Review of Reservoir Parameters to Optimize SAGD and Fast-SAGD Operating Conditions

Abstract

Abstract Although high recovery efficiency is expected from the SAGD process, high steam production costs and the substantial volumes of water required have made us focus on more effective recovery methods. One such method is the Fast-SAGD process which utilizes one or more offset horizontal wells parallel to the original SAGD well pair. In these studies, simulations were used to examine the reservoir parameters and operating conditions that need to be in place to optimize the SAGD process. Based on the simulation of a typical Cold Lake reservoir in Alberta, the studies found that relatively clean sand reservoirs with a minimum thickness of 20 m and a vertical permeability of 2.5 Darcy are good candidates for the application of SAGD. Also, reservoirs in a fining upward depositional environment are ideally suited for a SAGD operation. The results of our studies also showed that, for the same operating conditions, Fast-SAGD improved energy efficiency by 24% and productivity by 35% over SAGD. Fast-SAGD is therefore a more efficient recovery process requiring less steam and having lower operating costs to produce the same amount of bitumen. The case of two offset wells located on either side of one SAGD well pair promises the most effective Fast-SAGD configuration, even if a total of six offset wells with a SAGD well pair is still economic compared to the conventional SAGD process. Cumulative bitumen production is increased and at the same time the cumulative steam-oil ratio is decreased as a result of higher thermal efficiency. Introduction Alberta's oil sands contain the largest crude bitumen resource in the world, having approximately 259 billion cubic metres of initial oil in-place and 27.7 billion cubic metres of remaining established reserves (see Tables 1a and 1b)(1). Over 80% of these reserves can be produced only by using in situ recovery methods; therefore, research to find more effective in situ recovery methods is encouraged. The SAGD process has been tested in the field, and is now in a commercial stage of production in Western Canadian oil sands(2). The application of SAGD in various reservoir conditions has been studied, and recently research studies that can not only reduce the steam production cost but also enhance heat efficiency of the SAGD process have been conducted(3). In our studies, the characteristics of the SAGD recovery method were reviewed. In addition, the proper reservoir conditions and optimized operating conditions for the SAGD process were researched by conducting numerical simulation. The possibility of applying the Fast-SAGD process, a modification of the SAGD process(4), was also investigated in comparison to conventional SAGD. Finally, the operating conditions for the optimization of the Fast-SAGD process were studied. Variations of SAGD Process Enhancements The conventional SAGD process is a steam injection recovery method which uses two horizontal wells. In the Peace River area, a small pressure differential between adjacent pattern steam chambers was applied to enhance the SAGD process(5). A steam drive process can be applied to the SAGD operation once sufficient bitumen mobility has been obtained between steam chambers.