多层叠置含煤层气系统递进排采的压力控制及流体效应

Pressure control and fluid effect of progressive drainage of multiple superposed CBM systems

为了研究多煤层发育地区各含气系统排采次序及压力控制下的流体效应,以指导煤层气井排采制度设计,从贵州省织纳煤田选择了1口煤层气参数+试验井,在划分多层叠置含气系统的基础上,分析了各含气系统静止液面压力、储层压力、临界解吸压力特征,设计了各含气系统递进排采次序及排采压力控制方案;模拟了单含气系统分排、多含气系统合排及多含气系统递进排采各阶段的流体效应。模拟结果表明:①单独排采各含气系统时,产气量低,排采时间短,成本高;②多含气系统递进排采平均气产能和累计产能高、稳产期时间长,但多含气系统在合层排采时,由于各系统压力不同,系统间存在相互干扰,并非所有含气系统都有产能贡献;③多层叠置独立含煤层气系统可根据各系统内煤储层压力、临界解吸压力和产气压力来设计递进排采次序,先排采临界解吸压力和产气压力高的含气系统,当压力降到另一含气系统的临界解吸压力和产气压力时,再进行两个含气系统合排,依此递进排采所有含煤层气系统。

In order to understand the drainage order and pressure-controlled fluid effect of each CBM （coalbed methane） system in the areas with multiple coalbeds, this paper studied a parametric test well in the Zhina coalfield in Guizhou province of China. On the basis of the divi- sion of multiple superimposed CBM systems, we analyzed static liquid surface pressure, reservoir pressure and critical desorption pressure, designed progressive drainage sequence and pressure control scheme for each CBM system, and modeled fluid effects in each drainage stage for separate drainage of each CBM system, commingled drainage and progressive drainage of multiple CBM systems. The followings simulation results were obtained. For the separate drainage of each CBM system, gas production is low, drainage period is short and cost is high. In con- trast, for the progressive drainage of multiple CBM systems, both the average and accumulative gas production capacity are large and stable production period is long. However, not all the CBM systems contribute to production due to the interference among CBM systems with dif- ferent pressures. The progressive drainage sequence can be designed according to coalbed pressure, critical desorption pressure and production pressure. The CBM system with the highest critical desorption pressure and production pressure will be put into drainage first. When its pressures are lowered to be equal to the values of another system, the two systems will be put into commingled production. The process will continue till all systems are put into production.