Abstract

Cold heavy oil production with sand (CHOPS) has been applied successfully in many oil fields in Canada. However, only 5% - 15% of the original oil in place (OOIP) is recovered during cold production typically. Therefore, effective follow-up techniques are of great importance. Cyclic solvent injection (CSI), as a post-CHOPS process, has greater potential than continuous solvent injection to enhance heavy oil recovery. Continuous solvent injection results in early breakthrough due to the existence of wormholes; while in CSI process, the existence of wormholes can increase the contact area of solvent and heavy oil and the wormholes also provide channels that allow diluted oil to flow back to the wellbore.

In this study, the effects of wormhole and sandpack model properties on the performance of the CSI process are experimentally investigated using three different cylindrical sandpack models. The length and diameter of the base model are 30.48 cm and 3.81 cm, respectively. The other two models, one with a larger length (i.e. 60.96 cm) and the other with a larger diameter (i.e. 15.24 cm), are used for up-scaling study in the directions parallel and perpendicular to the wormhole, respectively. The porosity and permeability of these models are about 35% and 5.5 Darcy typically. A typical western Canadian oil sample with a viscosity of 4330 mPa · s at 15 °C is used. And pure propane is selected as the solvent. The experimental results suggest that (1) the existence of wormhole can significantly increase the oil production rate. The larger the wormhole coverage is, the better the CSI performance is; (2) a reservoir or well with wormholes developed at bottom is more favorable for Post-CHOPS CSI process; (3) the oil recovery factor is almost independent on the model diameter during the chamber rising phase; and the oil relative production rates in two different diameter models are close during the chamber spreading phase due to similar solvent dispersion rate; (4) the model length hardly affected the oil production rate comparing with the wormhole length; (5) the well with a horizontal wormhole is inclined to get a good CSI performance; (6) a relationship of oil production rate to drainage height is obtained and verified; (7) the mass transfer rate decreases verse time during the soaking period.

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