An Improved Approach to Analyzing the Flowing Pressures of CBM Column in Producing Wellbores

Abstract

An improved methodology is presented for the system analysis of flowing pressures in order to forecast the dynamic behavior and solve the forthcoming problems in coalbed methane (CBM) wellbores producing water. The computation of flowing pressures involves CBM temperature and compressibility factor with depth increments and friction factor with Reynolds number. The result of this work is a numerical integration technique used to calculate flowing pressures and pressure drops of CBM column from the bottom hole to well head. The relationships developed match the CBM reservoir behavior and wellbore conditions along the annulus with an overall accuracy of less than 2%. The effect of CBM column pressures is more obvious than that of CBM and water column pressures with the increases in dynamic water level. The pressure ratios of CBM column to the whole column increase rapidly, while water flow rates decline along the annulus. The decrease in CBM column pressure and increased increment of pressure drop are beneficial to CBM desorption and result in the increased CBM and water production. And it will control the falling speed of dynamic water level in producing wellbores and enhance CBM reservoir productivity. The decreases in CBM column pressure from 69.7 to 5.2 kPa result in the decreases in pressure in bottom hole from 2.252 to 1.328 MPa and the increases in CBM flow rate from 3327 to 6721 m3/d.