Numerical Modeling of Hydraulic Fracturing in Oil Sands

Hydraulic fracturing is a widely used and efficient technique for enhancing oil extraction from heavy oil sands deposits. Application of this technique has been extended from cemented rocks to uncemented materials, such as oil sands. Models, which have originally been developed for analyzing hydraulic fracturing in rocks, are in general not satisfactory for oil sands. This is due to a high leak-off in oil sands, which causes the mechanism of hydraulic fracturing to be different from that for rocks. A thermal hydro-mechanical fracture finite element model is developed, which is able to simulate hydraulic fracturing under isothermal and non-isothermal conditions. Plane strain or axisymmetric hydraulic fracture problems can be simulated by this model and various boundary conditions, such as specified pore pressure/fluid flux, specified temperature/heat flux, and specified loads/traction, can be modeled. The developed model has been verified by comparing its results to existing analytical and numerical solutions for thermo-elastic consolidation problems. The model has been used to simulate a laboratory experiment of hydraulic fracture propagation in oil sands. The results from the numerical model are in agreement with experimental observations. The numerical model and laboratory experiments both indicate that, for uncemented porous materials, such as sands (as opposed to rocks), a single planar fracture is unlikely to occur and a system of multiple fractures or a fracture zone consisting of interconnected tiny cracks should be expected.