Hydraulic Fracturing and Enhanced Recovery in Shale Reservoirs: Theoretical Analysis to Engineering Applications

Shale reservoirs are extensively exploited using hydraulic fracturing, which forms multiple cracks that connect with the existing natural fractures to create a continuous path for the gas stored in the kerogen to flow to the production well. Apart from the tedious nature of hydraulic fracturing, the mechanism of the storage and flow of gas is equally complex since multiple phases and scales are involved. An accurate understanding of hydraulic fracturing coupled with a strategy of analyzing the flow and overall recovery of gas is paramount to ensure efficient exploitation. In this work, a comprehensive review of the recent strategies used in analyzing the hydraulic fracturing, storage, flow, and recovery of gas is presented. To begin with, the experimental, analytical, and numerical approaches pertinent to hydraulic fracturing are deeply explored. Additionally, the flow of gas through the newly opened channels is accounted for by using a quadruple-domain approach where the mechanisms of flow in shale reservoirs at the nanoscale, microscale, mesoscale, and macroscale are considered. Furthermore, a strategy to capture the multiple phases, including gas, oil, and water, and recover both carbon dioxide and methane is explored through thermal and enhanced gas recovery approaches. This review provides a baseline for understanding how the hydraulic fracture evolves and propagates to create new channels that contribute to the flow of gas, how the gas flows through the created channels across the many scales of the shale reservoir, and how to improve recovery from shale reservoirs.