Dynamic solvent process (DSP) for enhancing heavy oil recovery

Solvent-based heavy oil recovery techniques, such as vapour extraction (VAPEX) and cyclic solvent injection (CSI), have been attracting increasing attention in the past two decades.VAPEX suffers from slow mass transfer and inefficient gravity drainage.CSI is a solventhuff-and-puff processand its production period is usually much shorter in comparison with the solvent injection and soaking periods, limiting the average oil production rate over theentireprocess.Thispaperproposesanewprocess,dynamicsolventprocess(DSP),toexploitthemeritsofVAPEX(continuousproduction)andCSI (stronger driving force) and reduce their respective limitations (inefficient gravity drainage and periodic production). DSP is a cyclic process and each cycle consists of two periods: a stable pressure period and a pressure reduction period, through which solvent is cyclically injected and oil is continuously produced. A set of laboratory experiments were performed to validate and analyze the DSP process. During the pressure reduction periodofDSP,afoamyoil flowphenomenonwasobservedwhenthepressurereachedtheso-calledpseudo-bubblepoint.Thefoamyoil flownotonly enhanced the oil production but also improved mass transfer due to the enlarged oil–solvent contact area. Experimental results showed that the oil production rates of VAPEX and CSI were respectively enhanced by 57–123% and 17–99% by DSP with different well configurations.