Study on novel method of production capacity analysis on lowpermeability and unsaturated coalbed methane well

In order to accurately have the physical performance parameters of the coalbeds methane well, based on the water drainage data at the initial production period, a new method of a easy production capacity analysis was provided.Firstly in consideration of the low permeability features of the seam generally, an investigation radius formula was introduced to calculate s front edge position of the pressure wave in the coal bed methane at each time.Secondly based on the continuous steady state method, the stress sensitivity considered at each time and the steady-state seepage equation of the pressure wave expansion was derived.Finally,a linear treatment was conducted on the seepage equation and a new method of the production capacity analysis suitable to the low permeability and unsaturated coal bed methane well was obtained.A study was conducted on the reliability and application of the method with the numerical simulation and site case comparison.The study results showed that the error between the permeability predicted with the new method and the actual permeability was 2.38% and the error of the epidermal factor was 6.59%.All those errors could meet the requirements of the site engineering application.The new method could accurately obtain the reservoir physical parameters and could provide the effective theoretical basis to the late production prediction of the gas well and the adjustment of the production system.