Disposal of Carbon Dioxide, a Greenhouse Gas, for Pressure Maintenance in a Steam-Based Thermal Process for Recovery of Heavy Oil and Bitumen

The world is moving towards a carbon constrained economy and there would be pressure to reduce greenhouse gas (GHG) emissions. The steam-based thermal processes are energy intensive and hence, high carbon dioxide (CO₂), a greenhouse gas (GHG), emissions. There are potentials for the reduction of CO₂ emissions by capturing and disposal of CO₂ for pressure maintenance during the later stage of these thermal operations. This paper describes the numerical investigation on the feasibility of using CO₂ for pressure maintenance during a steam-assisted gravity drainage (SAGD) wind-down process in an Athabasca bitumen reservoir in Northern Alberta, Canada.

It is found that SAGD wind-down process with CO₂ injection is feasible although oil recovery performance is slightly sacrificed. The oil recovery performance during the wind-down period with pure CO₂ injection is slightly better than those with other gas injections such as flue gas (i.e., a mixture of nitrogen (N₂) and CO₂) and pure N₂ mainly because CO₂ acts as a solvent in reduction of the bitumen viscosity.

From a GHG storage point of view, CO₂ storage capacity of approximately 2 × 10⁷ sm³ (or 37,244 tonne) in a single Athabasca-type SAGD pattern with dimensions of 100 m wide, 500 m long and 25 m thick can be achieved. CO₂ balance indicates that CO₂ stored during SAGD wind-down processes is less than the CO₂ emitted from steam generation during the initial SAGD period. However, "CO₂ credit" in the order of 10,000 tonne can still be claimed in a single SAGD pattern because using CO₂ as steam substitute during the wind-down process results in less CO₂ emission compared to continuously operating the SAGD process.

Recently, numerical prediction in this study has been validated qualitatively by the experimental observations of SAGD pressure maintenance from a low-pressure/low-temperature CT experiment and a high-pressure/high-temperature 2-D experiment conducted at the Alberta Research Council (ARC).