Planned activities are those necessary for exploration drilling and therefore planned to occur. In contrast, unplanned events include potential emergency situations.
During drilling activities, drilling discharges in the form of drill cuttings (drill solids), drilling fluids (muds) and solid additives (e.g. barite, bentonite), brine and cement chemicals will be generated. Heavier drill cuttings and particles will settle to the seabed around the wellhead while lighter, finer particles associated with drilling muds and cement discharges would be carried away with offshore currents and eventually settle to the seabed some distance from the rig. These discharges have the potential to impact environmental receptors through decreases in water quality and by physical alteration of the seabed.
The semi-submersible drill rig will be lit 24 hours a day using bright white artificial lighting. These lights are similar to those used by other offshore activities in the region, including shipping and fishing. The rig lighting system is normal practice for offshore petroleum activities. Chevron has considered all options for lighting the drilling rig to ensure they meet safety, operational and navigational requirements and regulations.
Black water, grey water, macerated food waste, brine, cooling water and oily water will be generated during exploration activities. The release of these liquid wastes from vessels in Australian Commonwealth waters is permissible under the Protection of the Sea (Prevention of Pollution from Ships) Act 1983, which reflect MARPOL Annex IV (sewage), Annex V (garbage) and Annex I (oil pollution) requirements appropriate to vessel class. The MARPOL pollution prevention standards are internationally accepted and implemented throughout the petroleum industry. The proposed control measures for the discharge of the liquid waste streams meet requirements of the Commonwealth Navigation Act 2012, Protection of the Sea (Prevention of Pollution from Ships) Act 1983, and the South Australia Protection of Marine Waters (Prevention of Pollution from Ships) Act 1987.
Physical presence and interaction relates to the physical presence of the rig, its support vessels and the safety exclusion zone (a 500 m radius around the rig) and how these interact with the marine environment. This includes the potential for marine fauna to be drawn into the rig’s dynamic positioning thrusters, collision between support vessels and marine megafauna and seabed disturbance due to the placement of a subsea accumulator module (SAM) that rests on a mud mat next to the blowout preventer (BOP).
The risk and impact risk assessment scoping exercise identified a number of environmental risks that were not considered credible or applicable. Risks identified as not credible or not applicable do not form part of the risk assessment.
Semi-submersible drill rigs typically produce low intensity continuous noise during drilling operations. It will emit underwater noise through a combination of drill pipe operation, seismic profiling, machinery and dynamic positioning (DP) thrusters. Other noise will be associated with the operation of machinery and the arrival and departure of supply vessels and helicopters. During normal operations, drill rig activities will generate noise at various levels 24 hours per day.