A Basis for Automated Control of Steam Trap Subcool in SAGD

Abstract

Summary Full steam conformance along the well pair of the steam-assisted gravity-drainage (SAGD) oil-sands-recovery process is essential for high thermal efficiency. Conformance can be improved by controlling injection and production strategies to ensure that steam is delivered to target regions in the reservoir. Smart wells use interval-control valves (ICVs) that, conceptually, can be dynamically controlled to yield uniform steam injectivity along the well pair. Dynamic control algorithms, such as proportional-integral-derivative (PID) control and their associated controller parameters, have not yet been developed for the SAGD processes that use ICVs. One control strategy would be to control the interwell subcool temperature difference—that is, the difference between the steam-injection temperature and the produced-fluids temperature. If this temperature difference is small, then the liquid pool above the production well is small and there is a likelihood of live steam production from the chamber. On the other hand, if the difference is large, the pool may rise above the injection well and gravity drainage is hindered because the chamber is largely filled with liquid. Here, the focus is on developing a simple, approximate theory for the behavior of the liquid pool at the base of the steam chamber to determine the ranges of values of control parameters to achieve a targeted interwell subcool temperature difference.