Fracture Face Damages and Numerical Investigation of Their Impacts on the Productivity of a Shale Gas Well

Abstract

Economic viability of unconventional gas developments hinges the effective stimulation of extremely low permeability reservoir rocks. As the most effective stimulation method, hydraulic fracturing made it possible for the extraction of resources, such as shale gas and tight gas, which are difficult to recover with regular drilling and completion procedures. However, when creating hydraulic fractures, extensive damages on hydraulic fracture face may occur, which will reduce fracture conductivity and thus threat well productivity. In this paper, the effect of retained fracture fluid, proppant scaling and proppant diagenesis in shale gas reservoirs were investigated. We first understood damage mechanism through a critical literature review of relevant published laboratory and field data, then built a fit-for-purpose simulation model representing drainage of a shale gas well. The three effects were tested on three presumed hydraulic fracture geometries. Damages were quantified in terms of decrease in cumulative gas production, gas rate and water recovery. Results indicate that retained foreign fluid poses severe threat to gas production when only a single-planar fracture is created. It could be alleviated when a fracture network is created. Proppant scaling only has marginal effect on gas production regardless of the fracture geometries. Proppant diagenesis greatly decreases gas production for cases with both single fracture and fracture network. The results presented in the study provide clear insights into the range of recovery factors one can expect from a fractured shale gas formation, the impact that three damage phenomena and relevant operation procedures have on these recovery factors, and the efficiency or inefficiency of contemporary shale gas production technology. The understanding helps engineers design more effective fracture treatments in shale gas reservoirs.