低渗透储层中人工裂缝对水驱油渗流规律的影响研究

为准确分析人工裂缝对水驱油效率的影响以及含裂缝岩心油水两相渗流规律,实验选取一组不同渗透率级别的岩心,并使用人工造缝技术沿岩心轴线方向造出一条贯穿缝,测定人工造缝前后水驱油过程中相关参数,运用对比分析的方法研究人工裂缝的存在对驱油效率及渗流规律的影响,并选取一块含天然裂缝岩心进行扩缝前后水驱油实验以检验实验结果。研究结果表明:裂缝性岩心相对渗透率曲线和造缝前岩心相对渗透率曲线差异明显,裂缝性岩心水驱油过程可分为三个阶段:裂缝出油段,裂缝逐渐闭合-基质出油段和裂缝闭合段。裂缝闭合后仍有一定的导流能力,水相渗透率仍高于造缝前。对于裂缝性岩心,油水相对渗透率曲线等渗点位置左移,根据等渗点位置判断岩心润湿性的规律不再适用;人工裂缝在降低驱替压差改善储层渗流条件的同时也极大的降低了水驱油效率,实验岩心造缝后渗透率约为造缝前渗透率的10～50倍,驱替压差约为造缝前的4%～16%,无水驱油效率约为造缝前的2%～16%,最终驱油效率约为造缝前的54%～69%。

Study on the Influence of Artificial Fractures on the Seepage Law of Water Flooding in Low Permeability Reservoirs

In order to accurately analyze the effect of artificial fractures on water flooding efficiency and the rule of two-phase seepage of fractured core,a set of cores with different permeability levels was selected for water flooding experiments.Then artificial fractures were made along the axis of the core,relevant parameters were measured in the process of water flooding before and after fracturing.It is found that the seepage in fractured cores can be divided into three sections as the fracture oil seepage section,the fracture closing-matrix oil seepage section and the fracture closure section.After the fracture closure section,there is still conductivity in the fractures and the permeability of water phase is still higher than before fracturing.For the fractured cores,the position of the isotonic point of the oil-water relative permeability curve shifts to the left,and the law of judging the core wettability according to the position of the isotonic point is no longer applicable.The fractures greatly reduce the oil displacement efficiency of the reservoir while improving the reservoir seepage conditions.The permeability of cores after fracturing was about 10~50 times before fracturing,and the displacement pressure is about 4%~16% before fracturing,The waterless oil displacement efficiency is about 2%~16% before fracturing,and the final oil displacement efficiency is about 54%~69% before fracturing.