Review of current developments in exploration geophysics

Abstract During the past year, exploration geophysics has made its greatest progress in the application to prospecting of instruments and techniques which were until recently only in the development stage. The most notable examples are magnetic recording and velocity logging, both of which are already being offered as commercial services. The use of magnetic recording permits greater flexibility in seismic interpretation; automatic time correction, facilitating compositing as well as preparation of record sections; and the ready storage of seismic data in a form suitable for any processing procedures that may be developed in the future. Interval velocity logs have given geophysicists a better understanding of the origin of reflections from a complexly layered section. This understanding should lead to a more realistic interpretation of reflection data, and may eventually make it possible to map stratigraphic as well as structural features. Other noteworthy developments in seismic prospecting during 1955 include new methods for generating seismic energy, novel approaches to the improvement of signal-to-noise ratio, and the application of high frequency techniques in oil exploration.Although current research in petroleum geophysics is concentrated more than ever on seismic techniques, there have been important developments in the application of other geophysical methods to petroleum prospecting, mining exploration, and engineering problems. The gamma-gamma logger now gives density data which are sufficiently reliable for gravity interpretation; an induced polarization method has been successful in finding ground water; and airborne electromagnetic methods have been widely used in the search for base metals in Canada. A new type of airborne magnetometer based on nuclear magnetic resonance has gone into service in prospecting for iron ore in the western United States. This device is particularly adapted for use in light aircraft.The rapidity of current technological improvement in exploration geophysics is attributed to the acceleration of geophysical research activity in the oil industry after World War II, to productive fundamental research, and to a widespread attitude among geophysicists of dissatisfaction with existing techniques.