Characteristics of Shale Gas Reservoirs and Multi-scale Transport Mechanisms

Abstract

The shale gas reserves in our country are extremely abundant and possess considerable exploitation potential. The shale reservoir is highly compact. To obtain industrial production, the staged fracturing technology of horizontal wells is required. After the fracturing operation, a highly complex fracture network will form in the transformed area. These fracture networks mainly consist of artificial fractures and the natural fractures connected to them, providing excellent flow channels for gas flow. The vast majority of the pores in the shale reservoir are mainly nanoscale pores. The shale gas occurring in shale mainly exists in the forms of free and adsorbed states. The flow of shale gas in the reservoir differs from that of gas in conventional reservoirs. The flow of gas in shale encompasses multiple migration mechanisms such as viscous flow, diffusion, desorption, and slippage. Through research in this paper, it is found that in nanoscale pore diameters, the surface diffusion of gas is very obvious. As the pore size increases, the effects of viscous flow, slippage, and Knudsen diffusion intensify. In large pores, the effect of viscous flow dominates, followed in sequence by the slippage effect, Knudsen diffusion, and surface diffusion.