Temperature effects on the phase behaviour, mutual interactions and oil recovery of a light crude oil–CO2 system

Abstract

In this paper, the temperature effects on the phase behaviour, mutual interactions, and oil recovery of a light crude oil–CO2 system are experimentally studied. First, six PVT tests are performed to measure the saturation pressures and the oil-swelling factors of three light crude oil–CO2 systems with different CO2 concentrations. Second, a series of saturation tests are conducted to determine the onset pressure (Pasp) of asphaltene precipitation from the light crude oil–CO2 system. Third, the minimum miscibility pressure (MMP) and the first-contact miscibility pressure (Pmax) of the light crude oil–CO2 system are determined by applying the vanishing interfacial tension (VIT) technique. Meanwhile, the oil-swelling effect, the initial quick and subsequent slow light-hydrocarbons extraction phenomena are observed during the dynamic interfacial tension (IFT) measurements. In particular, the onset pressure (Pext) for the initial quick light-hydrocarbons extraction by CO2 is noted. Finally, a total of eleven CO2-coreflood tests are undertaken to examine the temperature effect on the CO2-based oil recovery. All the above-mentioned experiments are conducted at a laboratory temperature of Tlab=27.0°C and at the actual reservoir temperature of Tres=53.0°C, respectively. It is found that the test temperature has a strong effect on the saturation pressure but a marginal influence on the oil-swelling factor of a given light crude oil–CO2 system. It is also found that the four onset pressures are in the order of magnitude: Pasp<Pext<MMP<Pmax. Furthermore, Pasp and Pext increase slightly but the MMP and Pmax increase significantly with the test temperature. Lastly, a higher test temperature leads to a higher oil recovery factor as long as the CO2 flooding is miscible.