鄂尔多斯盆地页岩油储层应力敏感性分析及水平井返排制度优化

Stress sensitivity analysis and optimization of horizontal well flowback system for shale oil reservoir in Ordos Basin

鄂尔多斯盆地长7段页岩油储层具有储层致密、孔隙结构复杂、地层压力系数低的特点,在多年的开发实践中逐渐总结出长水平井、大规模体积压裂的开发方式,与前期定向井或短水平井相比,开发效果获得了大幅提升。而在压裂液的返排过程中,由于页岩油储层的应力敏感特征,储层物性和地层能量将产生巨大变化,进而影响到初期含水下降速度和单井产量。通过改良的应力敏感实验,明确了页岩油压后储层与原始基质储层相比具有更强的应力敏感性,得出了应力敏感作用下的渗透率变化规律,采用数值模拟、现场统计等方法,优化了鄂尔多斯盆地页岩油水平井合理返排强度和返排时间。

Shale oil reservoir in Chang 7 Member,Ordos Basin,is characterized with tight reservoir rocks,complex pore structure,and low formation pressure.Decades of developing practices have proved that largescale volumetric fracturing in horizontal wells with long lateral length is effective in the basin,compared to previously drilled directional wells and short horizontal wells.However,the reservoir underground is stress-sensitive,and the large-scale volumetric fracturing will result in a huge change in reservoir properties and strata energy.Thus water saturation during initial production period and individual well production will be affected.Through improved stress sensitive experiment,it has been clear that the compacted reservoir of shale oil has more strong stress sensitivity compared with the original matrix reservoir.The permeability variation law under stress sensitivity is obtained.Numerical simulation and field statistics are used to optimize the reasonable flowback intensity and flowback time of shale oil horizontal wells in Ordos Basin.