Extended abstract version of the abstract (Geocat#73747) submitted in March 2012 and accepted for an oral presentation at the symposium.

This report covers the results of a seismic reflection traverse on a portion of the Giralia anticline which has been mapped in Mesozoic and Tertiary rocks in the North-West basin. The work constitutes a part of a general programme of investigation which the Bureau of Mineral Resources, Geology and Geophysics, has been carrying out on Permit areas held by Ampol Petroleum Ltd. in this area. The seismic traverse described herein lies along the main road joining Giralia and Bullara homesteads and crosses the northern end of the Giralia structure. Tests were made with shooting in shot holes and also by air shooting. In addition, a refraction spread was shot along the axis of the anticline. This report gives an account of this investigation. Technical matters, such as interpretation technique and the symbols used in plotting results, are briefly noted. The results of the study and subsequent conclusions are discussed.

Gravity surveys were conducted of the Gippsland Lakes district during 1949 and 1951. Both surveys showed an anomaly immediately to the north of Lake Wellington, the magnetic anomaly being a little displaced to the north-west of the gravity anomaly. The size and nature of the magnetic anomaly suggested that it might be due to rocks with higher than normal magnetic susceptibility in the basement complex. The gravity anomaly might be due to a buried hill in the Jurassic or basement, perhaps associated with the same feature which is responsible for the magnetic anomaly. Such a buried hill could result in a geological structure favourable to the accumulation of oil being present in the overlying Tertiary rocks, and in order to test whether or not a favourable structure existed a seismic reflection survey was undertaken by the Bureau. This report deals with the results of the seismic survey. Two north-south traverses and one running east-west and crossing the other two were surveyed.

A reflection traverse was shot across the centre part of the Giralia Anticline in the Carnarvon Basin of Western Australia, in an attempt to verify the unconformity between Mesozoic and Palaeozoic sediments shown by a previous traverse across the northern part of the anticline. Shallow seismic events recorded were of good quality and correlated very well with surface geology. They also indicated two faults in places where steep dips in surface beds might, by analogy with the northern end, be expected. Deep events were in general of poor quality and inconsistent. However, over approximately a mile of the traverse, they were of good quality and indicated nonconformity with the shallow events.

A seismic reflection survey was carried out in the Parish of Darriman, Victoria. The survey was planned to investigate a gravity anomaly, which may be an indication of a structure within the sedimentary section favourable to the accumulation of oil or natural gas. For the most part reflections were exceptionally good, and it was possible to trace one reflecting layer over most of the area. Contouring showed the presence of an anticlinal structure, plunging to the east, but rising and broadening to the west. On the flat crest of the structure, there is probable closure in two places. The thickness of the Tertiary sediments may be a maximum of 6,000 feet, but may be only 3,000 feet on the crest of the structure and 4,000 feet on the flanks.

Several seismic surveys were made by the Bureau of Mineral Resources, Delhi Australian Petroleum Ltd, -Phillips Petroleum Company, and L. H. Smart Oil Exploration Company Ltd during the period from 1959 to 1963 between Eula and the Queensland/South Australia border area of the Eromanga Basin. This report covers the seismic work done by the Bureau of Mineral Resources in 1962 and 1963 and also incorporates the results of the work done by the private oil exploration companies. It aims at providing information on the nature and structure of the rocks underlying the Mesozoic sediments of the Eromanga Basin. The seismic results have been interpreted with reference to the geology as known from the Delhi-Santos Orientos No. 1 and Dullingari No.1 wells near the Queensland/South Australia border and the Smart Oil Orient No. 2 well on the Grey Range.

Seismic reflection studies in the Perth Basin, between the coast and the Darling Range, 30 miles north of Perth, were conducted in an attempt to derive a suitable recording technique for obtaining reflections when shooting on the Coastal Limestone formation, to investigate geological structure in the basin,and to supplement hydrological studies being madeby the Geological Survey of Western Australia. Experimental work occupying half of the survey period failed to yield a technique for obtaining seismic reflections on the Coastal Limestone, but led to reflections being obtained across the major part of the basin, Record quality with a fairly heavy technique was poor to fair in the western half of the basin off the Coastal Limestone but improved considerably to the east. A complex geological section in the west gave way to a more concordant thick synclinal section in the east, terminated at its eastern end by the Darling Fault. Of interest is an apparent anticlinal reversal of dip in beds lying deeper than 7000 ft,with the reversal axis near the centre of the major gravity 'low' of the basin.

In November 1964, the Bureau of Mineral Resources Seismic Party No. 1 carried out a velocity survey in CBMR 12 (Cockroach) Well, Northern Territory, which had been drilled to 4000 feet and logged using sonic and other logging methods. The time/depth values obtained in the velocity survey were in good agreement with those obtained by integration of the sonic log. A curve showing the variation with time-of'the coefficient of reflection calculated from the sonic log showed an outstanding feature, which appeared to correlate with the best reflection recorded on an experimental seismic traverse nearby. According to the geological interpretation of the well log, this reflection arises from velocity changes near the boundary of the ArrinthrungaTormation and the Marqua Beds at a depth of 2,721 feet.

The Vibroseis method of seismic exploration was first introduced into Australia during 1963. In accordance with the programme for accelerated oil search, the Bureau of Mineral Resources employed a Vibroseis seismic party to demonstrate the performance of the method in various problem areas within the Otway and Sydney Basins, the locations of which are indicated on the regional map. The Experimental Vibroseis Seismic Survey was conducted by Seismograph Service Limited. Party 243. on behalf of the Bureau of Mineral Resources, Geology and Geophysics during the period from 11th May to 3rd October, 1964. The broad objective of the survey was to demonstrate the capabilities of the Vibroseis method in selected areas where previous conventional seismic surveys had experienced difficulties in obtaining results and where various seismic problems had been defined. The main aim of the survey was to obtain good quality results rather than a high production rate yielding poorer quality data. However, as a secondary objective, some short production traverses were recorded USing the optimum field technique developed during the course of the survey for comparison e with normal shot hole production techniques.

The Bureau of Mineral Resources has again'extended its geophysical programme in the search for oil to the continental shelf area of Australia by carrying out a combined gravity, and seismic survey in the Timor Sea/Joseph Bonaparte Gulf area of northwest Australia. The survey investigated the capabilities of the surface marine gravity meter for reconnaissance gravitywork at sea, and the penetration and quality of seismic reflections obtainable using a spark discharge source consisting of an array of electrodes. The possibility of operating the two methods simultaneously was also investigated. The seismic reflection sections recorded were much better than expected, with good-quality reflections being recorded to 1.6.sec. the gravity meter and seismic'equiPment were operated simultaneously at boat speeds of 8 to 9 miles per hour. The-seismic results have shown that a large Permian and Mesozoic sedimentary basin exists in the Joseph Bonaparte Gulf and extends to the north and north-west into the Timor Sea. It is an offshore extension of the Bonaparte Gulf Basin, and contains at least 10,000 feet of post-Permian sediments. .Although the trends of the gravity anomalies agree with the general shape of the basin as defined by the seismic results, a large positive anomaly occupies the central deep part of the basinand does not seem to be related to basement relief.