A comparison of three thermal EOR processes; SAGD (Steam Assisted Gravity Drainage), HASD (Heated Annulus Steam Drive) and CYS (Cyclic Steam Stimulation), has been made using a three dimensional thermal simulator by employing a combination of vertical and horizontal wells. Reservoir characteristics and thermal and fluid properties were maintained identical for process comparison. A 10-year project-time study was undertaken for CYS with vertical wells, CYS with horizontal wells, HASD with horizontal HAS pipe and aligned vertical injector and producer, HASD with offset vertical producers, and SAGD with horizontal injector and producer. The effect of reservoir heterogeneities on process performance was also examined. CYS vertical performed significantly better than CYS horizontal both in terms of cumulative % OOIP recovery and SOR. HASD recovered more oil, though the initial production rate in HASD was low. SOR in HASD was, however, very unfavorable (more than twice that of CYS vertical). HASD with offset wells made both SOR and % OOIP recovery more favorable. SAGD had better SOR than HASD; however, it recovered about half the oil recovered by HASD at the end of ten years. An unfavorable heterogeneity feature (low permeability layers or barriers) affected the recoveries and SORs for the horizontal well processes more adversely than vertical well processes.

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