Petrology, Diagenesis and Reservoir Quality in the Hawkesbury Sandstone, Southern Sydney Basin, Australia

Al Gahtani F

doi:10.4172/2381-8719.1000283

Abstract

Petrography of the Hawkesbury Sandstone was described by thin section, scanning electron microscope and Xray diffraction techniques. Quartz is dominant in the Hawkesbury Sandstone which contains very minor feldspar, lithic grains, mica and heavy minerals. The Hawkesbury Sandstone is quartzarenite to sublitharenite. Quartz includes monocrystalline and polycrystalline grains while the feldspar includes both K-feldspar and plagioclase. Volcanic, sedimentary and chert rock fragments are present. Thin section porosity occurs in the Hawkesbury Sandstone, particularly the coarse-grained deposits. Primary porosity is more common than secondary porosity in the Hawkesbury Sandstone. Thin sections and scanning electron microscopy were used to describe diagenetic alterations and their influence on porosity in Hawkesbury Sandstone. These diagenetic alterations include compaction, quartz overgrowths, authigenicclay minerals and carbonate cement. Compaction occurred in the Hawkesbury Sandstoneduring throughout diagenesis. The influence of chemical compaction on thin section porosity was greater in the Hawkesbury Sandstone. Quartz overgrowths are common in the Hawkesbury Sandstone where they have a strong influence on porosity. Authigenic clay minerals are the widespread in the Hawkesbury Sandstone filling pores and occurring as grain-coatings on detrital and authigenic grains. Where they coat quartz grains they preserve porosity by preventing growth of quartz overgrowths. Pore-filling carbonate cement reduced porosity whereas dissolution of carbonate resulted in secondary porosity. Dissolution of unstable feldspar and lithic grains is absent in the Hawkesbury Sandstone. The Hawkesbury Sandstone is characterized by primary and secondary porosity, thus it has good groundwater storage and flow potential. Medium- and coarse-grained sandstone beds are common in the Hawkesbury Sandstone but it shows vertical variations in porosity. A few impermeable shale and siltstone units occur in the Hawkesbury Sandstone forming local confining layers.

Highlights

This study includes the Permian-Triassic Hawkesbury Sandstone which forms part of the southern Sydney Basin, New South Wales
The purpose of this study is to investigate the diagenetic history of of primary porosity and the generation of secondary porosity in the the reservoir sandstones and the relationship between the preservation Hawkesbury Sandstone of Southern Sydney Basin, Australia
Petrography Petrographic data indicated that the sandstones are quartzarenite to sublitharenite containing abundant quartz, low feldspar and rock fragments, Q90.1%, F0.3%, R9.7% (Figure 2a)

Summary

Introduction

This study includes the Permian-Triassic Hawkesbury Sandstone which forms part of the southern Sydney Basin, New South Wales. It addresses influence of diagenetic alterations on porosity in the Hawkesbury Sandstone, Southern Sydney Basin, Australia. The study area consists of part of the southern Sydney Basin in the Illawarra district of New South Wales, Australia (Figure 1). Standard concluded that the composition of the Hawkesbury Sandstone consisted of detrital grains, heavy minerals and clay minerals [4]. He described the grain size, sorting and roundness of the sandstone. Porosity and permeability in the Hawkesbury Sandstone have been analysed by Griffith, Liu et al, Lee, Franklin and Freed [5,7,8,9,10]

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