Abstract
A numerical simulation approach of hydraulic fracture process, considering the couplings of the stress distribution, the fluid flow of the water-air mixture, the compression and dissolution of air, and the element damage evolution, has been developed to investigate the mechanisms of crack initiation and propagation in porous media during hydraulic fracturing. The concept of homogenized pore fluid has been adopted to represent the water air mixture. A large number of numerical analysis on hydraulic fracturing in clay with incipient injection slot have been carried out to study the mechanism of hydraulic fracturing in unsaturated soil with the characteristic of critical model I type of crack loading using stress intensity factorKIc. The results provide a numerical picture depicting the mechanisms of crack initiation and propagation during hydraulic fracturing. The numerical results are in good agreement with the experimental results, which confirms the adequacy and the power of the numerical approach.
Highlights
Hydraulic fracturing may be defined as the process of creating a fracture or fracture system in a porous medium by injecting a fluid under pressure through a well bore in order to overcome native stresses
Hydraulic fracturing techniques are applicable to both saturated soils and unsaturated soils to improve the flow of water and air, respectively
The concept of a “homogenized pore fluid” is that this mixture of gas and liquid can be considered to be an equivalent homogeneous pore fluid which completely fills the pores of the soil
Summary
Hydraulic fracturing may be defined as the process of creating a fracture or fracture system in a porous medium by injecting a fluid under pressure through a well bore in order to overcome native stresses. The hydraulic fracturing in unsaturated soil is coupling process of stress distribution, water flow, air flow, water-air interact, and damage evolution, which is arguably one of the most challenging problems. Many numerical methods have been developed for the simulation of hydraulic fracturing [10,11,12,13,14] Among these methods, FEM method is the most robust one in comparison with BEM, DEM, and DDM which cannot efficiently solve the elasticity-plasticity equation relating the fluid pressure to the fracture opening [15]. The material properties of the damaged element are reduced and the width of the facture in the damaged element can be calculated This approach can effectively simulate hydraulic fracturing [22,23,24] in rocks. The FEM is chosen because it can readily obtain the solutions of boundary value problems on nonconformal domains
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