基于离散裂缝模型致密储层压裂直井动态分析

摘要

Considering the non-linear seepage characteristics include threshold pressure gradient ( TPG ) and stress sensitivity effect of tight oil reservoir , a transient flow model of vertically fractured wells in tight oil reservoir is established based on discrete fracture model .Solve the transient flow model by finite volume method , which is easy to calculate the pressure gradient for the TPG , and perform sensitivity analysis .The results show that pressure derivative curve start to upward when the TPG and stress sensitivity effect are considered , and it will upturn more severe and become harder to divide the flow stages with the increase of TPG and permeability modulus ; the stress sensitivity effect makes the pressure derivative curve upturn after the pressure propagated to border which is differ -ent from TPG; the upward tendency caused by TPG and stress sensitivity effect will be more obvious with the de -crease of fracture half-length;the fracture conductivity has large influence on the early flow stage , and the pressure derivative curve will downward with the increase of fracture conductivity .%针对致密油藏渗流规律表现出的启动压力梯度和应力敏感等非线性特征,基于离散裂缝模型建立致密油藏压裂直井的不稳定渗流模型.由于有限体积方法具有物理意义明确的特点,易于计算压力梯度,方便考虑启动压力梯度的影响,采用该方法对模型进行数值求解,并对压力动态进行敏感性分析.结果表明:启动压力梯度与应力敏感的存在使得压力导数曲线上翘,启动压力梯度与渗透率模数越大,上翘幅度越大,流动阶段越难划分;与启动压力梯度不同,应力敏感使得边界响应段的压力导数曲线上翘;裂缝半长越短,启动压力梯度和压敏效应导致的曲线上翘越明显;裂缝导流能力对早期流动阶段的影响较大,随着裂缝导流能力的增大,压力导数曲线向下移动.