基于边界元方法的致密油藏体积压裂水平井多尺度、多机理耦合流动模型研究

After large scale fracturing, tight oil reservoir exists "matrix (nano scale)- natural microfracture (micron grade)- fracture network (millimeter scale)- fluctuant wellbore (meter scale)" multi-scale seepage medium. Single phase liquid seepage is affected by kinds of factors such as: stress sensitivity, interference between fractures, heterogeneity of reservoir and irregular reservoir boundary and etc. Reservoir seepage is pretty complicated. At present, it is difficult to establish a fast and accurate flow model of volumetric fracturing horizontal wells in tight reservoir considering the influence kinds of multiple seepage mechanisms on the basis of accurately depicting multi-scale seepage medium..Boundary element method is a boundary numerical algorithm and the discrete grids are significantly reduced comparing with the finite difference method and the finite element method. The analytical solution used in the study object achieves high accuracy. Based on the boundary element method, the multi-scale, multi-mechanism coupled flow model of volumetric fracturing horizontal well in irregular boundary and heterogeneity tight oil reservoir is established considering the influence of double medium seepage characteristics, stress sensitivity and mutual interference of fractures on the basis of accurately depicting the multi-scale seepage medium. This model is used to reveal the seepage law of volume fracturing horizontal well in tight reservoir and to study the technical countermeasure for improving the development effect of blocks. It lays a theoretical foundation for the efficient development of tight reservoir in China.

大规模压裂后致密储层存在“基质(纳米级)-天然微裂缝(微米级)-压裂缝网(毫米级-缝宽)-起伏井筒(米级)”多尺度渗流介质，单相液体渗流受到应力敏感、裂缝间相互干扰、储层非均质性以及不规则油藏边界等多种因素的影响；储层渗流异常复杂。目前致密油藏渗流模拟方法难以在精确刻画多尺度渗流介质的基础上考虑多种渗流机理的影响，建立快速、精确的致密油藏体积压裂水平井渗流模型。.边界元法属于边界型数值算法，相比于有限差分法和有限元法该方法所需离散网格大大减少且在研究对象内部使用解析解求解精度高。本课题基于边界元方法，在精确刻画多尺度渗流介质的基础上，考虑储层双重介质渗流、应力敏感以及裂缝间相互干扰等多种渗流机理的影响，建立不规则边界非均质致密油藏体积压裂水平井多尺度、多机理耦合流动模型。利用该模型揭示体积压裂水平井渗流规律，研究提高区块开发效果的技术对策，为实现我国致密油藏的高效开发奠定理论基础。

大规模压裂后致密储层存在“基质(纳米级)-天然微裂缝(微米级)-压裂缝网(毫米级-缝宽)-起伏井筒(米级)”多尺度渗流介质，单相液体渗流受到应力敏感、裂缝间相互干扰、储层非均质性以及不规则油藏边界等多种因素的影响；储层渗流异常复杂。本课题基于边界元方法，在精确刻画多尺度渗流介质的基础上，考虑储层双重介质渗流、应力敏感以及裂缝间相互干扰等多种渗流机理的影响，建立不规则边界非均质致密油藏体积压裂水平井多尺度、多机理耦合流动模型。取得了三个重要成果：① 建立了考虑致密油藏双重介质以及应力敏感特性的源函数；② 建立了考虑致密油藏渗透率各向异性以及裂缝倾角的面源函数；③ 基于边界元方法建立并求解了致密油藏体积压裂水平井耦合渗流模型。利用该模型揭示体积压裂水平井渗流规律，为实现我国致密油藏的高效开发奠定理论基础。