A method for controlling process parameters of finger-feeding acid fracturing

Abstract

The present invention discloses a method for controlling parameters of fingering acid fracturing process, including numerical simulation of acid fingering in mine-scale acid fracturing fractures to obtain numerical simulation results of acid fingering; obtaining characteristic characterization parameters of three stages of acid fingering from the numerical simulation results, selecting the characteristic characterization parameters of fingering when the front edge of the fingering reaches the boundary to draw relationship charts respectively; and multi-objective multi-parameter comprehensive optimization. The present invention overcomes the defects of poor repeatability, cumbersome experimental process, and abnormal similarity in size in the physical simulation experiment of acid fingering. The numerical simulation method can fully simulate the evolution process of acid fingering in three-dimensional fractures at the mine scale. It has strong operability, is less affected by the external environment, and has low cost. It can realize the analysis and research of different stages in the evolution process of acid fingering, and establishes a multi-objective comprehensive optimization method for acid fracturing process parameters, which has wide application value.

Description

Technical Field

[0001] The present invention relates to the field of enhanced oil and gas field stimulation, and specifically to a method for regulating and controlling the process parameters of finger acid fracturing. Background Art

[0002] From a global perspective, carbonate rock formation-lithology large oil and gas fields are a very important type of oil and gas fields. Their reservoirs account for about 52% of the world's oil reserves and 60% of the global total oil and gas production. Since the 1950s, in the development process of the world's oil industry, the exploration and development of large carbonate rock oil and gas resources have played a crucial role. China has extremely rich carbonate rock oil and gas resources. Recent exploration practices and research have shown that deep marine carbonate rocks are one of the key areas for future oil and gas exploration breakthroughs and large-scale reserve growth in China.

[0003] As a mainstream stimulation technology for carbonate rock reservoirs, the finger phenomenon of acid solution occurring in the formation fractures during acid fracturing can, on the one hand, form a non-uniform distribution of acid solution in the fractures to promote the non-uniform etching of the fracture walls by the acid solution, thereby improving the fracture conductivity. On the other hand, it can reduce the contact area between the acid solution and the wall, reduce filtration loss, and extend the effective action distance of the acid solution. Therefore, the finger phenomenon of acid solution has a crucial impact on the final acid fracturing effect.

[0004] Currently, the existing physical simulation experimental devices for acid solution finger have low automation, cumbersome experimental processes, and the experimental device models belong to geometrically distorted models, which cannot fully simulate the high-temperature and high-pressure environment of the actual formation. Most of the numerical simulation studies are aimed at the finger phenomenon occurring in porous media and microscopic pore throats, and there are usually limitations in the analysis and research of the finger morphology only when the "finger front reaches the boundary" for the finger phenomenon occurring in acid fracturing fractures. The finger feature characterization parameters used are also various. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for regulating and controlling the process parameters of finger acid fracturing in view of the problems existing in the prior art. This method uses numerical simulation means to perform numerical simulation of acid solution finger in acid fracturing fractures at the field scale, uses three finger feature characterization parameters to characterize the finger behavior in three stages during the finger evolution process, and draws corresponding charts for multi-objective comprehensive optimization, and then regulates and controls the acid fracturing process parameters to achieve finger acid fracturing to reduce filtration loss and increase non-uniform etching of the wall surface, providing guidance and support for acid fracturing design and construction.

[0006] The technical solution provided by the present invention to solve the above technical problems is: a method for regulating and controlling the process parameters of finger acid fracturing, including the following steps:

[0007] Step 1: Perform numerical simulation of acid solution finger in acid fracturing fractures at the field scale to obtain the numerical simulation results of acid solution finger;

[0008] Step 2: Obtain the fingering characteristic characterization parameters in three stages from the numerical simulation results of acid fluid fingering. The fingering characteristic characterization parameters include the fingering front velocity, the fingering fractal dimension, and the area sweep efficiency.

[0009] Step 3: Select the fingering characteristic characterization parameters when the fingering front reaches the boundary, and respectively plot the relationship charts of the fingering front velocity vs. acid fracturing process parameters, the fingering fractal dimension vs. acid fracturing process parameters, and the area sweep efficiency vs. acid fracturing process parameters.

[0010] Step 4: Determine the range of acid fracturing process parameters corresponding to the fingering front velocity greater than or equal to 1.35 m / s in the relationship chart of the fingering front velocity vs. acid fracturing process parameters.

[0011] Step 5: Determine the range of acid fracturing process parameters corresponding to the fingering fractal dimension greater than or equal to 1.45 in the relationship chart of the fingering fractal dimension vs. acid fracturing process parameters.

[0012] Step 6: Determine the range of acid fracturing process parameters corresponding to the area sweep efficiency between 0.45 and 0.5 in the relationship chart of the area sweep efficiency vs. acid fracturing process parameters.

[0013] Step 7: Finally, find the intersection of the three ranges of acid fracturing process parameters determined in Steps 4 - 6 to obtain the final range of acid fracturing process parameters.

[0014] A further technical solution is that the specific steps of the numerical simulation of acid fluid fingering in the acid fracturing fracture at the field scale in Step 1 are as follows:

[0015] Step 11: Collect the three-dimensional fracture size parameters at the field scale.

[0016] Step 12: Establish a three-dimensional fracture geometric model at the field scale based on the three-dimensional fracture size parameters at the field scale, and construct a mathematical model for acid fluid flow.

[0017] Step 13: Solve the physical quantity control equations, solve the phase function transport equations, and perform interface reconstruction to obtain the numerical simulation results of acid fluid fingering.

[0018] A further technical solution is that the three-dimensional fracture size parameters at the field scale include the fracture length, the fracture width, and the fracture height.

[0019] A further technical solution is that the mathematical model for acid fluid flow includes physical quantity control equations and definite solution conditions.

[0020] A further technical solution is that the physical quantity control equations include the continuity equation and the momentum equation; the definite solution conditions include the initial conditions and the boundary conditions; the boundary conditions are respectively the velocity inlet boundary condition and the pressure outlet boundary condition.

[0021] A further technical solution is that the continuity equation is as follows:

[0022]

[0023] where: ρ is the fluid density, kg / m 3 ; is the fluid velocity, m / s;

[0024] The momentum equation is as follows:

[0025]

[0026] where: φ is 1 in the continuity equation and represents velocity in the momentum equation; Γ represents the diffusion coefficient; S represents the source term.

[0027] A further technical solution is that the phase function transport equation is as follows:

[0028]

[0029] where: is the fluid velocity at (X, Y).

[0030] A further technical solution is that the three stages in step 2 include the starting stage of fingering, the growing stage of fingering, and the stage where the fingering front reaches the boundary.

[0031] The present invention has the following beneficial effects: The present invention overcomes the defects in the physical simulation experiment of acid fingering, such as poor repeatability, cumbersome experimental process, and abnormal similarity in size. By using the numerical simulation method, it can fully simulate the evolution process of acid fingering in the three-dimensional fracture at the field scale, with strong operability, less influence from the external environment, and low cost. It can realize the analysis and research of different stages in the evolution process of acid fingering, establish a multi-objective comprehensive optimization method for acid fracturing process parameters, and has wide application value. Description of the Drawings

[0032] Figure 1 is the numerical simulation result diagram of acid fingering;

[0033] Figure 2 is the relationship diagram between the fingering front rate and the viscosity ratio;

[0034] Figure 3 is the relationship diagram between the fingering fractal dimension and the viscosity ratio;

[0035] Figure 4 is the relationship diagram between the area sweep efficiency and the viscosity ratio;

[0036] Figure 5 is the multi-objective comprehensive optimization diagram. Detailed Implementation Modes

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] The present invention provides a method for regulating and controlling the parameters of the finger - advancing acid fracturing process, specifically including the following steps:

[0039] Step 1: Numerically simulate the acid finger - advancing in the acid - fractured wellbore at the field scale to obtain the numerical simulation results of acid finger - advancing;

[0040] Step 11: Collect the three - dimensional fracture size parameters (fracture length, fracture width, fracture height) at the field scale;

[0041] Step 12: Establish a three - dimensional fracture geometric model at the field scale according to the three - dimensional fracture size parameters at the field scale, and construct a mathematical model for acid flow; the mathematical model for acid flow includes physical quantity control equations and definite - solution conditions. The physical quantity control equations include a continuity equation and a momentum equation; the definite - solution conditions include initial conditions and boundary conditions; the boundary conditions are a velocity - inlet boundary condition and a pressure - outlet boundary condition respectively;

[0042] The continuity equation is:

[0043]

[0044] In the formula: ρ is the fluid density, kg / m 3 ; is the fluid velocity, m / s;

[0045] The momentum equation is:

[0046]

[0047] In the formula: φ is 1 in the continuity equation and represents velocity in the momentum equation; Γ represents the diffusion coefficient; S represents the source term;

[0048] The initial condition is that the flow field is stationary and the velocity field is zero, that is:

[0049] v(x,y,z) = 0

[0050] The velocity - inlet boundary condition is:

[0051] v(0,y,z,t) = v 0

[0052] The pressure - outlet boundary condition is:

[0053] P(xL , y, z, t) = P 0

[0054] Step 13: Solve the physical quantity control equations, solve the phase function transport equation, and perform interface reconstruction to obtain the numerical simulation results of acid fingering;

[0055] The phase function transport equation is as follows:

[0056]

[0057] In the formula: is the fluid velocity at (X, Y);

[0058] Step 2: Obtain the fingering characteristic characterization parameters (fingering front rate, fingering fractal dimension, area sweep efficiency) at three stages (beginning stage of fingering, growth stage of fingering, stage when the fingering front reaches the boundary) from the numerical simulation results of acid fingering;

[0059] Step 3: Select the fingering characteristic characterization parameters when the fingering front reaches the boundary and draw the relationship charts of the fingering front rate vs. acid fracturing process parameters, the fingering fractal dimension vs. acid fracturing process parameters, and the area sweep efficiency vs. acid fracturing process parameters respectively;

[0060] Step 4: Determine the range of acid fracturing process parameters corresponding to the fingering front rate greater than or equal to 1.35 m / s in the relationship chart of the fingering front rate vs. acid fracturing process parameters;

[0061] Step 5: Determine the range of acid fracturing process parameters corresponding to the fingering fractal dimension greater than or equal to 1.45 in the relationship chart of the fingering fractal dimension vs. acid fracturing process parameters;

[0062] Step 6: Determine the range of acid fracturing process parameters corresponding to the area sweep efficiency between 0.45 and 0.5 in the relationship chart of the area sweep efficiency vs. acid fracturing process parameters;

[0063] Step 7: Finally, take the intersection of the three ranges of acid fracturing process parameters determined in Steps 4 - 6 to obtain the final range of acid fracturing process parameters.

[0064] Example

[0065] First step: Obtain the three - dimensional fracture size parameters at the field scale, as shown in Table 1.

[0066] Table 1 Three - dimensional fracture size parameters

[0067] Basic parameters Value Length / m 100 Height / m 30 Width / mm 5

[0068] Second step: Establish a three - dimensional fracture geometric model at the field scale;

[0069] Step 3: Construct a mathematical model for acid fluid flow;

[0070] Step 4: Solve the equation and perform interface reconstruction to obtain the numerical simulation results of acid fingering, as Figure 1 shown;

[0071] Step 5: Obtain three fingering characterization parameters for three stages according to the numerical simulation results of acid fingering, as shown in Table 2 and Table 3;

[0072] Table 2 Statistics of fingering characterization parameters

[0073]

[0074] Table 3 Statistics of fingering characterization parameters

[0075]

[0076]

[0077] Step 6: Select the fingering characteristic characterization parameters when the fingering front reaches the boundary to plot the relationship plates of the fingering front velocity vs. viscosity ratio, fingering fractal dimension vs. viscosity ratio, and area sweep efficiency vs. viscosity ratio, as shown in Figure 2 , Figure 3 , Figure 4 shown;

[0078] It can be found from Figure 2 that when the viscosity ratio is between 150 and 300, the fingering front velocity is greater than 1.35 m / s, which belongs to the ideal range;

[0079] It can be found from Figure 3 that when the viscosity ratio is between 75 and 300, the fingering fractal dimension is greater than 1.45, which belongs to the ideal range. However, since the fingering fractal dimension basically remains unchanged after the viscosity ratio is greater than 200, increasing the viscosity ratio further at this time is meaningless. Therefore, the preferred viscosity ratio range is 75 - 200;

[0080] It can be found from Figure 4 that when the viscosity ratio is between 150 and 300, the area sweep efficiency is between 0.45 and 0.5, which belongs to the ideal range;

[0081] Step 7: Overlay Figure 2 , Figure 3 with Figure 4 to obtain Figure 5 and perform multi-objective parameter comprehensive optimization. At this time, when the viscosity ratio is between 150 and 200, the fingering front velocity, fingering fractal dimension, and area sweep efficiency are all within the ideal range. Therefore, during the acid fracturing construction process, it is recommended to control the viscosity ratio between 150 and 200. Similarly, other acid fracturing process parameters can be regulated according to this method.

[0082] As described above, this is not any form of limitation to the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments of equivalent changes by using the disclosed technical content within the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for controlling process parameters of finger acid fracturing, characterized in that: The following steps are involved: Step 1: numerically simulate the acid fingering in the mine-scale acid fracturing fracture to obtain the numerical simulation results of the acid fingering; Step 2, the fingering characteristic characterization parameters of the three stages are obtained from the numerical simulation results of acid fingering, and the fingering characteristic characterization parameters include the fingering front edge rate, the fingering fractal dimension, and the area sweeping efficiency; Step 3, selecting the fingering characteristic characterization parameters when the fingering front reaches the boundary, and drawing the relationship chart between the fingering front rate and the acid fracturing process parameters, the relationship chart between the fingering fractal dimension and the acid fracturing process parameters, and the relationship chart between the area sweeping efficiency and the acid fracturing process parameters; Step 4, determining the acid fracturing process parameter range corresponding to the finger front rate being greater than or equal to 1.35 m / s in the relationship chart between the finger front rate and the acid fracturing process parameters; Step 5, determining the range of acid fracting process parameters corresponding to the fingering fractal dimension being greater than or equal to 1.45 in the relationship chart between the fingering fractal dimension and the acid fracting process parameters; Step 6, determining the acid fracturing process parameter range corresponding to the area sweeping efficiency being between 0.45 and 0.5 in the relationship chart between the area sweeping efficiency and the acid fracturing process parameters; Step 7: Finally, the three acid fracturing process parameter ranges determined in steps 4-6 are intersected to obtain the final acid fracturing process parameter range.

2. The method for controlling the process parameters of the finger-feeding acid fracturing according to claim 1, characterized in that: The specific steps of the numerical simulation of acid fingering in the mine-scale acid fracturing fracture in step 1 are: Step 11, collecting field-scale three-dimensional fracture size parameters; Step 12: establishing a mine-scale three-dimensional fracture geometry model according to the mine-scale three-dimensional fracture size parameters, and constructing an acid flow mathematical model; Step 13: Solve the physical quantity control equation, solve the phase function transport equation, and reconstruct the interface to obtain the numerical simulation results of acid fingering.

3. The method for controlling the process parameters of the finger-feeding acid fracturing according to claim 2, characterized in that: The mine-scale three-dimensional crack size parameters include crack length, crack width, and crack height.

4. The method for controlling the process parameters of the finger-feeding acid fracturing according to claim 2, characterized in that: The acid flow mathematical model includes physical quantity control equations and solution conditions.

5. The method for controlling the process parameters of the finger-feeding acid fracturing according to claim 4, characterized in that: The physical quantity control equations include the continuity equation and the momentum equation; the solution conditions include initial conditions and boundary conditions; the boundary conditions are velocity inlet boundary conditions and pressure outlet boundary conditions respectively.

6. The method for controlling process parameters of finger-feeding acid fracturing according to claim 5, characterized in that: The continuity equation is: Where: ρ is the fluid density, kg / m 3 ; is the fluid velocity, m / s; The momentum equation is: Where: φ is 1 in the continuity equation and represents velocity in the momentum equation; Γ represents the diffusion coefficient; S represents the source term.

7. The method for controlling process parameters of finger-feeding acid fracturing according to claim 2, characterized in that: The phase function transport equation is: Where: is the fluid velocity at (X, Y).

8. The method for controlling process parameters of finger-feeding acid fracturing according to claim 1, characterized in that: The three stages in step 2 include the fingering start stage, the fingering growth stage, and the fingering front edge reaching the boundary stage.

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