R. Coates

SAGD Wind-Down: Lab Test and Simulation

As SAGD moves from pilot test to commercial operation, a number of issues need to be dealt with. These include diagnosing and solving operational problems and improving energy efficiency. One of the methods of improving energy efficiency is to prolong oil production after steam injection stops by using the energy remaining in place. The results of a laboratory experiment and corresponding numerical history matching are reported in this paper. The study showed that the hot chamber continued its expansion after steam injection was stopped and a gas injection was initiated. The continuous expanding period represented the most productive period in the gas injection wind-down process. A total of 12.5% of OOIP was recovered during wind-down. Successful history matching of both the oil production curve and temperature profiles at different times demonstrated that the numerical simulation could handle the gas/steam mixing phenomena. Gas concentration profiles from numerical simulation indicated that gas was concentrated at the region where oil saturation was experiencing big changes.

Numerical Study and Economic Evaluation of SAGD Wind-Down Methods

At a certain point in a SAGD operation, it is no longer economic to continue steam injection when the steam-oil ratio (SOR) becomes too high. A less energy intensive gas injection process following the SAGD process can prolong oil production by using the energy in place. Numerical studies of the injection of non-condensable gas, and a mixture of steam and non-condensable gas following a SAGD operation, were conducted using the CMGs STARS reservoir simulator. The simulation results suggest that, after three to five years of SAGD operation, when three quarters of the targeted reservoir is hot, it is appropriate to start a wind-down process. Injecting non-condensable gas results in a much lower production cost compared to continued steam injection; however, the oil production is reduced. Co-injection of steam with gas produces more oil than the gas-only injection process without substantially increasing the production cost. This is probably the desired wind-down process. Optimization is needed for the co-injection process. The choice of non-condensable gas depends on the cost and availability.