Part 1: Kinetics of Methane Exsolution From Bitumen in Thermal Recovery Processes – Experimental Study

Abstract Under the reservoir conditions, bitumen has minute volumes of dissolved methane that when heated through a thermal recovery process, leave the solution and can potentially accumulate in the reservoir, reducing the steam condensation temperature at the bitumen/vapor interface, thus impacting process efficiency and impeding the production rates. Accurate quantification of the rate of release of methane is crucial for understanding the underlying mechanisms and predicting the performance of the bitumen recovery process. This rate can vary between hours to weeks depending on the conditions, making their measurement significantly challenging. In this study a new testing approach and experimental setup are developed for reliable measurement of the kinetics of the rate of methane release from bitumen. A new experimental setup is designed, fabricated, and validated to measure the rate of minute volumes of methane released from bitumen. Moreover, a new analytical method is developed for modeling the complex kinetics of the release of methane from bitumen through a simple first-order reaction model with Arrhenius temperature dependency that can be incorporated into reservoir simulations without imposing a major numerical burden. Under a controlled testing environment, the methane release is initiated through imposing a sudden pressure drop to a pre-saturated bitumen/methane liquid mixture, therefore reducing the methane solubility and triggering its exsolution. To maintain the pressures at the new level, exsolved methane was then vented and measured using a precise gasometer. The results indicate that the exsolution rate is in a direct relationship with the temperature of the mixture. This could be explained by the effect of temperature on the viscosity of the liquid phase. At higher test temperatures, the methane release process was completed in several minutes, while at lower temperature conditions, the process lasted for weeks. The profiles of methane release at four different temperature conditions were then analyzed to extract the first-order reaction rate kinetic parameters that could effectively capture the behavior of exsolution over a wide range of temperature and pressure conditions. Since the kinetic parameters were obtained for the lab scale quantities of bitumen and released methane, a simulation study was conducted to scale the parameters to a simulation grid block of a size 1 meter cube. The results indicate that for the numerical simulation of highly permeable reservoirs, the kinetic parameters obtained from the laboratory experiments can be used in the simulator without further modifications or scaling.

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