PROBLEMS AND CHALLENGES OF MECHANICS IN SHALE GAS EFFICIENT EXPLOITATION

Abstract

Shale gas is unconventional natural gas stored in shale in free or absorbed forms and sometimes in free fluid phase. The exploitation of shale gas has become a promising field of green energy development in China. Although great success has been achieved in shale gas revolution in North America with the technique of hydraulic fracturing, there is only 5%~15% of the stored oil and gas could be exploited, which is still a puzzle for petroleum engineers. Compared with the North America, China's shale gas reservoirs are deep burial, the geologic construction conditions are complicated and natural quality is low, therefore, efficient exploitation is facing more difficulties and challenges. In recent years, aiming at the national major energy strategy and the frontier of technological development, China's academia and industry have carried out the preliminary study on some of the key scientific and technical issues. Around the new issues encountered in the shale gas extraction in Sichuan and Chongqing areas in recent three years, this paper introduces and summarizes the key mechanics problems and challenges that the high efficient shale gas extraction is facing, mainly includes the multifield coupling safe and high quality drilling mechanics, hydraulic fracturing and multi-scale fracture network formation mechanism and multi-scale seepage and desorption mechanism of shale gas, to solve the challenges in deep exploitation below 3500 meters in China, such as geologic sedimentation, different fracture development, increasing overburden pressure, the change of horizontal stress, etc. The deep shale gas exploitation is not only to adapt to the national energy demand, but also has scientific and engineering significance. To realize the efficient exploitation of shale oil and gas, it needs the interdisciplinary collaboration of mechanical engineering, petroleum engineering, geophysics, chemical engineering and environmental engineering to carry out basic theoretical research, physical simulation, numerical simulation and field experiment. It has been recognized that interdisciplinary research is the bridge and the key to breakthrough the technology bottleneck and realize the efficient exploitation of shale gas. It is necessary of the deep collaboration between mechanics, petroleum engineering, earth science and other disciplines to promote the development of shale gas and other unconventional oil and gas resources.