Offshore Basin Screening from Satellites

Nigel Press, Geoff Lawrence, John Milsom, Trevor Macklin, Mike Oehlers, M. Holliday, Richard Chiles

All oil bearing regions have oil seepage, although offshore the distribution of seepage has been poorly mapped. Oil slicks on the sea surface are good indicators of oil seepage but confusion with other sources of oil and the lack of an affordable and reliable detection system has inhibited explorers using this information in the past.

We present a method to map oil slicks systematically, to categorise their origin and to integrate this information with sedimentary basin structure and other sub-surface data. The method is based on data from the ERS-1 radar satellite and will be applicable to ERS-2, Radarsat and other future missions.

We have analysed 200 radar images covering 500,000 km² of ocean from the Mediterranean, Falklands Shelf and Southeast Asia. Radar inspects the ocean through cloud and at night. Using concurrent weather models, image and radar analysis and by integrating with sub-surface geology information, we are able to categorise seepage-related slicks from pollution and other sea-surface films. Results show close co-incidence with oil and gas accumulations and zones of faulting.

We have simultaneously developed methods to compute gravity from the radar altimeter of the same satellite. In order to achieve best resolution we have merged the close-spaced ERS-1 altimetry with that from several previous satellites. Excellent understanding of regional geological structure results from the interpretation of this gravity, which has been used to infill and link ship-borne gravity surveys.

The combination of these two satellite methods results in an offshore basin screening methodology to reduce risk on encountering hydrocarbon source and structure. It is especially suitable for pre-seismic appraisal of frontier regions at very low cost

The methods were developed with the help of funds from the UK Government and international oil companies over the last 18 months.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995