CN111680457A - Numerical simulation method for evaluating plugging effect of plugging agent in fracturing process - Google Patents
Numerical simulation method for evaluating plugging effect of plugging agent in fracturing process Download PDFInfo
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Abstract
The invention relates to the technical field of oil and gas engineering, in particular to a numerical simulation method for evaluating the plugging effect of a plugging agent in a fracturing process. The invention mainly solves the problems of migration distribution of the plugging agent in the fracture, evaluation of plugging effect and optimization of pumping parameters of the plugging agent in the fracturing process. The invention mainly comprises the following steps: establishing a fracturing fracture simulation model of an oil and gas reservoir; forming an information file for simulating plugging numerical value of the plugging agent according to the parameters of the fracturing fracture and the parameters of the plugging agent; simulating fluid flow by adopting a Computational Fluid Dynamics (CFD) method; simulating migration and plugging of the plugging agent by adopting a discrete element DEM method; and coupling and simulating the plugging state of the plugging agent in the fracturing fracture by adopting a CFD-DEM method. And evaluating the plugging effect of the plugging agent in the fracture through the number of the plugging agents and the inlet pressure. The invention truly simulates the migration and plugging process of the plugging agent in the fracturing process, can visually evaluate the plugging effect of the plugging agent, and provides a technical means for the execution of the measures for modifying the oil and gas well fracture.
Description
The technical field is as follows: the invention relates to the technical field of oil and gas engineering, in particular to a numerical simulation method for evaluating the plugging effect of a plugging agent in a fracturing process.
Background art: the oil and gas reservoir condition is complicated, when reforming transform the reservoir, in order to improve the fracturing crack to the control degree of oil and gas reservoir, through injecting the plugging agent into the fracturing crack, forms complicated fracturing crack system, increases the oil and gas reservoir drainage area, and then improves single well productivity after the fracturing. The distribution form and the laying thickness of the plugging agent directly determine the reconstruction effect of the fracturing crack.
The existing experimental method for simulating the plugging effect of the plugging agent in the fracturing process is single, most of the experimental methods are evaluated by using an improved plugging instrument, but the experimental method is limited by the experimental instrument, and the method is difficult to accurately simulate the plugging process of the plugging agent in the fracture. The experimental evaluation of the plugging effect of the plugging agent in some laboratories at home and abroad mainly focuses on the change of the permeability of the rock core caused by the plugging agent, and the simulation research of the supporting crack of the particle plugging agent is rarely reported. At present, plugging agent plugging indoor experiments are few, an evaluation method is single, no industrial standard exists, especially, experimental equipment is expensive, parameters which can be changed in experiments are few, and experiment repeatability is poor. The numerical simulation method can establish different fracture models through unstructured grid division, and is easy to change construction parameters. Finite element software is generally applied to simulate the temporary plugging process of the plugging agent, but the method ignores the key factor of particles as a discrete phase and cannot well simulate the plugging effect under different particle parameters. The invention can better simulate the plugging forms under different plugging agent parameters by a CFD-DEM method, and evaluate the plugging effect of the plugging agent by inlet pressure and the number of the plugging agents, thereby optimizing the plugging agent construction process in the fracturing process and providing technical guidance for the exploration and development of oil and gas reservoir reservoirs.
The invention content is as follows: the invention provides a numerical simulation method for evaluating the plugging effect of a plugging agent in the fracturing process, which can truly simulate the migration and plugging process of the plugging agent in a fracture in the fracturing process, can evaluate the plugging effect through the inlet pressure and the number of the plugging agents, and provides technical support for the research of temporary plugging mechanism and the execution of fracture reconstruction measures in the fracturing process of an oil and gas well.
The invention can solve the problems by the following technical scheme: a numerical simulation method for evaluating the plugging effect of a plugging agent in a fracturing process comprises the following steps:
the first step is as follows: determining a numerical simulation research area of a fracturing fracture of an oil and gas reservoir, determining fracturing fracture parameters including fracture length, fracture inlet opening and fracture outlet opening, and establishing a research area boundary;
the second step is that: forming information files of different plugging agent parameters including fracturing fracture parameters, fracture length and opening degrees of a fracture inlet and a fracture outlet according to the fracturing fracture parameters and the plugging agent parameters; the parameters of the plugging agent comprise the density, the particle size and the concentration of the plugging agent;
the third step: carrying out grid division on a research area, and establishing an oil and gas reservoir fracture simulation model; the grid division adopts unstructured grids, and grid precision is adjusted according to grid quality, so that the condition that simulation conditions including different construction conditions and intra-crack migration laying forms under crack conditions are met is ensured;
the fourth step: determining fluid parameters including fluid viscosity and fluid velocity in the fracture based on the divided grids; setting fracture boundary conditions including fracture length, fracture inlet opening and fracture outlet opening, and simulating the flowing state of fluid in a fracture by a CFD (computational fluid dynamics) method;
because the flow of the fracturing fluid in the fracture is influenced by the accumulation distribution of the plugging agent, the corrected Navier-Stokes equation is adopted for calculation, and the strong energy and momentum exchange exists in the flowing process of the fracture plugging agent and the fracturing fluid, so that the flowing process of the fracture plugging agent and the fracturing fluid conforms to the turbulent flow process; transient simulation in the turbulence model can directly solve an instantaneous turbulence control equation, the turbulence model in the particle fluid two-phase flow is calculated by adopting a standard k-model, and the turbulence equation and the turbulence diffusion equation are as follows:
turbulent kinetic energy equation:
turbulent diffusion equation:
in the formula: t-time, s; rho-fluid density, kg/m3(ii) a k-kinetic energy of turbulence, m2/s2；xi,xj-representing respectively one component of the vector x; u. ofi-represents a component of the velocity, m/s; μ -represents the hydrodynamic viscosity, mPas; mu.slViscosity increase due to turbulence, mPa · s; gkIndication due to average speedDegree gradient induced turbulent kinetic energy, kg/(m.s)3)；GbKinetic energy of turbulence caused by buoyancy, kg/(m.s)3) (ii) a Turbulent dissipation ratio, m2/s3，YM-diffusion induced fluctuations; sk，S-a dimensionless quantity; sigmak,σ-turbulent prandtl number; c1C2C3-a constant value;
the fifth step: determining parameters of the plugging agent in the fracture, including density, particle size and concentration of the plugging agent, on the basis of the divided grids, setting boundary conditions of the fracture, including fracture length, fracture inlet opening and fracture outlet opening, and simulating migration and distribution of the plugging agent in the fracture by a DEM (digital elevation model) method;
by integrating Newton's second law, the velocity distribution change of the plugging agent in the fracturing fluid is obtained, and the contact force between particles (the elastic force and the damping force between the particles) can be calculated by the following formula;
in the formula, Fi-contact force between particles, N; kn-normal contact stiffness, N/m;n-the normal action distance between the particles, m; gamma rayn-critical normal damping ratio; m is the mass of the particles, kg; vn-particle normal relative velocity, m/s; ks-shear contact stiffness, N/m;s-the normal action distance between the particles, m; gamma rays-critical shear damping ratio; vs-particle shear relative velocity, m/s; i-particle number, i ═ 1, 2;
the mechanical interaction between the particles and the contact shear will cause them to rotate, and the particle momentum can be calculated by the following formula;
Mi＝Ks s(x0-xi)
in the formula, Mi-momentum at the point of particle contact, kg · m/s; ks-shear contact stiffness, N/m;s-the normal action distance between the particles, m; x is the number of0-the position of the particle contact point;xi-the geometric centre position of the particle i;
and a sixth step: and (3) simulating the plugging state of the plugging agent in the crack in the fourth and fifth steps by adopting a CFD-DEM (computational fluid dynamics-dynamic effect model) method in a coupling manner, carrying out a numerical simulation experiment by changing relevant parameters such as fluid injection speed, plugging agent density, plugging agent particle size and plugging agent concentration, evaluating the plugging effect of the crack according to the crack pressure holding degree by the curve of inlet pressure and the change of the number of the plugging agents along with time, judging that the crack is effectively plugged when the pressure holding exceeds the horizontal stress difference of a research area, and optimizing the plugging agent construction process in the fracturing process according to the numerical simulation experiment result of the plugging effect of the plugging agent.
And the fracture in the first step adopts a PKN and KGD two-dimensional model.
The second step of the blocking agent is a particle type temporary blocking agent, the particle size is 20/40 meshes, 70/100 meshes, 100/120 meshes, 180/200 meshes, 200/300 meshes or 400/600 meshes, and the use concentration of the blocking agent is 0.5-5%.
And in the third step, the simulation area is subjected to grid division by adopting unstructured grids, and the grid quality is not lower than 90%.
In the fourth step, the viscosity of the fluid is 1-100 mPa.s, and the fluid speed is 0.2m/s-2 m/s; and (3) simulating the flowing state of the fluid in the fracture by adopting a CFD (computational fluid dynamics) method.
And in the fifth step, a DEM method is adopted to simulate migration and distribution of the plugging agent in the fracturing fracture.
And in the sixth step, a CFD-DEM method is adopted to simulate the blocking state of the blocking agent in the crack in a coupling manner.
Compared with the prior art, the invention has the following advantages:
(1) the method can be used for making up the defects of poor repeatability and difficult parameter change of a laboratory according to the conditions of fluid, plugging agent types and the like injected into the cracks, testing the simulation of matching of various temporary plugging particles, and coupling and simulating the dynamic process of plugging the cracks by carrying the plugging agent with fracturing fluid by adopting a CFD-DEM method;
(2) the invention can determine the plugging effect of the plugging agent in the fracture through the number of the plugging agents in the fracture and the pressure born by the fracture, and provides a more intuitive simulation method for evaluating the plugging effect of the plugging agent.
Description of the drawings: FIG. 1 is a flow chart of numerical simulation; FIG. 2 numerically simulates meshing; FIG. 3 the distribution pattern of the plugging agent in the fracture; FIG. 4 is a plugging agent inlet pressure profile; fig. 5 is a plot of the number of plugging agents.
The specific implementation mode is as follows: the invention will be further explained with reference to the following figures and examples:
a numerical simulation method for evaluating the plugging effect of a plugging agent in a fracturing process comprises the following steps:
the first step is as follows: determining a numerical simulation research area of a fracturing fracture of an oil and gas reservoir, determining fracturing fracture parameters including fracture length, fracture inlet opening and fracture outlet opening, and establishing a research area boundary;
the second step is that: forming information files of different plugging agent parameters including fracturing fracture parameters, fracture length and opening degrees of a fracture inlet and a fracture outlet according to the fracturing fracture parameters and the plugging agent parameters; the parameters of the plugging agent comprise the density, the particle size and the concentration of the plugging agent;
the third step: carrying out grid division on a research area, and establishing an oil and gas reservoir fracture simulation model; the grid division adopts unstructured grids, and grid precision is adjusted according to grid quality, so that the condition that simulation conditions including different construction conditions and intra-crack migration laying forms under crack conditions are met is ensured;
the fourth step: determining fluid parameters including fluid viscosity and fluid velocity in the fracture based on the divided grids; setting fracture boundary conditions including fracture length, fracture inlet opening and fracture outlet opening, and simulating the flowing state of fluid in a fracture by a CFD (computational fluid dynamics) method;
the fourth step: determining fluid parameters including fluid viscosity and fluid velocity in the fracture based on the divided grids; setting fracture boundary conditions including fracture length, fracture inlet opening and fracture outlet opening, and simulating the flowing state of fluid in a fracture by a CFD (computational fluid dynamics) method;
because the flow of the fracturing fluid in the fracture is influenced by the accumulation distribution of the plugging agent, the corrected Navier-Stokes equation is adopted for calculation, and the strong energy and momentum exchange exists in the flowing process of the fracture plugging agent and the fracturing fluid, so that the flowing process of the fracture plugging agent and the fracturing fluid conforms to the turbulent flow process; transient simulation in the turbulence model can directly solve an instantaneous turbulence control equation, the turbulence model in the particle fluid two-phase flow is calculated by adopting a standard k-model, and the turbulence equation and the turbulence diffusion equation are as follows:
turbulent kinetic energy equation:
turbulent diffusion equation:
in the formula: t-time, s; rho-fluid density, kg/m3(ii) a k-kinetic energy of turbulence, m2/s2；xi,xj-representing respectively one component of the vector x; u. ofi-represents a component of the velocity, m/s; μ -represents the hydrodynamic viscosity, mPas; mu.slViscosity increase due to turbulence, mPa · s; gkRepresenting the kinetic energy of turbulence due to the mean velocity gradient, kg/(m · s)3)；GbKinetic energy of turbulence caused by buoyancy, kg/(m.s)3) (ii) a Turbulent dissipation ratio, m2/s3，YM-diffusion induced fluctuations; sk，S-a dimensionless quantity; sigmak,σ-turbulent prandtl number; c1C2C3-a constant value;
the fifth step: determining parameters of the plugging agent in the fracture, including density, particle size and concentration of the plugging agent, on the basis of the divided grids, setting fracture boundary conditions including fracture length, fracture inlet opening and fracture outlet opening, and simulating migration and distribution of the plugging agent in the fracture by a DEM (digital elevation model) method;
by integrating Newton's second law, the velocity distribution change of the plugging agent in the fracturing fluid is obtained, and the contact force between particles (the elastic force and the damping force between the particles) can be calculated by the following formula;
in the formula, Fi-contact force between particles, N; kn-normal contact stiffness, N/m;n-the normal action distance between the particles, m; gamma rayn-critical normal damping ratio; m is the mass of the particles, kg; vn-particle normal relative velocity, m/s; ks-shear contact stiffness, N/m;s-the normal action distance between the particles, m; gamma rays-critical shear damping ratio; vs-particle shear relative velocity, m/s; i-particle number, i ═ 1, 2;
the mechanical interaction between the particles and the contact shear will cause them to rotate, and the particle momentum can be calculated by the following formula;
Mi＝Ks s(x0-xi)
in the formula, Mi-momentum at the point of particle contact, kg · m/s; ks-shear contact stiffness, N/m;s-the normal action distance between the particles, m; x is the number of0-the position of the particle contact point; x is the number ofi-the geometric centre position of the particle i;
and a sixth step: and (3) simulating the plugging state of the plugging agent in the crack in the fourth and fifth steps by adopting a CFD-DEM (computational fluid dynamics-dynamic effect model) method in a coupling manner, carrying out a numerical simulation experiment by changing relevant parameters such as fluid injection speed, plugging agent density, plugging agent particle size and plugging agent concentration, evaluating the plugging effect of the crack according to the crack pressure holding degree by the curve of inlet pressure and the change of the number of the plugging agents along with time, judging that the crack is effectively plugged when the pressure holding exceeds the horizontal stress difference of a research area, and optimizing the plugging agent construction process in the fracturing process according to the numerical simulation experiment result of the plugging effect of the plugging agent.
And the fracture in the first step adopts a PKN and KGD two-dimensional model.
The second step of the blocking agent is a particle type temporary blocking agent, the particle size is 20/40 meshes, 70/100 meshes, 100/120 meshes, 180/200 meshes, 200/300 meshes or 400/600 meshes, and the use concentration of the blocking agent is 0.5-5%.
And in the third step, the simulation area is subjected to grid division by adopting unstructured grids, and the grid quality is not lower than 90%.
In the fourth step, the viscosity of the fluid is 1-100 mPa.s, and the fluid speed is 0.2m/s-2 m/s; and (3) simulating the flowing state of the fluid in the fracture by adopting a CFD (computational fluid dynamics) method.
And in the fifth step, a DEM method is adopted to simulate migration and distribution of the plugging agent in the fracturing fracture.
And in the sixth step, a CFD-DEM method is adopted to simulate the blocking state of the blocking agent in the crack in a coupling manner.
Example 1
The gravelly gravel reservoir of the sand river sub-group of the creep gas field in the Daqing oil field is buried deeply and has large thickness, and the reconstruction effect is poor by adopting a conventional fracturing mode. In order to further enlarge the reservoir transformation volume and improve the transformation effect and construction controllability, research and field test on the SS10 well particle temporary blocking steering construction control process are carried out. The blocking effect of the particle temporary blocking agent is evaluated through the numerical simulation of the blocking effect of the blocking agent in the fracturing process, and the numerical simulation flow is shown in figure 1.
First, the study area of the SS10 well fracture was determined, and a SS10 well fracture simulation model was established. The perforating thickness of the SS10 well is 16.0m, the half length of a fracture simulation crack is 280.0m, the height of the fracture is 34.0m, and the width of the fracture is 0.5 cm;
and then forming information files of different plugging agent parameters. The particle size of the particle temporary plugging agent is 20/40 meshes +70/100 meshes, 20/40 meshes +100/120 meshes, 20/40 meshes +180/200 meshes, 20/40 meshes +70/100 meshes +100/120 meshes, 20/40 meshes +100/120 meshes +200/300 meshes, 20/40 meshes +100/120 meshes +400/600 meshes, and the density is 1100kg/m3The particle concentration was 3%.
Then, the simulation area is subjected to unstructured grid division, grid accuracy is adjusted according to grid quality, simulation conditions are guaranteed to be met, and grid quality is guaranteed to be more than 90%, as shown in fig. 2.
Based on the divided grids, the flow velocity of the fluid is 0.5m/s, the viscosity of the fluid is 1 mPa.s, and the density of the fluid is 1000kg/m3. Setting the fluid state to instantaneous flow, setting the fractureThe boundary conditions comprise that the inlet flow rate of the fracture is 0, the outlet flow rate of the fracture is 0, and the CFD method is adopted to simulate the flow state of the fluid in the fracture;
determining plugging agent parameters in the cracks through established plugging agent information files on the basis of the divided grids, setting the density, the particle size, the concentration and the like of the plugging agent, and setting the boundary conditions of the cracks to comprise that the inlet flow velocity of the cracks is 0 and the outlet flow velocity of the cracks is 0. And (3) simulating migration and distribution of the plugging agent in the fracture by adopting a DEM (dynamic effect model) method.
And (3) coupling and simulating the blocking state of the blocking agent in the crack by adopting a CFD-DEM method. As shown in fig. 3.
And finally, evaluating the plugging effect of the crack plugging agent through the number of the plugging agents in the DEM and the inlet pressure. The stress difference phase difference of SS10 well horizontal is 2MPa, the effective plugging of the temporary plugging agent can be realized only when the pressure is required to be more than 3 MPa. Different parameters are changed through numerical simulation to analyze the inlet pressure and evaluate the plugging effect. As shown in fig. 4.
Table 1 shows the plugging effect of the plugging agent in the second injection of SS10 wells with different particle size matching. It can be seen that the inlet pressure is continuously increased along with the continuous reduction of the secondary particle size, but the total pressure is less than 2MPa, so that the requirement of stratum plugging cannot be met.
TABLE 1 Inlet pressure values for two-stage injection with different particle size matching
| Particle size matching of plugging agent | Inlet pressure |
| 20/40 mesh, 70/100 mesh-1: 0.5 | 0.7MPa |
| 20/40 mesh, 70/100 mesh, 1:1 | 1.1MPa |
| 20/40 mesh, 100/120 mesh, 1:1 | 1.5MPa |
| 20/40 mesh, 180/200 mesh, 1:1 | 1.8MPa |
Table 2 shows the plugging effect of the plugging agent in the case of three-stage injection with different particle size matching. It can be seen that the tertiary injection pressure is significantly higher than the secondary injection, which can meet the field conditions.
TABLE 2 Inlet pressure values for three-stage injection with different particle size matching
| Particle size matching of plugging agent | Inlet pressure |
| 20/40 mesh, 70/100 mesh, 100/120 mesh, 1:1 | 3.2MPa |
| 20/40 mesh, 70/100 mesh, 100/120 mesh, 1:2 | 4.8MPa |
| 20/40 mesh, 100/120 mesh, 200/300 mesh, 1:1 | 6.5MPa |
| 20/40 mesh, 100/120 mesh, 200/300 mesh, 1:2 | 8.2MPa |
| 20/40 mesh, 100/120 mesh, 400/600 mesh, 1:1 | 10.1MPa |
| 20/40 mesh, 100/120 mesh, 400/600 mesh, 1:2 | 12.3MPa |
The number of the plugging agents in the cracks is rapidly increased along with the injection of the plugging agents, but when the number of the particles reaches a 3400 value, the increase of the number of the plugging agents is very slow and continuously fluctuates around the 3400 value, which shows that the optimal plugging agent value of the 3400 value is obtained. As shown in fig. 5.
According to the evaluation curves obtained by the figures 4 and 5, the plugging agent construction process in the fracturing process of the well is optimized by adjusting parameters, so that the aim of effectively plugging the cracks is fulfilled.
The method is applied to a numerical simulation method for evaluating the plugging effect of the plugging agent in the fracturing process, comprehensively and effectively evaluates the plugging effect of the plugging agent in the fracturing process, carries out a numerical simulation experiment by changing relevant parameters such as the density of the plugging agent, the particle size of the plugging agent, the concentration of the plugging agent and the like, evaluates the plugging effect of the crack by inlet pressure and the number of the plugging agents, simulates the distribution and migration processes of the plugging agent in the fracturing crack under different construction parameters, guides and optimizes the temporary plugging construction process in the fracturing process, and provides technical support for the temporary plugging mechanism research and the execution of crack transformation measures in the fracturing process of the oil and gas well.
Claims (7)
1. A numerical simulation method for evaluating the plugging effect of a plugging agent in a fracturing process is characterized by comprising the following steps: the method comprises the following steps:
the first step is as follows: determining a numerical simulation research area of a fracturing fracture of an oil and gas reservoir, determining fracturing fracture parameters including fracture length, fracture inlet opening and fracture outlet opening, and establishing a research area boundary;
the second step is that: forming an information file for simulating a plugging agent plugging numerical value according to the fracturing fracture parameters and the plugging agent parameters, wherein the information file comprises the fracturing fracture parameters, the fracture length and the opening degrees of a fracture inlet and a fracture outlet; the parameters of the plugging agent comprise the density, the particle size and the concentration of the plugging agent;
the third step: carrying out grid division on a research area, and establishing an oil and gas reservoir fracture simulation model; the grid division adopts unstructured grids, and grid precision is adjusted according to grid quality, so that the condition that simulation conditions including different construction conditions and intra-crack migration laying forms under crack conditions are met is ensured;
the fourth step: determining fluid parameters including fluid viscosity and fluid velocity in the fracture based on the divided grids; setting fracture boundary conditions including fracture length, fracture inlet opening and fracture outlet opening, and simulating the flowing state of fluid in a fracture by a CFD (computational fluid dynamics) method;
because the flow of the fracturing fluid in the fracture is influenced by the accumulation distribution of the plugging agent, the corrected Navier-Stokes equation is adopted for calculation, and the strong energy and momentum exchange exists in the flowing process of the fracture plugging agent and the fracturing fluid, so that the flowing process of the fracture plugging agent and the fracturing fluid conforms to the turbulent flow process; transient simulation in the turbulence model can directly solve an instantaneous turbulence control equation, the turbulence model in the particle fluid two-phase flow is calculated by adopting a standard k-model, and the turbulence equation and the turbulence diffusion equation are as follows:
turbulent kinetic energy equation:
turbulent diffusion equation:
in the formula: t-time, s; rho-fluid density, kg/m3(ii) a k-kinetic energy of turbulence, m2/s2；xi,xj-representing respectively one component of the vector x; u. ofi-represents a component of the velocity, m/s; μ -represents the hydrodynamic viscosity, mPas; mu.slViscosity increase due to turbulence, mPa · s; gkRepresenting the kinetic energy of turbulence due to the mean velocity gradient, kg/(m · s)3)；GbKinetic energy of turbulence caused by buoyancy, kg/(m.s)3) (ii) a Turbulent dissipation ratio, m2/s3，YM-diffusion leaderFluctuation of the wave; sk，S-a dimensionless quantity; sigmak,σ-turbulent prandtl number; c1C2C3-a constant value;
the fifth step: determining parameters of the plugging agent in the fracture, including density, particle size and concentration of the plugging agent, on the basis of the divided grids, setting boundary conditions of the fracture, including fracture length, fracture inlet opening and fracture outlet opening, and simulating migration and distribution of the plugging agent in the fracture by a DEM (digital elevation model) method;
by integrating Newton's second law, the velocity distribution change of the plugging agent in the fracturing fluid is obtained, and the contact force between particles (the elastic force and the damping force between the particles) can be calculated by the following formula;
in the formula, Fi-contact force between particles, N; kn-normal contact stiffness, N/m;n-the normal action distance between the particles, m; gamma rayn-critical normal damping ratio; m is the mass of the particles, kg; vn-particle normal relative velocity, m/s; ks-shear contact stiffness, N/m;s-the normal action distance between the particles, m; gamma rays-critical shear damping ratio; vs-particle shear relative velocity, m/s; i-particle number, i ═ 1, 2;
the mechanical interaction between the particles and the contact shear will cause them to rotate, and the particle momentum can be calculated by the following formula;
Mi＝Ks s(x0-xi)
in the formula, Mi-momentum at the point of particle contact, kg · m/s; ks-shear contact stiffness, N/m;s-the normal action distance between the particles, m; x is the number of0-the position of the particle contact point; x is the number ofi-the geometric centre position of the particle i;
and a sixth step: and (3) simulating the plugging state of the plugging agent in the crack in the fourth and fifth steps by adopting a CFD-DEM (computational fluid dynamics-dynamic effect model) method in a coupling manner, carrying out a numerical simulation experiment by changing relevant parameters such as fluid injection speed, plugging agent density, plugging agent particle size and plugging agent concentration, evaluating the plugging effect of the crack according to the crack pressure holding degree by the curve of inlet pressure and the change of the number of the plugging agents along with time, judging that the crack is effectively plugged when the pressure holding exceeds the horizontal stress difference of a research area, and optimizing the plugging agent construction process in the fracturing process according to the numerical simulation experiment result of the plugging effect of the plugging agent.
2. The numerical simulation method for evaluating the plugging effect of the plugging agent in the fracturing process according to claim 1, wherein the numerical simulation method comprises the following steps: the first step of fracturing fracture adopts a PKN and KGD two-dimensional model.
3. The numerical simulation method for evaluating the plugging effect of the plugging agent in the fracturing process according to claim 1, wherein the numerical simulation method comprises the following steps: the second step of the blocking agent is a particle type temporary blocking agent, the particle size is 20/40 meshes, 70/100 meshes, 100/120 meshes, 180/200 meshes, 200/300 meshes or 400/600 meshes, and the use concentration of the blocking agent is 0.5-5%.
4. The numerical simulation method for evaluating the plugging effect of the plugging agent in the fracturing process according to claim 1, wherein the numerical simulation method comprises the following steps: and thirdly, carrying out grid division in the research area by adopting unstructured grids, wherein the grid quality is not lower than 90%.
5. The numerical simulation method for evaluating the plugging effect of the plugging agent in the fracturing process according to claim 1, wherein the numerical simulation method comprises the following steps: fourthly, the viscosity of the fluid is 1 to 100 mPa.s, and the fluid speed is 0.2m/s to 2 m/s; and (3) simulating the flowing state of the fluid in the fracture by adopting a CFD (computational fluid dynamics) method.
6. The numerical simulation method for evaluating the plugging effect of the plugging agent in the fracturing process according to claim 1, wherein the numerical simulation method comprises the following steps: and fifthly, simulating migration and distribution of the plugging agent in the fracture by adopting a DEM (dynamic effect model) method.
7. The numerical simulation method for evaluating the plugging effect of the plugging agent in the fracturing process according to claim 1, wherein the numerical simulation method comprises the following steps: and sixthly, coupling and simulating the blocking state of the blocking agent in the crack by adopting a CFD-DEM method.
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