Effect of the Injection Pressure on Enhancing Oil Recovery in Shale Cores during the CO₂ Huff-n-Puff Process When It Is above and below the Minimum Miscibility Pressure

Abstract

In CO 2 injection, there is a minimum miscibility pressure (MMP) above that CO 2 can be miscible with oil, so that oil recovery will be high. This paper is to investigate the effect of the injection pressure on enhanced oil recovery in shale oil cores under huff-n-puff CO 2 injection, when the pressure is above and below the MMP. We first estimated the MMP for a Wolfcamp oil using slimtube tests. The slimtube test results showed that the estimated MMP for the CO 2 −Wolfcamp crude oil system was about 1620 psi at 104 °F. After that, we conducted 15 CO 2 huff-n-puff experiments using three different Wolfcamp shale cores at pressures below and above the MMP. These pressures were 1200, 1600, 1800, 2000, and 2400 psi. Each huff-n-puff test has 7 cycles. The huff-n-puff experiments for three cores showed that, below the MMP, the injection pressure had a significant effect on enhancing oil recovery. Higher than the MMP, the increased pressure further increased the oil recovery until the injection pressure was about 200 psi higher than the MMP. In the extremely low-permeability shale oil cores, additional pressure is needed to push gas into the deeper core to be miscible with the crude oil inside the core. The results indicated that, to have a high oil recovery in shale oil reservoirs during the CO 2 huff-n-puff process, the injection pressure should be higher (at least 200 psi in this case) than the MMP estimated from slimtube tests.

Huff-n-Puff Test For Minimum Miscibility Pressure Determination For Heavy Oil

“…To avoid the MMP change due to the low permeability that mentioned in his research (Li et al 2017), it was decided to use the standard samples of Berea sandstone drilled close to each other from one piece of the rock. Assuming that the samples are almost equal (Table 2), according to Li & Sheng (2016) such differences in core size we have are inessential, and permeability of samples is high enough to be inessential in the experiment either.…”

“…One of the most prominent technique is effective minimum miscibility pressure (eMMP) determination by the novel technique through Huff-n-Puff injection, starting now referred to as "HnP MMP Test", proposed by Li & Sheng (2016). According to Li et al (2017) eMMP is almost equivalent to MMP, the problem was that Li et al (2017) used shale samples with ultra-low permeability that decreased the measured MMP in comparison with MMP obtained by STT. But it is should be mentioned that experiment with the almost similar procedure was done by Rudyk et al (2009b), this research was almost unnoticed for inexplicable reasons.…”

A new approach for predicting oil recovery factor during immiscible CO2 flooding in sandstones using dimensionless numbers

“…Pressure difference between injection pressure and minimum miscibility pressure (MMP) shows the state of injection. In the immiscible condition (where injection pressure is lower than MMP), injection pressure plays an important role in altering the ultimate recovery of CO 2 core flooding (Li et al 2017). Injection at pressure values closer to MMP affects the oil recovery and hence, in this study, the pressure ratio number (P r ) considers the effect of operational conditions.…”

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

“…Recent years, CO 2 HnP method has been applied to enhance unconventional oil recovery in light oil and tight reservoirs. [26][27][28] Song et al (2013) compared water and CO 2 injection experiments on cores of Bakken tight formation, and obtained that the degree of CO 2 recovery under near-miscible and miscible conditions was higher than that under water ooding. 29 Gamadi et al (2014) did experiments to study the cyclic CO 2 injection in shale oil EOR using mineral oil and cores from Mancos and Eagle Ford.…”