Marine Seismic Surveys

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ABSTRACT The frontiers of petroleum exploration are principally in offshore areas where seismic surveys provide the only technical data for prospect evaluation. The marine seismic industry has grown from 15 crews at work in 1960 to 75 crews today. Worldwide expenditures on marine seismic surveys last year totaled $450 million. The average cost per mile of marine seismic data today is the same as it was 9 years ago. New technology has reduced operating costs counteracting inflation. Significant improvements have been made also in data quality and resolution. MARINE SEISMIC SURVEYS In offshore areas such as the Atlantic OCS and the Bering Sea, seismic surveys commonly provide the only source of technical data on which decisions can be made concerning lease acquisition. In such frontier areas few wells are available for use in conventional exploration techniques. Other methods used on land, such as surface geology, photo mapping, and satellite imagery, are not applicable in marine areas. Last year, the petroleum industry spent more than $450 million on marine seismic surveying, including the associated data processing and interpretation. This may seem like a large amount of money, but it is almost negligible compared with the additional outlay that is made based on the geophysical data. For example, the Atlantic offshore sale last year was preceded by 68 crew months of seismic work at a cost of $35 million. In that sale the petroleum industry bid $3.5 billion based principally on the seismic data. Geophysics for many years has played a key role in petroleum exploration, but it is only in the past 15 years that its use in offshore areas has become significant. In terms of the number of seismic crews in the field, most of the activity is onshore (Fig. 1). Only 15 marine crews were at work in 1960, but this has increased to an average level of 75 in 1976. These figures are for the free world only. Essentially all of the work in 1960 was carried out in the Gulf of Mexico, while today marine crews are surveying the shelf areas off of every continent. Due to higher mobility, a marine crew typically records 10 times as much data as a land crew. For this reason, it is more useful to look at statistics in terms of line-miles of data recorded (Fig. 2). In 1960, only 21 percent of the seismic data was recorded by marine crews. Last year, more than 800,000 line-miles of data were recorded offshore and this represented 67 percent of the total seismic activity. This reflects the increased dependence on offshore areas for new major discoveries. The increases in activity in 1973 and 1974 reflect the response to the energy crisis. The drop in activity in 1975 and 1976 is principally due to adverse government regulations and tax policies in the United States, Canada, and the Far East. In 1971, the petroleum industry began placing an increased emphasis on finding new reserves in the United States.