Provenance and diagenesis of sandstones in the deep wells Annapolis G-24, Balvenie B-79, Crimson F-81, Weymouth A-45, and Newburn H-23, Scotian Basin, offshore Nova Scotia

Abstract

Deep-water sandstones have been a target for oil and gas exploration in the Scotian Basin for many decades. Little is known about the sedimentary petrography of these sandstones, both as indicators of provenance and for evaluation of the effects of diagenesis on reservoir quality. The purpose of this study was to determine how the sandstones present in deep water wells differ in sedimentary petrography, both detrital and diagenetic, from those on the Scotian Shelf. Sparse side wall cores and heavy mineral separates from cuttings samples have been studied using petrographic and scanning electron microscopes (SEM) to identify the minerals present. Heavy mineral samples from cuttings were mostly swamped by diagenetic siderite and drilling mud contaminants, but the petrography of lithic clasts and the mineral chemistry of tourmaline, chromite/spinel, feldspar and micas are of value in determining provenance. These are similar to the mineralogy of sandstones in the Glenelg field, and indicate a predominant source from the Sable River draining southern Labrador and the northern Appalachians. Lithic clasts suggest some supply from the Meguma terrane. High abundance of sodic trachyte clasts in Newburn H-23 and to a lesser extent Weymouth A-25 may indicate supply from a cryptic Cretaceous volcanic source on the inner La Have Platform. Diagenetic paragenesis is generally similar to that in wells on the Scotian Shelf. There is no evidence for chlorite rims on framework quartz grains that are important for preserving primary porosity in many deltaic sandstone reservoirs on the Shelf. Cementation by ferroan calcite and siderite is widespread, but the presence of late ankerite, dolomite, sphalerite and barite is evidence of persistent fairways for fluids similar to those found in the Onondaga and Glenelg fields. This Open File provides backscattered electron (BSE) images, the mineralogy of the studied rocks, energy dispersive spectroscopy (EDS) analyses of minerals, and an explanatory text and figures that summarize mineral chemistry and diagenetic paragenesis.