Natural mineralized fractures from the Montney-Doig unconventional reservoirs (Western Canada Sedimentary Basin): Timing and controlling factors

Characterizing the origin of natural fractures in organic-rich fine-grained deposits is key to constraining permeability evolution these potential source rocks and tight reservoirs, as well assess hydraulic connectivity fluid systems which they develop. Differently oriented calcite-filled (i.e. veins), hosted by mudrocks Lower-Middle Triassic Montney-Doig unconventional resource play (Western Canada Sedimentary Basin), were sampled sub-surface cores from British Columbia. A multidisciplinary approach (including sedimentology, Rock-Eval pyrolysis, petrography, O–C–Sr isotope geochemistry inclusion microthermometry) was applied host-rocks fracture filling calcites. The results demonstrate relevance usefulness such studies gather insights on: 1) lithology-related factors controlling occurrence; 2) timing opening circulating paleo-fluids; 3) openness system through time. More specifically, host-rock facies (particularly grain size) vertical changes appear be leading occurrence. less relevant role played occurrence diagenetic carbonates, while TOC possibly did not control Three generations calcite cemented identified. Vertical (first generation) post-dated onset oil generation (Late Cretaceous). Horizontal, bedding-parallel (second gas opened close maximum burial, corresponding peak hydrocarbon (CH4) Cretaceous - Early Paleogene). (third horizontal ones during basin uplift (Middle Late consistent petrographic geochemical features all cements point parent fluids equilibrium with lithologies, that behaved a closed Paleogene time; this would support hypothesis that, at least portion investigated, Montney Fm also acted rock system.