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A Geological Study Of The Basal Jurassic Sandstones In The Grafton Range Field.

Yong, Lee A.

Honours Degree, 1988

University of Adelaide


The Grafton Range Gas Field, located twenty-four kilometres northeast of Roma, Queensland, is one of a number of small fields on the Roma Shelf in the Surat Basin. The field is covered by Production Leases #4 and #3, and produces gas from three Basal Jurassic sand units referred to as the P sand unit of the Lower Precipice Sandstone and the C and D sand units of the Upper Precipice Sandstone. Sand distribution is complex and laterally discontinuous. Sedimentological and wireline log correlation studies suggest that the P sand unit was deposited in a fluvial environment whereas the C and D sand units were deposited in a regressive marine or lacustrine environment. The occurrence of acritarchs with a thin oolitic section which is overlain by some forty feet of dark grey shale confirms that the C and D sand units were associated with a brief marine incursion.

Production and gas analysis data indicate that Grafton Range field consists of five discrete gas pools. Trapping appears to have combined structural and stratigraphic control. The construction of net gas sand distribution and sand quality maps resulted in the proposal of one potential development well location for drilling.

Australian School of Petroleum



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