Abstract: Steam Assisted Gravity Draining(SAGD ) has been proved to be an effective way for extra heavy oil, supper heavy oil re-covery. Aiming at the commonly used two well configurations namely double horizontal wells and the combination of vertical and horizontal wells, this paper gained the maps of temperature field , pressure field , and residual oil saturation field of the
steam chamber section at the initial stage, the fastigium stage and the evening stage. These maps intuitively and visually char-acterized the forming and expanding process of the steam cham-ber and the shape and the drainage mechanism at the different drainage moments. Further more, this paper also made a com-parison between the two well configurations and these provided a theoretic foundation for the expansion of SAGD.

Key words: heavy oil reservoir, mechanism, Steam Assisted, Gravity Draining (SAGD), well pattern, numerical simulation