致密油藏长缝压裂直井基质-裂缝耦合流动模型

Matrix-fracture coupling flow model of long-crack fracturing vertical well in tight oil reservoirs

致密油藏长缝压裂压力动态和产量变化规律目前尚未明确,开发方案设计缺少理论模型指导。针对长缝压裂基质-裂缝复合流动问题,建立了考虑储层启动压力梯度、裂缝内高速非达西渗流影响的长缝压裂直井基质-裂缝复合流动模型,并运用Laplace变换、点源函数、Stehest数值反演等方法进行求解,明确了致密油藏长缝压裂井压力响应特征和影响因素。研究结果表明,无因次压力及压力导数随启动压力梯度的增加而增大,但启动压力梯度对无因次压力及压力导数的前期影响较小,后期影响较大;非达西渗流系数对无因次压力及压力导数曲线的前期影响较大,随着非达西渗流系数的增大,无因次压力及压力导数增大;裂缝中非达西渗流系数越大,压裂井的产量越低,且压裂井的最佳裂缝半长越小。研究成果为致密油藏长缝压裂方案设计、试井分析等工作提供理论指导。

Long-crack fracturing pressure behavior and production change laws of tight oil reservoirs have not been clarified clearly,and the development scheme is designed without the guidance of theoretical model.To deal with the matrix-fracture combined flow of long-crack fracturing,this paper established a matrix-fracture combined flow model of long-crack fracturing vertical well which considers the influences of threshold reservoir pressure gradient and intra-fracture high speed non-Darcy flow.Then,it was solved by means of Laplace transformation,point source function and Stehest numerical inversion.Finally,the pressure respond behaviors of long-crack fracturing well in tight oil reservoirs and their influential factors were determined.It is indicated that dimensionless pressure and pressure derivative increase with the increase of threshold pressure gradient,but the influence of threshold pressure gradient on dimensionless pressure and pressure derivative is less in the early stage and greater in the late stage.Non-Darcy flow coefficient has greater influence on dimensionless pressure and pressure derivative in the early stage.And with the increase of non-Darcy flow coefficient,dimensionless pressure and pressure derivative increase.The higher the non-Darcy flow coefficient of fracture is, the lower the production rate of fracturing well is and the shorter the optimal half fracture length of fracturing well is. Theresearch results provide the theoretical guidance for long-crack fracturing scheme design and well test analysis of tight oil reservoir.