ASA 126th Meeting Denver 1993 October 4-8

4pAB10. Recording, analysis, and verification of low-frequency sounds produced by Arctic offshore drilling equipment.

Kenneth D. Brewer John D. Hall

Coastal & Offshore Pacific Corp., P. O. Box 31554, Walnut Creek, CA 94598

Digital recordings of underwater sounds produced by anchored and bottom-founded Arctic offshore drilling equipment (drilling rigs) were made during drilling and idle conditions in open water and under sea ice. Sound production was verified by recording the frequencies produced by specific pieces of equipment aboard the rigs using a single axis accelerometer. It was determined that most of the sound energy produced by both the anchored and bottom-founded drilling equipment was in the frequency band from 1 Hz to 1 kHz. The drill turntable and drive equipment on the bottom-founded drilling rig produced sounds as low as 1.8 Hz. The broadband [20 Hz to 20 kHz source level (dB re: 1 (mu)Pa[sup 2]@1 m] of the bottom-founded drilling rig (146.2 dB) was about 30 dB less than the broadband source level of the anchored drilling rig (178.6 dB). Acoustic transmission loss in the inshore areas of the Alaskan Beaufort Sea, where water depths are less than 100 m, was found to be slightly greater than cylindrical spreading (-11.0 to -13.0 log R dB) at the two sites about 350 km apart. [Work supported by ARCO Alaska, Inc.]