A Holistic EOS Model for Characterization of Northern Kuwait Extra-Heavy Oil Mixed with Liquid Solvents

Abstract

Abstract Liquid solvent injection is envisaged for extra-heavy oil extraction from the Lower Burgan Abdali (ADBG) reservoir in North Kuwait. This is a deep reservoir (9000 ft) where steam-assisted EOR methods are associated with a wide array of tehno-ecnomic challenges. This paper presents a methodology for creating a holistic Equation of State (EOS) describing the thermophysical properties of the selected solvents, extra-heavy oil, and their blend at different conditions. Such a model is essential for studying subsurface-to-surface variations in the mixture properties to assess the viability of solvent-assisted production. Representative extra-heavy downhole oil samples and two multi-component liquid solvents were investigated by performing high-pressure laboratory testing. Fluid density and viscosity were measured under varying conditions. A cubic EOS model was built to reproduce the extra-heavy oil lab-based PVT data. Simultaneously, another EOS model was developed for the two solvents. These EOS models were merged into a unified model to ensure pseudo-component overlap representation and lumping of the components for a correct extra-heavy oil and solvent mixture prediction. The viscosity modelling challenges and solutions for extra heavy-oil (with and without minor dissolved gas) and solvent mixtures were also investigated in detail. Lab evaluation using representative downhole oil samples (with minor dissolved gas) showed significant differences in the molecular weight of C36+ and the measured viscosity. A single EOS model was created using multi-fluid regression. The heaviest fraction had to be split into two pseudo-components coexisting in both samples but at different molar fractions. The components existing in both extra-heavy oil and solvent were lumped to avoid overlapping. It was demonstrated that the resulting EOS model can accurately reproduce the phase and volumetric behaviour of extra-heavy oil, solvent and their blend at different pressures and the reservoir temperature. Furthermore, it was noticed that the modified Lohrenz-Bray-Clark (LBC Heavy Oil) can predict the viscosities at isothermal conditions. For non-isothermal conditions, the viscosity of each pseudo-component is to be calculated at different temperatures in a tabulated format.