There are a large and growing number of Western Canadian heavy oil deposits that have been depleted using primary cold production (CHOPS) methods. At their economic limit these methods leave behind 85 % to 90 % of the OOIP while significantly altering the reservoir conditions from their initial state. The oil remaining is a significant target for a follow up process; however, presently there is no demonstrated EOR process that can economically recover additional oil from these deposits in their current condition.
The application of in situ combustion in a reservoir that has under gone CHOPS has several attractive features. The wormhole network created during primary production provides the injectivity required to initiate and sustain high temperature combustion. The interconnected wormhole channels between adjacent wells supplies a conduit for mobilized oil to flow to production well thus minimizing liquid blockage and ineffective conformance.
To assess the potential of in situ combustion as a post CHOPS process a laboratory study was carried out examining the behavior of in situ combustion under conditions representative of the reservoir at the end of CHOPS. A total of seven physical simulation experiments were carried out in the Heavy Oil and Oil Sands laboratory of the Alberta Research Council (now part of Alberta Innovates – Technology Future). Test conditions of these experiments included high permeability channel vs. no high permeability zone, partially filled high permeability channel vs. completely open channel, dead oil vs. live oil dry combustion vs. wet combustion, and normal air vs. enriched air injection,.
Results of the experiments are encouraging for the application of in situ combustion in CHOPS reservoirs. The high permeability wormhole channels provided injectivity to initiate and sustain combustion and the presence of the channel lead to improved conformance with no gravity overriding of the combustion front. Localized coke plugging of the channel prevented the combustion front from prematurely breaking through to the production well, even with a completely open wormhole channel.