Variation of porosity and permeability with diagenetic minerals in the Scotian Basin, offshore eastern Canada and its implications for reservoir quality

Abstract

The Scotian Basin is an under-explored offshore basin that has produced gas and minor oil from Jurassic-Cretaceous deltaic sandstones. Reservoir quality is an important exploration risk in the basin. This study investigates whether there are systematic stratigraphic or geographic variations in diagenetic mineral assemblages that relate to reservoir permeability. Three data sets are used: a compilation of all available core-plug porosity and permeability measurements (3271 in total), a subset of 577 corresponding to thin sections with lithofacies assignments, and a subset of 35 thin sections principally from reservoir sandstones, in which modal abundance of diagenetic minerals has been determined by image analysis of scanning electron microscope backscattered electron images. Abundances above a threshold of ~ 4% diagenetic kaolinite, calcite and ankerite correlate inversely with permeability, but chlorite and possibly siderite correlate positively. Diagenetic assemblages show no systematic variation with stratigraphy or geography, both of which may have variable detrital supply. Permeability shows the well-known variation with grain size and depth of burial, but after correcting for these effects is greatest in estuarine channel and river-mouth turbidite sandstones. Local effects such as facies distribution, architecture of channel sandstones, fluid pathways related to complex salt tectonics, and the effects of overpressure are more important than predictable basin-wide effects such as detrital supply, regional depositional lithofacies or sequence stratigraphy in controlling sandstone reservoir quality.