Lithofacies Characterization and Sequence Stratigraphy of the Gas- Bearing Horn River Shale, Northeastern British Columbia
Michael S. Kennedy, Tian Dong, and Nicholas B. Harris
The Horn River Shale is a gas-bearing mudstone formation that was deposited along the passive margin of the Western Canada Sedimentary Basin during the Givetian-Frasnian Stages of the Middle Devonian. Here we have undertaken an integrated sequence stratigraphic investigation of the Horn River Shale by incorporating core descriptions, geochemistry, and well logs. Core descriptions focused on establishing a meaningful lithofacies scheme that could be identified in hand specimen in core, and related to specific depositional environments. Ten lithofacies were identified and further investigated using optical and electron-optical microscopy. Two of the lithofacies, occurring predominantly in the middle Otter Park shale unit, were interpreted as lowstand deposits based upon: (1) the abundance of storm beds; (2) intense bioturbation; (3) elevated thorium and potassium gamma ray counts; and (4) elevated Al2O3 + K2O + Na2O + TiO2 concentrations from bulk geochemistry, indicating high detrital influx. These two lithofacies form the backbone of our sequence stratigraphic interpretation and can be correlated across the basin using gamma ray logs. At least three 3rd order sea level cycles are preserved within the 6-8 m.y. of Horn River Shale deposition, and these occurred within a 2nd order transgression. The 3rd order transgressions offer the best reservoir zones in terms of organic matter preservation and silica content, in contrast to the diluted clay-rich lowstands.
AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013