Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Detailed Mineralogical Characterization of the Upper Montney Fine-Grained ‘Shale’ Interval Using Micro-CT and Electron Microprobe Analyses
(1) University of Alberta, Edmonton, AB, Canada.
The Lower Triassic Montney Formation consists primarily of shoreface and turbidite deposits which accumulated along the north-western coast of Pangea. It records the deposition of sandstone, siltstone and dolomitic packstone/grainstone (coquina) with a mineral content consisting dominantly of quartz, dolomite, potassium feldspar, plagioclase, and mica (primarily muscovite). Clay minerals rarely occur in excess of 2 to 8%. In addition to numerous conventional oil and natural gas reservoirs, in the past several years the Montney Formation has become one of the primary focuses of unconventional gas exploration. Despite this recent interest in the ‘shale’ intervals of the Montney, however, the overall composition remains poorly understood. Past publications have focused largely on the conventional reservoir intervals (such as the Coquinal Dolomite Member and the Montney Turbidite interval) which comprise less than 10% of Montney Formation. Fine-grained intervals, despite comprising the bulk of the Montney’s thickness, have received scant attention and thus our understanding of the sedimentologic and stratigraphic evolution of the Montney Formation remains lacking. Until this void is filled, regionally predictive facies models will remain conjectural. By using a micro-computed tomographic (micro-ct) scanner, in partnership with an electron microprobe, 3-D analyses of the mineral composition and fabric of the Montney fine grained intervals have been attained.
Samples of the Upper Montney Formation (obtained from core from the Kobes area of northeastern British Columbia, Canada) are utilized in this study. Mineral phases have been correlated with specific density signatures identified with the micro-ct scanner, thereby characterizing the mineralogy of fine-grained Montney samples. Traditional techniques such as point counting are generally used to determine the mineral content in fine grained successions (such as the Montney), however these techniques are time intensive and may be inaccurate. By calibrating measurements obtained in the micro-ct scanner with elemental maps obtained with an electron microprobe, the need for thin section analysis can be largely eliminated. Problems associated with traditional thin section analysis, where grain size can be misinterpreted because of random grain orientation, can thus be avoided and the scanner has the ability to measure at resolutions as high as 1um allowing for very small mineral grains to be quantified.