THAI-CAPRI Process: Tracing Downhole Upgrading of Heavy Oil

Abstract Worldwide conventional oil production is expected to peak in the present decade, and the need to reevaluate the potential of heavy oil resources becomes ever more imperative. Steamflooding is reliable, but it is not very energy efficient. It also has large water requirements and does not significantly upgrade oil. In situ combustion (ISC), properly configured and operated holds considerable promise for both mobilizing and upgrading heavy crude oils with less energy expenditure. The THAI-CAPRI process appears to eliminate many of the pitfalls of conventional ISC and yield substantially upgraded oil. Although extensive documentation on the performance of the process is available, only basic upgrading data have been reported. The present study aims to quantify the extent and nature of oil upgrading during an experimental run that incorporates dry and wet phases over each toe-heel air injection (THAI) and THAI with catalyst (CAPRI) modes. Gas, oil, water and solid residue analyses are used to infer mechanisms of upgrading and to begin to gauge the economic (sweep and recovery) and environmental (gas emissions and produced water quality) impact associated with the eventual field operation of the process. Introduction Easily accessible conventional oil reserves need to be supplemented by other hydrocarbon sources during the transition from the fossil to a hydrogen fuel economy, e.g. Haaland et al. (1). In the near term, heavy oil (< 20oAPI) exploitation can compete with conventional oil if new approaches are applied to facilitate its recovery and moderate its quality detractors and environmental impact. Steamflooding is by far the most commonly applied enhanced oil recovery (EOR) method. This approach, however, is energy intensive with up to 50% BTU equivalent of oil recovered required to generate steam (2). Steamflooding imparts only minor improvements in oil quality and has a significant environmental impact (greenhouse gas emissions and water contamination). Other EOR approaches include in situ combustion (fireflooding), gas injection / solvent extraction and microbial treatment. Of these, in situ combustion (ISC) has the greatest potential for both increasing recovering rates and improving the quality of oil. Although ISC has been applied for decades, difficulties in process control, reservoir unsuitability, operational practices and oil combustion characteristics have led to its near extinction as an EOR method (Sarathi, 1998) (3). In the last decade, conceptual, bench, pilot and commercial scale approaches to improve the ISC recovery method have been promoted: Operating strategies for spot pattern and line drive (4, 5). Employment of various well configurations (6–11). "Pressure cycling" (12 – 15). "Combustion override split - horizontal well" or COSH (16). "Toe-to-Heel Air Injection" (THAI) and catalyst additive (CAPRI) (17–20). Downhole or near wellbore approaches to ISC are summarized by Weissman et al. (21). Low API gravity, high viscosity, high sulfur and metals content and high acidity will substantially reduce the price realized for oil produced by any EOR method. In some regions, the refining capacity for heavy oils is limited. Large heavy oil operations, therefore, have moved upgrading capability to the site of heavy production (e.g., northern Alberta).