An Integrated Experimental and Numerical Approach to Assess the Performance of Solvent Injection into Heavy Oil

Abstract

Abstract Injection of gaseous solvent in heavy oil reservoirs is considered as an alternative recovery technique to thermal processes. The feasibility and performance of this technique, although numerous issues remain, are assessed at the macroscopic scale through an integrated approach in four steps. This paper describes: The design of the optimum solvent composition: Thermodynamic simulations were carried out to obtain the composition of the relevant solvent, which must be gaseous and close to miscibility under reservoir conditions. The following composition was achieved: 80%C2 and 20% C3.The PVT analysis of both reservoir oil and several mixtures with injected solvent: Results of the PVT experiments carried out to characterize the multi-phase behavior, the evolution of viscosity and density versus the amount of injected solvent are presented. A Peng Robinson equation of state, tuned on one of the oil-solvent mixtures, predicts correctly the properties (Psat, GOR, density) of the other ones. On the other hand, the usual Lohrenz-Bray-Clark correlation underestimates the viscosity decrease of the saturated oil.The design of the long core experiment: the injection rate for a stable displacement is determined according to the conclusions of simulations performed both in 1D and 2D. Finely gridded 2D simulations are carried out to investigate the effect of small-scale heterogeneity and show some fingering of the diluted oil into the original heavy oil.The core flood experiment under reservoir conditions: Solvent is injected top-down into an unconsolidated 35-cm long core. New insights into recovery, oil and solvent produced rates, GOR and composition of produced oil versus time are reported. The saturation profiles monitored by 1D X-Ray source are consistent with a gas-drive stabilized by capillarity. Conclusions about the main mechanisms involved in this solvent coreflood are presented; they should be confirmed by the history match of the experimental results.