夹层型页岩油储层CO_(2)驱替特征——以鄂尔多斯盆地长7页岩为例

CO_(2) displacement characteristics of interbedded shale reservoir:A case study of Chang 7 shale in Ordos Basin

针对鄂尔多斯盆地长7夹层型页岩油储层动用困难的问题,利用一维、二维核磁共振技术评价方法,从微观角度对页岩油注CO_(2)驱替特征进行研究。结果表明:随着驱替流量的增加,驱油效率增大,中孔与大孔驱油效率贡献也增大,绝对驱油贡献率均在60%以上;增大驱替流量可以显著提高基质渗透率较小的岩样驱油效率;岩样赋存状态以游离油为主,饱和原油后体积分数为40.51%~62.40%,驱替过程中游离油相对驱替体积分数在50%以上;随着驱替流量的增大,游离油/吸附油相对驱替体积分数减小;干样渗透率越大,渗透率随驱替流量的增长速率也越大。研究成果为页岩油有效开发提供理论依据。

In view of difficult producing of Chang 7 interbedded shale oil reservoir in Ordos Basin,by using evalua-tion methods of 1D and 2D nuclear magnetic resonance(NMR)technology,displacement characteristics of shale oil with CO_(2) injection are studied from microscopic aspect.The results show that with the increase of injection volume,displacement efficiency increases,and displacement efficiency contribution of mesopore throat and macropore throat increases with ultimate absolute displacement efficiency contribution of>60%.Increasing injection volume significantly increases the displacement efficiency of rock samples with low matrix permeability.Occurrence state in rock samples is mainly free oil,with relative volume content ratio of 40.51%~62.40%after saturated with oil and relative displacement volume fraction of free oil of>50%during displacement process.With the increase of injec-tion volume,relative displacement volume fraction ratio of free oil/adsorbed oil decreases.The higher the permea-bility of dry samples is,the higher the permeability increasing rate with injection volume is.The research provides theoretical basis for effective development of shale oil.