Experiments in the use of directed line sources in refraction profiling Arckaringa Basin – 1971

Abstract

During investigations of the Arckaringa Basin, four types of pre-Permian dolomite were intersected in stratigraphic wells and these can be distinguished by differences in density and seismic velocity. Knowledge of the limits of each dolomite is of importance in establishing the history of the Basin, and a seismic survey was carried out in May and June, 1971 to determine whether seismic refraction profiling could be used to map these rock types. To increase mobility and reduce costs, experiments were conducted using 'Geoflex' (trade mark of Imperial Chemical Industries Ltd.), a detonating cord, as an energy source. The Geoflex was ploughed to a depth of about 18 inches below the ground surface before being detonated. The results obtained in six widely separated localities were mostly fair to good. The quality of the primary and secondary refraction events appears to be largely independent of the size of the charge and is related to the entry angle of the input signal. This is determined by the velocity of the Geoflex and the surface and near-surface materials, and the length of the Geoflex array. Results show that over a wide area of the western Great Artesian Basin in South Australia, a directed line source can be used to obtain good quality refraction data at a cost considerably lower than that resulting from the use of conventional shot hole drilling and dynamite or other explosives.