Gasflooding-assisted cyclic solvent injection (GA-CSI) for enhancing heavy oil recovery

Cyclic solvent injection (CSI) process has showed great potential to enhance heavy oil recovery because it takes advantages of solution-gas drive and foamy oil flow for oil production. However, CSI suffers from solvent release during the production period so that the viscosity of the solvent-diluted heavy oil is re-increased and its mobility is re-decreased. How to effectively recover the solvent-diluted heavy oil becomes a key technical challenge in a CSI process. This paper first experimentally analyzed a conventional CSI process that used a solvent injector as an oil producer alternately. It is found that foamy oil was induced and flowed to the producer during the production period of a cycle but some foamy oil was pushed back by solvent during the solvent injection period of the following cycle. Such "back-and- forth'' movement of foamy oil seriously hindered the productivity of the CSI process. On the basis of this knowledge, this study proposed a new process, gasflooding-assisted cyclic solvent injection (GA-CSI), to enhance the performance of CSI. In a GA-CSI process, the solvent injector and the oil producer were placed horizontally apart. An additional solvent gasflooding process was applied immediately after the pressure drawdown process to produce the foamy oil that lost its mobility due to solvent release. The experimental results showed that the oil production rate of the newly proposed GA-CSI process is 3-4 times of that for a conventional CSI process. (C) 2014 Elsevier Ltd. All rights reserved.