Facies analysis and reservoir geometry of the Crystal Viking Field, Tp. 45 and 46, Rg. 3 and 4W5, Central Alberta
Authors: Reinson G E 
Published: November 2010

The Viking Formation in the Crystal field contains a linear sandstoneconglomerate deposit which attains thicknesses of 30 m and is aligned in a north-south direction. The thickness and alignment trends of this reservoir 'sand' body contrast sharply with other
established Viking sandstone reservoirs, which are generally much thinner and oriented more in a northwest-southeast direction. Another contrasting feature of Crystal compared to other Viking oil fields, is that the producing reservoir consists of two distinct, hydrodynamically-separated oil pools
('A' and 'H' pool). The Crystal Viking 'A' pool contains ninety-six percent of the estimated recoverable reserves of 5.8 x 10 6 m 3
, with the 'H' pool being situated higher stratigraphically, and partially overlapping the main producing zone on the western side. Two major facies constitute the Viking Formation at Crystal, channel and estuary-bay fill. The combined association of the two facies represents an estuarine tidal
channel-bay complex. Detailed log and core correlations indicate that: 1) the estuarine channel-bay complex is unconformable with underlying and adjacent innner shelf-lower shoreface deposits of the regional Viking facies and; 2) the linear reservoir sand body consists of four depositional units;
the lower three units are representative of successsive and partially-superimposed channel-fill stages (A, B, C), and the uppermost unit (H) is a shallow channel-bar deposit representative of the final episode
of estuary bay-fill deposition. The multistage channel depositional events are interpreted to be the record of progressive estuarine valley fill under conditions of rising sea level, with each channel depositional stage corresponding to a stillstand during an overall transgressive period. Each
channel stage modified the estuary on the eastern side while subtidal estuary-fill muddy deposits accumulated as facies equivalents to the channel-fill deposits, on the western side. The superimposed channel-fill deposits (A, 8, C), constitute the bulk of the reservoir and form the Crystal Viking
'A' pool, whereas the shallow channel-bar deposits (H) constitute the much smaller producing zone of the Crystal Viking 'H' pool. The occurrence of two separate pools, and the variability in reservoir capacity, continuity and performance trends of the 'A' pool, are controlled directly by
depositional factors. The depositional model of progressive estuarine valley fill under transgressive conditions readily explains the presence of the 'H' pool as a discrete reservoir separated from the main oil-bearing 'A' zone pool. The highly productive wells of the 'A' pool correspond to specific
channel stage deposits, or are situated in the areas where channel deposits of successive stages are highly superimposed. In contrast, marginally productive wells and poor reservoir communication between producing wells, occur in the are as where the diff erent channel-stage deposits are shown to
diverge. Given the observed relationship between depositional trends and overall reservoir behavior, it is apparent that facies distribution and channel-stage geometries must be considered during both the planning and evaluation phases of any secondary recovery scheme.