低渗透气藏水平井产能分析

Productivity analysis of horizontal gas wells for low permeability gas reservoirs

近年来随着低渗透油气田的开发,有关启动压力梯度渗流问题逐渐得到广泛的关注。水平井作为提高油气井产能的一项开发技术,以其在技术和经济效益方面具有常规直井无法比拟的优越性已成为高效开发油气的重要技术支撑。通过大量调研发现,低渗透气藏中水平井的产能预测均没有考虑启动压力梯度的影响,导致预测的产能与实际产能存在一定差异。为此,通过对低渗透气藏气体渗流速度运动方程的变形,得到气体渗流产生的压降等于达西流动产生的压降、考虑启动压力梯度影响产生的压降及高速非达西效应影响产生的压降三项之和的结论。鉴于此,基于椭圆柱模型提出了描述含启动压力梯度及高速非达西效应的产能公式,并分析了启动压力梯度对低渗透气藏水平井产能的影响。研究表明:启动压力梯度影响水平气井的整个渗流过程,且它对气井产量的影响较大;随着启动压力梯度增加,导致地层中的压力损失增大,同时水平气井产量也呈直线下降。

In recent years,with the rapid development of low-permeability oil and gas fields,the problem of seepage with threshold pressure in low permeability formation has become an important issue which has been widely concerned.Horizontal wells,as a development means of enhancing the deliverability of oil and gas wells,has become one of the most important technologies to efficiently exploit oil and gas reservoirs for its unparallel advantages in technological and economic aspects compared with conventional vertical wells.Through extensive survey and study,it is shown that current deliverability prediction for horizontal wells in low permeability gas reservoirs does not take the impact of threshold pressure into account,which leads to the difference between the predicted deliverability and the actual one.By transforming the flow velocity equation,we can conclude that the differential pressure caused by the gas flow is due to the Darcy flow,threshold pressure,and the high-speed non-Darcy.In view of this,the deliverability equation with consideration of the threshold pressure gradient and high-speed non-Darcy effect,and the effects of threshold pressure on the deliverability of horizontal wells in low permeability gas reservoirs are presented and analyzed in this paper.Studies have shown that the level of the threshold pressure affects the entire flow process and has great impact on the gas production of horizontal wells,and that the pressure loss in the formation increases with the increase of the threshold pressure gradient,and the level of gas production in horizontal wells also shows linear decline.