The Solvent Requirements for Vapex Recovery

Abstract

SPE Members Abstract In both SAGD and VAPEX, recovery agents are introduced into the reservoir and these displace oil to horizontal wells located at the base. In each process it is desirable to inject at a pressure equal to or slightly below the pressure of the surrounding reservoir, so as to prevent flow of fluids to outside the recovery pattern. The pressure in the recovery pattern is reduced by allowing production to draw vapour almost to the production well. The recovery agent that is produced is liquid (water condensate or dissolved solvent). This agent is separated and recycled. The recycled quantity is about 2–6 tonnes per tonne (t/t) of produced oil for SAGD and 0.3–0.5 t/t for VAPEX. Recycle is much simpler for VAPEX. The pore volume that contained the produced oil becomes filled with recovery agent either vaporized (steam or solvent vapour) or liquid (water or dissolved solvent). The net requirement of recovery agent is equal to the make-up supplied to the system to maintain operation. For VAPEX, it is this quantity of solvent that determines the net cumulative solvent-to-oil ratio (NCSOR) before blowdown. Subsequently, during blowdown, a considerable fraction of this net solvent is recovered. P. 465