Mechanical frontiers in shale-gas development

The development ofshale gas involves two critical processes including fracturing andtransportation. To realize reticular fractures in the shale layerof multi-phase under more than 2000 m subjected to complexgeo-stress and to collect the free and adsorbed gases encapsulatedin the layer, we face many key mechanical challenges to beaddressed. There are several cut-on-edge research topicsassociated with shale gas development: the huge span in structuralsize and fracture eveents from nanoscale to even severalkilometers, free and adsorbed gas transporting at temperal scalesfrom microseconds to the life-long mining of a shale-gas well, thefluid-solid interaction at different time and length scales, andthe in-situ monitoring on internal damage states duringfracturing. In view of the achievements in shale-gas explorationand the mechanical research frontiers for subsequent development,we give a comprehensive review on the basic characteristics anddevelopment techniques of shale-gas reservoirs. We cover in thisreview six aspects of the latest research progress, the mechanicalproperties of shales and their characterization, shale gasreservoir experimental techniques, shale gas micro-flow mechanismand fluid-solid coupling characteristics, numerical simulation ofhydraulic fracturing process, micro-seismic monitoring technologyof hydraulic fracturing process and high-efficiency andenvironmentally friendly waterless fracturing technology.Combining with the engineering practice of shale-gas reservoirdevelopment, the key issues of mechanics are presented, to providea theoretical basis for the practitioners engaged in thedevelopment and research of shale-gas field. We suspect that theprogress summarized here may help guide general research inmechanics, especially in geotechnical mechanics.