Geological unit division and development countermeasures of deep coalbed methane in Southern Yanchuan Block

Deep coalbed methane resources have great potential, accounting for 62.8% of the total resources. However, effective development faces many challenges such as strong heterogeneity, high geostress, difficult process matching and low production capacity. Taking the deep coalbed methane in Southern Yanchuan Block as an example, the key parameters are overlaid and analyzed, the development geological units of the gas field are finely divided according to the five controlling factors of “sedimentation coal-control, tectonic influenced accumulation, hydrodynamic gas-control, geostress seepage-control, physical property production-control”. The key geological attributes and development constraints of each development geological unit are clarified, and the differentiated development countermeasures are formulated. It has formed a series of treatment countermeasures for different main causes of low efficiency, such as blocking in the formation, scaling near the well, difficult transformation of deep coal seam, high fluid volume and difficult pressure reduction, and a series of efficiency increasing technologies suitable for “dredging and plug removal, disturbance and permeability enhancement, effective support, liquid extraction and pressure reduction” under complex geological conditions of deep CBM. On this basis, a set of geological engineering integration and technology based on the geological attribute of “multi element coupling gas reservoir control unit” is proposed. In view of the decline of gas wells caused by coal powder blocking the seepage channel in high-yield area, the “nitrogen disturbance” is adopted to form pressure wave disturbance to solve the problem of inner layer dredging. The water breakthrough efficiency of 21 wells is 90%, and the daily increase of single well is 400 m³. It is recognized that the high mineralization degree of deep coal seam is easy to scale in the near wellbore area, resulting in low production. In order to realize the effective utilization of resources in high stress area, the effective transformation of deep coal reservoir is achieved through “long-distance effective support and large-scale volume transformation”. All the 16 wells have achieved good results, and the daily increase of single well is 1500 m³, and the gas production level is increased by 5-6 times. Meanwhile, the potential of high-yield and low-efficiency wells is continuously explored, and the effect of fluid lifting and pressure reduction is initially shown. The successful research and development of the key technology system of integrated efficiency enhancement has played a leading and exemplary role in the cost-effective development of deep coalbed methane in China.