52nd U.S. Rock Mechanics/Geomechanics Symposium,
2018. American Rock Mechanics Association
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36 since 2007
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ABSTRACT: We have developed a new micro-mechanical modeling framework to study the combined effect of shear and normal stress upon preexisting rough fractures. The surface roughness and aperture of preexisting fractures is highly dependent upon the dynamic stress behavior within rock formations. Due to shear slippage, or variation in normal stress, pre-existing fractures may become more or less conductive. Where such changes are caused by purely elastic deformation, plastic deformation, material failure, or a combination thereof. The numerical modeling framework demonstrated herein is based upon the meshless Material Point Method (MPM). In using MPM, the framework captures large deformations due to applied shear and normal stresses, where no special geometric treatment is required at the point of contact between fracture surfaces. Initial fracture geometries are synthetically generated based upon a statistical approach. This work investigates the effect of increased constraining forces on the total amount of dilation produced during shear deformation.
Since the key goal of hydraulic fracturing is to produce a connected network of fractures (Curtis, 2002), understanding their conductivity is paramount. Dilation of fractures that have failed via hydraulic forces can promote or hinder conductivity (Hossain et.al, 2002). As the overall goal for this fracture network generation is promoting fluid flow, being able to understand better the dilation effects on conductivity may provide valuable insight.
Modelling in the context of hydraulic fracturing has typically focused on the production and maintenance of fractures that have failed due to tensile loading (Al-Busaidi et.al, 2005). This would be when the fluid pressure opens a fracture surface, allowing water, proppant, and eventually hydrocarbons to flow within. While this may represent the dominant mode of conductivity generation, it is not the only factor. During the flow process and under general geomechanical loading, shearing of the fractures planes can occur. If a fracture has closed, this may mean dilation is possible, promoting more fluid flow, or conversely, flow constriction.
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