Early porosity generation in organic-sulfur-rich mudstones

Abstract

Abstract High organic sulfur (Sorg) content (i.e., Type IIS kerogen) is well known to significantly influence kerogen transformation but the effect of Sorg content on organic porosity evolution has rarely and indirectly been investigated. This study demonstrates that organic porosity is generated at lower thermal maturity in mudstones containing Type IIS kerogen relative to those with Type II kerogen. The implications of this work are relevant for the characterization of organic-rich mudstones as cap rocks, unconventional hydrocarbon reservoirs, and disposal reservoirs for CO2 or nuclear waste because pore systems control storage volumes and matrix fluid flow. Five thermally immature core samples were selected from three organic-rich mudstone units. In order of increasing Sorg content, the studied formations were the Late Devonian Duvernay Formation (Canada), middle late Miocene Onnagawa Formation (Japan), and early Jurassic Gordondale member of the Fernie Formation (Canada). Hydrous pyrolysis was used to artificially mature splits of the immature samples to 4 maturity stages, upon which petrophysical and organic geochemical properties were measured and compared to baseline immature samples.