Union-Kern-A.O.G. Cabawin No. 1 spudded on 6th October, 1960, was drilled as a structural test of the petroleum potential of sediments underlying a major unconformity within the Surat Basin. The age and nature of the section below the unconformity was questionable prior to drilling the well, but it was presumed to be partly Triassic and partly Permian in age and related to the sedimentation of the Bowen Geosyncline. The drilling of the well confirmed this prognosis.
In addition to providing stratigraphic information related to the petroleum potential of the Bowen Group, the well also provided information of regional significance on the Mesozoic rocks of the Great Artesian Group. Under a thin veneer of Tertiary rocks the drill penetrated the Roma, Blythesdale, Walloon and Bundamba Formations of the Great Artesian Group, and the Cabawin, Kianga, and Back Creek Formations of the Bowen Group, before bottoming in volcanic rocks of (?)Permo-Carboniferous age at a depth of 12,035 feet.
The drilling of the well confirmed the presence of hydrocarbons in the Surat Basin. During the drilling operation a blowout occurred at a depth of 9938 feet, surfacing free gas and condensate. The blowout was caused by formation pressures, in excess of the mud weight, within an eight-foot sand body of the Permian Kianga Formation. In addition significant gas shows and a flow of salt water were encountered in weathered andesite of the Cracow Formation. Minor gas shows were recorded in the Permian Back Creek Formation, and in the Lower Triassic Cabawin Formation, and Significant shows of hydrocarbons were also present in porous and permeable sandstones of the lower member of the Triassic-Jurassic Bundamba Formation.
The number of occurrences of oil and gas showings indicated that only a sustained testing programme through casing would properly evaluate the potential of these hydrocarbons. After reaching total depth, 5 1/2" casing was cemented at 12,033 feet, and there followed a series of production tests of all significant shOWings of oil and gas encountered during the drilling operation. Results were negative with the exception of the one zone in the Permian Kianga Formation. This zone proved to be the only producing horizon. After 22 days of continuous production, this zone was producing 62 barrels per day of 490 API gravity crude through 22/64" choke, with casing and tubing well-head pressures at 550 p.s.i. and 300 p.s.i. respectively, and 534 Mcf/D of gas. A total of 1761 barrels of crude oil and 13,744 Mcf of gas were produced during the testing period. Pressure and temperature surveys were
conducted, and the well was shut in and suspended on 17th June, 1961, retained in a condition for production at any future time.
