天然裂缝性油藏的离散裂缝网络数值模拟方法

Numerical simulation method of discrete fracture network for naturally fractured reservoirs

针对裂缝性油藏中大裂缝、微细裂缝和孔隙等多种储渗介质共存的现象,将大裂缝作为控制流体流动的一维实体,组成离散裂缝网络,进行显式表示,将孔隙和微细裂缝组成的系统作为基岩介质,建立了天然裂缝性油藏两维两相数值模拟模型。采用加权余量法,建立有限元方程并进行了求解。对油藏有无裂缝及大裂缝的方位、长度和分布对水驱油的影响进行了研究。结果表明:大裂缝的存在会严重改变水驱油藏中注入水前缘的前进方向和速度,大裂缝与注采井间连线夹角越小及长度越大,都会导致注入水窜进越严重,从而使得油井见水早,含水率高;多条大裂缝的存在会造成剩余油分布的极度非均质及剩余油富集区的形成。

The storage and seepage spaces of naturally fractured reservoirs consist of big fractures,micro-fractures and pores.The big fractures controlling the fluid flow were taken as one-dimensional entities to compose the discrete fracture network and expressed explicitly.The pores and the micro-fractures were treated as matrix.Based on the above assumptions,the 2D and two-phase mathematical model for the numerical simulation of naturally fractured reservoirs was established.The weighted residual method was used to establish the finite element equations.The effects of fracture exsisting state in reservoir,fracture azimuth,fracture length and fracture distribution on the oil saturation were discussed.The existence of the fracture can change the direction and velocity of the waterfront.The smaller angle between the fracture orientation and the injection-production line and the longer of the fracture would result in more serious water breakthrough and higher water cut.The multi-fracture system can cause the heterogeneity of remaining oil distribution and accumulation of remaining oil.