A review of deep and ultra-deep shale gas fracturing in China: Status and directions

After over a decade of innovation in shale gas fracturing theory and engineering technology, China has established a theoretical and technical system for the development of shallow and medium-depth marine shale gas. The recoverable reserves of deep and ultra-deep shale gas in China account for 56.63 % of the total recoverable shale gas resources. Therefore, deep and ultra-deep shale gas reservoirs will become the main focus of shale gas development. Recently, deep and ultra-deep shale gas development experiments and explorations have commenced in the Sichuan Basin and Ordos Basin, where a series of deep and ultra-deep shale gas wells have been drilled and fractured. However, well production rates have demonstrated significant variations, failing to achieve the desired results, with hydraulic fracturing designs primarily using traditional methods from shallow-to-middle reservoirs. This study first summarizes the preliminary exploration and practical understanding of deep and ultra-deep shale gas fracturing in China and systematically reviews the current status of five key theoretical research areas for deep-ultra-deep shale gas fracturing, including: deep shale fracture networks fracturability theory, dynamic evolution propagation theory of fracture networks under complex structures, proppant transport and fracture conductivity under high closure stress theory, casing deformation mechanics and control theory, fracturing real-time monitoring and post-fracturing evaluation theory. There are still certain limitations in deep and ultra-deep shale gas fracturing theories. Therefore, six research directions for deep and ultra-deep shale gas fracturing technology in China are proposed. This research contributes to the efficient development of shale gas.