Reservoir And Production Properties Of The Toolachee And Patchawarra Formations, Cooper Basin, South Australia.
Bon, Nubia J.
Honours Degree, 1999
University of Adelaide
AbstractSolid core is required to fully assess the quality and to predict production in a hydrocarbon reservoir. Detailed description of cuttings by rock-typing and direct petrographic comparison with core allows extrapolation of core-derived data into uncored zones. This study produces a catalogue of rock types based on petrographic features plotted against porosity and permeability for a number of samples from the Fly Lake-Brolga Field in the Permian Cooper Basin succession in South Australia. The samples were selected using production and perforation data to isolate zones of both good and poor hydrocarbon deliverability.
Local structure and production contour maps were produced, suggesting a deepening to the north- west, towards the centre of the Patchawarra Trough. North-west-trending channels cut across the north-east-trending Fly Lake-Brolga high. Wells in the area were correlated using coals and shales. Production data were used to determine the major producing sandstones of the region. The sandstones were labelled A to J, with E and D as the main sources of production.
The information for the rock-type catalogue was obtained by petrographic analysis on samples identified after core logging. Thin section description, scanning electron microscopy, X-ray diffraction and cathodoluminescence techniques were used. From these studies, it was found that sandstones with higher amounts of quartz overgrowths generally have less total clay (kaolin and illite) and retain better primary porosity. Kaolin, when pore-filling, occludes porosity but the crystal habit of kaolin (booklets), allows for hydrocarbon storage and some permeability. This is especially the case for dickite, which is coarser-grained than kaolinite and allows for greater hydrocarbon flow. Illite, as a pore-filling form, has hair-like fibres, which partially blocks pore throats and reduces permeability to a greater extent than kaolin. Much of the illite and kaolin form from the alteration of feldspar grains and rock fragments. These replacement clays occur as discrete areas and have little effect on porosity and permeability. Only when the minerals grow beyond the altered grains does the clay affect reservoir quality.
Porosity and permeabilty data were compared to clay content from X-ray diffraction. No simple trend could be interpreted between these two data sets or from the production data available. It was therefore determined that no one geological parameter controls reservoir quality, but many factors are involved, including clay distribution, clay type, quartz cement, compaction and pore throat geometry. Many of the important parameters that control quality do however, influence the visual aspect of the rock and this allows a rock-type catalogue to provide a useful adjunct to cuttings description.