Summary

Incorporating some heat injection along with solvent injection appears to bethe most viable option for improving the oil-drainage rate of vapour-assistedpetroleum extraction (VAPEX) in extraheavy-oil formations. This study wasintended to quantify the maximum possible increase in VAPEX drainage rate thatcan be obtained by heating the formation to a target temperature. Theexperimental phase of this study involved conducting VAPEX experiments in alarge high-pressure physical model, packed with 250-darcy sand, using propaneas the solvent. The physical model was preheated to 40, 50 and 60°C, andpropane was injected at the same test temperature but different injectionpressures to observe how injection pressure affects oil-drainage rate atelevated temperatures. In the experiments at elevated temperatures, but withoutincreasing the injection pressure, higher rate of oil production was achievedin the early stages of the process. However, a stabilized rate of oilproduction did not show pronounced improvement caused by a lower solubility ofpropane in the oil at higher temperatures. Increasing injection pressure alongwith increasing the test temperatures was successful in accelerating the oilproduction. The oil used in these experiments was found to become mobile withthe increase in temperature even without solvent dissolution. As a result, thetotal rate of oil production appeared to be controlled by two mechanisms: (1)by solvent dissolution and oil mobilization at the boundaries of the vapourchamber and (2) by pure free-fall gravity drainage beyond the vapour chamberwherever gravity head was sufficient to push the mobile oil toward theproduction well. The results of this these tests define the upper limit of oilrates achievable with heated solvent injection. They can also be used to assessthe applicability of VAPEX to warm reservoirs naturally (e.g., in Venezuela)and reservoirs with mobile oil in place.

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