 mm.

[0059] In a preferred embodiment, the maximum and minimum values of the main fracture width are 6 and 0.5 mm, and the corresponding maximum and minimum values of the secondary fracture width are 3 and 0.125 mm respectively. In a combined embodiment, the combinations of the main fracture-secondary fracture widths 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. Among them, the 6-3 mm embodiment can be used for model verification.

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

[0061] In addition, for the working condition parameters related to the proppant, in a preferred embodiment, the proppant is considered as spherical particles, and its 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 recovery 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 transportation simulation also include the transportation speed, the viscosity of the fracturing fluid, and the proppant concentration. Among them, the transportation 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, 5%.

[0063] In step S3, as Figure 3As shown, taking the "Reynolds number" and "particle size / (secondary fracture width / primary fracture width)" as the vertical and horizontal coordinates respectively, an optimization chart for proppant diversion into fractures is established. Figure 3 Twenty-three simulated working conditions are shown in Figure 3 . Since the fluid mechanics-discrete element coupling method used in this application can directly track the movement trajectory of proppant particles in fractures, the chart can be divided according to whether the proppant can divert into the fracture under the working conditions. It can be seen that the proppant cannot enter the secondary fracture in the working conditions numbered 3, 5, 8, 17, 19, and 21. Therefore, in Figure 3 the optimization chart is divided into a first region and a second region. The working conditions in the first region indicate that the proppant can divert into the secondary fracture, while the second region indicates that the proppant cannot divert into the secondary fracture. That is, the first region is the "effective fracture entry zone", and the second region is the "difficult fracture entry zone".

[0064] In step S4, the working condition determination and parameter optimization can be carried out according to the Figure 4 flow chart shown in Figure 4 . For a specific working condition, the flow Reynolds number and particle size / (secondary fracture width / primary fracture width) are calculated through the proppant transport velocity, fracturing fluid viscosity, and fracture width parameters. Substituting the calculation results into the optimization chart can quickly determine whether the specific working condition belongs to the "effective fracture entry zone" or the "difficult fracture entry zone". If the working condition is in the "difficult fracture entry zone", it is obvious that the support requirement for the secondary fracture cannot be met at this time, and parameter optimization is needed to make the corresponding working condition result located in the "effective fracture entry zone".

[0065] If the working condition is in the "effective fracture entry zone", the short-board factors restricting the proppant diversion into the fracture can be further analyzed through the relative relationship between the particle number ratio of the secondary to primary fractures and the liquid flow ratio of the secondary to primary fractures. The short-board factors are the parameters to be optimized, that is, the main influencing parameters restricting the proppant diversion into the fracture. By optimizing the main influencing parameters, the adjusted working condition is moved away from the boundary between the two regions and towards the hinterland of the "effective fracture entry zone", that is, in the direction shown by the arrow in Figure 5 Figure 5 , so as to provide an improvement strategy for parameter optimization.

[0066] As Figure 5As shown in the figure, when the main-secondary slit width is 1 - 0.5 mm, under the working condition No. 12 with a migration speed of 0.05 m / s and a viscosity of 5 mPa·s, the main influencing parameter restricting the proppant from turning into the slit is "particle size" (the corresponding short board in the figure); under the working condition No. 22 with a migration speed of 0.05 m / s and a particle size of 100 / 200 mesh, the short board factor restricting the proppant from turning into the slit is "viscosity"; under the working condition No. 14 with a viscosity of 5 mPa·s and a particle size of 100 / 200 mesh, the short board factor restricting the proppant from turning into the slit is "speed"; therefore, the parameter optimization directions for the above three working conditions are respectively reducing the particle size, increasing the liquid viscosity, and increasing the conveying speed. Therefore, for the fracture interaction node model with a main-secondary slit width of 1 - 0.5 mm, the staff can conclude that optimizing the 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 turn into the slit more smoothly and increase the effective support volume of the secondary fracture.

[0067] Thus, it can be seen that the method for optimizing the parameters of the multi-stage fracture global support in hydraulic fracturing provided by the present invention can quickly determine whether the proppant can turn into the secondary fracture under a specific working condition, and can quantitatively give the parameter optimization scheme for the proppant to smoothly turn into the slit, solving the problem of limited optimization effect of single factor in the current hydraulic fracturing construction, and can provide guidance for the optimization design of the multi-stage fracture global support technology in hydraulic fracturing.

[0068] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing, comprising the following steps: S1. Establish a numerical model for the transportation of proppant particles, which simulates the transportation process of proppant in multi - stage fractures; S2. Use the numerical model to simulate the transportation process of proppant in multi - stage fractures under multiple working conditions, and obtain the simulation results of proppant turning into fractures corresponding to the multiple working conditions; S3. Construct a two - dimensional optimization chart with "Reynolds number" and "particle size / (secondary fracture width / principal fracture width)", substitute the simulation results of proppant turning into fractures in step S2 into the optimization chart, and divide the optimization chart into different regions according to the simulation results of proppant turning into fractures; S4. Analyze the position of the working condition to be optimized in the optimization chart, judge the proppant entry situation corresponding to the working condition to be optimized according to the position, and optimize the parameters according to the judgment result.

2. The method for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing according to claim 1, wherein in step S1, a multi - phase coupled transportation numerical model of fracturing fluid - proppant particles is established by using the computational fluid dynamics - discrete element coupling method.

3. The method for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing according to claim 1, wherein the proppant particle sizes in step S2 include 40 / 70, 70 / 140, 100 / 200 or 200 / 400 mesh.

4. The method for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing according to claim 1, wherein the regions of the optimization chart in step S3 include a first region and a second region. When the proppant can turn into the secondary fracture, it is located in the first region; when the proppant cannot turn into the secondary fracture, it is located in the second region.

5. The method for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing according to claim 1, wherein the method for determining the Reynolds number in step S3 is: Re = ρvw / μ Among them, Re is the Reynolds number; ρ is the density of the fracturing fluid, v is the liquid flow velocity, w is the width of the principal fracture; μ is the viscosity of the fracturing fluid.

6. The method for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing according to claim 1, wherein optimizing the parameters according to the judgment result in step S4 further includes: Analyze the proppant and flow distribution between the principal fracture and the secondary fracture under different parameter conditions, determine the main influencing parameters, and optimize the main influencing parameters.

7. The method for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing according to claim 6, wherein the parameters include proppant particle size, fracturing fluid viscosity, and fracturing fluid velocity.

8. A system for optimizing the global support parameters of multi - stage fractures in hydraulic fracturing, comprising the following modules: A numerical simulation module for simulating the transportation process of proppant in multi - stage fractures; A data storage module for storing the data of proppant turning into fractures corresponding to multiple working conditions calculated by the numerical simulation module; A chart drawing module, which constructs a two - dimensional optimization chart with "Reynolds number" and "particle size / (secondary fracture width / principal fracture width)", transmits the fracture entry data calculated by the data storage module to the chart drawing module, and draws the optimization chart according to the fracture entry data; The parameter optimization module is used to analyze the position of the working condition to be optimized in the optimization chart, judge the proppant injection situation corresponding to the working condition to be optimized according to the position, and perform parameter optimization according to the judgment result.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, the steps of the hydraulic fracturing multi-stage fracture global support parameter optimization method according to any one of claims 1-8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, the steps of the hydraulic fracturing multi-stage fracture global support parameter optimization method according to any one of claims 1-8 are implemented.

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