济阳坳陷页岩油注二氧化碳开发技术

Shale oil recovery by CO_(2) injection in Jiyang Depression,Bohai Bay Basin,East China

围绕页岩油注CO_(2)开发存在的问题,通过室内实验、数值模拟与压裂工艺相结合的方式,开展了页岩油注CO_(2)萃取置换机理、CO_(2)前置液对页岩力学性质影响的室内实验,模拟了CO_(2)前置压裂和吞吐补能对开发效果的影响,并将成果应用于CO_(2)前置压裂和单井吞吐矿场实践。研究表明:CO_(2)吞吐作用效果受微纳尺度效应及干酪根、吸附油存在等的影响,适当延长焖井时间可提高原油动用程度。在CO_(2)“注、焖”阶段,CO_(2)通过溶解扩散和传质作用提高重烃的动用程度,在CO_(2)“吐”的阶段,CO_(2)主要将较大孔隙中的原油排出至周边更大的孔隙或层理缝中流入生产井。注入CO_(2)前置液有助于保持岩心脆性,降低破裂压力,CO_(2)易沿层理面滤失,从而提高裂缝复杂程度。前置CO_(2)注入量增加会提升增能效果,从而增强地层能量的补充作用。页岩基质渗透率越低、地层压力越低、原油重烃含量越高,注CO_(2)吞吐开发后,采收率提高幅度越大。矿场实践表明,CO_(2)前置压裂后压力保持良好,单井CO_(2)吞吐后可有效补充地层能量,提高单井产能,效果良好。

Laboratory experiments,numerical simulations and fracturing technology were combined to address the problems in shale oil recovery by CO_(2) injection.The laboratory experiments were conducted to investigate the displacement mechanisms of shale oil extraction by CO_(2) injection,and the influences of CO_(2) pre-pad on shale mechanical properties.Numerical simulations were performed about influences of CO_(2) pre-pad fracturing and puff-n-huff for energy replenishment on the recovery efficiency.The findings obtained were applied to the field tests of CO_(2) pre-pad fracturing and single well puff-n-huff.The results show that the efficiency of CO_(2) puff-n-huff is affected by micro-and nano-scale effect,kerogen,adsorbed oil and so on,and a longer soaking time in a reasonable range leads to a higher exploitation degree of shale oil.In the "injection + soaking" stage,the exploitation degree of heavy hydrocarbons is enhanced by CO_(2) through its effects of solubility-diffusion and mass-transfer.In the "huff" stage,crude oil in large pores is displaced by CO_(2) to surrounding larger pores or bedding fractures and finally flows to the production well.The injection of CO_(2) pre-pad is conducive to keeping the rock brittle and reducing the fracture breakdown pressure,and the CO_(2) is liable to filter along the bedding surface,thereby creating a more complex fracture.Increasing the volume of CO_(2) pre-pad can improve the energizing effect,and enhance the replenishment of formation energy.Moreover,the oil recovery is more enhanced by CO_(2) huff-n-puff with the lower shale matrix permeability,the lower formation pressure,and the larger heavy hydrocarbon content.The field tests demonstrate a good performance with the pressure maintained well after CO_(2) pre-pad fracturing,the formation energy replenished effectively after CO_(2) huff-n-puff in a single well,and the well productivity improved.