Review and development trends of coalbed methane exploitation technology in China

Coalbed methane (CBM) resources are abundant in China, but a single well production is generally low because of its complicated adsorbed-phase conditions, difficulties in exploration and development, poor versatility of CBM development techniques under different geological conditions. In this paper, first, the achievements and key technological progresses of CBM in drilling, completion, stimulation, drainage and production, enhanced CBM and artificial intelligence in recent years were summarized. Then, the applicability of different technologies in different coal reservoirs were reviewed and analyzed. After that, the problems and challenges of CBM development were summarized, including complex coal seam geological conditions, lack of theoretical understanding on the occurrence characteristics of CBM and stimulation mechanisms, under-developed applicable technologies for different geological conditions of coal seams in China and immatured theories and technologies for geology-engineering integration. Therefore, the overall CBM development strategy was proposed:specific condition+adaptable techniques, and co-production of multi-gases and integration of coal mining and gas production. Several innovative ideas of CBM exploitation were put forward, including injecting supercritical CO2 into deep coal seam by radial wells+shock fracturing+CCUS, liquid nitrogen-gas nitrogen cyclic fracturing, horizontal well segmented cavitation by hydraulic jet, intelligent decision-making system of CBM well completion and drainage, coal and CBM co-mining “four zones” combined well up and down pumping mode, etc. Finally, some suggestions were proposed for the development of the CBM industry under the background of carbon peaking and carbon neutrality goals. The basic concept is to realize intellectualized, low carbon, packaging, economization, and sustainable development. The goal is to develop intelligent exploration-drilling-completion-production equipment and establish an intelligent energy platform and data center. Based on the core idea of geology-engineering integration, it is proposed that the fundamental researches are consolidated, the pilot projects are implemented, the original, cutting-edge and breakthrough technologies are promoted, and the AI CBM fields are established. The purpose of the paper is to provide a reference for the efficient, economic and sustainable development of CBM. © 2022 China Coal Society. All rights reserved.