Causes of High Water Yield from CBM Wells in Yanchuannan Block and Draining Measures

In order to determine the causes of high water yield in CBM(coalbed methane)wells in Yanchuannan Block of Ordos basin and its impact on the productivity of CBM wells,the geologic conditions,fracturing operation and production performance of CBM wells with different water yield in Yanchuannan Block were analyzed,the cause of water formation was discussed,and draining method for high water yield wells was proposed.The results show that excessive fracture height connecting the fractured sandstone aquifer in Lower Permian Xiashihezi Formation is the key factor of causing high water yield in some CBM wells in Yanchuannan Block;high water yield would lead to gas reservoir pressure lower than the critical desorption pressure,and decrease in the productivity of CBM wells.In addition,high water yield would pose challenge to drainage which requires selection of proper equipment.At first,the wells with high water yield should be drained to allow even and fast drop of bottom hole flowing pressure and early gas production,the speed of drainage may be slowed down properly after gas appearance.The application of this strategy achieved good effect,providing a new technical support for CBM wells with high water yield.