Recently several articles have been published regarding the innovation and field applications of the Steam-Assisted-Gravity-Drainage (SAGD) process using a single horizontal well for the recovery of heavy oil. In the process, an insulated concentric coiled tubing, inserted into the horizontal wellbore, injects high quality steam to the toe of the well. The steam condensate and reservoir fluids enter the wellbore and flow back along the annulus to the heel to be produced.

There remain some arguments on whether the SAGD mechanism is working in field operations, and on what oil rates can be achieved in the long run. In an attempt to answer these questions, numerical simulation studies were pursued in the present work. The studies focused on three major aspects: (1) the possible counter-current fluid exchange pattern between the reservoir and the well; (2) the means that could be exploited to promote the initiation of a steam chamber; and (3) the potential oil rates that could be expected under possible field operating conditions. The results showed that the presence of small capillary pressure near a horizontal wellbore is a physical constraint preventing counter-current exchange of steam and oil. It was also demonstrated that vertical undulation in well-profile or a certain level of formation dilation around the wellbore could potentially overcome the capillary pressure constraint and promote the initiation of a steam chamber under field operating conditions.

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