为了研究页岩油CO2-烃类混合气体的吞吐过程,明确不同参数的影响规律以及纳米—微米级孔喉中的流体动用程度,利用核磁共振实验揭示了最终采出程度变化、T2分布曲线变化和不同孔径中的原油动用程度等吞吐特征,并阐明了混合气体类型、注入方式和TOC对吞吐效果的影响。结果表明:与CO2+CH4相比,CO2+C3H8与原油的混溶性更强,在相同的注气压力条件下,CO2+C3H8吞吐的最终采出程度可提高3.21个百分点,混合气体中C3H8对页岩油采出程度的贡献更大;结合CO2+CH4的强压缩性和CO2+C3H8的强混溶性,注CO2+CH4/CO2+C3H8可以有效动用页岩大孔、中孔和小孔中的原油,最终采出程度可达28.97个百分点;随着页岩TOC的增加,饱和过程中被吸附溶解的原油增加,采出程度降低,但同时扩散进入干酪根中的混合气量增加。该研究为页岩油CO2-烃类混合气体吞吐现场实施奠定了理论基础。
To study the injection process of CO2-hydrocarbon gas mixtures in shale oil and understand the impact of various parameters and the fluid production degree in nano-micron-sized pore throats, nuclear magnetic resonance (NMR) experiments were conducted to reveal the huff-n-puff characteristics such as changes in final recovery, T2 distribution curves, and the mobilization of crude oil in different pore sizes during injection, and explain the effects of gas mixture type, injection method, and total organic carbon (TOC) on the huff-n-puff efficiency. The results show that CO2 + C3H8, compared with CO2 + CH4, has stronger miscibility with crude oil. Under the same gas injection pressure conditions, the final recovery of CO2 + C3H8 huff-and-puff can be increased by 3.21 percentage points, with C3H8 contributing more to shale oil recovery. Combining the strong compressibility of CO2 + CH4 and the strong miscibility of CO2 + C3H8, injecting CO2 + CH4/CO2 + C3H8 can effectively produce crude oil in large, medium, and small pores of the shale, with the final recovery reaching 28.97 percentage points. As TOC of the shale increases, more crude oil is adsorbed and dissolved during saturation, reducing recovery but increasing gas mixtures diffused into kerogen. This study provides a theoretical basis for the field implementation of huff-n-puff injection of CO2-hydrocarbon gas mixtures in shale oil.
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