Geochemical, petrophysical and geomechanical properties of stratigraphic sequences in Horn River Shale, Middle and Upper Devonian, Northeastern British Columbia, Canada

  • Author / Creator
  • The Middle and Upper Devonian Horn River Shale, comprising the Evie and Otter Park members and the Muskwa Formation, northeast British Columbia, Canada is recognized as a significant shale gas reservoir in the Western Canada Sedimentary Basin. However, many aspects of this shale formation have not been adequately studied, and the published geochemical, petrophysical and geomechanical data are limited. This work aims to document the controls of geochemical composition variation on petrophysical and geomechanical properties and the relationship of rock composition to lithofacies and stratigraphic sequences. A detailed core-based sedimentological and wireline log analysis was conducted by my colleague Dr. Korhan Ayranci as a parallel study, in order to classify lithofacies, interpret depositional environments and establish sequence stratigraphic framework across the basin. Major and trace elements concentrations, key trace element ratios and Corg-Fe-S relationships were used to understand the effect of sea level fluctuation on detrital flux, redox conditions, productivity and therefore organic carbon enrichment patterns. Detrital sediment flux indicated by the concentration of aluminum and titanium to the basin was found to be higher during transgressions than regressions. Redox conditions, exhibiting strong correlation to TOC content, were the primary controls on the organic carbon deposition. The bottom water conditions are more anoxic during transgressions than regressions. The presence of biogenic silica, identified by crossplot of silica versus zirconium concentrations, makes the use of total silica problematic as a detrital proxy; biogenic silica concentrations may be useful as a proxy for productivity. The depositional environments for the Evie and Muskwa intervals, depositing during high sea level, represented favorable conditions for organic matter accumulation, including anoxic bottom water conditions, high primary productivity and less clastic dilution. The Otter Park Member, deposited during sea level falling stage, has relatively low organic matter concentrations, which may have been due to high clastic dilution and dysoxic to oxic bottom water conditions. Geochemical controls on petrophysical properties (porosity, permeability, pore morphology, pore size and pore throat size distribution) within Horn River shale reservoirs were investigated by an integrated analysis of porosity and permeability measured by helium pynconometry and GRI method, nitrogen adsorption analysis, mercury injection analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Porosity ranges from 0.62% to 12.04%, and the measured matrix permeability values increase with increasing porosity, ranging between 1.7 and 42.8 nanodarcy. Among the organic matter and inorganic components, TOC content exerts the strongest control on porosity and permeability. Pore size and pore throat size distribution are strongly associated with TOC content, decreasing with increasing TOC content. SEM and TEM images suggest that several kinds of sites for porosity development are present, including organic matter, pyrite framboids, clay platelets, quartz rims, carbonate grains and microfractures. High porosity and permeability are associated with specific depositional facies. Massive and pyritic mudstones, which are rich in TOC and quartz, have relatively high porosity and permeability. Laminated mudstone, bioturbated mudstone and carbonate, which are rich in clay and carbonate content, have relatively low porosity and permeability. Rock mechanical properties were evaluated by hardness measurements and Young's modulus, Poisson's ratio and brittleness calculated from dipole sonic and density log data. Clay content is the most significant factor controlling the brittleness of shale rocks. The effect of quartz content on rock mechanical properties depends on the type of the quartz present in the rock. Authigenic quartz is positively correlated with brittleness, but detrital quartz has little or no effect. Factor analysis indicates that carbonate increases brittleness, while no obvious correlation between TOC content and brittleness was observed in this study. Brittleness in Horn River Shale shows both geographic and stratigraphic variability. Increasing brittleness in the northwest part of the basin largely results from greater distance from the sediment source and decreased clay content. The Otter Park member represents a period of major relative sea level fall and is more ductile than the underlying Evie Member and the overlying Muskwa Formation because of its high clay content.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.