Perforation hole sand inlet amount-based hole cluster design scheme optimization method

Abstract

The invention discloses a hole cluster design scheme optimization method based on perforation hole sand inlet amount, which comprises the following steps: firstly, obtaining sand fracturing analogue simulation key parameters, then establishing a shale gas horizontal well sand fracturing sleeve internal fluid and sand particle flow mathematical model based on the key parameters, and then designing a plurality of different hole cluster schemes. The method comprises the following steps: establishing a corresponding geometric model, carrying out grid division on each model to obtain a numerical simulation grid, establishing a numerical calculation format of sand-carrying fluid flow in a casing in a horizontal well sand fracturing process by adopting a finite element algorithm, carrying out analogue simulation, and obtaining the sand inlet amount of a single hole of a shaft in a steady state; and finally, according to calculation results of the sand feeding amount of the single hole of different hole cluster design methods, a hole cluster design scheme with the most uniform sand feeding amount of the single hole is optimized. According to the method, the uniformity degree of the sand feeding amount of a single hole in the sand fracturing process is fully considered, the hole cluster scheme is designed based on the uniformity degree of the sand feeding amount of the single hole, and the sand fracturing effect can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of horizontal well fracturing, and more particularly to a method for optimizing a hole cluster design scheme based on the sand injection amount of a perforation hole. Background Art

[0002] Shale oil and gas reservoirs have low porosity and permeability, high original gas content, and low natural production capacity. Large-scale sand fracturing is a necessary means to achieve efficient development of shale oil and gas reservoirs. Through sand fracturing, a fracture network can be created in the reservoir, the effective seepage area can be expanded, and the fluid contact area between the reservoir and the wellbore can be increased, thereby significantly improving oil and gas production capacity. However, sand fracturing operations in shale oil and gas wells are generally characterized by large scale, large displacement, and high sand content. In this process, the sand-added fracturing fluid is pumped into the formation through the casing and perforations, which can easily cause erosion and abrasion to the production string, especially the casing perforation system of the fracturing fluid outlet. However, the resulting problems such as damaged wellbore integrity, sand accumulation and blockage, and fracturing fluid leakage have become one of the technical difficulties restricting the safe and efficient development of shale oil and gas reservoirs.

[0003] Since the early 20th century, the erosion problem has attracted extensive attention from researchers. Through experimental research and simulation experiments, scholars simulated the downhole environment, controlled the experimental conditions, and quantitatively evaluated the effects of different parameters on erosion wear, forming a complete casing erosion evaluation system. Similarly, scholars have simulated the flow and erosion process of fracturing fluid in casing and perforation holes through numerical simulation research, including numerical simulation methods such as computational fluid dynamics (CFD) and discrete element method (DEM). By establishing appropriate numerical models and boundary conditions, the effects of different parameters on erosion wear were successfully analyzed, the hole cluster design and fracturing parameters were optimized, and the integrity of the wellbore was improved. However, under the premise of considering the strength of casing erosion by the holes, ensuring the uniformity of the sand injection volume in a single hole is one of the important indicators for evaluating the effect of sand fracturing in shale oil and gas reservoirs. The existing experimental and simulation studies focus on reducing the erosion effect of sand fracturing fluid on the casing system through injection parameter design, fracturing fluid system selection, and fracturing parameter optimization, ignoring the uniformity of sand injection volume in a single hole of all holes in the entire fracturing section. Therefore, it is of great significance to evaluate the effect of sand fracturing in shale oil and gas reservoirs by considering the uniformity of sand injection into the perforations during sand fracturing to design the hole cluster scheme. Summary of the invention

[0004] In view of the problems and defects existing in the above-mentioned prior art, the present invention provides a method for optimizing the hole cluster design scheme based on the sand injection amount of the perforation holes. This method fully considers the uniformity of the sand injection amount of a single hole during the sand fracturing process, and designs the hole cluster scheme based on the uniformity of the sand injection amount of a single hole, which is beneficial to improving the sand fracturing effect.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0006] A method for optimizing hole cluster design schemes based on the sand penetration rate of perforation holes comprises the following steps:

[0007] S1. Based on the shale gas well conditions and fracturing construction design, obtain the key parameters of sand fracturing simulation;

[0008] S2. Establish a mathematical model of fluid and sand particle flow in the casing of a shale gas horizontal well with sand fracturing;

[0009] S3. Design a variety of different hole cluster schemes based on field data, establish corresponding geometric models, and use unstructured tetrahedral grids to mesh each scheme model to obtain numerical simulation grids; so as to simulate the flow process of sand-carrying fluid in the casing during sand fracturing;

[0010] S4. Using finite element algorithm to establish the numerical calculation format of the flow of sand-carrying fluid in the casing during the sand fracturing process of the horizontal well, simulate the flow of sand-carrying fluid in the casing during the sand fracturing process, and obtain the sand injection amount of a single hole in the wellbore under steady state;

[0011] S5. According to the calculation results of the sand feeding amount of a single hole of different hole cluster design methods, a mean square error test is performed on each scheme, and the hole cluster design method is optimized to select the hole cluster design scheme with the most uniform sand feeding amount of a single hole.

[0012] Preferably, the key parameters simulated by the sand fracturing simulation include: displacement, fluid viscosity, fluid density, sand concentration and casing size.

[0013] Preferably, the mathematical model of fluid and sand particle flow includes: a continuity equation for fluid flow in the wellbore, a momentum conservation equation, a turbulence model, a particle motion model, an inlet boundary condition and an outlet boundary condition.

[0014] Preferably, the calculation expression of the fluid flow continuity equation is as follows:

[0015]

[0016] Where ρ is the fluid density and u is the fluid velocity.

[0017] Preferably, the calculation expression of the momentum conservation equation is as follows:

[0018]

[0019] Where, ρ is the fluid density; u is the fluid velocity; P is the pressure; τ is the viscous stress acting on the fluid; ρ g is the gravity acting on the fluid; S Mis the momentum increment generated by the particle on the fluid.

[0020] Preferably, the turbulence model is a standard k-ε model, and the calculation expression is as follows:

[0021]

[0022]

[0023] Where ρ is the fluid density; u is the fluid velocity; P is the pressure; ρ g is the gravity of the fluid; s; C1 and C2 are constants; μ1 is the turbulent viscosity; k is the turbulent kinetic energy; ε is the turbulent dissipation rate; p k is the shear turbulence kinetic energy.

[0024] Preferably, the calculation expression of the particle motion model is as follows:

[0025]

[0026] Among them, u p is the particle flow rate; u is the fluid velocity; ρ p is the particle density; F D is the drag force per unit mass; F z is the additional force; g is the acceleration due to gravity.

[0027] Preferably, the inlet boundary condition is a mass flow inlet with a gauge pressure of zero.

[0028] Preferably, the outlet boundary condition is a perforation hole with a gauge pressure of zero.

[0029] Beneficial effects of the present invention:

[0030] 1. The present invention designs different hole cluster schemes based on actual on-site data, which are closely related to the actual on-site conditions and have reliable reference value.

[0031] 2. The present invention realizes the effective statistics of the sand injection amount of a single hole during the sand fracturing process of the horizontal well section, which is conducive to evaluating the sand fracturing effect under different hole cluster design schemes and injection parameters, and can provide a reference for the temporary plugging of subsequent perforation holes.

[0032] 3. The present invention selects the best hole cluster scheme by the average degree of sand injection in a single hole, which can provide favorable guidance for the design of sand fracturing construction schemes for shale oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The foregoing and following detailed description of the present invention will become more apparent when read in conjunction with the following drawings, in which:

[0034] Figure 1 is a flow chart of the method of the present invention;

[0035] Figure 2 A schematic diagram of the perforation position of the present invention;

[0036] Figure 3 It is a schematic diagram of the numerical simulation grid of the present invention;

[0037] Figure 4 This is a schematic diagram of the statistical results of the amount of sand entering the hole according to an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of the variance of sand injection amount in each hole cluster design scheme in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions for achieving the purpose of the present invention will be further described below through several specific embodiments. It should be noted that the technical solutions claimed for protection in the present invention include but are not limited to the following embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0040] The technical solution for achieving the purpose of the present invention is further described below by means of specific embodiments. It should be noted that the technical solution claimed for protection by the present invention includes but is not limited to the following embodiments.

[0041] Since the early 20th century, the erosion problem has attracted extensive attention from researchers. Through experimental research and simulation experiments, scholars simulated the downhole environment, controlled the experimental conditions, and quantitatively evaluated the effects of different parameters on erosion wear, forming a complete casing erosion evaluation system. Similarly, scholars have simulated the flow and erosion process of fracturing fluid in casing and perforation holes through numerical simulation research, including numerical simulation methods such as computational fluid dynamics (CFD) and discrete element method (DEM). By establishing appropriate numerical models and boundary conditions, the effects of different parameters on erosion wear were successfully analyzed, the hole cluster design and fracturing parameters were optimized, and the integrity of the wellbore was improved. However, under the premise of considering the strength of casing erosion by the holes, ensuring the uniformity of the sand injection volume in a single hole is one of the important indicators for evaluating the effect of sand fracturing in shale oil and gas reservoirs. The existing experimental and simulation studies focus on reducing the erosion effect of sand fracturing fluid on the casing system through injection parameter design, fracturing fluid system selection, and fracturing parameter optimization, ignoring the uniformity of sand injection volume in a single hole of all holes in the entire fracturing section. Therefore, it is of great significance to evaluate the effect of sand fracturing in shale oil and gas reservoirs by considering the uniformity of sand injection into the perforations during sand fracturing to design the hole cluster scheme.

[0042] Based on this, this embodiment proposes a method for optimizing the hole cluster design scheme based on the sand injection amount of the perforation holes. This method fully considers the uniformity of the sand injection amount of a single hole during the sand fracturing process, and designs the hole cluster scheme based on the uniformity of the sand injection amount of a single hole, which is beneficial to improving the sand fracturing effect.

[0043] This embodiment discloses a method for optimizing the hole cluster design scheme based on the sand injection amount of the perforation holes. Figure 1 , the method comprises the following steps:

[0044] Step S1: Based on the well conditions of the shale gas well and the fracturing construction design, key parameters of the sand fracturing simulation are obtained, including parameters such as fracturing fluid displacement, fracturing fluid viscosity, fluid density, sand concentration, and casing size. The specific parameters are shown in Table 1.

[0045] Table 1 Specific parameters of sand fracturing

[0046]

[0047]

[0048] S2. According to the key simulation parameters obtained in step S1, a mathematical model of the flow of fluid and sand particles in the casing of a shale gas horizontal well with sand fracturing is established, wherein the model includes: a continuity equation for the flow of fluid in the wellbore, a momentum conservation equation, a turbulence model, a particle motion model, an inlet boundary condition, and an outlet boundary condition.

[0049] The calculation expression of the fluid continuity equation is as follows:

[0050]

[0051] The momentum conservation equation is calculated as follows:

[0052]

[0053] The turbulence model is a standard k-ε model, and the calculation expression is as follows:

[0054]

[0055]

[0056] The calculation expression of the particle motion model is as follows:

[0057]

[0058] Where: ρ is the fluid density, unit is kg / m 3; u is the fluid velocity, in m / s; P is the pressure, in Pa; τ is the viscous stress acting on the fluid, in N; ρ g is the gravity of the fluid, in N; S M is the momentum increment generated by the particle on the fluid, in kg·m / s; C1C2 is a constant; u p is the particle flow velocity, in m / s; ρ p is the particle density, in kg / m 3 ; μ1 is the turbulent viscosity, in Pa·s; k is the turbulent kinetic energy, in J; ε is the turbulent dissipation rate, in m 2 / s 3 ;p k is the shear turbulence kinetic energy, in J; F D is the drag force per unit mass; F z is the additional force; g is the acceleration due to gravity.

[0059] In the present invention, the inlet boundary condition is generally the mass flow inlet, which is related to the displacement we simulate, the unit is generally m3 / min, and the gauge pressure is 0; the outlet boundary condition refers to the perforation hole, and the gauge pressure is 0.

[0060] S3. Design a variety of different hole cluster schemes based on field data, establish corresponding hole cluster geometric models, and use unstructured tetrahedral grids to mesh each scheme model to obtain numerical simulation grids; so that they can be used in the sand-carrying fluid flow process in the casing during sand fracturing.

[0061] In the present invention, the hole clustering schemes commonly used on site include: 7 clusters of 6 holes, 9 clusters of 7 holes, and 9 clusters of 9 holes, etc. Different hole clustering schemes correspond to different geometric models, and there is a one-to-one correspondence between the geometric models and the hole clustering schemes.

[0062] In this embodiment, according to field data, during the sand fracturing process of the horizontal well, the length of a single perforation section is generally designed to be 75m and 90m, the number of perforation clusters in a single section is generally 7 clusters, 9 clusters and 12 clusters, and the number of perforation holes in a single cluster is generally 6 holes, 7 holes and 9 holes. The hole cluster design scheme is shown in Table 2.

[0063] Table 2 Hole cluster design scheme

[0064] plan Single section length (m) Perforation Cluster Number of holes per cluster 1 75 7 6 2 75 7 7 3 75 7 9 4 75 9 6 5 75 9 7 6 75 9 9 7 75 12 6 8 75 12 7 9 75 12 9 10 90 7 6 11 90 7 7 12 90 7 9 13 90 9 6 14 90 9 7 15 90 9 9 16 90 12 6 17 90 12 7 18 90 12 9

[0065] The geometric model is established according to the hole cluster design plan, and the perforation position diagram is referred to the attached manual Figure 2 The geometric model is meshed using unstructured tetrahedral meshes to obtain numerical simulation meshes. Figure 3 shown.

[0066] S4. The finite element algorithm is used to establish the numerical calculation format of the flow of sand-carrying fluid in the casing during the sand fracturing process of the horizontal well, and the simulation of the flow of sand-carrying fluid in the casing during the sand fracturing process is performed to obtain the sand injection volume of a single hole in the wellbore under steady state.

[0067] In the present invention, the steady state generally refers to the dynamic balance of fluid flow, at which the amount of sand fed into a single hole substantially does not change.

[0068] In this embodiment, by simulating the flow of sand-carrying fluid in the casing during sand fracturing of the sand-added fracturing pipe wall of each scheme, the sand feeding amount of a single hole corresponding to each hole cluster design scheme can be obtained. The holes are numbered from the root end to the toe end, and the sand feeding amount of each hole is counted. An example is given here, and the parameter specification is attached. Figure 4 shown.

[0069] S5. According to the calculation results of the sand feeding amount of a single hole of different hole cluster design methods, a mean square error test is performed on each scheme, and the hole cluster design method is optimized to select the hole cluster design scheme with the most uniform sand feeding amount of a single hole.

[0070] In this embodiment, the calculation results of the variance of the sand injection amount of each hole cluster design scheme refer to the attached manual. Figure 5 As shown in the figure, the single hole sand feeding amount variance of scheme 5 is the smallest, 1.27%, and the single hole sand feeding amount variance of scheme 10 is the largest, 2.75%. Therefore, the optimal hole cluster design scheme is 9 clusters × 7 holes.

[0071] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for optimizing hole cluster design schemes based on the sand injection amount of perforation holes, characterized in that: The following steps are involved: S1. Based on the shale gas well conditions and fracturing construction design, obtain the key parameters of sand fracturing simulation; S2. Establish a mathematical model of fluid and sand particle flow in the casing of a shale gas horizontal well with sand fracturing; S3. Design a variety of hole cluster schemes based on field data, establish corresponding geometric models, and use unstructured tetrahedral meshes to mesh each scheme model to obtain numerical simulation meshes; S4. Using finite element algorithm to establish the numerical calculation format of the flow of sand-carrying fluid in the casing during the sand fracturing process of the horizontal well, simulate the flow of sand-carrying fluid in the casing during the sand fracturing process, and obtain the sand input volume of a single hole in the wellbore under steady state; S5. According to the calculation results of the sand feeding amount of a single hole of different hole cluster design methods, a mean square error test is performed on each scheme, and the hole cluster design method is optimized to select the hole cluster design scheme with the most uniform sand feeding amount of a single hole.

2. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 1 is characterized in that: The key parameters of the sand fracturing simulation include displacement, fluid viscosity, fluid density, sand concentration and casing size.

3. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 1 is characterized in that: The mathematical model of fluid and sand particle flow includes: a continuity equation of fluid flow in a wellbore, a momentum conservation equation, a turbulence model, a particle motion model, an inlet boundary condition and an outlet boundary condition.

4. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 3 is characterized in that: The calculation expression of the fluid flow continuity equation is as follows: Where ρ is the fluid density and u is the fluid velocity.

5. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 3 is characterized in that: The calculation expression of the momentum conservation equation is as follows: Where, ρ is the fluid density; u is the fluid velocity; P is the pressure; τ is the viscous stress acting on the fluid; ρ g is the gravity acting on the fluid; S M is the momentum increment generated by the particle on the fluid.

6. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 3 is characterized in that: The turbulence model is a standard k-ε model, and the calculation expression is as follows: Where ρ is the fluid density; u is the fluid velocity; P is the pressure; ρ g is the gravity of the fluid; s; C1 and C2 are constants; μ1 is the turbulent viscosity; k is the turbulent kinetic energy; ε is the turbulent dissipation rate; p k is the shear turbulence kinetic energy.

7. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 3 is characterized in that: The calculation expression of the particle motion model is as follows: Among them, u p is the particle flow rate; u is the fluid velocity; ρ p is the particle density; F D is the drag force per unit mass; F z is the additional force; g is the acceleration due to gravity.

8. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 3 is characterized in that: The inlet boundary condition is a mass flow inlet with a gauge pressure of zero.

9. The method for optimizing hole cluster design scheme based on the sand injection amount of perforation holes according to claim 3 is characterized in that: The outlet boundary condition is the perforation hole and the gauge pressure is zero.

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