Page 141 - Environmental Control in Petroleum Engineering

128 Environmental Control in Petroleum Engineering

The effect of chronic noise from underwater drilling on the behavioral
and physiological responses of belukha whales has also been studied
(American Petroleum Institute, 1986b). It was found that belukha
whales, like other toothed cetaceans, have a hearing range of greatest
sensitivity different from the frequency range of most industrial
sounds. The only response to the sound observed was a startle res-
ponse at the start of each playback session in a pool containing four
whales. Thus, little effect on whale health or behavior is expected from
drilling activities.

3.11 EFFECTS OF OFFSHORE PLATFORMS

When properly managed, the actual environmental impact of offshore
exploration and production activities is very low. In some cases, the
presence of offshore platforms can be beneficial. The subsea structure
(jacket) provides a substrate for marine flora to grow. This growth is
particularly important in areas where few rocks are found on the bottom
to provide such a substrate, e.g., in the Gulf of Mexico or other deltaic
systems. This flora then attracts fauna of different types and sizes.
Eventually large fish are attracted to the platform, yielding a much higher
fish concentration than is found in the open ocean. This high fish concen-
tration provides enhanced commercial and recreational fishing opportunities,
When an offshore field is abandoned, the platform must be removed.
The least expensive and safest method for platform removal has been to
use explosives to sever the piles and conductor pipes below the mudline.
The use of underwater explosives for this purpose, however, can be lethal
to aquatic life swimming nearby. Monitoring of the surrounding area
(within 1,000 yards) is now required in some areas before the charges
can be detonated. Any endangered species in the area, such as sea turtles,
must be removed before detonation. Other methods to sever the platform
from its anchorage that have been considered include acid cutting,
embrittlement through liquid nitrogen freezing, solid fuel cutting torches,
water blasting, and mechanical cutters. These methods, however, may
result in greater safety hazards to the personnel implementing them.

3.12 RISK ASSESSMENT

Risk assessment provides a numerical estimate of the probability of
potentially adverse health effects from human exposure to environmental