Discovery of a large gas field of deep coalbed methane in the Shenfu block and its implications

Background After explorations of unconventional natural gas for nearly two decades in the Shenfu block on the eastern margin of the Ordos Basin, deep coalbed methane (CBM) with reserves of 100 billion m³ was discovered in this block in 2023. However, the preliminary exploration of deep CBM in this block faces challenges of insufficient understanding of geological laws, immature fracturing technologies, and a lack of production technologies and experience.

Methods and Results Driven by both management and technological innovations, encouraging exploration results have been achieved. The management innovations include: (1) The implementation of a complementary and three-dimensional exploration model of deep CBM and tight sandstone gas. (2) The removal of the barriers of disciplines, organization, and businesses. (3) The preformation of one strategy for one well. (4) The efficient promotion of the drilling, fracturing, and drainage integration. The technical innovations encompass: (1) The deep CBM accumulation pattern featuring microfacies-controlled coal development, thermal maturity-controlled hydrocarbon generation, and temperature- and pressure-controlled occurrence states. (2) The criteria for exploration target selection, allowing for the identification of the enrichment areas of deep CBM, and the assessment technology for geological-engineering dual “sweet spots”. (3) The exploration of a composite technique for three-dimensional fracture network stimulation to maximize the stimulated volumes and optimize the seepage capacity of coal reservoirs. (4) A production approach comprising rapid backflow of fracturing fluids, multi-stage pressure control, and stepped steady increase in production developed according to local conditions. This assists in forming two production systems, namely undersaturated- and saturated-CBM wells, determining the targets and principles of different stages, and establishing three decline modes of bottomhole flow pressure to achieve the designed capacity and steady production of exploration wells.

Significance These management and technological innovations have contributed to the discovery of the large gas field in the Shenfu block, demonstrating great prospects for the exploration and production of deep CBM on the eastern margin of the Ordos Basin. Therefore, this study serves as a significant guide for resource exploration in similar basins, along with the reserve growth and production addition of unconventional oil and gas, in China.