井筒气液两相流对致密气压裂水平井试井的影响

多段压裂水平井技术是目前开采致密气最常用的方法之一,在致密气压裂水平井试井测试中常常伴随着一定的产水量,井筒气液两相流会增加井筒流体的流动阻力,加大井筒流体流动对试井解释的影响.为了明确井筒气液两相流对致密气藏压裂水平井试井的影响,提高产水致密气压裂水平井的试井解释精度,建立了一种井筒气液两相流与地层渗流耦合的试井模型,采用数值方法对模型进行求解,获得了考虑井筒气液两相流的压裂水平井试井理论曲线、压力场分布及裂缝产量分布.研究结果表明:井筒气液两相流会增加试井理论曲线中压力和压力导数值,造成靠近入窗点的压力扩散要快于远离入窗点的压力扩散,引起靠近入窗点的裂缝产量要高于远离入窗点的裂缝产量.现场实例分析进一步说明,不考虑井筒两相流可能会对产水压裂水平井的试井解释结果产生很大误差,主要表现为水平井筒假设为无限大导流能力会使得拟合得到的表皮系数偏大,将测试点视为入窗点会使得拟合得到的原始地层压力偏小.所建立的考虑井筒两相流的压裂水平井试井模型为产水致密气井试井资料的正确解释提供了重要技术保障. 

EFFECT OF WELLBORE GAS-LIQUID TWO-PHASE FLOW ON WELL TEST OF FRACTURED HORIZONTAL WELLS IN TIGHT GAS RESERVOIR

Multistage fracturing horizontal well technology is one of the most commonly used methods for the exploitation of tight gas.Well testing of fractured horizontal wells in the tight gas reservoir is often associated with water rate.Wellbore gas-liquid two-phase flow will increase the flow resistance of wellbore fluid, which increases the effect of wellbore fluid flow on the well test interpretation.In order to understand the effect of wellbore gas-liquid two-phase flow on well test and improve the precision of well test interpretation of fractured horizontal wells producing water in tight gas reservoir, this paper presents a coupling well test model including gas-liquid two-phase flow in wellbore and seepage flow in tight reservoir.Well test type curves, pressure fields and fracture flow rate of fractured horizontal wells considering wellbore gas-liquid two-phase flow are obtained by using numerical solving method.The results show that the gas-liquid two-phase flow will increase the pressure and pressure derivative value in the well test type curves.It also will cause that pressure diffusion near the window point is faster than that away from the window point and flow rate of fractures near the window point is greater than that of fractures away from the window point.Hence, it can be concluded that the results interpreted by well test analysis may have large error without consideration for the wellbore gas-liquid two-phase flow in the fractured horizontal well test model.The assumption that the horizontal wellbore has infinite conductivity will cause the skin factor obtained by curve matching to be too large.The pressure of the test point considered as the pressure of window point will cause the initial formation pressure obtained by matching to be too small.The well test model of fractured horizontal wells considering wellbore two-phase flow proposed in this paper will provide an important technical support to interpret the well test data of tight gas wells producing water correctly.