Effective viscosification of supercritical carbon dioxide by oligomers of 1-decene.

Viscosification of carbon dioxide by polymers can make large scale CO2 sequestration safe and efficient. We present solubility of branched hydrocarbon oligomers in CO2 and viscosification measurements at relevant subsurface conditions. Polymers of 1-decene (P1D) with about 20 repeating units are found to be effective in CO2 viscosification, increasing it by 6.5-fold at 1.8 wt% concentration at 308 K and 31 MPa. We reason that methyl groups and branching promote solubility and viscosification. Low molecular weight oligomers can have lower solubility in CO2 than higher molecular weight ones and the trend in solubility is non-monotonic at constant pressure and temperature. Analysis of solubility trend of P1D oligomers in CO2 advances our understanding of molecular structure and functionality and opens the path to engineering of oligomers effective in viscosification and widespread use of CO2.

Assessment of low salinity waterflooding in carbonate cores: Interfacial viscoelasticity and tuning process efficiency by use of non-ionic surfactant.

HYPOTHESIS: A large number of papers discuss merits and mechanisms of low salinity waterflooding. For each mechanism proposed, there are counter examples to invalidate the stated mechanism. The effect of wettability from low salinity water, which is predominantly stated in literature as the dominant mechanism, may not be valid. We introduce a direct correlation between oil-brine interfacial viscoelasticity and oil recovery from waterflooding. EXPERIMENTS: The oil recovery is investigated in carbonate rocks for three light crude oils, by injection of a wide range of aqueous phases, ranging from deionized water to very high salinity brine of 28 wt%, and low concentration of a non-ionic surfactant at 100 ppm. The oil-brine interfacial viscoelasticity is quantified and supplementary measurements of interfacial tension and wettability are performed. FINDINGS: In our experiments, oil recovery is higher from high salinity water injection than from low salinity water injection. A strong relationship is observed between interface elasticity and oil recovery for different concentrations of salt in the injected brine as well as for ultra-low concentration surfactant. An elastic oil-brine interface results in high oil recovery. The surfactant molecule we have selected prefers the oil-water interface despite high solubility in the oil phase and makes ultra-low concentration of 100 ppm in injection water very effective. Contrary to widespread assertions in the literature, we find no definitive correlation between oil recovery and wettability.

Improved Oil Recovery in Carbonates by Ultralow Concentration of Functional Molecules in Injection Water through an Increase in Interfacial Viscoelasticity.

Injection of sea water is the most common practice to displace oil in porous media in subsurface formations. In numerous studies, conventional surfactants at concentrations in a range of one weight percent have been proposed to be added to the injected water to improve oil recovery. Surfactants accumulate at the oil-water interface and may reduce the interfacial tension by three orders of magnitude or more, resulting in higher oil recovery. Recently, we have proposed the addition of ultralow concentration of a non-ionic surfactant to the injected water to increase interface viscoelasticity as a new process. The increase in interface viscoelasticity increases oil recovery from porous media. This alternative approach requires only a concentration of 100 ppm (two orders less than the conventional improved oil recovery) and therefore is potentially a much more efficient process. In this work, we present a comprehensive report of the process in an intermediate-wet carbonate rock. There is very little adsorption of the functional molecules to the rock surface. Because the critical micelle concentration is low (around 30 ppm), most of the molecules move to the fluid-fluid interface to form molecular structures, which give rise to an increase in interface elasticity. We also demonstrate that interface elasticity has a non-monotonic behavior with the salt concentration of injected brine, and an optimum salinity exists for maximum oil recovery.