Enhancing Steam-Assisted Gravity Drainage Applications in Challenging and Non-Challenging Oil Sands Reservoirs

Date
2018-08-13
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Abstract
Unlike the relatively clean or non-challenging ones, difficult-to-produce oil sands reservoirs with respect to Steam-Assisted Gravity Drainage (SAGD) are so named because of adverse geological features present in them, e.g. lean zones, inclined heterolithic strata (IHS), breccia/mud clasts. The presence of one or more of these features creates a challenge for SAGD since they harm the growth of the steam chamber leading to poor thermal efficiency, increased water use and high greenhouse gas (GHG) emissions. In the research documented here, five research questions are posed: (1) How well do we understand heat and fluid flow dynamics of steam propagation in bitumen reservoirs? (2) What occurs in the reservoir when steam interacts with co-injected non-condensable gas (NCG)? Is there an optimum time to start NCG co-injection? (3) How does an overlying top water reservoir with a thick IHS layer affect SAGD performance? How can the operation be altered to raise SAGD performance in this system? (4) What can be done to improve SAGD performance in heterogeneous oil sands reservoirs? (5) Can automated control, using seismic data, improve SAGD performance both with respect to steam conformance and steam-to-oil ratio (SOR)? To answer these questions, thermal reservoir simulation was used to model SAGD in oil sands reservoirs. The results reveal that: 1) Heat transfer is enhanced by warm mobilized bitumen fingering into cold bitumen as SAGD evolves. 2) The benefit of NCG co-injection is best seen in the mid or late life of SAGD. 3) In a reservoir with an IHS interval and overlying top water zone, the IHS, though a resistance to steam chamber growth, slows top water drainage into the basal sand and may benefit SAGD and depending on the injection pressure applied, the impact of top water can be delayed. 4) Steam can be optimally allocated in a strongly heterogeneous reservoir by varying steam injection rate by using a new allocation algorithm based on seismic interpretation which automates steam injection in SAGD fitted with outflow control devices (OCDs). By using the new algorithm, the rate-controlled case (i.e. OCDs with control) yields an increase of cumulative oil of 10.7% and 6.16% and decrease of cumulative SOR of 11.7% and 6.5% when compared to the base and OICDs without control cases, respectively, after 6 years of operation. This translates to a significant reduction of water usage and GHG emissions.
Description
Keywords
SAGD, Oil Sands, Thermal fingering, Seismic-based control, Top water, Heat Transfer, Fluid dynamics
Citation
Austin-Adigio, M. E. (2018). Enhancing Steam-Assisted Gravity Drainage Applications in Challenging and Non-Challenging Oil Sands Reservoirs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/32814