b'Ted Tynes best of Exploration geophysicsFeatureissue (Dooley, ed., 1990) containing papers from a symposiummobility. Severe sandstorms were prevalent. It was found that on engineering geophysics. Wood discussed seismic andGeoflex records imparted less energy into the ground than resistivity methods, gamma-ray logging, and measurementdynamite sources, with higher frequencies and less noise. The of effects of industrial vibrations; he briefly mentions remoterate of traversing was increased by a factor of 2.5 compared sensing, and warns against overselling of geophysics and thewith conventional drilling practice in this area.need for checking results by drillingtopics which featureIn an account of the discovery and development of the strongly in the recent papers. Mackerel Field, Gippsland Basin, Maughan (1980, 434) sounded Vol. 2 No. 1 contained also the first original scientific papersa few warnings on interpretation of seismic results. Two holes (Williams, 1971a, 718; 1971b, 717), which described a simplifiedtargeting supposed crests found gullies instead. The importance method of interpreting TURAM results, and a nomogram andof accurate velocity analysis was emphasized here, as well as computer programs to assist in the interpretation. in the succeeding paper (Denham, 1980, 151), in which it was shown that random errors incurred during velocity analysis might exceed errors in reflection times. The situation could be Early Conferences improved by smoothing velocity anomalies rather than average Two conferences, entitled Southwest Pacific Symposia, werevelocities. Denham illustrated this point with reference to the held in Sydney in 1975 and 1977. Kingfish Field, Gippsland Basin. Further warnings on possible misinterpretations of seismic results, with a few examples of The proceedings of the first (Falvey and Packham, eds, 1975)past problems, were given in the account of the first Petroleum consisted of extended abstracts. Most of the papers wereGeophysics Workshop held in Melbourne in February 1983 divided into regional sectionsEast Australia, younger(Smith, ed., 1983).Pacific arcs, New Zealand, Solomon Islands, and Papua NewSpathis (1983) showed how to design digital filters which Guinea, while a final section contained papers on the seismic,approximate ideal low-pass Butterworth filters, and to derive volcanic, and kinematic processes at plate boundaries. Generalhigh-pass, band-pass, and band-reject filters from these by acceptance of plate-tectonic theory and its applicability in thissimple frequency transformations. Computer programs were part of the world is evident. listed.The second meeting (Coleman, ed., 1978) consisted almostHaren (1984, 295) reviewed the use of electrical methods in entirely of papers on the evolution of plates and platepetroleum search in Australia, including several tests conducted boundaries in the offshore Australasian region. by CSIRO in Australian sedimentary basins. The most promising An important contribution to mineral prospecting was theparameter was apparent resistivity; this often correlated with special issue on the Elura orebody (Emerson, ed., 1980, 203).chargeability over hydrocarbons. Negative SP effects were also This massive sulphide orebody, at the northern end of theassociated with hydrocarbon accumulations. The effects were Cobar field, was located by geophysical methods, mainlyclaimed to be related to chemical changes in the overlying magnetic and gravity, about 1972, and subsequently wasrocks, caused by a plume of escaping hydrocarbon vapours. subjected to a number of field tests by various geophysicalHenderson et al. (1984, 315) claimed that low-amplitude, high-methods to determine the most effective methods of locatingwavenumber magnetic anomalies occurred over hydrocarbons, a similar orebody in the particular environment. It is a dense,owing to reduction of haematite to diagenetic magnetite.very conductive, moderately polarisable orebody, with aNelson (1984, 493) proposed that the seismic reflection highly magnetic core, lying at depth under a thick weatheredtechnique might be used for deep targets in mineral conducting layer. Electrical and EM methods showed distinctexploration, partly for stratigraphy, but also for direct orebody anomalies which could be associated with the orebody, butdetection. Reflections in the latter case might be due to density careful field and interpretation procedures were necessary tovariations rather than changes in elastic constants. Experiments avoid confusion from anomalies due to weathering and somesuggested that seismic data should have a white spectrum over other rock types. more than two octaves, and upper limiting frequencies greater Beginning in Adelaide in 1979 (Emerson, ed., 1979b), ASEGthan 200 Hz.has held a series of general geophysical conferences, initiallyPapers presented at the 1985 Conference in Sydney (Gunn, ed., biennially but more frequently recently; proceedings from1985) included discussions of the problems in acquisition and most of these have been issued either as Journal numbersprocessing of seismic data, such as velocity determination and or as special publications. Papers from these, together withelimination of noise from artificial sources. Three- dimensional those from specialist conferences on various topics, have beensurveys, both reflection and refraction, received substantial included where appropriate in the topical summaries below. attention. The tau-p and Nth-root stack methods of analysis were presented. A triaxial downhole system for acquisition of Petroleum Exploration S as well as P data was described by James and Nutt (1985a, 353). James and Nutt (1985b, 352) also described extension of The main method used here is of course seismic reflection,downhole vertical seismic profiling to inclined boreholes and though aeromagnetic surveying, and possibly electricaloffset surface-energy sources.measurements, also play an important part. Blackburn (1986a, 50) discussed the possibility of direct Gray (1971) described what was believed to be the first use ofhydrocarbon detection in the Gippsland Basin by seismic Geoflex in the desert areas of Australia, near Lake Hope in thereflections. Gas is present in most Australian crudes, and only a Cooper Basin. Drilling was difficult because of the long distancesmall quantity is needed to produce a satisfactory impedance to the nearest water supplies, and the sand dunes restrictingcontrast. Their high API gravities should also be favourable for 39 PREVIEW FEBRUARY 2020'