Compositional and diagenetic evolution of a siltstone, with implications for reservoir quality; an example from the Lower Triassic Montney Formation in western Canada

Diagenetic models for silt-rich mudstone (siltstone) are less advanced than those sandstone and clay-rich mudstone. In addition, the influences of diagenetic processes on reservoir quality in siltstone formations poorly understood. Here we examine roles depositional facies, detrital composition, compositional evolution Lower Triassic Montney Formation, a prominent siltstone-dominated western Canada with very large reserves oil, gas-liquids natural gas. We applied advanced, high-resolution petrographic methods including SEM (SE, BSE, EDX SEM-CL), XRD, QEMSCAN technologies, as well He-pycnometry samples from 17 different locations within basin that represent range depths thermal maturities. Cross-cutting overgrowth relationships volumes authigenic phases demonstrate massive precipitation quartz, feldspar, dolomite, calcite anhydrite cements at shallow burial depths, leading to homogeneity among lithofacies. propose cement resulted high fluid flux through formation depth, possibly driven by reflux concentrated seawater nearshore saltpans. Siltstones preserve relatively porosity permeability differing mudstones. contrast sandstones, deep diagenesis played minor role Formation is expressed form pressure solution amounts fibrous illite precipitation.