Applicability analysis and technique of combined coalbed methane drainage at same pressure in deep and shallow depth seam

According to the influences from the well hole internal pressure during the joint coalbed methane drainage process of the deep and shallow seams, the production of the joint drainage wells could not reach the pre-scheduled production and even lower than a single seam production. With the analysis on the deep and shallow seam features, the joint drainage operation status in the well hole could be divided into three conditions: shallow coal seam, deep coal seam and both of them taking state of two-phase flow. The joint drainage feasibility under each condition was analyzed. A pressure model within the well hole was established. Based on the compatible data allowed the pressure difference Δp as the basis, the commingled production technique was conducted with the pressure adjustment in the well hole. With the calculation conducted on the demo wells, when Δp value was 0.4, 0.6, 0.8 and 1.0 MPa individually, the commingled production increased as Δp raise up and the most fix state was maken under Δp was 1.0 MPa. The data results showed that the commingled production technique with the pressure adjustment could be suitably applied to the joint drainage operation in the multi seams.