Air injection into light and medium heavy oil reservoirs: Combustion tube studies on West of Shetlands Clair oil and light Australian oil

Four combustion tube tests were performed at a high initial water saturation using Bath University's High Pressure Combustion Tube Facility. Two tests were conducted on Clair medium heavy oil (19.8 degrees API) at 75 and 100 bar pressure, with initial oil saturations of 48% and 60%, at 80 degrees C initial bed temperature. Maximum combustion temperatures exceeded 600 degrees C during the early period, settling down to around 400 degrees C. The combusted zone extended over about 30% of the sandpack length. Oil recovery was mainly affected by the large steam flood generated ahead of the combustion front, due to in situ vapourization of the original water in place, reducing the oil residual down to 21%. The thermal cracking reactions taking place ahead of combustion front converted part of the residual oil to lighter components, which were displaced with the gas flow, at the same time producing about 10% coke (fuel) for the combustion process. Two tests were carried out on a light Australian oil (38.8 degrees API), starting at low initial oil residuals of S-o = 41 and 45%, at an operating pressure of 70 bar and initial bed temperature of 63 degrees C. The combustion temperature was about 250 degrees C in both tests. The axial temperature profile in the sandpack was similar to that normally associated with a moving combustion front, but at a relatively low temperature. Also, there was no steam plateau condition, which was very observable in the Clair oil tests. High combustion front velocities were achieved in all four tests, varying from 0.15 to 0.31 m h(-1). Fuel consumption, air requirement and oxygen utilization were generally favourable as regards improved oil recovery.