Economic Optimum Operating Pressure for SAGD Projects in Alberta
Authors: Neil Edmunds - Clearwater Engineering, Harbir Chhina – EnCana Corporation
Source: JCPT Distinguished author series, Journal of Canadian Petroleum technology - December 2001, Volume 40, No. 12
During the recent Surmont gas-over-bitumen Alberta Energy and Utilities Board (EUB) hearing, a number of technical issues regarding the optimum operating pressure for steam assisted gravity drainage (SAGD) schemes were raised. From the evidence presented, the EUB concluded that there was a detrimental effect on SAGD recovery with decreasing gas pool pressure. The objective of this paper is to present technical and practical evidence of what is the most economical optimum operating pressure for a SAGD project in northeast Alberta. We believe that the effect of operating pressure on SAGD recovery has been misunderstood, and that economics will in fact drive SAGD producers to develop low pressure recovery technology over time, regardless of the presence or status of contiguous gas caps. We first present historical evidence that the high recoveries associated with SAGD will remain so at very low pressures. Secondly, analytical predictions of oil rate and steam-oil ratio (SOR) vs. pressure are considered. Finally, the effects of pressure on full-cycle scheme design and economics are calculated, based on simulation studies typical of oil sands reservoirs in northeast Alberta. The results support an economic optimum SAGD pressure in the range of 300 – 900 kPa.