New directions for marine 3-D surveys

Abstract

In the late 1960's and early 1970's there were severe constraints on how a marine three-dimensional (3-D) seismic reflection survey could be designed. Streamer location techniques were almost nonexistent, and seismic data processing procedures were developed only for 2-D surveys. For these reasons and others, 3-D surveys were designed as a collection of parallel 2-D seismic lines. Geologic considerations had a minimal impact because 3-D surveys were designed with the concept of dip direction and strike direction. As survey sizes grew, this simple geologic picture broke down. Modern 3-D data processing systems and modern acquisition technology place fewer constraints on the design of 3-D surveys. We should exploit this new freedom in those cases where geology and straight lines are not compatible or where costs can be significantly reduced. Successful marine 3-D surveys have been shot using parallel 2-D lines, crossed grids of parallel 2-D lines, collections of randomly oriented 2-D lines, and as a series of overlapping circular shot lines. A 3-D seismic survey was recently conducted over a salt dome by shooting a continuous series of concentric circles. All 3-D methods seem to have advantages and shortcomings. The more we learn about and use different techniques, the more we realize that our first ideas, such as considering a 3-D survey as a collection of parallel 2-D lines, may not necessarily be the best ideas.