THE DEVELOPMENT GEOLOGY OF THE TUBRIDGI GAS FIELD

Abstract

The Tubridgi Gas Field is located in the south of the Barrow Sub-basin, onshore in the Carnarvon Basin, Western Australia. The accumulation was discovered by Pan Pacific Petroleum NL in June 1981 with the drilling of the Tubridgi-1 well. Subsequent to Tubridgi-1, eight appraisal wells have been drilled, six of which were successful. The latest wells, Tubridgi-7 and-8, drilled in September 1990 by current operator Doral Resources NL, have enabled geological and petrophysical models for the field to be refined. These models were utilised for reserve determinations which were used to negotiate gas supply contracts and secure project financing to ensure the fields successful commercial development. Tubridgi gas is trapped within a broad, low relief, northeast-trending anticlinal closure. Reservoirs for the accumulation are the Middle to Upper Triassic Mungaroo Formation, Upper Cretaceous Flacourt Formation of the Barrow Group and Birdrong Sandstone of the Cretaceous Winning Group. All three units exhibit porosities averaging 29-30 per cent, with permeabilities of 3-16 D in the Mungaroo and Flacourt Formations and 157 mD in the Birdrong Sandstone. Vertical seal for the accumulation is the Muderong Shale of the Winning Group.

The Tubridgi Gas Field is the first onshore Carnarvon Basin hydrocarbon accumulation to be commercially developed. Gas production into the Dampier-to-Bunbury Natural Gas Pipeline commenced on 26 September 1991 and within one month had reached contract volumes averaging 22 MMCFD (623 000 m3/d). Field life is anticipated to be ten years.