煤层气井的排水量不一定等于煤层的产水量

Water Discharge from Coalbed Methane(CBM) Well May Not Be Equal to Water Production from Coalbed

煤层气井动态分析过程中,通常把井筒的排水量作为煤层的产水量。基于井筒储集效应,分析了井筒排水量与煤层产水量之间的关系,比较了动液面不同变化情况下的井筒排水量和煤层产水量,认为煤层气井的井筒排水量不一定等于煤层产水量,并建立了煤层产水量修正公式。在此基础上,利用沁水盆地TS井组XX井的生产数据进行计算,结果表明,井筒排水量和煤层产水量在生产第一阶段差值较大,其差值最高达到了井筒排水量的72%;在第二阶段和第三阶段由于存在压力的大幅度变化,最大煤层产水量高出最大井筒排水量25%.同时,根据生产数据通过机理模型模拟了沁水盆地TS井组XX井的井筒排水量和煤层产水量的差异对生产造成的影响,结果表明,将井筒排水量等效视为煤层产水量会加快地层压降的速度,见气时间提前79 d,同时产气高峰时间提前180 d.研究认为,在煤层压力改变时,井筒排水量不等于煤层产水量,将井筒排水量等效视为煤层产水量会对煤层气井的动态分析、生产制度的确定和实施以及数值模拟均带来错误的影响。

The water discharge from CBM well is usually regarded as the water production from coalbed during dynamic analysis of thiskind of wells. Based on wellbore storage effect, the paper analyzes the relationship between water discharge from wellbore and water produc-tion from coalbed, compares the 2 water productions with different working fluid levels, concludes that wellbore water discharge may not beequal to water production from coalbed and establishes a modified formula of coalbed water production. Then the calculation results of theproduction data from Well XX of TS well group, Qinshui basin show that there is an obvious gap between wellbore water discharge and coal-bed water production during the first production stage with the peak value difference reaching 72% of wellbore water discharge; the maxi-mum coalbed water production is 25% higher than the maximum wellbore water discharge due to sharp pressure variations at the secondand third production stages. Meanwhile, the influence of the difference between wellbore water discharge and coalbed water production onproduction is simulated with a mechanism model and based on production data in Well XX of TS well group, Qinshui basin. The resultshows: if the wellbore water discharge is considered to be equal to the coalbed water production, coal seam pressure drop rate will be accel-erated, the gas breakthrough time will be 79 days in advance and the peak of gas production will be reached 180 days in advance as well. Itis concluded that the water discharge from CBM well is not equal to the water production from coalbed when the pressure changes in thecoal bed. Otherwise, dynamic analysis, production system determination and implementation and numerical simulation for CBM wells willbe wrong.