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. Introduction Solvent-based processes for recovery of heavy oil have attracted increasing attention in the past few years as, compared to steam-based processes, they may reduce the energy consumption and greenhouse gas production. The Vapour Extraction (VAPEX) process was proposed by Butler and Mokrys1 for the first time as an alternative to Steam Assisted Gravity Drainage (SAGD) for thin reservoirs where the heat losses to the underburden and overburden preclude the economical interest of the latter. The VAPEX process is closely related to the SAGD concept where the steam chamber is replaced with a chamber containing light hydrocarbon vapours close to its dew point at the reservoir pressure. The heavy oil has its viscosity reduced by dissolution of the injected solvent and is subsequently produced by a gravity drainage mechanism.
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