Numerical Simulation of In-Situ Combustion Experiments Operated Under Low Temperature Conditions

Abstract

Abstract During in-situ combustion (ISC) processes, different chemical reactions occur depending on the temperature level. In heavy oils and bitumens, low temperature oxidation (LTO) reactions dominate below 300ºC, increasing the density and viscosity and producing coke which could prevent the success of ISC. Above 350ºC, combustion reactions dominate, known as high temperature oxidation (HTO), producing carbon oxides and water. Numerical models tend to include only thermal cracking and HTO reactions, as LTO reactions are not well understood. In the present work, ISC experiments operated under LTO were simulated, using Saturates, Aromatics, Resins and Asphaltenes (SARA) fractions to characterize the Athabasca bitumen. Concentration profiles and coke deposition for individual temperatures were matched for isothermal experiments from 60ºC to 150ºC. Based on these results, ramped temperature oxidation (RTO) experiments were then modelled, incorporating the heat of reaction at LTO. Different reaction models were studied to match temperature profiles along the reactor, oxygen consumption, coke formation and fluids production. This research will greatly increase the understanding of LTO reactions occurring in Athabasca bitumen during ISC and contribute to the creation of a reliable numerical model that predicts ISC performance under ideal (HTO) and, importantly, non-ideal (LTO) temperature conditions. Introduction ISC is a promising but complex oil recovery process in which thermal energy is generated inside the reservoir owing to combustion reactions between the heaviest fractions of the oil and an injected oxygen containing gas. For heavy oils and bitumens, ignition temperatures above 350°C are required to promote the combustion reactions (HTO). At lower temperatures, other types of reactions predominate, involving the addition of oxygen to the bitumen, producing heavier oxidized compounds. The LTO reactions are detrimental to oil production; hence, ISC processes are designed to operate under the high temperature combustion regime (HTO). However, LTO reactions occur if the air flux becomes too low to sustain the combustion reactions, leading to lower-than-estimated production yields. It has been proven in laboratory experiments that oil recovery is considerably reduced when LTO reactions occur to some extent, compromising the success of the ISC.