Numerical study of air assisted cyclic steam stimulation process for heavy oil reservoirs: Recovery performance and energy efficiency analysis

- AACSS is evaluated as a primary recovery technique for heavy oil reservoirs.
- The recovery performance and energy efficiency of AACSS are investigated.
- The effects of oil viscosity, LTO reaction and air to steam ratio are studied.

Cyclic steam stimulation (CSS) has been widely applied as an effective technique for heavy oil reservoirs, but it is increasingly concerned in recent years for its limited oil recovery performance, low energy efficiency, high water consumption and great environmental footprints due to greenhouse gas emissions. The hybrid injection of air and steam in terms of low temperature oxidation (LTO) is an innovative technique for the development of heavy oil reservoirs, which can be operated based on the conventional well configuration and was firstly proposed as an enhanced oil recovery (EOR) process for mature heavy oil reservoirs encountered with low reservoir pressure, poor steam sweep efficiency and high water cut. In this study, numerical simulation study is conducted to evaluate the potentials of air assisted cyclic steam stimulation (AACSS) process as an alternative to CSS technique for heavy oil reservoirs. Effects of oil viscosity, LTO reaction and operated air to steam ratio on the well performance are examined for typical heavy oils. The results indicate that AACSS process can effectively improve oil recovery, enhance the energy efficiency and reduce CO2 emissions in comparison with CSS alone, which can be attributed to the thermal effect due to oil oxidation, reservoir repressurization and gas driving offered by air injection, and the AACSS process can be more economically and environmentally attractive than CSS alone. The production performance of AACSS process for ultra heavy oil reservoirs can be more pronounced in comparison with that of ordinary heavy oils, and the LTO characteristics of different oils and the feasible air to steam ratio are reservoir specific for field operation.