Li Lei, Wang Chengwei, Li Dongsheng, Fu Jingang, Su Yuliang, Lv Yuting
Key Laboratory of Unconventional Oil & Gas Development (China University of Petroleum (East China)), Ministry of Education Qingdao China
School of Petroleum Engineering, China University of Petroleum (East China) Qingdao China.
RSC Adv. 2019 Sep 13;9(49):28857-28869. doi: 10.1039/c9ra05347f. eCollection 2019 Sep 9.
CO Huff-n-Puff (HnP) is an effective technique for enhancing oil recovery (EOR) that can be applied to shale oil reservoirs faced with poor natural productivity and low water injectivity. The main objective of this study is to investigate the interactions of CO and formation crude oil, and evaluate the CO HnP performance in shale oil reservoirs in the Qianjiang depression in China. In this study, the variation rules of oil phase behavior, viscosity, saturation pressure, and swelling factor at different CO contents of 0 to 65% were studied. A series of HnP experiments were conducted. The factors affecting the oil recovery were discussed, and Nuclear Magnetic Resonance (NMR) tests were conducted on core samples at different stages of the HnP process. The results show that the injected CO can make an positive change in the crude oil phase behavior. The oil-gas two-phase region enlarges and the saturation pressure increases as more CO is dissolved in the formation oil, which is beneficial to oil production. The dissolution of CO in the oil phase increased the oil swelling degree by 1.492 times, and the viscosity decreased from 1.944 to 0.453 mPa s. The HnP experimental results demonstrate that the soaking time should be determined based on the injection pressure. Miscible conditions is a viable option for CO HnP as 10% more oil can be produced using miscible HnP and save more than half of the soaking time. The results illustrate that fracture is the most important factor affecting oil recovery, and the performance of HnP EOR on core samples with fractures is almost 25% better than those without fractures. However, the core matrix permeability has an almost negligible effect on the performance of CO HnP. The NMR tests show that the oil recovered in the first cycle was dominated by macropores and mesopores, followed by small pores. In the latter HnP cycles, the oil in small pores and micropores becomes the main oil-producing area. This study may provide a better understanding of the CO HnP enhanced recovery strategy for shale reservoirs.
CO Huff-n-Puff（HnP）是一种提高采收率（EOR）的有效技术，可应用于天然产能差和注水能力低的页岩油藏。本研究的主要目的是研究CO与地层原油的相互作用，并评估中国潜江凹陷页岩油藏的CO HnP性能。在本研究中，研究了在0至65%的不同CO含量下油相行为、粘度、饱和压力和膨胀因子的变化规律。进行了一系列HnP实验。讨论了影响采收率的因素，并在HnP过程的不同阶段对岩心样品进行了核磁共振（NMR）测试。结果表明，注入的CO可使原油相行为发生积极变化。随着更多的CO溶解在地层油中，油气两相区域扩大，饱和压力增加，这有利于采油。CO在油相中的溶解使油的膨胀程度增加了1.492倍，粘度从1.944降至0.453 mPa·s。HnP实验结果表明，浸泡时间应根据注入压力来确定。混相条件是CO HnP的一个可行选择，因为使用混相HnP可以多采出10%的油，并节省一半以上的浸泡时间。结果表明，裂缝是影响采收率的最重要因素，有裂缝的岩心样品上HnP EOR的性能比没有裂缝的样品几乎好25%。然而，岩心基质渗透率对CO HnP的性能影响几乎可以忽略不计。NMR测试表明，第一个周期采出的油以大孔和中孔为主，其次是小孔。在随后的HnP周期中，小孔和微孔中的油成为主要产油区。本研究可能有助于更好地理解页岩油藏的CO HnP强化采收策略。
