裂缝对鄂尔多斯盆地陇东地区长7致密岩心水驱渗流特征的影响

Impact of Fractures on Water Flooding Seepage Features of Chang 7 Tight Cores in Longdong Area,Ordos Basin

在分析鄂尔多斯盆地长7天然裂缝和体积压裂人工裂缝特征的基础上,采用等效处理岩心实验法探索裂缝对长7致密岩心水驱渗流特征的影响。实验结果表明:不论是以基质渗流或者以裂缝渗流为主的岩心,油相相对渗透率都呈现出靠椅型相渗曲线特征;同时随着裂缝与基质渗透率级差和驱替压差的增大,与基质渗流为主的岩心相比,裂缝岩心渗透率曲线等渗点左移,油水相渗透率增大,但两相共流区变窄,含水上升加快,残余油饱和度升高。在同一驱替压差下,随着裂缝与基质渗透率级差的增大,致密岩心水驱油具有低含水时间短,见水后含水上升快的特征。随着驱替压差增大,以基质渗流为主的岩心,见水提前,但无水期驱油效率和最终驱油效率都增大;以裂缝渗流为主的岩心,见水提前,无水期驱油效率和最终驱油效率都降低。

Based on the analysis of the characteristics of natural fractures and artificial volume fracturing fractures in Chang 7 reservoir of Ordos Basin,the influence of fracture on water flooding seepage characteristics of the Chang 7 tight cores was studied by equivalent treatment core experiment. The experimental results show that：（1）whether matrix or fracture seepage is dominated,the relative permeability curve of oil phase always presents chair-shaped; with the increase of the permeability difference between fracture and matrix and the core displacement pressure difference,compared with the cores dominated by matrix seepage,the equivalent permeability point on the permeability curves of the cores dominated by fracture seepage shifts towards the left,the relative permeability of water phase and oil phase becomes greater,however,the two-phase flow zone becomes narrower,the water cut and residual oil saturation rapidly increase.（2）Under the same displacement pressure difference,the low water-cut displacement time of the tight cores becomes shorter and the watercut increasing speed after water breakthrough becomes greater with the increase of the permeability difference between fracture and matrix.（3）With the increase of the core displacement pressure difference,the water breakthrough of the cores is ahead of time,the displacement efficiency before water breakthrough and ultimate displacement efficiency of the cores dominated by matrix seepage will increase,while those of the cores dominated by micro-fractures seepage will decrease.