Studies of Hydraulic Fracture-Propagation Behavior in Presence of Natural Fractures: Fully Coupled Fractured-Reservoir Modeling in Poroelastic Environments

摘要

In this paper, the propagation behavior of an induced hydraulic fracture in the presence of a natural fracture is described. A complex meshing and finite-element technique are employed to couple a poroelastic formation, a hydraulic fracture, and an arbitrarily oriented natural fracture. Possibilities of fracture deviation, arrest, and crossing for various angles of approach are investigated under different scenarios of in situ stress contrast, rock strength, and natural fracture geometry (length). Results of this study show that orientation of natural fracture and its length have a profound effect on induced hydraulic fracture propagation. It has been observed that, in most cases, the induced hydraulic fracture crosses short natural fractures (＜10 m). As the induced hydraulic fracture approaches the natural fracture, fluid leak off increases, and consequently, the width of the induced fracture at the wellbore (fracture mouth) decreases. Once the induced hydraulic fracture breaks out of the natural fracture, the fluid leak off decreases, thus increasing the width of the induced fracture. It has been also observed that propagation of induced fracture is blocked or diverted by the presence of a long natural fracture (＞ 10 m). With an increase in the injection rate, however, the induced fracture is likely to cross a long natural fracture (＞ 10 m). The new understandings derived from the fully coupled poroelastic model have many beneficial applications, including design and optimization of hydraulic fracture treatments in naturally fractured reservoirs (tight gas and shale gas reservoirs) and permeability enhancement by fluid-induced shear displacement of fracture surfaces [enhanced geothermal systems (EGS)].