Modeling analysis of coalbed methane co-production interference: A case study in Eastern Yunnan Basin, China

Abstract

The interlayer interference in coalbed methane (CBM) co-production wells restricts the effective development of CBM resources in multi-seam areas; however, the establishment of quantitative interference indicators still remains difficult to date resulting from the complex geological formation evolution and reservoir development techniques. In this paper, the reverse flow rate and the water production inhibition index of the coal seam were derived from the transient inflow performance relationship (IPR) curve to characterize the interlayer interference. The IPR curves of different reservoir and aquifer parameters were calculated on the modified reservoir model using a CBM well as a case in East Yunnan Basin. From the data processing for obtaining interlayer interference indicators, the pressure difference between coal reservoirs was found to be the most critical factor in generating reverse fluids, with a 15% difference and the interference amounting to 244.08 m3 d·KPa−1, followed by coal seam thickness and permeability (∼18.00–25.00 m3 d·KPa−1). Gas content, Langmuir pressure, and Langmuir volume contribute slightly to the interlayer interference. Second, any increase in thickness or permeability of the aquifer will significantly increase the water production rate of the coal seam due to water influx. Significantly, the reverse flow rate will be increased when the aquifer is located in a higher fluid pressure system. Instead, the reverse flow rate will be decreased in the case of a lower pressure system. Finally, continuous pressure drops lead to the coal seam and aquifer recharge capacity higher than the set drainage system, resulting in the coal seam water not being removed effectively. The coal seam's water production inhibition index shows a positive correlation with the thickness and permeability of the aquifer and a negative correlation with the drainage intensity. The results of this paper bridge the gap between the identification interference indicators and the possible combination of production layers, and it also provides new insights for enhancing CBM development in the East Yunnan Basin.