TO EXPLAIN THE NATURE OF CORE POROSITY USING RESULTS OF PETROGRAPHY ANALYSIS
Abstract
The Permian to Triassic Tirrawarra Sandstone succession in the Cooper Basin of Central
Australia is characterized by its low permeability. Ambient core porosity averages
8.96% and ambient permeability 0.9 mD. Most samples studied have permeabilities less
than 3mD. Despite its overall poor reservoir characteristics, the Tirrawarra Sandstone is
one of the major oil and gas targets in Australia. A total of 17 core plugs from 6 wells
were studied petrographically using optical petrography, SEM and XRD. These results
were integrated with core analysis data.
Petrographic study revealed the diagenetic events, mainly mechanical and chemical
compaction, cementation and alteration have modified the reservoir quality. Ductile components
such as rock fragments, clay and matrix influence mechanical compaction, which
are the main cause of reservoir quality reduction. Quartz cementation and clay distribution
also affected the porosity, but particularly permeability. Mechanical compaction as
well as quartz cementation have reduced and blocked pore-throats to isolate intergranular
pores. The alteration of feldspar to kaolin has changed intergranular porosity to
microporosity. Illite occurs as either cement, alteration of rock fragments or kaolinite. All
of these diagenetic events also affect fluid movement in the reservoir.
This paper presents the evaluation of the determination of effectiveness of porosity in
the delivery of gas from sandstone reservoir in the Cooper Basin using integrated petrography
analysis and core measurements.
Keywords
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DOI: https://doi.org/10.29017/SCOG.30.3.979
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