双重介质低渗油藏斜井压力动态特征分析

Dynamical characteristics of inclined well in dual medium low permeability reservoir

斜井在油藏开发中的应用日趋普遍,然而当前对斜井试井的研究仍然比较少。考虑到低渗油藏存在的压敏效应和启动压力梯度现象,引入渗透率模量与启动压力梯度来建立双重介质低渗油藏的斜井数学模型,利用格林函数和汇源叠加求得了该模型的井底压力响应,并绘制了斜井试井曲线。结果表明:该试井曲线可以划分为6个流动段:纯井筒储集段、过渡流段、井斜角控制段、裂缝径向流段、窜流段与晚期径向流段。此外,当模型考虑启动压力梯度或应力敏感时会导致压力与压力导数曲线晚期均大幅上移,并且启动压力梯度引起的上移幅度相对较大。同时考虑这2种因素时,它们的作用相互叠加,曲线上移幅度更大。另外,当井斜角大于30°时,压力导数曲线与水平井压力导数曲线相似,出现垂直径向流段,反之则与直井相似。该模型求出了相应的解析解,参数解释结果更加精确,可为斜井开发低渗油藏提供理论指导。

Inclined wells have been widely used in the development of reservoirs,but the well test interpretation techniques in inclined wells are currently less studied.At the same time,considering the phenomenon of stresssensitivity effect and threshold pressure gradient in low permeability reservoirs,we introduced permeability modulus and threshold pressure gradient to establish a mathematical model of inclined well in dual-medium low-permeability reservoir.By using sink source superposition and Green function,the bottom hole pressure response of this model was obtained and the plots of inclined well test curves were drawn.The results show that:the well test curve can be divided into six flow sections:wellbore storage section,transition flow section,well inclination control section,crack radial flow section,cross flow section and late radial flow section.In addition,the effect of threshold pressure gradient or stress-sensitivity effect led to a sharp upturn in the later stages of the pressure and the derivative curve,and the upturns caused by the effect of threshold pressure gradient was relatively larger.Otherwise,considering these two factors at the same time,their effects overlapped each other,so the upturn was obvious.When the deviation angle was greater than 30°,the pressure derivative curve characteristics were similar to that of horizontal wells and there was a vertical radial flow section,otherwise it was similar to that of vertical wells.The analytical solution was obtained by this model,and the parameter interpretation result was more accurate.Therefore,it can provide a theoretical guidance for developing low permeability reservoirs with inclined wells.