煤层气同心管气举排水工艺参数的确定方法

煤层气井在产气之前需要进行排水降压作业,同心管气举通过在生产油管中加入小油管,可以为气举提供注气通道的同时,又不影响油套环空作为气井的产气通道。结合固相颗粒在垂直气液两相流中的运移模型,给出了同心管气举条件下,不同粒径煤粉颗粒排出井筒所需要的气液流速条件。通过同心管环空气液两相流压力计算,给出了同心管气举阀安装位置的设计方法,并结合煤层气井排采过程中煤层气井的生产动态特征,给出了注气量的确定方法。对同心管气举排水工艺进行了现场试验,分析了试验气井的实际排采曲线,证明同心管气举排水工艺的可行性,以及气举参数设计的合理性。通过计算排采阶段同心管的气举效率,表明该工艺在整个试验阶段可以保持较高的举升效率。根据煤粉排出的临界条件,判断以及预测煤粉在井底沉积的可能性和时间。

A method to determining concentric pipe gas-lift parameters for CBM well dewatering process

Coalbed methane Wells need dewatering operation before producing gas. Concentric pipe gas lift by adding a small tubing in production tubing, can inject compressed gas through the gas lift channel, and shall not affect gas flow in casing-tubing annulus as the gas production channel of the CBM wells. On the base of solid particles migration model in vertical gas-liquid two phase flow, the critical conditions is obtained that the gas-liquid velocity required to pulverized different particle size of coal fine particles from wellbore which concentric tube gas lift was applying. Using gas liquid two phase flow pressure calculation model in concentric pipe annulus, the depth of gas injection point and gas lift valve placement can be designed. In consideration of production dynamic characteristics of the CBM wells during dewatering and production process, a method for determining of the concentric pipe gas injection rate is presented. A field test of concentric pipe gas lift dewatering process is also presented. Through the analysis of actual production curve of the test gas well, it is proved that concentric pipe gas-lift dewatering process is feasibility, and the designed parameter of gas lift is reasonable. By calculation of concentric tube gas lift efficiency during dewatering process, it is concluded that the process in the whole test can keep high lifting efficiency. According to discharge critical condition, the likelihood and time of coal fine particle depositing in the bottom of wellbore can be judged and predicted.