Grid adaptive method for multi-scale expansion of hydraulic fracturing crack

Abstract

The invention discloses a grid adaptive method for multi-scale expansion of a hydraulic fracturing crack. The grid adaptive method comprises the following steps of fluid-solid coupling result calculation, multi-scale fracture judgment, stress error estimation and grid re-division. The coupling method based on the finite element, the discrete element and the finite volume method overcomes the difficulty of high-precision simulation of the multi-scale problem in a traditional numerical method, the multi-scale extension behavior of the hydraulic fracturing fracture network can be effectively simulated, the simulation result is more accurate and effective, the Darcy law is integrated into the model, the percolation effect is considered, fluid leakage is controlled, complete coupling discretization of single-phase flow in the fractured porous medium is achieved through a finite volume method, the problem of grid division of a traditional finite element in a fracture tip area is solved, the difficulties in the aspects of large-scale fractures of an engineering model and small-scale fractures of a laboratory model are solved, and the problem that it is difficult to reliably and effectively solve the multi-scale expansion of the hydraulic fracturing crack is solved.

Description

technical field [0001] The invention relates to the technical field of large-scale development of shale oil and gas, in particular to a grid self-adaptive method for multi-scale expansion of hydraulic fracturing fractures. Background technique [0002] The development of shale oil and gas in China has gradually started. The large-scale development of shale oil and gas mainly relies on the key technology of hydraulic fracturing to improve the permeability of reservoirs. When the liquid is pumped into the well, high pressure is generated at the bottom of the well or between the wells blocked by the packer. When the pressure exceeds the fracture pressure of the rock near the well wall, cracks will be generated and a complex fracture network will be formed. Complex fractures show typical multi-scale characteristics. The time span of fracture formation extends from the microsecond level of dynamic fractures to the hour level of quasi-static fractures; On the order of hundreds of...

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Problems solved by technology

[0003] At present, in the research of hydraulic fracture network, it is difficult to obtain the continuous expansion behavior of fractures by on-site monitoring. Due to the small size of the sample, it is difficult to show the shape and evolution process of hydraulic fractures under multi-scale conditions in indoor physical experiments. Numerical methods are used. Simulation has become an effective research solution, but there are still some difficult problems in the current numerical models and simulation methods for simulating large-scale and multi-scale hydraulic fracture propagation. Due to limitations and implicit algorithms, it is difficult to understand the dynamic expansion mechanism of fractures. Traditional finite elements limit the reliable expansion of fractures due to grid division in the fracture tip area, and lack of effective simulation of fracturing fluid-driven fractures at engineering and laboratory scales. Numerical simulation schemes for scale expansion. In recent years, many calculation methods for solid crack expansion have been established and developed at home and abroad. Describe the displacement discontinuity at the fracture surface to obtain the deformation field inside the rock mass; based on the traditional finite element and numerical popular element methods, it has certain advantages in dealing with discontinuity problems such as faults and joints in the rock mass, but it is flexible and efficient to solve three-dimensional multi-dimensional There are still some difficulties in the problem of large-scale fractures; the discrete fracture network method based on the classical analytical or semi-analytic fracture model adopts a simple planar fracture model, which has high efficiency in solving, but the simplified model is also difficult to deal with multi-scale fractures, making it The application is limited. The grid-based numerical method for simulating multi-scale fracture propagation has the difficulty of grid division, especially the grid size of the fracture tip becomes the key to simulate fracture expansion at different scales. Low-quality grids are difficult to efficiently , Accurately simulate the multi-scale expansion behavior of hydraulic fracturing fracture network, therefore, the present invention proposes a grid adaptive method for multi-scale expansion of hydraulic fracturing fractures to solve the problems existing in the prior art

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