An innovative air assisted cyclic steam stimulation technique for enhanced heavy oil recovery

Air assisted cyclic steam stimulation (AACSS) is an innovative technique for enhanced heavy oil recovery, in which air is injected along with steam injection during a conventional CSS process. It can be applied for heavy or ultra heavy oil reservoirs in the late stage of CSS process to increase the performance of steam injection and mitigate the problems of low reservoir pressure, poor steam sweep efficiency and high water cut. In this study, the application of the AACSS technique in a typical ultra heavy oil reservoir of Liaohe oilfield (China) was described and its field performances were analyzed along with a numerical reservoir simulation study to reveal its mechanism. The field data shows that the AACSS can significantly increase oil production, reduce water cut and prolong the effective production period. A reaction model for the oxidation of heavy oil components with oxygen in the temperature range of 50-300 °C was established, based on the experimental results of thermogravimetric analysis (TGA), to simulate the conversion of air into flue gas and its thermal effect. The performance of AACSS was investigated and the contribution of thermal effect induced by LTO reactions was analyzed through numerical simulation. The simulation results indicate that air injection can improve oil recovery on the basis of CSS, in which over 11% of the incremental oil production can be attributed to the thermal effect, and the rest is accounted for a complex effect of flue gas driving.