Testing the injection of air with methane as a new approach to reduce the cost of cold heavy oil recovery: An experimental analysis to determine optimal application conditions

Abstract

We propose a new approach to reduce the associated cost of CSI (cyclic solvent injection) by using air with methane to pressurize the reservoir and improve the foaminess process. This reduces the cost as the amount of methane injected is curtailed, but the process needs to be optimized by determining the optimal application conditions by maximizing final heavy oil recovery. To study the use of air for a technical and economic improvement of CSI with methane, pressure depletion tests were performed at a pressure depletion rate of −0.51 psi/min in a cylindrical sandpack, placed in a 150 cm long and 5 cm diameter sandpack holder supplied with eight evenly distributed pressure transducers and three thermocouples. Production profiles (pressure at every port, pressure differences, and pressure gradient) and saturation distributions were studied to determine the conditions yielding the best sweep and the highest oil and gas recovery factor with minimal use of gas injected. Different injection/production schemes (alternate or co-injection of an air-methane pair and different injector-producer alignments), depletion rates, and soaking times were tested to determine the conditions to maximize the recovery factor. Furthermore, observational experiments at a macroscopic and microscopic scale after the PVT tests were performed by recombining the heavy oil sample with sole air, sole methane, and a mixture of air and methane at a volume ratio of 1. Using a mixture of air and methane not only expanded the volume of oil (gas bubbles trapped into the oil) by 2.5 but also delayed the defoaming process at both macroscopic and microscopic scales. Numerous tiny gas bubbles were initially observed, which kept its size and number for more time than the methane case, which is an indication of restraining fast bubble growth and subsequent coalescence. The best injection strategy for a single-well injection scheme was the simultaneous injection of air and methane on a soaking period of 2–3 days, whereas for a multi-well injection scheme an alternating injection strategy on a soaking period of 4–5 days offered the best performance. Cumulative oil and gas recovery factors were as high as 27.46% and 76.68%, respectively, when air was accompanied by methane. Using air as a foamy oil ameliorative was observed to save up to 26% on methane use in single-well injection schemes and up to 51% on multi-well injection schemes.