Organic and Inorganic Composition Controls on Pore Development in the Horn River shale, Middle and Upper Devonian, Northeastern British Columbia, Canada
Samples from the Middle and Upper Devonian, Horn River Group shalewere examined in order to develop a better understanding of compositionalfactors that control porosity development in mudstones.Samples have been analyzed by helium porosimetry, SEM imagingofion milledsamples, nitrogen adsorption measurements and mercury injection analysis.Samples obtained from Evie, Otter Park and Muskwa members exhibit a range oforganic carbon content and mineralogical components.
Porosity development is a combined function of organic matter, minerals, fabric and fractures. SEM images suggest that in mature mudstones, several kinds of sites are provided for porosity development, including organic matter, pyrite framboids, clay plates, quartz rims and fractures. A moderately strongpositive relationship between TOC and porosity indicates that manypores are developed inorganic matter. A positiverelationship between quartz and porosity is due to the positive relationship between quartz and TOC, as quartz is mainly biogenic origin.
Pore structure is also a complicated function, independent of any single factor.Pores less than 10 nm, especially less than 2 nm (micropores),dominatein terms of frequency; however, pores more than 10 nm (mesopores) dominatein terms of volume. However, samples with extremely low TOC and quartz have extremely low surface area and pore volume. Samples with high quartz tends to havelarger connected pores (more macropores), in comparison, samples have low quartz are likely to have more mesopores and micropores.
AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects