Effects of Paraffinic Group on Interfacial Tension Behavior of CO₂–Asphaltenic Crude Oil Systems

Abstract

The interfacial tension (IFT) of a crude oil/CO 2 system is recognized as the main property affecting the efficiency of CO 2 flooding during an enhanced oil recovery (EOR) process. The addition of a paraffin group hydrocarbon to asphaltenic crude oils as an asphaltene precipitant component is aimed to mimic the asphaltene precipitation process during crude oil production and transportation. Asphaltene precipitation would critically affect the interfacial behavior of crude oil/CO 2 systems. In the first part of this study, the equilibrium densities of oil samples which contain nheptane at different ratios were measured over varying pressures at 323 K. Then, the equilibrium IFT between CO 2 and the crude oil samples was measured using the axisymmetric drop shape analysis (ADSA) technique. This investigation was followed by measuring the minimum miscibility pressure (MMP) of the oil/CO 2 systems using the vanishing interfacial tension (VIT) technique. The results showed that the density of oil sample increases linearly with pressure. Moreover at a constant pressure and temperature, the density was linearly decreased with nheptane content of the crude oil sample. Linear correlations between density, n-heptane content, and pressure at the temperature of 323 K for each oil sample were also noticed. The results of IFT tests indicated that asphaltenic crude oil samples have two slope IFT-pressure behavior. It was found that for oil samples with high asphaltene content (9 wt %), the higher the n-heptane content of the oil sample is, the lower is the pressure of the IFT's slope change, while for low asphaltenic oil sample (0.56 wt %) an increase of n-heptane has little effect on the point of the slope change of the IFT. Consequently, it was found that asphaltenes increase the rate and magnitude of the light component extraction in oil/CO 2 systems. The experimental results showed that the MMP of the oil samples decreased linearly with the n-heptane content of the oil sample. The linear relation between the MMP and n-heptane content revealed the crucial role of the paraffinic group as the controlling miscibility component of the crude oils.

Exploring the effects of four important factors on oil–CO2 interfacial properties and miscibility in nanopores

“…For example, the CH 4 -dominated HCs pre-saturated live light oil-CO 2 system was found to have a higher IFT/MMP, whereas the intermediate HCs pre-saturated one has a lower IFT/MMP in comparison with that of the dead light oil-CO 2 system. 18 Similar results were also found in terms of the effect of injection gas composition on the IFT/MMP studies. 15 Moreover, the effect of feed ratio of injection gas to oil on the measured IFT/MMP cannot be ignored although there is no general consensus on it.…”

“…This is because the addition of CH 4 -dominated produced gas into oil sample reduces the CO 2 solubility in the oil phase. 18 Two respective MMPs are determined to be 11.6 and 26.5 MPa from the DIM at T ¼ 53.0 and 116.1 C, both of which are slightly lower than 13.7 and 29.7 MPa of the Pembina live oil-pure CO 2 system at the same temperature. The effects of initial oil composition on the determined MMPs are further summarized in Fig.…”

Structural Effects of Nonionic Surfactants on Their Ability to Reduce the Dissolution Pressures of Heavy Hydrocarbons in Supercritical CO2

“…Solubility of components of the crude oil in CO 2 is crucial to the recovery rate. It has been found that light alkanes (C 3-10 ) compared with heavier alkanes were recovered faster and more from the crude oil phase because of their better solubility in CO 2 (Cao & Gu, 2013;Rudyk, Spirov, & Sogaard, 2013); in addition, IFT between light alkanes and CO 2 are lower than those between the heavy alkanes and CO 2 (Mahdavi, Zebarjad, Taghikhani, & Ayatollahi, 2014a). In the extraction fields, a high extraction rate of a compound largely depends on its good solubility in CO 2 .…”

“…According to Luo, Zhang, Wang, and Huang (2012), solubility of n-hexane in CO 2 is as high as 6.18 mol % at 328 K, 8.95 MPa. Using a mixed solvent (CO 2 with alkanes, light petroleum, or alcohols) instead of pure CO 2 is a common way to increase the solubility (Catchpole, Grey, & Noermark, 1998;Mahdavi, Zebarjad, Taghikhani, & Ayatollahi, 2014b;Zolghadr, Escrochi, & Ayatollahi, 2013). De Lucas, Gracia, Rincon, and García (2007) studied the solubility of squalene, orange roughy, spiny dogfish, and cod liver oil in scCO 2 , finding that the solubility was obviously improved by the addition of ethanol, 7.75% of ethanol resulted in an improvement in the solubility of cod liver oil from 4.81 to 9.07 g kg −1 at 333 K, 20 MPa.…”

Interfacial Tensions of Ethoxylated Fatty Acid Methyl Ester Solutions Against Crude Oil

“…Ethoxylated fatty acid methyl esters are new biodegradable surfactants that easily hydrolyze to nontoxic and non-surface active components in sewage systems [24][25][26][27]. Compared to ethoxylated alcohols, they have better properties, lower aquatic toxicity and higher biodegradability [27,28].…”