Research progress in theories and technologies of shale gas development in China

The shale gas reservoirs in China are unconventional gas reservoirs that have been developed with volumetric fracturing engineering technologies to achieve effective production. However, shale reservoirs differ from conventional reservoirs in that they have widely distributed nanoscale pores, low porosity and permeability, and widely distributed microfractures. Shale reservoirs have various gas flow mechanisms, including desorption, diffusion, slippage, and seepage, which result in a cross-scale and multifluid coexistence flow through matrix microfractures and artificial fractures. Conventional oil and gas development theories and technologies are not directly applicable to shale gas reservoirs. Therefore, to establish shale development theories and technologies and realize the efficient development of shale gas reservoirs in China, targeted research is required. This article summarized the basic laws of shale gas flow, the multifluid, multiscale, and multifield coupled transport mechanism and porous flow laws of shale gas flow, and the multiscale and nonlinear unified flow equation based on desorption, diffusion, slippage, and porous flow. The full multiscale flow pattern was also provided. The multizone and multifield coupling nonlinear porous flow theories for multistage fractured horizontal shale gas wells were established to detect the production range and development dynamics of flow field zone reserves in shale gas reservoirs. A production decline model for shale gas production was developed based on the characteristics of China's shale gas reservoirs. Based on the abovementioned theory, development design methods and classification and optimization target evaluation methods that are suitable for China's shale gas reservoirs have been proposed. The progress of the adaptability technology for China's shale gas fracturing development process was summarized. The future developmental direction of efficient shale gas development theory was forecasted on this basis to provide guidance for shale gas theory and technology research in China.