Analysis of interlayer interference in combined development of coalbed methane wells and discussion on combined production methods: A case study of Shoushan No.1 Coal Mine in Pingdingshan

The combined development of multiple coal seams is a key technology to increase the production of single CBM wells. However, in engineering practice, most coal seams have interlayer interference problems, resulting in an insignificant increase in combined development gas production. In order to improve the gas production and development efficiency of combined development in coalbed methane wells, taking the combined production of coalbed methane in the No.4-2 coal seam and the No.2-1 coal seam of the Shoushan No.1 Coal Mine in Pingdingshan as an example, this paper analyses the influence factors and interference rules of interlayer interference, and proposes the control methods of interlayer interference, based on the geological conditions of CBM deposits. The results show that the main factors causing the low multi-coal seam drainage production of the two coal seams are the reservoir pressure gradient, critical desorption pressure and permeability. Among them, the reservoir pressure gradients of the two coal seams are 1.05 MPa/hm and 0.519 MPa/hm respectively; the permeability are 0.25×10^–3 μm² and 1.4×10^–5 μm² respectively; the critical desorption pressures are 1.16-1.69 MPa and 0.40-0.46 MPa respectively; in addition, the distance between the two coal seams is large, about 170 m on average. The differences in the above-mentioned main influence factors result in prominent interlayer contradictions and serious interference, causing low overall production and low efficiency of CBM development in the well group. Based on the current problems, this paper explores and proposes a large-spacing, multi-coal seam, large borehole and double-casing layered control co-production method to achieve the goal of combined production capacity with separate control of two coal seams, so as to improve the combined production and development effects of CBM wells. The research results will provide a new technical approach for efficient drainage of the multi-coal seam development in Pingdingshan and other mining areas with similar geological conditions.