Explicit Modeling of Hydraulic Fracture Propagation in Fractured Shales

Abstract

Abstract Recently a combined application of two technologies, horizontal drilling and multi-stage massive hydraulic fracturing (HF) has made vast resources of shale gas commercially viable. The HF is a well-established reservoir stimulation technique, which has been developed over the last half century. There are reliable tools for designing HF in conventional reservoirs, in which a planar HF is assumed. On the contrary, in shale gas fracturing, micro-seismic observations have illuminated a complex internal structure resulting from the interaction of the induced hydraulic fractures with natural fractures. It is widely speculated that the stimulated natural fractures make a significant contribution to the gas production. The mechanics of the interaction between multiple fractures during a HF treatment is very complicated. In this paper we present the results of state-of-the-art modeling of an explicit interaction between a propagating hydraulic fracture and a statistically generated discrete fracture network. A sensitivity study reveals a number of interesting observations including importance of initial fracture conductivity for growth of the fracture system, effect of the dilation angle on the generated conductivity and net pressure and uneven distribution of fracture aperture that is critical for proppant placement. This work strongly links the production technology and geomechanics and suggests an approach for modeling and designing HF treatments in unconventional shale gas plays. Introduction Natural gas and light oil production from shale formations has become the focus of much attention in the past decade. The economic success of the development of these unconventional resources owes to a combined application of two key and well-known technologies: horizontal drilling and multi-stage hydraulic fracturing (King, 2010). The horizontal wellbore sections, commonly with length ranging from 750 m to over 1600 m, are either cased and cemented or isolated with packers to enable multi-stage fracture stimulation (Cipolla, 2009). Hydraulic fracturing (HF) is a well-established reservoir stimulation technique, which has been developed over the last half century. It is not an exaggeration to say that in ultra-tight reservoirs such as shales the connected reservoir conductivity is created in the process of hydraulic fracturing and that enables any measurable hydrocarbon production.