SAGD Pad Performance in an Ultra-Defined Athabasca Point Bar Deposit
- Jing Yi Jacky Wang (University of Calgary) | Ian Donald Gates (University of Calgary) | Yi Su (University of Calgary)
- Document ID
- Society of Petroleum Engineers
- SPE Heavy Oil Conference-Canada, 11-13 June, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2013, Society of Petroleum Engineers
- 5.1 Reservoir Characterisation, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.2.2 Fluid Modeling, Equations of State, 5.4.6 Thermal Methods, 4.1.2 Separation and Treating, 5.1.3 Sedimentology, 4.3.4 Scale, 5.3.9 Steam Assisted Gravity Drainage, 5.1.5 Geologic Modeling, 1.6.9 Coring, Fishing, 5.5 Reservoir Simulation, 1.2.3 Rock properties, 1.6 Drilling Operations, 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment, 5.1.1 Exploration, Development, Structural Geology
- McMurray, Well pad, cSOR, SAGD, Point Bar
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It has been shown that the performance of a Steam-Assisted Gravity Drainage (SAGD) well pair is affected by its orientation and position within a point bar. In typical commercial operations, multiple wellpairs, usually arranged parallel to each other, are arranged in pads within oil sands reservoirs. Thus, the overall performance of the recovery process in a point bar is not that of a single well pair but reflected by oil accumulation differences, interactions between well pairs (pressure and fluid flow), and how the well pairs interact with the structure and geometry of the point bar including the arrangement of inclined heterolithic strata relative to the SAGD well pairs. This research describes how the point bar structure impacts the performance of a pad of SAGD wellpairs and the impact of pad orientation on performance of the pad. The results show that the performance of well pairs in a SAGD pad are affected by the orientation of the pad within the point bar. Also, the results show that the variability of the performance of the well pairs within the pad is large and thus, single well pair models do not provide sufficient analysis of process performance due to the heterogeneity of the point bar. In other words, pad-scale models are required for recovery process evaluation and design.
This study focuses on the operation of a pad of Steam-Assisted Gravity Drainage (SAGD) well pairs in the Lower Cretaceous McMurray Formation in Alberta, one of the largest oil sands accumulations in the world. The basic depositional unit of the Middle McMurray Formation is the point bar which consists of inclined heterolithic strata (IHS) of sandwiched sand-shale/siltstone sequences and abandoned mud channels (Strobl et al., 1997; Fustic, 2007; Fustic et al., 2012; Hubbard et al., 2011; Labrecque et al., 2011; Musial et al., 2011, Su et al. 2013). Due to the presence of those shale/siltstone interbeds, many SAGD operations in the McMurray Formation suffer in performance due to extensive vertical barriers which prevent vertical steam rise and oil drainage. During SAGD operation (Fig. 2), steam injected into the oil sands formation through a horizontal well transfers its heat to oil sand (Gates et al., 2007; Peacock, 2009; Hubbard et al., 2011; Gates, 2011). As the process evolves, the steam chamber grows both vertically and laterally within the reservoir. As the result, the viscosity of the bitumen drops and the mobilized oil flows, under the action of gravity, to the production positioned below the injection well (Gates et al., 2007). In typical practice, the separation between injection and production wells is equal to ~5 m and the length of the injection/production wellpair is typically between 500 and 1,000 m (Gates et al., 2007; Peacock, 2009). SAGD is the ideal process for the ideal reservoir, however, it is widely known that oil sands are heterogeneous and that the recovery process is adversely impacted by this lithological heterogeneity (Yang and Butler, 1992; Chen et al., 2008; Gotawala and Gates, 2010).
It is not clear how to orient well pairs and pads of well pairs within point bar deposits. In many instances, operators have drilled their well pairs with either East-West or North-South orientation yet this direction for the well pairs may have nothing to do with the underlying point bar structure. Here, we have constructed an ultra-defined point bar reservoir model consisting of about 85 million cells conditioned to geological (fluid compositional, logs, core, and seismic) data from an oil sands formation. As part of a continuing study on the performance of single SAGD wellpair operation in point bar systems, we have evaluated the impact of the placement of a pad of 9 parallel SAGD well pairs within the point bar on overall pad performance.
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