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Geological and Geochemical Studies of Northwest European Continental Shelf |
Tenneco Oil Co. & Tenneco United Kingdom Inc., Drada House, 84 Lower Mortlake Road, Richmond, Surrey TW9 2JG
Tenneco Oil Company has conducted extensive bottom sampling 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 x 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 up to 2 m in length. Overall core lengths varied from 0.5 m in hard sand to 2 m in clay. For geochemical analysis, 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 extracts. 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.
After an independent assessment of the geochemical data was completed, the resultant geochemical interpretation was integrated with geological and geophysical data. Comparison of the geochemical maps with those produced as a result of geophysical and geological interpretation revealed remarkable similarity between the structural and geochemical interpretations. This suggests focussing of upward movement of hydrocarbons by geologic structure.
This exercise demonstrates that geochemical data of this type can greatly aid in the evaluation of the hydrocarbon potential structures, but should not be used alone as a prospecting method.
