CN-116244994-B - Artificial crack dynamic seam width calculation method combining discrete element method and finite element method

CN116244994BCN 116244994 BCN116244994 BCN 116244994BCN-116244994-B

Abstract

The invention discloses a method for calculating the dynamic seam width of an artificial crack by combining a discrete element method with a finite element method, which is a method for determining the intrinsic parameters of a proppant particle body by using the discrete element method and applying the intrinsic parameters to finite element numerical simulation of the seam width closure of the crack, so that the efficient prediction of the dynamic seam width of the artificial crack in the mining process is realized; the method fully considers the mechanical characteristics of the proppant particle stack, adopts a discrete element method to obtain the constitutive characteristic parameters of the proppant particle stack, breaks away from the dependence on triaxial experiments of the particle stack, eliminates the influence of the granularity heterogeneity of the proppant particle stack, effectively reduces the cost and improves the efficiency, and compared with the traditional technical scheme, the method not only considers the discrete mechanical characteristics of the proppant particle stack, but also considers the solving efficiency of an engineering scale model, and is more suitable for field application.

Inventors

QI MINHUI
LI YANLONG
WU NENGYOU
HU GAOWEI
CHEN QIANG
LI MINGZHONG

Assignees

青岛海洋地质研究所

Dates

Publication Date: 20260505
Application Date: 20230316

Claims (5)

1. The method for calculating the dynamic slit width of the artificial slit by combining the discrete element method with the finite element method is characterized by comprising the following steps of: step A, acquiring particle size distribution data of a propping agent for a site, and carrying out three-dimensional scanning on single particles to acquire the geometric shape of the single particles; step B, constructing a single-particle discrete element model, and acquiring discrete element modeling parameters of single particles; Step C, combining the discrete element modeling parameters obtained in the step B, establishing a discrete element model of the proppant particle stack, and obtaining the elastoplastic constitutive mechanical parameters of the proppant particle stack; step D, applying the elastic-plastic constitutive mechanical parameters of the proppant stack to the dynamic seam width closed finite element calculation in the artificial crack exploitation process, so as to realize the calculation of the dynamic seam width of the artificial crack; The finite element calculation comprises the steps of establishing an engineering scale reservoir three-dimensional model containing an artificial fracture, setting the geometric dimensions of the fracture and the reservoir in the model according to on-site fracture monitoring results, determining elastoplastic constitutive parameters of the model according to discrete element simulation results in the step C, solving a solid phase mass balance equation, a fluid mass balance equation, a Biot effective stress equation and a Kozeny Carman permeability response equation in the reservoir exploitation process by using a finite element method, calculating the closing quantity of the artificial fracture under the reservoir fluid solid coupling effect in the reservoir exploitation process, and analyzing main factors affecting the closing characteristics of the fracture.
2. The method for calculating the dynamic slit width of the artificial slit by combining the discrete element method with the finite element method according to claim 1, wherein the step B is realized by adopting the following modes: And C, constructing a single-particle discrete element model according to the particle size distribution data and the geometric shape obtained in the step A, carrying out a single-particle uniaxial compression experiment, applying the same pressure condition as that of the single-particle uniaxial compression experiment to the single-particle discrete element model, obtaining a single-particle uniaxial compression stress-strain curve in the loading process, adjusting the effective modulus, the rigidity ratio and the friction coefficient of the discrete element linear model, and fitting the stress-strain curve obtained by simulation with a single-particle uniaxial compression experiment result to determine the constitutive characteristic parameters of the single particles, thereby obtaining the discrete element modeling parameters of the single particles.
3. The method for calculating the dynamic slit width of the artificial slit by combining the discrete element method with the finite element method according to claim 1, wherein the step C specifically comprises the following steps: step C1, establishing a discrete element model of the proppant particle stack, wherein the particle size in the model is set according to the particle size distribution in the step A, and the effective modulus, the rigidity ratio and the friction coefficient of the particles are the same as the fitting result in the step B; And C2, applying closing pressure to the proppant particle stacking discrete element model, simulating the uniaxial compression process of the proppant particle under the action of confining pressure, recording a stress-strain curve in the compression process, and acquiring parameters of elastic modulus, stress yield strength and tangential modulus of the proppant particle in the elastic stage, and based on the stress-strain curve.
4. The method for calculating dynamic slit widths of artificial fractures by combining discrete element method with finite element method according to claim 1, wherein in the step D, the three-dimensional model of the reservoir with the artificial fractures comprises a simulated well bore, a simulated fracture and a reservoir matrix, initial values and boundary conditions are given to the three-dimensional model of the reservoir with the artificial fracture, wherein the simulated fracture is set as an elastoplastic material, the reservoir matrix part is set as an ideal elastic material, parameters of the elastic material are from physical property parameter testing of a reservoir core, a deformable and permeable interface is set between the simulated fracture and the reservoir matrix, and a pressure interface is set as a reservoir matrix interface.
5. The method for calculating the dynamic slit width of the artificial slit by combining the discrete element method with the finite element method according to claim 1, wherein the step D is specifically solved according to the following principle: After the model is initialized, firstly solving a seepage field in the production process of the reservoir based on a fluid mass conservation equation to obtain a reservoir pore pressure distribution rule, solving effective stress change induced by pore pressure change based on a Biot effective stress principle, solving a continuity equation to calculate a reservoir solid-phase unit deformation equation, establishing a relation between strain, porosity and permeability according to a Kozeny-Carmen equation, updating reservoir pore permeability data after each time step is finished, carrying out calculation of the next time step after checking model convergence, and checking the closing condition of a support crack seam width after reaching a calculation set time step.

Description

Artificial crack dynamic seam width calculation method combining discrete element method and finite element method Technical Field The invention belongs to the technical field of hydraulic fracturing in oil and gas field development, and particularly relates to a dynamic slit width calculation method for an artificial slit by combining a discrete element method with a finite element method. Background Hydraulic fracturing is an important oil and gas well production and injection increasing means, and is a necessary technology for efficient development of reservoirs such as hypotonic reservoirs and shale reservoirs at present. However, after the fracturing and casting of the oil and gas well, the supporting seam width of the artificial sand filling crack can be closed under the effective stress caused by the reservoir fluid-solid coupling effect, and the degree of the supporting seam width has time-varying property along with the development and the dynamics of the reservoir. Particularly for reservoirs with higher closure pressure, the closure of the artificial fractures by stress disturbance is more pronounced. In the current numerical reservoir simulation, the fracture width is set as a fixed value, and the fracture conductivity loss caused by the closure of the fracture width is not considered, so that the accuracy of productivity prediction is affected, and the well selection and layer selection of repeated fracturing are not facilitated. Dynamic slot width closure of a fracture under long-period mining conditions is difficult to obtain experimentally, subject to geometry and time scale. The fracture width damage obtained based on the fracture conductivity tester mainly originates from proppant embedding, and the fracture closure under the influence of reservoir fluid-solid coupling induced stress cannot be considered. Numerical simulation is an effective means for solving the problem, but the current dynamic closing model of the crack width does not consider the constitutive characteristics of the supporting crack, and the selection of parameters such as Young modulus of the supporting crack in the model lacks basis. Because single-particle elastic parameters of commonly used proppants (such as ceramsite, precoated sand and quartz sand) are difficult to obtain, researchers have proposed the concept of apparent Young's modulus to characterize the constitutive behavior of a proppant particle stack, and formed a method for obtaining the apparent Young's modulus under closed pressure loading conditions through steel plate conductivity testing. However, the constitutive characteristics of the particle stacking body are influenced by complex factors such as particle size, particle properties, particle shape, sand spreading concentration, closing pressure and the like, experimental simulation test is high in cost, long in period, complex in sample preparation and harsh in conditions, and a set of available apparent Young modulus prediction plates does not exist at the present stage, so that the field application of the method is restricted. In view of the complexity of the physical characteristics of the particle stacking mechanism, conventional numerical simulation methods such as finite element method, finite difference method and boundary element method have limitations in analyzing deformation behaviors of the particle bodies. The discrete element rule of the particles can reveal the dispersion mechanical phenomenon which cannot be explained by the conventional mechanical theory, is not limited by the deformation amount, can effectively simulate the discontinuous mechanical phenomenon of the particle stacking medium, and is the most mature numerical simulation method of the mechanical characteristics of the particles at present. Therefore, a method for determining the constitutive characteristic parameters of the proppant particulates by using a discrete element method and applying the constitutive characteristic parameters to finite element numerical simulation of crack width closure is needed to be proposed so as to realize efficient prediction of the dynamic crack width of the artificial crack in the exploitation process. Disclosure of Invention Aiming at the problem that the dynamic seam width prediction method for the artificial crack after engineering scale fracturing is missing in the prior art, the invention provides the dynamic seam width calculation method for the artificial crack by using the discrete element-finite element combination, which is applicable to calculation under engineering scale and long-period exploitation conditions and meets the requirements of on-site fracturing design and productivity prediction. The invention adopts the following technical scheme that the method for calculating the dynamic slit width of the artificial slit by combining a discrete element method with a finite element method comprises the following steps: step A, acquiring particle size distribution data of