East China Bureau of Petroleum, SINOPEC, Nanjing ,China

Based on the results of exploration and drainage practices for many years in South Yanchuan Block CBM Field, the influence of stress sensitivity of deep coal reservoirs on gas and liquid production in coalbed methane wells as well as the reasonable drainage system are investigated and discussed. The results show that due to the charactersitics of low porosity, low permeability and strong stress sensitivity of deep coal reservoirs, high drainage rates are likely to result in significant compressive deformation of coal seams which leads to a decrease in permeability and a difficulty in the expansion of pressure drop funnels, and eventually a low productive efficiency of coalbed methane well. Through the comparison of the optimization processes of coalbed methane well drainage systems over different periods in South Yanchuan block, the drainage system of balanced drainage and stepped decompression is proposed. This system can delay and weaken the adverse effect of stress sensitivity on the coal reservoirs. As a result, the pressure relief areaes are continuously expanded so that high and stable yields of coalbed methane wells can be guaranteed. The scientificity and applicability of the proposed drainage system have been confirmed in South Yanchuan Block CBM.