低压气井排水采气用喷射器的性能

Performance of the steam ejector used for low pressure gas well drainage gas recovery

目前传统排水采气工艺对于低压气井的适应性较差,为解决此问题,本工作提出了一种新型的喷射器复合排水采气工艺。通过采用高压气体作为驱动流体,防止二次污染,并通过与泡排组成复合工艺的方式解决效率低下的问题,其中喷射器技术是核心。采用数值模拟的方法,以引射比为性能指标,通过对喷射器气相内部流场流动特征进行分析,得到了喷射器的结构尺寸、运行工况对喷射器引射比的影响规律。结果表明,喷射器在引射过程中存在抽吸作用和剪切加速作用;剪切加速作用只能使引射流体最多被加速至音速;在壅塞工况下,喷射器运行表现主要由抽吸作用决定,增加喷嘴渐扩段锥度和面积比,能减缓壅塞工况。运行工况主要通过影响激波强度与喷射器运行状态影响喷射器运行表现,工作压力的增大和出口压力的下降均会提高引射比,但会导致壅塞状态的发生。壅塞工况下,引射比受工作压力影响且与出口压力无关。

At present,traditional drainage gas recovery technology is not suitable for low-pressure gas wells.In this work,a new type of ejector drainage gas recovery technology was proposed to solve this problem.High-pressure gas was used as a driving fluid to prevent secondary contamination.The problem of low efficiency was solved by forming a composite process with the foam scrubbing,and the ejector was the core of the technology.The aim of this study was to investigate the ejector flow characteristics for gas flow field by Computational Fluid Dynamics(CFD),the entrainment ratio was selected as the performance index,and the influence of ejector structure size and operation condition was obtained.The results showed that the ejection process both of pumping action and shear acceleration action existed in ejection process,and the shear acceleration action only made the ejection fluid to run up to sonic speed.The mass flow rate of ejection fluid was controlled by area and speed together,if the flow area was steady,and the gas speed could not increase in any condition,so that the flow state was in chocking phenomenon.In the chocking condition,the performance of ejector was determined by pumping action.Furthermore,the chocking condition retarded with the increasing of diffused segment conical degree and area ration of the ejector nozzle.In addition,the shear acceleration action played the major role if the flow was not in chocking condition.Operation parameters had an impact on shock wave intensity and ejector flow state,the increasing of operation pressure and the decreasing of outlet pressure would enhance entrainment ratio and cause the chocking condition occur.