Improving the Performance of SAGD

Abstract

Abstract In the recent years several SAGD projects have been initiated for therecovery of heavy oil and bitumen. Every operator is coming across new learningalmost every day, although most of this information is proprietary. This paperpresents a general discussion, supported by simulation and analytical results, on the different aspects of improving the performance of SAGD operations. Thefirst component is the well bore design, which has to match with the gravitydrainage rate. Operating pressure plays a significant role in the rate ofrecovery. Lower operating pressure reduces the SOR, lower H2S production, mayreduce the silica dissolution, thereby, reduce the water treatmentissues. However, low pressure operation increases the challenges oflifting the fluid to the surface. Steam additives may be the other option toincrease the energy efficiency of the process. Introduction The enormous potential of the Athabasca oil sand dwarfs the resources ofmany oil producing nations throughout the world. The growth plan for thedevelopment of these resources runs into hundreds of billions of dollars ininvestment. Figure 1 presents the forecast for the growth of the westernCanadian oil sand production in relation to production from other resources. More than 50% of the oil sand production is planned to be extracted by in siturecovery processes. A list of the announced projects for the near futuredevelopment is presented1 in Table 1. Except for a few projects that involvesextraction of the near surface resources through mining, about 2.6 million bpdout of the total 3.5 million bpd is planned to be recovered through SAGD (SteamAssisted Gravity Drainage) process. SAGD in Athabsca reservoir is different from application of this process inheavy oil reservoirs or equivalent API reservoirs in a different geologicalsetting. Most part of the Athabasca reservoir is thicker than 15 m (close toSAGD economic cut off), shallow (suitable for steam injection) and fairlyhomogeneous without significant barrier for the growth of the steam chamber. The bitumen is virtually immobile at the reservoir condition with very littleinitial gas saturation. Compared to these, the Venezuelan resources withequivalent API are present in a deeper formation at higher temperatures andhave higher initial GOR and significantly lower in situ viscosity. This is verysimilar to the conditions of a conventional heavy oil reservoir. Therefore, SAGD may not appear as effective compared to other recovery processes. However, for the Athabasca resources at the current state of recovery technologies, SAGDremains the primary recovery mechanism and is the most effective solution.