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  • AUTHORS

    Stacy C. Atchley � Baylor University, Depart- ment of Geology, One Bear Place #97354, Waco, Texas 76798-7354; stacy_atchley@baylor.edu

    Stacy Atchley received his B.S. and M.S. degrees from Baylor University in 1984 and 1986, and Ph.D. from the University of Nebraska, Lincoln, in 1990. After working for ExxonMobil from 1986 to 1995, he rejoined Baylor where he directs the applied petroleum studies program and is a researcher within the paleoclimate research group.

    Nathaniel H. Ball � Baylor University, Department of Geology, One Bear Place #97354, Waco, Texas 76798- 7354; present address: Nexen Petroleum USA Inc., 5601 Granite Parkway, Suite 1400, Plano, Texas 75024-6654

    E&P NOTE

    Reservoir characterization and facies prediction within the Late Cretaceous Doe Creek Member, Valhalla field, west-central Alberta, Canada Stacy C. Atchley, Nathaniel H. Ball, and Luke E. Hunt

    Nathaniel Ball received both his B.S. (2006) and M.S. (2009) degrees in geology from Baylor University. He recently began his career as a geologist with Nexen Petroleum U.S.A. Inc. and is currently working in the Gulf of Mexico.

    Luke E. Hunt � Baylor University, Department of Geology, One Bear Place #97354, Waco, Texas 76798-7354; present address: Husky Energy, 707 8th Ave. SW, Box 6525, Station D, Calgary, Alberta, Canada T20 3G7

    Luke Hunt received his honors B.S. degree in geo- sciences from McMaster University in 2007 and his M.S. degree from Baylor University in 2009. He currently works for Husky Energy as a member of the geological services exploration team.

    ACKNOWLEDGEMENTS

    Results documented in this manuscript were com- pleted in association with the Applied Petroleum Studies program of Baylor University. Financial support was provided by Husky Energy as admin- istered by Jim Beckie, Craig Lamb, and Dave Stuart. Special thanks are extended to Ben Grossberndt, Laurie Wilcox, and the other helpful staff members (particularly the core handlers) at the Alberta Energy Resources Conservation Board Core Research Center, Calgary. Computational and analytical assistance was provided by Kris Friedel, Todd Gustafsson, Dorian Holgate, John McCrossan, Anne Young, and Joanna Zhou of Husky Energy. Subsurface correlation, mapping, and data analysis were facilitated by software donations to Baylor University by Halliburton GeoGraphix®, IHS Energy AccuMap®, and ACD Sys-

    ABSTRACT

    Oil resources atValhalla field of west-central Alberta, Canada, are stratigraphically trapped within the Upper Cretaceous DoeCreekMember of the Kaskapau Formation. The reservoir is subdivided into four thin (1–10 m [3–33 ft]), cyclic alter- nations of offshore mudrock and shoreface sandstone that are designated the I − 1, I, I + 1, and I + 2 units. The thickest andmost widespread I sandstone is the primary reservoir. Op- timum reservoir quality corresponds to coarser grain shoreface sandstone; however, reservoir quality may be diminished by postdepositional calcite cement commonly observed near the top of shoreface sandstones. Open-hole well logs are used to predict depositional facies and calcite cement occurrence in wells that lack core control. Decreasing shale volume (Vsh) and increasing deep resistivity values correspond to progressively shallower water deposits. Zones of calcite-cemented shoreface sandstone greater than 0.5 m (1.6 ft) thick are interpreted when the neutron porosity exceeds the density porosity by more than 7%. Facies distributions predicted for the I sandstone close- ly match trends of the sandstone gross pore volume and daily total fluid production, and suggest that open-hole well logs may be used to anticipate reservoir quality and continuity.

    Regional and local observations support previous interpre- tations that attribute the Doe Creek to forebulge erosion and southwestward sediment transport toward a foredeep where

    tems Canvas™. The manuscript benefited from re- views provided by Gretchen M. Gillis, Dale A. Leckie, William C. Stephens Jr., and an anonymous reviewer. The AAPG Editor thanks the following reviewers for their work on this paper: Dale A. Leckie, William C. Stephens Jr., and an anonymous reviewer.

    Copyright ©2010. The American Association of Petroleum Geologists. All rights reserved.

    Manuscript received March 25, 2009; provisional acceptance May 19, 2009; revised manuscript received June 24, 2009; final acceptance July 2, 2009. DOI:10.1306/07020909062

    AAPG Bulletin, v. 94, no. 1 (January 2010), pp. 1–25 1

  • shoreface sandstones accumulated within a coastal embayment to theWestern Interior seaway. Region- ally, the Doe Creek interval thins northeast of Val- halla and is truncated beneath the K1 unconformity, and shoreface sandstone bodies are encased within offshoremudrocks and detached from their contem- poraneous shoreline. Locally at Valhalla, the Doe Creek reservoir progrades toward the southwest and is extensively and commonly uniformly burrowed by a relatively diverse assemblage of trace makers.

    INTRODUCTION

    Reserves and Objectives

    Conventional in-place oil resourceswithin theWest- ern Canada sedimentary basin (WCSB) are esti- mated to total 48 billion bbl (7.7 million m3) and are primarily contained within reservoirs of Devo- nian and Cretaceous age (36 and 49% of in-place oil resources, respectively) (Allan and Creaney, 1991). Upper Cretaceous reservoirs account for 23% of in-place oil resources that are highly prized because of their characteristically low gravity (API gravity greater than 30°) and low sulfur content (generally less than 0.5%) (Allan and Creaney, 1991). One such Upper Cretaceous reservoir is the Doe Creek Member of the Kaskapau Formation at Valhalla field (Figure 1). In-place oil resources at Valhalla are stratigraphically trapped within shoreface sandstones of the Doe Creek and total 279 million bbl (44,370 � 103 m3) of light (API gravity of 38°), low-sulfur oil (Hogg et al., 1998; AERCB, 2008). Oil was discovered within the Doe Creek at Valhalla in 1979 and widespread devel- opment drilling followed in 1982. An extensive, 40-ac vertical drilling program was initiated during the 1990s for secondary recovery of oil through a patternedwaterflood. By the end of 1996,more than 90% of Valhalla was producing oil through sec- ondary recovery (Hogg et al., 1998). To further en- hance oil recovery, a fieldwide drilling program of horizontal production and water injection wells was initiated in 2004 and as of this writing is ongoing.

    Additional increases in recoverable reserves within the Doe Creek at Valhalla field will likely

    2 E&P Note

    require the application of tertiary recovery meth- ods. The efficacy of both secondary and tertiary re- covery schemes is reliant upon the accurate depic- tion of preferred flow pathways within the reservoir interval. This study evaluates flow continuitywithin theDoeCreekMember atValhalla field by address- ing the following questions. (1)What control do de- positional facies and diagenesis have on reservoir quality? (2) Is it possible to predict the occurrence

    Figure 1. Stratigraphic correlation chart and third-order sea lev- el history for the Late Cretaceous within west-central Alberta (lithostratigraphic designations are modified from Bhattacharya, 1994; age designations and sea level history are from Caldwell, 1983; Ogg et al., 2004). Following sea level lowstand and Dunvegan Formation deposition, the study interval was deposited during the ensuing third-order Greenhorn transgression (Caldwell, 1983).

  • of depositional facies and diagenetic products in wells that lack core control? (3) What is the spatial distribution of depositional facies within a time- stratigraphic framework, and does this distribution correspond to historic trends of fluid production? Finally, do answers to these three applied questions provide serendipitous insight into the ongoing dis- cussions regarding the depositional and stratigraph- ic origins of the Doe Creek Member?

    Geologic Setting

    TheValhalla field area is located within west-central Alberta and, during the LateCretaceous (Cenoma- nian), was situated along the westernmargin of the Western Interior seaway (WIS) near its coastline

    terminus against the northwest-trending Laramide deformational front (Figures 1, 2) (Varban and Plint, 2005; Kreitner and Plint, 2006). Regionally, theDoe CreekMember thickens to approximately 115 m (377 ft) near the axis of theWCSB foredeep and thins northeastward to less than 30 m (98 ft) thick, approximately 75 km (~47 mi) northeast of Valhalla field (Kreitner and Plint, 2006). From its outcrop exposures near the Alberta-British Colum- bia border, the Doe Creek Member pinches out approximately 90 km (∼56 mi) to the southeast (Wallace-Dudley and Leckie, 1993). Eastward thin- ning is related to both accommodation loss away from the WCSB foredeep axis and erosional trun- cation beneath the regional K-1 intraformational unconformity surface (Plint et al., 1993; Plint,

    Figure 2. (A) Late Cretaceous (early Turonian) paleogeography of North America highlighting the position of the Western Interior seaway in gray (modified from Williams and Stelck, 1975; Irving et al., 1993, as cited by Varban and Plint, 2005). The area enlarged in panel B is indicated. (B) Paleogeography of west-central Alberta and east-central British Columbia during the Late Cretaceous (upper Cenomanian) Doe Creek deposition (modified from Kreitner and Plint, 2006). Doe Creek sandstone bodies occur within the central part of a coastal embayment to the Western Interior seaway and are detached from their contemporaneous shoreline. Panels A and B are reprinted with permission from the Bulletin of Canadian Petroleum Geology.

    Atchley et al. 3

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