柿庄南区块煤层气高产井排采制度分析

Analysis on drainage system of coalbed methane high production well in south block of Shizhuang

为了研究排采制度对柿庄南区块煤层气井产气量的影响,通过对柿庄南区块4口高产井排采曲线进行对比分析,探索总结了高产井排采曲线的共同特征,优选出了适合柿庄南区块的排采制度。结果表明:高产井的排采曲线呈现阶梯状变化规律特征。产气后井底流压的变化分为4个阶段,即:缓慢下降阶段、逐级降压阶段、迅速下降阶段和稳定阶段;缓慢降压阶段为排采初期排水降压阶段到不稳定产气阶段的过渡阶段;逐级降压阶段储层压力逐渐下降,压降漏斗稳定向远端延伸;在迅速下降阶段,出现了井间干扰使得压降漏斗相互叠加并向深处扩展,产气量陡增;稳定阶段,是井底流压下降到一个较低水平并保持长期稳定,气体稳定解吸,产气量稳定在一个较高水平。迅速下降阶段之前稳定套压,之后缓慢释放套压,有利于储层防护。井底流压见气前平缓下降,见气后阶梯状变化的排采制度有利于柿庄南区块排采井的高产。

In order to study the drainage system affected to the gas production of the coalbed methane wells in the South Block of Shizhuang,a comparison analysis was conducted on the drainage curves of four high production wells in the south block of Shizhuang. The paper discovered and summarized the common features of the gas drainage curves from the high production wells and optimized the drainage system suitable to the south block of Shizhuang. The results showed that the drainage curves of the high production wells had ladderstyle variation law and features. After the wells in the gas production,the variation of the bottom flowing pressure had four stages and they were a slow pressure drop stage,steady pressure reduction stage,rapid drop stage and stable stage. The slow pressure drop stage was a transitional stage from the water pumping and pressure drop stage to the instable gas production stage in the gas drainage initial period. The reservoir pressure at the steady pressure reduction stage would be steadily reduced and the pressure drop hopper would be stably extended to a far end. In the pressure rapid drop stage,the interferences occurred between the wells would make the pressure drop hoppers overlapping and expanded to the deep section and the gas production would be sharply increased. The stable stage would mean the bottom flowing pressure drop to a low level and keeping a long period stable,the gas would be stably desorbed and the gas production would be stable at a high level. Before the rapid pressure drop stage,the casing pressure should be kept in stable,then the casing pressure could be slowly released and would be favorable to protect the reservoir. The bottom flowing pressure should be steadily reduced before the gas occurred in the well and after the gas occurred in the well,the drainage system with a ladder-style variation would be favorable to the high production of the gas drainage wells in the study area.