Experimental Investigation of Asphaltene Content Effect on Crude Oil/CO2 Minimum Miscibility Pressure

Minimum Miscibility Pressure (MMP) is regarded as one of the foremost parameters required to be measured in a CO2 injection process. Therefore, a reasonable approximation of the MMP can be useful for better development of injection conditions as well as planning surface facilities. In this study, the impact of asphaltene content ranging from 3.84 % to 16 % on CO2/heavy oil MMP is evaluated. In this respect, slim tube miscibility and Vanishing Interfacial Tension (VIT) tests are used. Regarding the VIT test, the Interfacial Tension (IFT) is measured by means of two methods including pendant drop and capillary apparatuses, and thereafter the MMP measurement error between slim tube and VIT methods are calculated. Based on the results, by increasing the asphaltene content, the measured MMP by slim tube method increases linearly while that by VIT follows no clear trend. The results also indicate that there is an asphaltene content range within which the MMP error between slim tube and VIT tests is minimized. IFT measurement by pendant drop and Capillary Glass Tube (CGT) methods show that by increasing asphaltene content up to 10.15 %, IFT declines, whereas for further increase in content, IFT increases because of the irregular dispersion of asphaltene in oil droplets

The effect of CO2-philic thickeners on gravity drainage mechanism in gas invaded zone

The rate of mass transfer between the fractures and matrix in gas invaded zone can significantly influence on the oil recovery during the forced gravity drainage process. However, in this study, a new approach was suggested to improve the gravity drainage process in gas invaded zone. Poly(fluoroacrylate) (PFA), as a CO2-philic thickener, was injected into the gas invaded zone to illustrate the impact of interfacial mechanisms such as gas diffusion coefficient and interfacial tension (IFT) on oil recovery. Also, the cloud point pressures were measured to ensure that the PFA did not come out of the solution due to a phase change during IFT, gas diffusion coefficient, and gravity drainage experiments. Results showed that the CO2-PFA thickener (20000 ppm) could decrease the IFT from 56 to 24 dyne/cm compared to the pure CO2 scenario, improving the gravity drainage mechanism in the gas invaded zone. In addition, the CO2 diffusion coefficients were increased approximately more than two times during CO2-PFA injection in comparison with pure CO2 injection in both porous media and bulk oil phase scenarios at reservoir conditions. Also, an incremental oil recovery of 16 percent was achieved during PFA/CO2 compared to pure CO2 injection in the gas invaded zone. Therefore, gas gravity drainage is the most important mechanism once gas thickener or CO2 enters the fractures in the gas invaded zone

The role of direct asphaltene inhibitors on asphaltene stabilization during gas injection

There are a large number of investigations, which evaluate the impact of the liquid-based inhibitors on the asphaltene stabilization. In those studies, a specific volume of inhibitor was added to the oil sample and the asphaltene precipitation is then studied. However, this method is indirectly applicable to processes like gas injection. For that reason, in this work, the metal oxide nanoparticles (GO, TiO2, SiO2, and MgO) have been considered in the liquid-free mode as direct asphaltene inhibitors (DAIs) on asphaltene stabilization for the duration of miscible CO2 injection. The dissolution of DAIs in CO2 was investigated by measurement of cloud point pressure to evaluate the pressure/temperature conditions, need for certifying that the CO2/DAIs mixtures have the single-phase condition. Afterwards, the impact of DAI was studied on asphaltene precipitation and deposition by static and dynamic approaches. Results show that the total size of asphaltene particles which precipitated during injection of miscible CO2/DAIs mixture is significantly lower than that for immiscible pure CO2 injection. The amount of asphaltene deposition significantly decreased during injection of miscible CO2/DAIs mixtures compared to immiscible pure CO2 injection. Additionally, themetal oxide nanoparticles hinder the phase separation of asphaltenes kinetically and prevent growth. It is conducted by stabilizing the colloidal suspension of the asphaltene particles, which are in sub-micrometre size to significantly slow the asphaltene flocculation onset

An Experimental Study of Surfactant Alternating CO2 Injection for Enhanced Oil Recovery of Carbonated Reservoir

Core flooding experiments were conducted with the objective of evaluating near miscible surfactant alternating CO2 injection and the effect of surfactant concentrations on gas-oil and water displacements in porous media. The core samples were provided from a low permeability mixed wet oil reservoir at 156 °F and 1900 psia. In addition, very few studies of surfactant adsorption on carbonate minerals have been conducted. Hence, the surfactant adsorption on carbonate rock was determined by core flooding and crushed tests. It was found that for the crushed rock, the required equilibrium time is approximately five hours, while it is more than four days for the flow-through tests. Hysteresis effects demonstrated that the irreducible water saturations were 5 to 10% higher than the initial connate water saturation after drainage cycles during 5000 ppm surfactant solution. Furthermore, near-miscible surfactant alternating CO2 injection process led to a 4-17% increase in the recovery factor in comparison to water alternating gas process

Decreasing Asphaltene Precipitation and Deposition during Immiscible Gas Injection Via the Introduction of a CO2-Soluble Asphaltene Inhibitor

In this study, the ability of dilute concentrations of toluene to act as a CO2-soluble asphaltene stabilization agent capable of inhibiting asphaltene precipitation during immiscible CO2 injection was assessed. Phase behavior results indicated that 1,000 to 20,000 ppm toluene could readily dissolve in CO2 at cloudpoint pressures that are well below the formation pressure and typical CO2 minimum miscibility pressure (MMP) values during gas-based enhanced oil recovery (EOR). Single-phase solutions of the modified gas (CO2/toluene) were then combined with asphaltenic oils in oil swelling phase behavior tests to demonstrate that the presence of toluene increased the amount of CO2 that dissolved into reservoir crude oil at a specified temperature and pressure. However, asphaltene precipitation diminished, apparently because the effect of the increased asphaltene solvent strength of toluene was more significant than the increased amount of CO2 (an asphaltene antisolvent) that entered the oil-rich phase. During the injection of CO2/toluene solution into cores initially saturated with crude oil and brine, compared to the injection of pure CO2, asphaltene deposition declined during the injection of CO2/toluene mixtures for asphaltenic volatile and intermediate oils from 3.7 wt% to 0.7 wt% and 5.9 wt% to 1.7 wt%, respectively. Based on the asphaltene particle-size analysis, the CO2/toluene mixtures can stabilize oil particles and simultaneously reduce asphaltene aggregation more effectively than pure CO2

Enhanced oil recovery through synergy of the interfacial mechanisms by low salinity water alternating carbon dioxide injection

During this study, a comprehensive investigation of low salinity water alternating CO2 injection was performed for enhanced oil recovery in oil-wet carbonate reservoirs. A synergy of interfacial mechanisms such as IFT, wettability alteration, CO2 solubility, oil swelling, water shielding effect, and rock dissolution was considered in two and three-phase systems. Results showed that the monovalent ions, such as NaCl or KCl, inhibit the dissolution of carbon dioxide in brine in excess of divalent salt solutions, e.g. CaCl2 or MgCl2 due to the salting-out effect. In addition, more water shielding effect was observed in low salinity formation water than it in low salinity seawater. The significant change in the reservoir wettability of oil/brine/CO2 system compared to oil/brine referred to the CO2 solubility in brine which could cause stronger carbonated water in the reservoir. Consequently, the low salinity alternating CO2 injection overpowers the late-production problem that occurred commonly in conventional WAG injection