Project: Numerical modeling of hydraulic fracturing in weak discontinuous rock mass
Vast resources of natural gas occur in very low permeability and fine-grained rocks, referred to as gas shales and tight sands. Successful exploitation of gas from gas shales and tight sands requires drilling horizontal boreholes and completions that include inducing fractures into the surrounding rock mass thereby creating enhanced permeability through larger surface areas for gas production.
The stability of the boreholes during horizontal drilling is dependent on the trade-off between pressure maintained in the borehole and the stress regime. The inducement of fractures into the reservoir rock is normally accomplished by pumping fluids with or without proppant under high pressures into the formation. The success of the horizontal boreholes as well as the volume of rock that is fractured (stimulated reservoir volume) during the fracturing process is dependent on mechanical properties of the rocks and the natural fracture network in the rock mass, the in-situ stress field and the mechanics of drilling and fracturing. The drilling of horizontal boreholes and subsequently fracturing (fracing) the reservoir rock is extremely expensive. In British Columbia, wells costing between 3 and 10 million dollars are typical in plays currently under development such as in the Horn River Basin. Thus optimally designing boreholes and the fracturing program to maximize production, and hence economic returns, are critical. The key to better borehole and fracture design involves understanding the effect of natural fracture network on hydraulic fracture propagation as well as response of the reservoir rock to in-situ and induced stresses during drilling and completions of fracing, which is the primary goal of this research.