Surface Geochemical Exploration in the North Sea

programmes over several known but undeveloped oil and gas fields in the North Sea. Samples over one example, Beatrice Field in U.K. waters, were distributed on an approximate 2 • 2 km grid over the entire licence block containing the field. Shipboard samples were collected from the ocean floor using a modified gravity-coring device that delivered cores upto 2 m in length. Overall core l ngths varied from 0.5 m in hard sand to 2 m in clay. For geochemical nalysis, samples were taken from the lower 0.5 m of the core. In the laboratory, samples were analysed for light gases using gas chromatography. These results are expressed as parts per billion (1012) dry weight of sample. Fluorescence intensity over two peaks was recorded from hexane xtracts. These results were expressed as relative peak intensities. Data were subjected to a variety of analytical techniques including mapping of both individual variables and specific ratios, cross-plotting and regression of variable pairs to determine subtle interrelationships, and to a battery of multivariate pattern recognition techniques to isolate recurrent, mappable geochemical signatures