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 saturatio n 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 degre es C during the early period, settling down to around 400 degrees C. The co mbusted zone extended over about 30% of the sandpack length. Oil recovery w as mainly affected by the large steam flood generated ahead of the combusti on front, due to in situ vapourization of the original water in place, redu cing the oil residual down to 21%. The thermal cracking reactions taking pl ace ahead of combustion front converted part of the residual oil to lighter components, which were displaced with the gas flow, at the same time produ cing about 10% coke (fuel) for the combustion process. Two tests were carri ed out on a light Australian oil (38.8 degrees API), starting at low initia l 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 ab out 250 degrees C in both tests. The axial temperature profile in the sandp ack was similar to that normally associated with a moving combustion front, but at a relatively low temperature. Also, there was no steam plateau cond ition, which was very observable in the Clair oil tests. High combustion fr ont 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 gener ally favourable as regards improved oil recovery.