Optimization of multi-layer commingled coalbed methane production in Zhijin area, Guizhou province

Abstract

Coal seams of the Longtan Formation in the Zhijin area of Guizhou province present the characteristics of multiple layers and small individual thickness. Compared with single thick-layered coal seam, multiple coal seams have differences in reservoir pressure gradient, formation liquid supply capacity, permeability and desorption pressure, which affect the efficiency of combined mining and the degree of resource utilization. In order to enahance the production potential of coalbed methane and improve the economics, it is valuable to optimize commingled production and establish a multi-seam development sequence. In view of these problems, this paper carried out a study on the differences of geological conditions of multiple coal seams. Combined with drainage practice and desorption theory, the influencing factors of multi-layer commingled production in the Zhijin area were discussed, and the production strategy was optimized. The results showed that desorption liquid level height, longitudinal span, pressure gradient, liquid supply capacity and permeability difference are the key factors affecting multi-layer commingled production. The main coal seams in the Upper Permian Longtan Formation in the study area have small differences in liquid supply capacity, pressure gradient and permeability, hence these have less impact on commingled production. The differences in longitudinal span and desorption liquid level height are the key factors affecting commingled production in the study area. A 90 m span can be used as a development combination for coal seams no. 16/17/20/23/27/30. A practice in large well group obtained a stable production of 2 000 m3/d, proving that commingled production is viable.

Keywords

• multiple coal seams
• desorption liquid level height
• optimization of commingled production horizon
• longtan formation
• zhijin area