Feasibility of in-situ combustion of tar from a tarmat reservoir

Combustion-tube tests were conducted on a tar of physical and chemical characteristics similar to a natural reservoir tar. Ottawa sand of 20-30 mesh size was used to prepare tar-sand mixtures of about 37% porosity, 19 to 25% water saturation and 21 to 32% tar saturation. In runs with distilled water, a combustion front was successfully initiated and moved into the sand pack. Later, however, the front's temperature dropped below 500°C causing the front to stagnate and become extinguished a short distance away from the tube's inlet. When ferric nitrate was added to the water, sustained combustion was achieved with front temperatures maintained above 500°C and high oxygen utilization. It appears that a minimum iron concentration in the water of about 2700 ppm is required for stable combustion. Concentrations above 4200 ppm did not enhance combustion performance.