Experimental investigation of shale oil recovery from Qianjiang core samples by the CO₂ huff-n-puff EOR method

Abstract

CO 2 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 2 and formation crude oil, and evaluate the CO 2 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 2 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 2 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 2 is dissolved in the formation oil, which is beneficial to oil production. The dissolution of CO 2 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 2 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 2 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 2 HnP enhanced recovery strategy for shale reservoirs.

Huff-n-Puff Technology for Enhanced Oil Recovery in Shale/Tight Oil Reservoirs: Progress, Gaps, and Perspectives

“…H-n-P core floods were performed by Adel et al in the same study community, and showed a continuing rise in recovery as pressure increased above the MMP . The CO 2 sweep amount was examined by Li et al…”

“…Using an unconfined core H-n-P apparatus, oil changes of up to 100% are possible. Many organizations have described detailed accounts in immersions in such experimental setups. ,,,,,,,,− Table shows some oil recovery results obtained using various cores and core holders. Since natural gas is investigated as an injection agent for EOR in unconventional oil reservoirs, laboratory studies of natural gas effectiveness for EOR usually have the composition of natural gas (see Table ).…”

“…Effect of the pressure on the oil recovery of different studies, based on literature published between 2014 and 2020. [Data taken from refs , , , , , , , , , , and . ]…”

“…While experiments with higher permeability samples are easier to conduct, decisions based on these tests may not be applicable to shale/tight reservoirs, because of the dissimilarities in oil recovery mechanisms. As predicted, the approach to analysis varies 189 Lower Bakken/USA 3.8 0.005 unconf 32 Li et al 242 Wolfcamp/USA 7.5 0.0002 unconf ∼35−70 Li et al 53 Wolfcamp/USA 8.5 0.0003−0.0005 unconf ∼65 Habibi et al 142 Montney/Canada 14−15.5 2−5 conf 66−77 Qian et al 249 Changqing/China 12.20−13.34 0.36−0.81 conf 27−53 Lei et al 250 Qianjiang/China 8.6−14.5 0.27 unconf 25.9−55.4 Li et al 196 EF/USA 7.5 0.0003 conf 61 Ma et al 263 Junggar/China 11.8−13.2 0.03−0.5 conf 16−28 Elwegaa et al 254 EF/USA 9.5−13.9 0.0005−0.0014 unconf 27−63 Du et al 60 Baikouquan/China 9.3 0.9 conf 37 Song et al 116 Duvernay/Canada 2.8 0.000125 conf <50 Li et al 197 Ordos significantly, based on core properties and the core holder method used. For example, experiments using confined core H-n-P injections 62,117,146,247,257 yield different recoveries than experiments using an unconfined core system (free-path holder), the core is soaked in high-pressure steam, allowing the injected gas to circulate across the core container, maximizing the sample's surface area (Figure 14d).…”

Impact of in-situ gas liberation for enhanced oil recovery and CO 2 storage in liquid-rich shale reservoirs

“…Previous studies of CO2 injection in shale oil systems considered reduced conditions where the oleic phase did not contain dissolved gases, which is called dead crude oils [23][24][25] . Dead crude oil models do not capture the mechanism of gas liberation from 'live oils'.…”