vibratory energy may couple into the rig structure and radiate into the water 

 from submerged portions of the structure, or couple into the ocean bottom from 

 which noise may be re-radiated into the water. The engine or turbine exhaust 

 may produce high noise levels in the air, and couple into the water to be 

 radiated also as underwater noise. Various elements of the drill string may 

 be noise sources, from the point of application of energy at the drill 

 platform, along the drill string, and down to the bit itself as it bites into 

 various rock formations. Vibratory energy from the drill system may radiate 

 by various paths, including drill to earth to water, drill string to water, 

 drill string to platform to water, etc. 



The above discussion illustrates the complexity of the sound 

 emission process at an oil platform. Studies conducted to date have been 

 insufficient to determine which of the various individual source and radiation 

 mechanisms are the important ones. It is expected that the mechanisms will 

 vary from platform to platform, and with the particular operation on the 

 platform, such as drilling vs. production, type of drilling, type of prime 

 power source, and type of vibration isolation, muffling, etc. As stated 

 earlier, the analytic approach used in this report treats the source as a 

 simple, localized, omnidirectional source. Future work which looks in detail 

 at the distribution of vibration in different parts of the structure and in 

 the vicinity of various mechanical sources will be required to understand the 

 noise radiation process, and to provide a scientific base for noise mitigation 

 if it is required. 



G-13 



