Improved recovery of light oil by air injection

In recent years, high pressure air injection (HPAI) into a light oil reservoir has been proven as one of valuable EOR technologies. HPAI is applied for light oil reservoirs where reduction of viscosity by thermal effect is not so important, because the original viscosity of light oil is not as high as heavy oil. As one of the most important recovery mechanisms of HPAI is immiscible flue gas flooding, HPAI process has sometimes been comparable to flue gas or nitrogen injection in general. But this is true only when the oil saturation of the reservoir is high enough and if the reservoir is waterflooded, distillation process by its thermal effect at combustion front is a critical factor for improved oil recovery. This paper discusses the applicability of HPAI for highly water saturated light oil reservoirs, by combustion tube tests (CT tests) and numerical simulation studies. One CT test was conducted with waterflooded core. Additional oil recovery was confirmed in this test, which implies the successful oil recovery from highly water saturated light oil reservoirs. To investigate oil recovery mechanism, a series of simulation studies of CT test was conducted. Through these studies it was clarified that the important oil recovery mechanism for high water saturation reservoir is the distillation process. By this mechanism oil bank was created at the combustion front and significant oil production was observed after some amount of water production in both CT test and its simulation.