Steam alternating non-condensable gas injection for more heavy oil recovery

Abstract

Recent studies and field operations show that co-injection of steam and non-condensable gas could reduce the steam-oil ratio significantly, which means the steam and gas push process (SAGP) could be more environmentally friendly than the conventional steam-assisted gravity drainage (SAGD) process. However, this modification may eventually cause a drop in the cumulative volume of produced oil. In this paper, we develop a technique to overcome the adverse impact of SAGP on the final oil recovery: this technique employs alternate steam and a mixture of steam and non-condensable gas injection into the viscous oil reservoir to take advantage of a high steam chamber volume, pushing pressure at the reservoir top and lower heat loss to overburden rocks, simultaneously. The technique (so-called SANG) is examined numerically in a reservoir with average properties from Athabasca, and the results are compared to the conventional SAGD and SAGP. Effects of changing reservoir properties and operating conditions on the performance of the SANG together with a cost-benefit analysis and CO2 emissions are elucidated. Based on the results, the SANG would effectively improve the performance of the thermal gravity process within viscous oil reservoirs and, provided it is validated, it can replace the conventional SAGD and SAGP.