Study on identification and control system construction of low efficiency coalbed methane wells

The existence of extensive low-efficiency wells has serious negative impact on improving the coalbed methane (CBM) production conversion rate and resource utilization rate， which has made it urgent to analyze the causes of low-efficiency wells and carry out effective renovation.Based on well drilling， well measuring， logging， fracturing， drainage and experimental data of more than 1 000 CBM wells in Shizhuangnan Block of Qinshui Basin， this study was dedicated for low-efficiency well identifying， origin analyzing and renovation mechanism establishing.The study results prove that at different drainage stages， the low efficiency wells can be defined by setting gas production rate as the main index， combining parameters such as liquid level height， bottom hole flow pressure， and drainage time.And factors such as well drilling， fracturing and drainage processes can all affect the gas production efficiency in different degrees； Four classes of reconstructable geological type were determined based on key geological parameters such as superposition of tectonic， gas content， reservoir pressure and permeability and assists from fuzzy evaluation， and production capability prediction shows that classes of Ⅰ，Ⅱ and Ⅲare of good reconstructable potential.With the help from combing methods of hierarchical optimization， a mechanism for dissecting the origin of the low efficiency wells was constructed and the formation of low-efficiency wells was divided into three main types and 13 subtypes.Furthermore， we proposed a comprehensive renovation systems for low efficiency wells by combining geology， engineering and drainages， which could ensure the effectiveness for resource and reservoirs， enhance the high efficiency connection of fractures network， and achieve scientific drainage and regional cooperative depressurization.This study could have positive impact on improving CBM single well gas production and gas recovery rates.