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Abstract

AAPG Bulletin, V. 101, No. 5 (May 2017), P. 655-682.

Copyright ©2017. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/08241616014

The use of microresistivity image logs for facies interpretations: An example in point-bar deposits of the McMurray Formation, Alberta, Canada

Howard Brekke,1 James A. MacEachern,2 Tania Roenitz,3 and Shahin E. Dashtgard4

1Consultant, 450 Hidden Valley Grove NW, Calgary, Alberta, Canada T3A 5X2; [email protected]
2Applied Research in Ichnology and Sedimentology Group, Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6; [email protected]
3Statoil Canada Ltd., 3600, 308 – 4th Ave SW, Calgary, Alberta, Canada T2P 0H7; [email protected]
4Applied Research in Ichnology and Sedimentology Group, Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6; [email protected]

ABSTRACT

Well logs such as spontaneous potential and gamma ray historically have been the only tools available for facies evaluation of noncored wells in the McMurray Formation. The addition of microresistivity image logs has greatly improved facies identifications and interpretations, particularly when integrated with core data sets. In the case of McMurray channel complexes, core descriptions provide detail about bedding contacts, sedimentary texture, stratification, bioturbation intensity, and trace fossil diversity. Image logs provide texture, fabric, bedding contact style, dip directions and angles, and bedding architecture information, yielding paleoflow and lateral accretion directions. This study characterizes facies by integrating interpretations from 414 image logs with core-based descriptions from 138 of these wells. The reservoir targets, and most prolific depositional facies in this study, are associated with channel systems and their associated point-bar deposits. Facies identifications are based on several image log criteria. Mud clast breccias display variable dip angles and dip directions. Cross-stratified sands comprise vertical successions of stacked, internally consistent bedsets with high dip angles (>15°) that indicate paleoflow direction. Lateral accretion beds show consistent dip directions with a progressive change from shallow-to-steep-to-shallow dip angles (e.g., <4 to 15° to <4°) from the base to the top of the succession, as well as beds that dip toward the thalweg of the paleochannel. Flat-lying (<4°) mud records vertical accretion associated with point-bar tops or channel abandonment. Although this facies classification is specific to the McMurray Formation in the study area, the principles provided here are applicable to other subsurface studies and demonstrate the enhanced reliability of integrated core–image log data sets.

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