Method for matching fracture width and particle size in hydraulic fracturing multi-stage fracture global support

Abstract

The present application relates to a hydraulic fracturing multi-stage fracture global support fracture width-particle size matching method, comprising the steps: S1, establishing a fracturing fluid-supporting agent particle multiphase coupling transport numerical model and a multi-stage fracture interactive node grid model; S2, setting different working condition parameters for numerical simulation, obtaining the corresponding steering into the fracture simulation results of the proppant under different working condition parameters; S3, constructing a two-dimensional optimization chart with "Reynolds number" and "particle size / secondary fracture width", and dividing the optimization chart into different regions according to the proppant steering into the fracture simulation results in step S2; S4, analyzing the position of the to-be-optimized working condition in the optimization chart, and judging whether the particle size and fracture width of the to-be-optimized working condition are matched. The present application can quickly judge whether the designed particle size and fracture width are matched according to the optimization chart, and can quantitatively determine the upper limit of the particle size of the proppant for smooth steering into the fracture under a specific width condition, providing theoretical guidance for the optimization design of hydraulic fracturing multi-stage fracture global support technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas field development engineering, and particularly relates to a method for matching the fracture width and particle size of hydraulic fracturing multi-stage fractures. BACKGROUND

[0002] The horizontal well staged multi-cluster fracturing technology is a key means for the effective development of unconventional oil and gas reservoirs represented by shale and tight sandstone. At present, it generally presents the characteristics of "large-scale fluid high-speed injection, mixing of multiple proppant particle sizes, and high-strength sanding operation", aiming to increase the effective propped range of fractures and improve the flow capacity of propped fractures. Field fracturing test coring observation results show that the reservoir after fracturing is prone to form the structural characteristics of "main fracture + branch fracture + secondary micro-fracture", but the fracture propped volume is limited, and the effective propped fracture length and height are greatly different from the artificial hydraulic fracture. The main reasons for this problem are: (1) the proppant particles carried by low-viscosity or high-viscosity gel-breaking fracturing fluid have a fast settling rate, which easily settles and accumulates at the bottom of the fracture, resulting in a lack of effective support in the far end and height direction of the fracture; (2) the fracture width is narrow, and the proppant is difficult to turn into the secondary fracture, resulting in a lack of effective support for the secondary fracture. Therefore, under the existing construction method and construction parameters, a large number of artificial hydraulic fractures are wasted, causing a mismatch between the increase in construction scale and the production of fractured wells, and it is urgent to improve the development level of unconventional oil and gas reservoirs through technological innovation of hydraulic fracturing.

[0003] The "multi-stage fracture global propping 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 propping, and main fracture three-dimensional propping, realize the effective connection of matrix-micro-fracture-main fracture, and achieve the purpose of global propping and improving recovery. In view of the problem of insufficient effective propped volume of branch fractures and secondary micro-fractures, the global propping technology requires the introduction of 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 the effective propping 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 establish the matching relationship between the width of multi-stage fractures and the particle size of proppants is the key to ensuring that the proppants turn into various stages of fractures and obtain effective propping. SUMMARY

[0004] In order to overcome the problems in the prior art, the present application provides a method for matching the fracture width and particle size of hydraulic fracturing multi-stage fractures.

[0005] In a first aspect, the present invention provides a method for matching the width-particle size of a multi-stage hydraulic fracturing fracture across a wide range of supported fractures, comprising the following steps:

[0006] S1. Establish a numerical model of multiphase coupled transport of fracturing fluid and proppant particles and a multi-level fracture interactive node mesh model;

[0007] S2. Set different working parameters to simulate the proppant delivery process in multi-level cracks and obtain the proppant turning into the crack simulation results under different working parameters.

[0008] S3. Construct a two-dimensional optimization pattern using "Reynolds number" and "particle size / secondary crack width", substitute the proppant diversion into the crack simulation results in step S2 into the optimization pattern, and divide the optimization pattern into different regions according to the proppant diversion into the crack simulation results.

[0009] S4. Analyze the position of the working condition to be optimized in the optimization pattern, and determine whether the particle size and slit width of the working condition to be optimized match based on the position.

[0010] A further technical solution is to establish a numerical model using the CFD-DEM coupling method in step S1.

[0011] A further technical solution is to use a structured meshing method to establish a multi-level crack interactive node mesh model in step S1.

[0012] A further technical solution is that the operating parameters in step S2 include the primary-to-secondary fracture width ratio, proppant particle size, proppant concentration, fracturing fluid viscosity, and fracturing fluid velocity.

[0013] A further technical solution is that the operating parameters in step S2 satisfy one or more of the following operating parameters:

[0014] The width of the primary crack is 0.5–6 mm, and the width of the secondary crack is 0.125–3 mm.

[0015] Or the particle size of the proppant may include 40 / 70, 70 / 140, 100 / 200 or 200 / 400 mesh;

[0016] Or the proppant concentration is 1% to 5%;

[0017] Or the fracturing fluid viscosity is 2–10 mPa·s;

[0018] Or the fracturing fluid velocity is 0.03–0.08 m / s.

[0019] A further technical solution is that the operating parameters in step S2 are set as follows:

[0020] The widths of the primary cracks are 0.5, 0.75, 1, and 6 mm, and the widths of the secondary cracks are 0.125, 0.1875, 0.375, 0.15, 0.25, 0.3, 0.5, 1, and 3 mm, and are combined according to the widths of the primary cracks and the widths of the secondary cracks.

[0021] A further technical solution is that the method for determining the Reynolds number in step S3 is as follows:

[0022] Re = ρvw / μ

[0023] Where Re is the Reynolds number; ρ is the fracturing fluid density; v is the fluid velocity; w is the main fracture width; and μ is the fracturing fluid viscosity.

[0024] A further technical solution is that the optimized pattern area in step S3 includes a first area and a second area, wherein the support can be effectively inserted into the seam in the first area, while the support is difficult to insert into the seam in the second area.

[0025] A further technical solution is that, in step S4, if the working condition to be optimized is located in the second region, the proppant particle size is reduced so that the optimized material is located in the first region.

[0026] In a second aspect, the present invention provides a computer device, including 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, it implements the steps of the hydraulic fracturing multi-stage fracture global support fracture width-particle size matching method as described in any one of the preceding claims.

[0027] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that, when the computer program is executed by a processor, it implements the steps of the hydraulic fracturing multi-stage fracture global support fracture width-particle size matching method as described in any one of the preceding claims.

[0028] This invention provides a method for matching fracture width and particle size for full-domain support of multi-stage fractures in hydraulic fracturing. By simulating the turning process of proppant at the fracture interaction point and statistically analyzing the proppant turning into the fracture under different working conditions, an optimized chart for judging whether the fracture width and particle size are matched is established. Based on the optimized chart, it is possible to quickly determine whether the design particle size matches the fracture width, thereby providing technical guidance for achieving full-domain support of multi-stage fractures. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0031] Figure 2 This is the crack interaction node mesh model in the embodiment of the present invention;

[0032] Figure 3 This is a numerical model statistical result of the deflection angle distribution during the proppant turning process in the embodiments of the present invention;

[0033] Figure 4 These are the experimental statistical results of the deflection angle distribution during the proppant turning process in the embodiments of the present invention;

[0034] Figure 5 This is a simulated migration trend of 100 / 200 mesh proppant particles in an embodiment of the present invention;

[0035] Figure 6 This is an optimized diagram in an embodiment of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The purpose of this invention is to provide a method for matching the width and particle size of a multi-stage hydraulic fracturing fracture with full-domain support. To make the above-mentioned objectives, features and advantages of this invention more apparent and understandable, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] In existing technologies, a method for matching fracture width with proppant particle size has not yet been established, and the theoretical basis for full-domain propping technology for multi-stage fractures in hydraulic fracturing is lacking. Therefore, as... Figure 1 As shown, this invention provides a method for matching the width-particle size of a multi-stage hydraulic fracturing fracture, comprising the following steps:

[0039] S1. Establish a numerical model of multiphase coupled transport of fracturing fluid and proppant particles and a multi-level fracture interactive node mesh model;

[0040] S2. Set different working parameters to simulate the proppant delivery process in multi-level cracks and obtain the proppant turning into the crack simulation results under different working parameters.

[0041] S3. Construct a two-dimensional optimization pattern using "Reynolds number" and "particle size / secondary crack width", substitute the proppant diversion into the crack simulation results in step S2 into the optimization pattern, and divide the optimization pattern into different regions according to the proppant diversion into the crack simulation results.

[0042] S4. Analyze the position of the working condition to be optimized in the optimization pattern, and determine whether the particle size and slit width of the working condition to be optimized match based on the position.

[0043] In step S1, the computational fluid dynamics (CFD)-discrete element method (DEM) coupling method demonstrates superior ability to capture the fine characteristics of proppant particle size distribution, tracking particle trajectories in complex flow environments and is suitable for capturing particle entry into the fracture. Therefore, the CFD-DEM coupling method is preferred for establishing a multiphase coupled numerical model of fracturing fluid-proppant particle transport.

[0044] Specifically, when establishing a numerical model for multiphase coupled transport of fracturing fluid and proppant particles, the Navier-Stokes equations can be used to describe the dynamic behavior of fracturing fluid in narrow fractures, Newton's second law and the law of conservation of angular momentum can be used to describe the translation and rotation of proppant particles, and Hertz's elastic contact theory and Coulomb's friction law can be used to describe the normal and tangential contact forces between particles and between particles and the wall.

[0045] Specifically, the Navier-Stokes equations are used to describe the dynamic behavior of fracturing fluid in narrow fractures, and their expression is as follows:

[0046]

[0047] In the formula: ρ f α is the liquid phase density; f The volume fraction of the liquid phase; u f τ is the liquid phase velocity; t is time; p is the flow field pressure; f For liquid phase shear stress tensor, μ is the dynamic viscosity of the liquid phase; g is the acceleration due to gravity; S fp This is the momentum exchange term between the liquid phase and the solid phase particles.

[0048] The translational and rotational motions of the proppant particles satisfy Newton's second law and the conservation of angular momentum, respectively, as expressed below:

[0049]

[0050] Where: m p For particle mass; u p Fc is the particle velocity; Fc is the contact force between particles and between particles and the wall; F d For drag force; G is gravity; Fe is other additional forces affecting particle motion (such as buoyancy, lift, virtual mass force, etc.). p ω is the moment of inertia of the particle. p ω is the particle angular velocity; Mc is the contact torque; M s This represents the torque caused by fluid shear. The liquid-solid momentum exchange term S fp With traction force F d Coupling is achieved through the calculation of two-phase volume fraction and momentum transfer. The formula for calculating two-phase volume fraction is as follows:

[0051]

[0052] α f =1-α s

[0053] In the formula: α s N represents the volume fraction of the solid phase. s To calculate the number of particle samples within a grid cell; N t This represents the total number of samples within the grid cell.

[0054] The normal and tangential contact forces between particles and between particles and the wall are described using Hertz's elastic contact theory and Coulomb's friction law, respectively, and their expressions are as follows:

[0055]

[0056] F t ≤μ s F n

[0057] In the formula: E * For effective Young's modulus; R * δ is the effective radius; μ is the particle overlap; δ is the effective radius; μ is the particle overlap. s E is the coefficient of friction. * and R * Further expressed as:

[0058]

[0059] 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.

[0060] like Figure 2As shown, a "primary-secondary" crack interaction node mesh model is established based on the structured mesh subdivision method.

[0061] In step S2, it can be based on Figure 2 The multi-level crack interactive node mesh model shown is used to simulate different working conditions. Figure 2 The horizontal crack shown is the primary crack, and the inclined crack is the secondary crack. In the preferred embodiment, the angle between the primary crack and the secondary crack is 60°. The intersection of the primary crack (i.e., the main seam) and the secondary crack (i.e., the secondary seam) is set at 2 / 3 of the length of the main seam. The lengths of the primary crack and the secondary crack are 150 mm and 50 mm, respectively, and the height of each is 30 mm.

[0062] In a preferred embodiment, the width of the primary crack is set to 0.5–6 mm, and the width of the corresponding secondary crack is set to 0.125–3 mm. In a preferred embodiment, the combination of primary and secondary crack widths can be set as follows: 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, and 0.5–0.125 mm, wherein the 6–3 mm embodiment can be used for model verification.

[0063] In a preferred embodiment, the crack interaction node mesh model is set with a main crack-secondary crack width of 1-0.5mm. Taking the intersection of the main crack and the secondary crack as the boundary, 500 and 200 meshes are set in the length direction of the main crack before and after the intersection, respectively; 10 meshes are set in the width direction of the main crack; and 120 meshes are set in the height direction of the main crack. 250, 5, and 120 meshes are set in the length, width, and height directions of the secondary crack, respectively. When the crack width is less than 0.5mm, the mesh number is set at a ratio of 4-5 meshes / mm.

[0064] Furthermore, regarding the proppant-related operating parameters, in the preferred embodiment, the proppant is considered to be spherical particles with particle sizes that can be set to 40 / 70, 70 / 140, 100 / 200, and 200 / 400 mesh, and a density of 2650 kg / m³. 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.

[0065] In addition, the variables considered in the proppant delivery simulation also include delivery speed, fracturing fluid viscosity and proppant concentration. The delivery speed can preferably be 0.03, 0.05 and 0.08 m / s, the viscosity can be set to 2.5, 5, 7.5 and 10 mPa·s, and the proppant concentration can be set to 1, 3 and 5%.

[0066] in, Figure 3 The statistical results of the proppant deflection angle distribution during proppant reversal are presented under simulated conditions where the primary and secondary crack widths are 6-3 mm. Figure 4 The indoor experimental statistics under the corresponding conditions show that the results of numerical simulation are basically consistent with the results of experimental testing. Figure 5 The data shows the migration of 100 / 200 mesh proppant under different crack widths. It can be seen that as the width of the secondary crack decreases, the difficulty of proppant turning into the crack gradually increases.

[0067] In step S3, as Figure 6 As shown, a chart for optimizing proppant orientation parameters is established by using "Reynolds number" and "particle size / secondary crack width" as the ordinate and abscissa, respectively. Figure 6 The paper presents 22 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 6 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".

[0068] In step S4, the established chart can be used to determine whether the proppant particle size matches the crack width. If the condition to be optimized is in the "difficult entry zone," it indicates that the proppant is unlikely to veer into the secondary crack. Therefore, technicians can optimize the condition by reducing the proppant particle size, etc., to improve the overall proppant support effect.

[0069] Therefore, the proppant width-particle size matching method for multi-stage hydraulic fracturing full-domain support provided by this invention can quickly determine whether the proppant particle size matches the fracture width, and can quantitatively give the upper limit of the particle size that can smoothly turn into the fracture for a specific fracture width, thereby providing theoretical guidance for the optimized design of multi-stage hydraulic fracturing full-domain support technology.

[0070] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for matching the width-particle size of a multi-stage hydraulic fracturing fracture, comprising the following steps: S1. Establish a numerical model of multiphase coupled transport of fracturing fluid and proppant particles and a multi-level fracture interactive node mesh model; S2. Set different working parameters to simulate the proppant delivery process in multi-level cracks and obtain the proppant turning into the crack simulation results under different working parameters. S3. Construct a two-dimensional optimization pattern using "Reynolds number" and "particle size / secondary crack width". Substitute the proppant diversion and crack entry simulation results from step S2 into the optimization pattern. Divide the optimization pattern into different regions based on the proppant diversion and crack entry simulation results. The regions of the optimization pattern include a first region and a second region. In the first region, the proppant can effectively enter the crack, while in the second region, the proppant has difficulty entering the crack. The method for determining the Reynolds number in step S3 is as follows: Re= ρvw / μ Where Re is the Reynolds number; ρ This refers to the density of the fracturing fluid. v It is the liquid flow rate; w The width of the main crack; μ This refers to the viscosity of the fracturing fluid. S4. Analyze the position of the working condition to be optimized in the optimization pattern, and determine whether the particle size and slit width of the working condition to be optimized match based on the position.

2. The hydraulic fracturing multi-stage fracture width-particle size matching method as described in claim 1, wherein a numerical model is established in step S1 using a CFD-DEM coupling method.

3. The hydraulic fracturing multi-stage fracture global support fracture width-particle size matching method as described in claim 1, wherein a structured mesh generation method is used in step S1 to establish a multi-stage fracture interactive node mesh model.

4. The hydraulic fracturing multi-stage fracture propping width-particle size matching method as described in claim 1, wherein the operating parameters in step S2 include the primary-secondary fracture width ratio, proppant particle size, proppant concentration, fracturing fluid viscosity, and fracturing fluid velocity.

5. The hydraulic fracturing multi-stage fracture width-particle size matching method as described in claim 4, wherein the operating parameters in step S2 satisfy one or more of the following operating parameters: The width of the primary crack is 0.5~6 mm, and the width of the secondary crack is 0.125~3 mm; Or the particle size of the proppant may include 40 / 70, 70 / 140, 100 / 200 or 200 / 400 mesh; Or the proppant concentration is 1%~5%; Or the fracturing fluid viscosity is 2~10 mPa·s; Or the fracturing fluid velocity is 0.03~0.08 m / s.

6. In the hydraulic fracturing multi-stage fracture propping width-particle size matching method as described in claim 5, in step S4, if the working condition to be optimized is located in the second region, the proppant particle size is reduced so that the optimized fracture is located in the first region.

7. 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, it implements the steps of the hydraulic fracturing multi-stage fracture full-domain support fracture width-particle size matching method according to any one of claims 1-6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the hydraulic fracturing multi-stage fracture global support fracture width-particle size matching method according to any one of claims 1-6.

Images