Combustion assisted gravity drainage - Experimental and simulation results of a promising in-situ combustion technology to recover extra-heavy oil

Combustion Assisted Gravity Drainage (CAGD) is a novel in-situ combustion process that utilizes a horizontal injector at the top of the reservoir with a horizontal producer located parallel to and near the bottom of the reservoir. Air is injected, and combustion is initiated with the aid of an electric heater. The heated oil begins to flow downward to the underlying horizontal producer by gravity drainage. The combustion front then develops towards the heel-end of the injector and extends laterally. Direct oil production and short distance traveled by the injected air lead to preserving thermal upgrading and efficient oxygen consumption. This paper presents experimental and numerical simulation studies of the CAGD process. In-situ combustion experiments have been carried out using a rectangular 3D combustion cell with dimensions of 0.62 m, 0.41 m, and 0.15 m. The sand mix consists of 8.2 degrees API Athabasca bitumen, water, and 100 mesh sand and is packed into the cell. Combustion was initiated with air injection, however, to sustain combustion enriched air (50 mol% Oxygen, 50 mol% Nitrogen) was later injected. Experimental and simulation results show that oil displacement occurs mainly by gravity drainage. Vigorous combustion was observed at the early stages near the heel of the injection well, where a peak temperature of 560 degrees C was recorded. Final bitumen recovery was 72% of OOIP, with produced bitumen being upgraded by more than 2 API. In addition, a thermal simulator (CMG STARS (TM)) was used to history match the laboratory data and to capture the main combustion characteristics and drive mechanisms. Simulation results are in good agreement with experimental data in terms of fluid production rate and recovery, combustion temperature profile and produced the gas composition.