ABSTRACT: Scotia -- Gas Resource in a Fractured Andesite Reservoir

O'SULLIVAN, T., AGL Petroleum Limited, Brisbane, Queensland, Australia

In 1983, following the hydraulic fracturing of the volcanics in one of the wells, Scotia 1, a high initial flow rate of 5 MMcfd was recorded but this rapidly declined to 0.6 MMcfd. Hydraulic fracturing is no longer considered to be the appropriate developmental technique for the naturally fractured Camboon Volcanics but rather the drilling of directional wells perpendicular to the predominant orientation of the open fracture planes - a developmental strategy which has been adopted successfully in other naturally fractured areas of the world.

Core analysis has shown that the Scotia volcanics contain appreciable matrix porosity, up to 15% in some samples. Petrographic analysis has revealed that this porosity has been generated by the devitrification of volcanic glass which was finely disseminated throughout the andesitic lavas. The small void size of this porosity together with the clay minerals formed as by-products of the devitrification process result in a reservoir highly susceptible to formation damage. Because of this formation sensitivity, the volcanic section

will be drilled with air in a re-entry of Scotia 1 scheduled for late 1991. The re-entry will entail the drilling of a deviated hole with a deviation angle of 60 degrees and an azimuth perpendicular to the orientation of the fracture planes as interpreted from Formation MicroScanner data. The proposed total depth of the re-entry is 3500 m.

At this stage an accurate gas in-place estimate is not possible. However, the magnitude of the individual parameters namely, structural size, porosity, expansion factor and net pay (albeit from rudimentary log analysis) all point to the presence of a substantial gas resource at Scotia.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)