Review on gas flow and recovery in unconventional porous rocks

This study summarizes gas flow process in unconventional porous rocks, including the transportation in tight or shale reservoirs and the spontaneous imbibition happened in them. Fluids flow is greatly affected by the pore structure together with the pore size distribution of porous media. The MRI and BET measurement show peaks in pore throat radius ranging from 2 to 20 nm, whereas the diameter for methane and helium are 0.38 and 0.26 nm, respectively. Yet for different types of reservoir, distinct mechanisms should be utilized based on the flow regimes. Besides, experimental measurement techniques for conventional reservoirs are no long accurate enough for most of the unconventional reservoirs. New attempts have been implemented to obtain more valuable data for accurate reservoir prediction. By reviewing large numbers of articles, a clear and comprehensive map on the gas flow and recovery in unconventional reservoirs is made. Factors influencing the gas flow and recovery are investigated in detail for mathematical simulation process. Reservoir conditions and the sweep efficiency play an important role during gas production process. Besides, adsorbed gas contributes a lot to the total gas recovery. The overall investigations suggest that many parameters that influence the gas flow in unconventional porous rocks should be taken into consideration during the evaluation. Among them, permeability, adsorbed gas dynamics, stimulated reservoir volume as well as the unstimulated reservoir volume, and imbibition effect are the most important ones. This study provides valuable data and reasonable exploitations for characterizing gas flow and recovery in unconventional porous rocks.