Summary
Practical methods of operating dual-/triple-tubing strings, on the basis of temperature monitoring that is currently available, to achieve uniform steam-chamber development and enhanced production in a steam-assisted-gravity-drainage (SAGD) process, are presented. The work is motivated by the fact that numerous operators use dual-tubing strings for designing and optimizing steam-chamber development. Flow in the region of the SAGD horizontal well pair is often irregular, and dual-tubing strings may help to even out and improve both injection and production. Problems that operators have with multiple tubing strings in wells include their control and design. In this work, the injector and the producer will have two tubing strings each: one landed at the toe and the other at the heel. Control points are applied on each injection tubular. Injection at these control points is regulated by a proportional- integral-derivative (PID) feedback controller monitoring temperature differences between injected and produced fluids. A brief examination and discussion of the performance of control points in the production tubulars are also included. The PID controller will attempt to accomplish two goals: (i) to achieve evenness in injection and production conformance along both wells and (ii) to enforce a specified temperature offset between the injector and producer in order to improve oil production and reduce steam production and injection. Sensitivity of the feedback controller will be examined for (a) heterogeneity where several synthetic permeability patterns will be tested to gauge the effectiveness of coping with reservoir complexity, (b) update frequency where a comparison will be made between instantaneous and periodic updating of the controller error terms, and (c) ability of the controller to cope with early temperature rises in produced fluids. Well monitoring is accomplished through the use of high-temperature fibre-optic temperature sensing that is currently available. Results and further discussion are offered on whether an additional tubular landed at the midpoint of both wells will benefit production from a heterogeneous reservoir.
