Experimental investigation of cyclic solvent injection based on mixture solvent of carbon dioxide and propane

In this study, three CSI tests by the mixture solvent (60% mol. CO2 and 40% mol. C3H8) with the decline rate of 12.5 kPa/min, 5.0 kPa/min and 1.0 kPa/min respectively were conducted in a sand-pack model with the diameter of 15.24 cm and the length of 30.48 cm. Three pure propane CSI tests from previous study, also with the decline rate of 12.5 kPa/min, 5.0 kPa/min and 1.0 kPa/min respectively, were used to perform comparison analyses with three mixture solvent CSI tests for better understanding driving mechanisms of the CSI process. Comparison results show that pure propane tests had larger recovery factor and average oil production per single cycle than mixture solvent tests. The amount of the propane diffusing into the heavy oil in mixture solvent tests was lower than that in pure propane tests because of the negative effects of the carbon-dioxide. The asphaltene precipitation and production time significantly impacted the recovery factor of diluted oil in mixture solvent tests. It's indicated that the effects of the decline rate on the asphaltene precipitation were more sensitive in mixture solvent tests. As well as in pure propane tests, the decline rate can also be optimized in mixture solvent tests. It's suggested that 5.0 kPa/min is the optimal decline rate with the largest recovery factor and average production per single cycle in mixture solvent tests. In addition, hysteresis of the declined pressure of the sand-pack model led to a high pressure difference and intensive oil production between 300 kPa and 200 kPa in the 1.0 kPa/min mixture solvent test.