5 Safety and the environment
5.2 Environmental management
Management of the environmental impact of projects is not only a legislative requirement, but also good business. It is cost effective, provides a competitive advantage, responds to the public demand for scrutiny, and allows operations to continue in an area. Environmental management, like safety, is now an integral part of all phases of the petroleum business, from early exploration activity through to decommissioning a petroleum field.
Base-line studies and environment impact assessments are commonly used schemes for describing the potential impact of a project on the local environment. A base-line study describes the initial natural state of the flora, fauna and land/seabed conditions prior to any activity. Such a benchmark allows future changes to be identified and provides a reference point if restoration or improvement is required. Such studies are often conducted by independent scientific specialists in order to provide rigour and objectivity.
Environmental impact assessments (EIAs) are detailed ecological studies that are linked to the planned activities of a particular phase of work. They build on the findings of the base-line study and aim to develop or use specified techniques and procedures to minimise the impacts on the environment. These measures may range from using ‘soft-start’ airguns at the start of a seismic survey in order to alert nearby marine mammals, which can be disoriented by repeated loud noises, to avoiding drilling in fish spawning grounds and reducing the use of oil-based drilling muds. Effective EIAs involve widespread co-operation and consultation amongst the industry and stakeholders in order to achieve the best possible outcomes. As an example, the Atlantic Frontier Environmental Network (AFEN) focuses on the Atlantic waters to the west of Orkney and Shetland, and involves a consortium of oil companies, government bodies and conservation organisations.
5.2.1 Environmental risks
The most significant environmental risks from petroleum production come from oil spills. Despite precautions, accidents do occur. Perhaps the best documented case history is provided by the Exxon Valdez, which ran aground in 1989 in Prince William Sound off Alaska. Some 37,000 tonnes of oil were spilled (roughly equivalent to 125 Olympic-sized swimming pools), to affect more than 2000 km of coastline. Whilst this spill was not the highest ever in terms of volume, it is widely considered the worst in terms of damage to the environment, because of the rugged shoreline and abundance of wildlife. The clean-up (remediation) process cost more than 2 billion dollars and took several years. Today there is only very localised evidence of the spill.
Two much larger spills, from the Braer (85,000 tonnes) and Sea Empress (72,000 tonnes), caused far less environmental damage and had only short-lived effects. The Braer, which foundered in 1993 on the Shetland Isles, was carrying a relatively light and easily biodegradable crude oil which was quickly dispersed into the water column by storm force winds and high seas. Similarly, the Sea Empress was transporting a light crude oil when she grounded approaching the oil refinery at Milford Haven, South Wales in 1996. Although more than 100 km of outstanding coastline were initially polluted, the combination of efficient clean-up operations and rapid natural dispersion restored their visually aesthetic appeal within six months. The point is that whilst oil spills are never good news, their long-term effect is rarely enduring.
Despite the increasing number of large tankers carrying crude oil around the world, the number of large spills shows a significant decrease over the last several decades (Figure 13). This is encouraging but it does not provide grounds for complacency and maritime safety systems continue to be improved. Nevertheless, many analysts contend that more oil is ‘spilt’ each year by the deliberate flushing of tanks at sea than is lost by accident.
Figure 13: Annual number of large oil spills (over 700 tonnes) worldwide. (The horizontal bold red lines represent the 10-year averages.)
Aside from oil spills, there are several other significant environmental concerns for the petroleum industry. Gas venting and flaring has traditionally been used to dispose of excess gas in fields where no containment or transport facilities existed. This practice releases large amounts of methane and carbon dioxide into the atmosphere, both of which are greenhouse gases. The World Bank estimates that the annual volume of natural gas being vented and flared is about 100 billion cubic metres, enough fuel to provide the combined annual gas consumption of Germany and France. There is now an increasing effort to make commercial use of excess gas, as in the Clair field west of Shetland. That field was inaugurated in 2005, some 27 years after it was first discovered. With an estimated 5 billion barrels of oil in place it was considered one of the largest undeveloped resources on the UK continental shelf. The oil is being exported to the Sullom Voe Terminal in Shetland via a 105 km pipeline and the gas will be transferred to the Magnus field and re-injected there to enhance oil recovery.
5.2.2 Dealing with environmental issues
One of the most promising schemes for dealing with greenhouse gases is known as gas sequestration. This involves injecting carbon dioxide into a depleted underground reservoir and monitoring the integrity of the trapped gas with time-lapse seismic data. Successful trials in Norway indicate that this technique has the capacity to make significant reductions to the carbon dioxide emissions throughout northern Europe. Interestingly, at pressures of a few atmospheres and temperatures below 30–40 °C, carbon dioxide forms a stable liquid that is denser than water (Figure 14). At temperatures lower than 10 °C it can combine with water to form an ice-like substance known as a gas hydrate (see also Section 7.2). Provided the temperature in a depleted petroleum reservoir is below that where pressured carbon dioxide is only stable as a gas, storage can be indefinite. Methane can also be stored in similar settings, or in underground salt caverns, and recovered according to demand. The key issues now appear to be cost and legislation, rather than feasibility.
Figure 14: Results from experiments conducted at the Monterey Bay Aquarium Research Institute, California to test the feasibility of sequestering carbon dioxide in deep ocean basins. (a) A typical ocean water column temperature profile (solid red line) for Monterey Bay, California overlain on a diagram showing physical states in which carbon dioxide occurs at different pressures and temperatures. (b) Liquid carbon dioxide being poured onto the sea bed at a depth of around 900 m.
The safe disposal of waste products such as drill cuttings and oily water is subject to increasingly tight regulations and innovative solutions have emerged. For offshore installations this may involve transporting all waste to the shore for proper treatment and recycling; for example, drill cuttings are commonly recycled as cat litter, fertiliser or used in the construction of footpaths. Alternatively they are cleaned on site and re-injected underground. On a far larger scale there remains the challenge of decommissioning the 6500 offshore installations worldwide as they come to the end of their productive life. Most will be completely removed from their current location and brought to shore for reuse or recycling. The remainder will be examined on an individual basis to establish what is technically feasible and safe to remove. The debacle of the Brent Spar (Box 3) illustrates the need to resolve the technical, commercial and environmental debate before embarking on a prescribed course of action.
Box 3: The Brent Spar incident
In 1995 the giant oil company, Royal Dutch/Shell, needed to decide how to decommission a disused North Sea oil storage platform called the Brent Spar. Nearly 150 m long, this enormous structure had been in service for 20 years and had the capacity to store 50 000 t of crude oil. Shell considered various disposal options and two made it through to final consideration: deep-sea disposal and on-shore dismantling. These are summarised in Table 5.
Table 5: Two possible disposal options.
|Deep-sea disposal||On-shore dismantling|
|Tow the Brent Spar to the North Atlantic.||Tow the Brent Spar into a deep harbour.|
|Use explosives to sink the platform in deep water.||Decontaminate the structure.|
|Allow the structure to settle on the sea bed.||Dismantle and reuse the materials.|
|Recognise that there will be local pollution for 12–14 months.||Dispose contaminants safely onshore.|
|Technically the easiest option.||Technically complex and with a greater hazard to the workforce.|
|Cost estimate about £10 million.||Cost estimate about £40 million.|
Shell decided on the deep-sea disposal option and gained the necessary permissions from the Government and regional authorities. Greenpeace, the environmental group, argued that Shell were underestimating the amount of contaminants that remained in Brent Spar and saw no reason to pollute the ocean when an alternative existed. They further argued that Brent Spar would set a precedent for deep-sea disposal in the future. Greenpeace orchestrated a successful campaign that influenced public opinion against Shell's preferred option and it extended to a boycott of Shell petrol stations in parts of Europe.
Faced with growing opposition, Shell decided to review its options and towed the Brent Spar to Norway. Some 2 years later they dismantled it and recycled parts as a foundation for a new ferry terminal. The Brent Spar episode will be remembered as a bruising conflict in which both protagonists were accused of manipulating technical and emotional opinions to their own advantage. For example, Greenpeace have since admitted that their counter-arguments over the amount of contaminants remaining in Brent Spar were flawed. It is clear that the issue of how North Sea structures will be abandoned in the future demands full co-operation between all the stakeholders and a firm hand from the legislators.
The combination of legislation and good practice has led to a significant reduction in the environmental impact of the petroleum industry over the last decade. Quite properly, this shows no sign of slackening. However, the lasting damage done to the environment by petroleum is not primarily caused by ongoing operations or oil spills, but through society's deliberate use of petroleum products as fuels.