Phase Behaviour and Viscosity Reduction of CO2-Heavy Oil Systems at High Pressures and Elevated Temperatures

Abstract

Techniques have been developed to experimentally and theoretically determine phase behaviour and viscosity reduction of CO 2 -heavy oil systems at high pressures and elevated temperatures. Experimentally, vapour-liquid phase boundaries (i.e., saturation pressure lines) and the swelling factors are measured by conducting PVT tests at pressures up to 11094.0 kPa and temperatures up to 362.75 K, respectively. The viscosity of CO 2 -saturated heavy oil is measured at 319.15 K. Theoretically, the heavy oil sample is respectively characterized as a single-and multi-pseudocomponent(s). An exponential distribution function is used to split the plus fraction of heavy oil up to C 105ϩ , while a logarithm-type lumping method is used to group the single carbon numbers (SCNs) into multiple pseudocomponents. Then, the Peng-Robinson equation of state (PR EOS) coupled with the modified alpha function is applied to quantify the phase and volumetric behaviour of the CO 2 -heavy oil systems. The binary interaction parameters (BIPs) for CO 2 -pseudocomponent(s) pair are tuned to match the measured saturation pressures. Compared with the characterization scheme of treating heavy oil as a single pseudocomponent, the absolute average relative deviation (AARD) for the predicted saturation pressures can be improved from 5.27% to 4.56% by characterizing the heavy oil as six pseudocomponents. With the optimum BIPs, the swelling factors are predicted by the PR EOS with and without the volume translation technique, respectively. It is found that the introduction of the volume shift to each (pseudo)component in the PR EOS is able to provide more accurate prediction in both characterization schemes with AARD of 1.88% (oil as a single pseudocomponent) and 1.39% (oil as six pseudocomponents), respectively.

Nonequilibrium Phase Behavior of Alkane Solvent(s)–CO2–Heavy Oil Systems under Reservoir Conditions

“…The following modified alpha function employed in the PR EOS has been found to more accurately describe the phase behavior of both pure substances and alkane solvent(s)–CO 2 –heavy oil systems by treating heavy oil as one pseudocomponent − and multiple pseudocomponents. − In this study, the PR EOS together with the modified alpha function has been employed to determine the moles of the evolved gas under thermodynamic conditions, n em , for the alkane solvents–CO 2 –heavy oil systems.…”

Characteristics of Fracture Propagation Induced by Supercritical CO2 in Inter-Salt-Shale Reservoir

“…Supercritical CO 2 has great potential as a fracturing fluid to stimulate this special reservoir, which can cause wettability alteration on the low permeability reservoir and lower the surface tension and viscosity of the oil to improve the displacement [9][10][11][12]. The studies by Zhang et al [13] indicate that SC-CO 2 is considered as an ideal nonaqueous fracturing fluid which can produce a denser crack network.…”

Determination of Multiphase Boundaries for Pressure–Temperature (P–T) and Enthalpy–Temperature (H–T) Phase Diagrams of C3H8/CO2/Water/Heavy Oil Systems at High Pressures and Elevated Temperatures

“…Nevertheless, few attempts have been made to determine the phase behavior of solvent/CO 2 /heavy oil mixtures with the existence of water/steam at high pressures and elevated temperatures. This is due to the following reasons: (1) it is technically difficult to perform three-phase ALV PVT tests at high pressures and elevated temperatures; (2) emulsion phenomenon makes it challenging to clearly observe the interface between water and heavy oil; and (3) temperature limitation of the current PVT equipment makes it impossible to conduct experiments at high temperatures. , Also, no studies have been found on the investigation of multiphase boundaries for solvent/CO 2 /water/heavy oil systems in the H – T diagrams, which is crucial for the field design of steam-solvent coinjection processes for heavy oil reservoirs.…”