Incorporating some heat injection along with the solvent injection appears to be the most viable option for improving the oil drainage rate of Vapex in extra-heavy oil formations. This study was aimed at quantifying the potential increase in Vapex drainage rate that can be obtained by increasing the formation temperature.
The experimental phase of this study involved conducting Vapex experiments in a large high-pressure physical model, packed with 250 Darcy sand, using propane as the solvent. The physical model was warmed up to 40, 50 and 60 °C and propane was injected at the same test temperature but different injection pressures to observe how injection pressure affects oil drainage rate at elevated temperatures.
In the experiments at elevated temperatures but without increasing the injection pressure, higher rate of oil production was achieved in the early stages of the process. However, stabilized rate of oil production did not show pronounced improvement due to lower solubility of propane in the oil at higher temperatures. Increasing injection pressure along with increasing the test temperatures was successful in accelerating the oil production.
The oil, used in these experiments, was found to become mobile with the increase in temperature even without solvent dissolution. As a result, the total rate of oil production appeared to be controlled by two mechanisms. First, by solvent dissolution and oil mobilization at the boundaries of the vapor chamber and second by pure free fall gravity drainage beyond the vapor chamber wherever gravity head was sufficient to push the mobile oil toward the production well.
The results of this these tests define the upper limit of oil rates achievable with heated solvent injection. They can also be used to assess the applicability of Vapex to naturally warm reservoirs such as in Venezuela and reservoirs with mobile oil in place.