Drainage feature about coalbed methane wells in different hydrogeological conditions in Fanzhuang area

Abstract

It is an important guarantee to enhance the production of coalbed methane (CBM) and reduce the project investment by finding out the drainage feature about CBM wells in different hydrogeological conditions. Based on the CBM exploration and development data on the Fanzhuang block in southeast Qinshui Basin and combined with the seepage principle and lithology on the roof and the bottom coalbed, the mathematical model of integrated permeability was established. By permeability experiments of the different lithologies on the roof and the floor within the 20 m range combined with the log curves, the integrated permeability of different lithological combinations were obtained. The starting pressure gradient and permeability of the roof and the floor for different lithologies was tested by “differential pressure-flow method”. The relationships between the starting pressure gradient and the integrated permeability were obtained. The critical distance of limestone water penetrating into coal reservoirs was calculated. According to the drainage feature of CBM wells combined with the drainage data of some CBM wells, the results show that, when limestone water can penetrate into coal reservoirs, the daily water production is high and the daily gas production is low although there is no gas at the beginning of the drainage process, the CBM wells stop discharging water within 6 months after the gas began to come out, and the gas production is steadily improved. When limestone water can not penetrate into coal reservoirs, the daily water production is low and the daily gas production is high at the beginning of the drainage process, and it almost stops discharging water after some time when the gas come out, the daily gas production increases, and the cumulative water production is much lower.