Marine Oil and Gas

Potential environmental effects arising from marine oil and gas exploration and production include:

Blowouts and oil spills

The risk and consequences of oil spills is probably the greatest environmental concern associated with marine oil and gas operations. While most oil enters the oceans unseen, massive oil spills highlight the catastrophic effects that oil can have on marine wildlife and human communities. ²¹⁸⁰  There has been only one major deepwater blowout, which was the Deepwater Horizon well in the Gulf of Mexico, which blew catastrophically in 2010. So far, there have been no major well blowouts in New Zealand, but the risks may increase as oil and gas activity expands. Because this country is so far away from any offshore oils and gas servicing ports, it would take a long time for international aid to respond. ²¹⁸¹

Formations deep in the ground, where hydrocarbons are located, are sometimes under intense pressure.  Controlling these pressures is fundamental to successfully drilling wells. Various ‘barriers’ are employed to ensure pressures are controlled throughout the life of the well, including the initial drilling phase. The key principle is that there are always two tested barriers in place (“the two barrier rule”). 

The high pressure drilling fluids called “mud”, which are pumped down the centre of the drill string during drilling, create a primary barrier which exerts hydrostatic pressure to stop hydrocarbons coming to the surface. Mud weights are adjusted during drilling to ensure balance is maintained. The blowout preventer generally acts as the second barrier, if the mud fails, when drilling an exploration well. ²¹⁸²

Well blowouts occur when the pressure in the reservoir being drilled overwhelms the primary mud barrier, and the blowout preventer and other secondary barriers are unable to stop the flow. This can be a result of faults in the safety device which is intended to seal the well, poor well design, and/or human error. Often it is the result of a combination of these factors. Blowouts can sometimes be brought under control quickly, but in other situations they can last for a prolonged period. In 1979, when the Ixtoc 1 drilling rig sank as the result of a blowout, it took engineers nearly a year to stem the flow of oil into the Gulf of Mexico. ²¹⁸³

A report by the Chemical Safety Board, an independent investigative arm of the USA federal government, concluded that the 2010 Deepwater Horizon disaster was caused by the blowout preventer failing to properly close the well when a surge of natural gas from the deep formation caused a blowout. The blowout preventer itself punctured the riser pipe, allowing oil to start leaking into the Gulf of Mexico close to the seabed. This triggered the worst offshore oil spill in history. About five million barrels of oil flowed into the Gulf before the well was closed off, 87 days later. ²¹⁸⁵

The impact of such oil spills can vary from minimal, to the large scale mortality of marine life, depending on the sensitivity of the environment and its ability to recover. The Ixtoc 1 disaster contaminated the Gulf of Mexico waters with millions of barrels of crude oil. Fisheries had to close, birds and other wildlife perished, and vast lengths of coastline were soiled. ²¹⁸⁶

The figure below ²¹⁸⁷  highlights some of the key potential environmental impacts resulting from oil spills, caused by oil and gas drilling, including well blowouts. Oil spills from vessels and their impact on the environment are discussed elsewhere.

Ship equipment and movement, light, noise, emissions

Other environmental impacts can result from equipment and ship movements, the use of artificial light, increased noise levels and air emissions. The figure below ²¹⁹⁵  identifies some of these potential direct and indirect environmental impacts. Many of these impacts are confined to a small area surrounding the activity. Ways of addressing these potential impacts are discussed in the best practice section below. ²²⁰⁶

Fisheries

Permanent production activities may affect fisheries through direct effects on fished species. Fish may move away from the area of influence due to increased levels of activity. ²²⁰⁷  In addition, the new structures will alienate a small area of seafloor, so that it no longer provides foraging habitat for demersal fishes (which live and feed on or near the sea floor). However, these same structures may provide new artificial reef-like surfaces and increase reef habitat in the area. ²²⁰⁸

There may be impacts on fisheries management as production platforms and pipelines invariably have a zone of restricted access around them that restricts fishing access in these areas. Unless commercial fish quota is bought by the petroleum company, and retired for the duration of the petroleum activities, commercial fishing will be displaced into the remainder of the quota management area increasing pressures on fish populations there. The impact of a single production facility is unlikely to be great, but the cumulative impact could be significant if multiple production facilities and pipelines are located within a single quota management area. ²²⁰⁹ There are fisheries exclusion zones around oil and gas infrastructure (e.g. rigs and pipelines) in the North Sea. It has been estimated that in the North Sea, where there are more than 500 platforms and thousands of kilometres of pipelines, the loss of fishing area was only around one per cent. ²²¹⁰

Seabed/benthic life

Marine life present on the seabed where drilling occurs will be directly impacted, in particular by the legs of a jack-up rig or fixed platform, the well bore and wellhead itself, and any mooring chains and anchors.

The type of drilling lubricant used (oil-based, synthetic or water-based) has a large bearing on the toxicity of drill cuttings and the speed of impact if cuttings from the well are discharged into the water column and then settle on the seabed rather than being collected and disposed of on land. ²²¹¹  If a submerged pipeline is built, to bring the oil or gas onshore, then the seabed will be damaged during construction and any associated trenching.

The impacts of an individual platform and associated infrastructure are localised, but there may be more significant cumulative impacts from multiple production facilities and pipelines in a single region. The level of this impact will depend on whether the area contains vulnerable benthic species, and whether these are limited in range or are rare.

The effects during decommissioning will depend on whether the infrastructure is dismantled and removed, sunk to the seafloor and abandoned, or left intact for another use such as carbon sequestration. If left intact, the effects of the structure being present will continue as for the production phase. Removal of the structure will have some impact on the seafloor and benthic organisms, as well as on the creatures which have become attached to the structure, and in some cases the environmental impacts may be less if it is left in situ. If the infrastructure is abandoned, any oils and toxic substances will need to be cleaned off the structure, to ensure that they do not dissipate into the marine environment. The platform will slowly rust and disintegrate, and this may cause negative effects over a long-term. ²²¹² Some structures like the Rena 

Marine mammals, seabirds and other fauna

Seismic surveys may have an acoustic impact on marine fauna. The acoustic impact of seismic surveys on marine mammals is particularly well documented. The consequences will vary from none to behavioural (may leave the area), from no injury to acute injury (ear drum damage) to serious (death) depending on the noise level encountered, the species and the habitat. There may also be cumulative effects from repeated exposure. ²²¹³

Seismic streamers may attract fur seals, sea lions and whales, during deployment and retrieval, creating a risk of entanglement and injury or drowning.

Lights at night (such as those on a drilling platform) typically attract and disturb seabirds and may cause them to collide with the above sea surface structure. Subsurface activity and lights may affect marine mammals. Fauna may also interact with the infrastructure. For example, seal haul-outs occur on the leg bracing struts of some platforms. ²²¹⁴

Survey and support vessels create a risk of ship strike of marine mammals. In addition, the installation of the production platform, pipeline construction and trenching, underwater inspection using ROVs or submersibles, drilling activities, and routine maintenance and pumping will produce some underwater noise that could affect marine mammals, mainly causing them to avoid the area. ²²¹⁵

Biosecurity

Oil drilling platforms create biosecurity risks as they are large structures which lie stationary in coastal waters for long periods of time, which enables organisms to grow on the immersed parts. Drillships brought in from overseas can potentially bring with them invasive marine pests. More recently, the other types of rigs have been brought into New Zealand to support oil and gas product on heavy lift vessels so biosecurity can be well managed.

The South African brown mussel (Perna perna) was detected in Tasman Bay following the cleaning of a semi-submersible oil rig’s submersed surfaces that had arrived from Australia in November 2007. ²²¹⁶ In total, 10 non-indigenous species were found on the rig. This resulted in a clean-up operation to remove the risk of the exotic pests establishing in New Zealand. Transported species are unlikely to survive independently of the rig in deep offshore waters – the risk is that the platform acts as a stepping stone for non-indigenous species to invade shallow coastal habitats. The risk can be lowered by cleaning and/or fresh antifouling if necessary. ²²¹⁷

Biosecurity risks and impacts are discussed more in Chapter 5: Marine biosecurity.

Amenity effects

Nearshore oil and gas activities can potentially have the following amenity effects:

• Noise from the operation could affect residents and visitors to the area, if operations are close to the shoreline
• Vessels passing regularly through the marine area can create an unwelcome visual impact, particularly in areas which are normally little used by vessels
• The presence of oil rigs in the sea can industrialise the natural ocean landscape

Other impacts

Nearshore oil and gas activities may negatively impact on areas and resources of importance to iwi and hapū. These could include kaimoana areas and wāhi tapu or urupa sites which lie on or under the seabed.

There may be other ecological impacts resulting from increased light and noise in the deep ocean environment. These are poorly understood but could impact on fish and marine mammals that are dependent on sound for locating prey, navigating and communicating. ²²¹⁸  There is also the risk of accidents leading to spillages and loss of equipment within the marine environment.

Last updated at 3:15PM on February 11, 2018