志丹油区长7页岩油储层CO_(2)吞吐室内实验

Indoor Experiment on CO_(2)Huff-n-Puff in Chang7 Shale Oil Reservoir in Zhidan Oil Region

为了评价页岩油储层CO_(2)吞吐驱油效果及不同尺度孔喉下原油可动性,选取延长油田志丹油区长7储层天然岩心,基于高温高压长岩心CO_(2)吞吐实验和短岩心剩余油在线核磁共振实验,在评价驱油效果的基础上,分析不同测压点CO_(2)混相状态及驱替规律,对比纳米、微米级孔喉尺度下混相吞吐与非混相吞吐效果,评价页岩油储层不同尺度空间原油可动性。研究表明:CO_(2)非混相吞吐波及效果较差,岩心内部压力增加不明显,压力波及范围小;CO_(2)混相吞吐波及范围广,压力梯度大,单位时间产油量高,驱油效果明显好于CO_(2)非混相吞吐,在注入相同孔隙体积倍数条件下,采收率较CO_(2)非混相吞吐提高8.24个百分点;CO_(2)混相吞吐前2周期生产压差大,混相吞吐区间距离长,混相驱特征明显;在整个岩样孔喉中,微米级孔隙占比低,纳米级、亚微米级孔隙是原油主要贡献者。该研究成果可为页岩储层补充地层能量、提高采收率提供重要参考。

In order to evaluate the oil displacement effect of CO_(2)huff-n-puff of shale oil reservoirs and the mobility of crude oil under different scales of pore throats,a natural core of Chang7 reservoir in Zhidan Oil Region of Yanchang Oilfield was selected,based on high temperature and high pressure CO_(2)huff-n-puff in long cores and residual oil in short cores online NMR test experiments,and on the basis of evaluating the oil displacement effect,the mixed-phase state of CO_(2)and the displacement law at different pressure measurement points were analyzed,the effect of mixed-phase huff-n-puff was compared with that of non-mixed-phase huff-n-puff at nano-and micron-scale pore throats,and the mobility of crude oil in different scale spaces of shale oil reservoirs was evaluated.The study shows that the effect of CO_(2)non-mixed-phase huff-n-puff was poor,the pressure inside the core increase was not obvious,and the pressure affecting range is small;under the condition of injecting the same pore volume multiplier,the recovery efficiency was increased by 8.24 percentage points compared with CO_(2)non-mixed-phase huff-n-puff;the production pressure difference in the first 2 cycles of CO_(2)mixed-phase huff-n-puff was large,the distance between CO_(2)mixed-phase huff-n-puff intervals was long,and the characteristics of CO_(2)mixed-phase displacement were obvious;in the whole pore throat of the rock sample,the proportion of micron-level pores was low,and nano-and submicron-level pores were the the main contributor of the crude oil.The study results can provide an important reference for shale reservoirs to replenish formation energy and improve recovery efficiency.