New algorithms for steam assisted gravity drainage using combinations of vertical and horizontal wells

New algorithms have been presented for steam assisted gravity drainage (SAGD) in oil sand reservoirs using vertical injectors-producers and vertical injectors-horizontal producers. Although SAGD with a pair of horizontal wells has been reported to be promising, it may be necessary to use a combination of vertical and horizontal wells for the optimum utilization of a given reservoir. SAGD with a single vertical injector-producer would utilize a dual-completed well. This vertical well algorithm was extended to account for steam chamber confinement due to adjacent vertical wells. The production rates in the vertical well processes were found to be significantly lower than in the horizontal well processes due to the near-well congestion phenomenon. This observation was consistent with the results of physical model studies conducted by other investigators. In the second part of the paper, a new model for the SAGD process using vertical injectors and horizontal producers has been developed and the results have been compared to the results of SAGD with a horizontal well pair. The oil production from the vertical-horizontal combination approches about 40% of the production from the horizontal well pair. The oil-steam ratios of the vertical-horizontal combination and the horizontal well pair are comparable. Thus SAGD with a combination of vertical and horizontal wells has been demonstrated to be a viable scheme for the development of oil sand reservoirs.