Environmental Impacts

All four main phases of the offshore oil and gas development process involve operations causing environmental impact:

Exploration - Geophysical surveying and exploratory drilling
Development - Construction of facilities and well drilling
Production - Extraction of petroleum hydrocarbons and transport via pipelines and marine vessels
Decommissioning - Well capping and removing some or all of the equipment.
Miscellaneous - Domestic waste from everyday rig activities and other incidental accidents

The environmental impact is a function of:

Exploration

The primary environmental concern associated with the exploration phase is the potentially lethal impacts of seismic surveys to some forms of marine life. Mortalities can occur in close proximity to seismic shooting (Richardson et al., 1995), however, sub lethal impacts such as injury and behavior modification may occur at substantial distances as some organisms use sound to communicate, navigate and hunt (Popper, 2003a; Richardson et al., 1995). Birds may also be disturbed by seismic surveying either during nesting (Strong et al., 2002), or diving for prey (RSC, 2004). The range and extent of these effects remains debated, as short and long term impacts associated with seismic shooting are not clearly understood and are extremely difficult to test for.

Development - Construction/Drilling (treatments of cuttings, mud) (Extracts from SFU, 2004)

Depending on the type of rigs constructed, structures attached to the sea floor can result in the loss of benthic ("bottom dwelling") habitat. However, rigs also attracts fish, corals and other species that seek fixed structures for habitat. Drilling, both for exploration and production, has the largest amount of environmental impact. During drilling, fluid and solid pollutants are discharged from drillships, exploratory drilling rigs and other equipment. Drilling wastes are primarily composed of cuttings and muds.

Drill cuttings reflect the type of rock being drilled under the ocean floor. Cuttings can contain heavy metals (mercury, lead, cadmium, zinc, chromium and copper), drilling mud components and sometimes even naturally occurring radioactive materials (NORMs) (Bornholdt and Lear, 1997; Kenchington, 1997). Cuttings typically resemble the consistency of sand or finer materials.

Three types of drilling muds may be used: water-based mud (WBM), synthetic/alternative based mud (ABM), and oil-based mud (OBM). WBMs are primarily composed of seawater. ABMs are primarily composed of paraffin oils , nonmineral oils or synthetic oils. WBMs are the least harmful to marine life, though impacts from WBM contamination are observed in scallops and may occur in other species (Boudreau 1998 in Canada, 1999; Cranford and Gordon 1992 in Kenchington, 1997). OBMs are the most toxic to marine life (Leonov, 1999; AGRA Earth and Environmental Ltd. (AGRA), 1998; Bornholdt and Lear, 1997; Neff, 1987; Sanders and Tibbets, 1987). Today, WBMs and ABMs are generally used in place of OBMs because they are less toxic. However, OBMs may be used in deeper drilling with casings in place where muds and cuttings are drawn up through drilling equipment, separated from cuttings, and possibly reused. Many jurisdictions regulate the potential use of OBM. ABMs can also be toxic to marine life (Kenchington, 1997; Payne et al. 1998, 2001a, 2001b in JWEL, 2001; Leaver et al., 1987), and appear to be no more biodegradable than OBMs (Wills ,2000; Society of Petroleum Engineers 1998-2000 in RSC, 2004). Many biocides in muds—such as sodium salts of hypochlorite, formalin releasers, glutaraldehyde, biguanidine, and quaternary ammonium—are also toxic, and a number of nations have regulated their use (Patin, 1999).

Drilling wastes are commonly disposed of back to the sea, back into wells, or onshore. During the initial drilling of a well, cuttings and muds are not contained by casings and are thus discharged directly to the marine environment. The total amount of wastes generated during drilling is a function of the number of wells drilled, their diameter and their depth. Upwards of 1,500 tonnes of cuttings and muds are disposed per well (GESAMP, 1993). While cuttings, WBMs, and ABMs are typically discharged to the sea, the industry typically reinjects OBMs into disposal wells by permit (JWEL, 2001).

Drilling wastes can cause a number of physical changes to the marine environment near drilling rigs. First, the input of wastes alters the local habitat by burying the original sea floor, smothering the local benthic community and providing a new substrate for colonization (Canada, 1999; Neff, 1987). However, these discharges tend to create anoxic (low oxygen content) conditions in the piles that form on the seabed, making colonization of the new substrate much more difficult (Kenchington, 1997). Turbidity in the water column is increased due to discharges. The resulting cloudy plumes reducing light penetration and may affect organisms in the water column and on the seabed (Krautter, 2003; Patin, 1999).

Other concerns regarding drilling wastes and their disposal centers on their potential adverse effects on the marine biota, particularly toxic effects from associated heavy metals and hydrocarbons. These toxic effects can be either lethal or sub-lethal, and may affect survival or reproductive success. This relates to both pelagic organisms as well as benthic organisms. While it is recognized that a need exists to minimize the use of heavy metals, at present their elimination is not possible. The petroleum regulator is responsible for routine sampling of the drilling discharge and monitoring the heavy metal content. Any discharge of heavy metals is expected to disperse rapidly and therefore limit the exposure (WCOEEAP, 1986; COGLA and BCMEMPR, 1988). However, it would be beneficial to continue to monitor the bioaccumulated levels in the resident populations, particular those of the benthos that may suffer from the most continuous input. It is more than likely that new developments will continue to be made and used in the field in order to increase mud effectiveness while decreasing the need for negative additives.

Development - Other Environmental Concerns (Extracts from SFU, 2004)

Noise associated with offshore operations, both underwater and airborne, is unavoidable. Underwater noise from a rig is expected to be less than that generated by the regular vessel traffic. The impact of underwater noise on mammal vocalization and hearing must be considered. Much of the airborne noise generated by the drilling operation will be from support helicopters. Birds are particularly susceptible to helicopter noise, especially near breeding areas. Observations have shown that cliff nesting seabirds will leave nests as a helicopter approaches within 250m. This can lead to egg and chick loss. Most BC coastal bird populations nest in burrows however, and so far there are no direct observations of the effects of helicopter noise on BC birds (WCOEEAP, 1986). It therefore seems prudent that studies be undertaken to determine and monitor the effects of helicopter noise on the bird populations of the area.

Marine mammals typically exhibit avoidance and other behavioral responses when aircraft fly nearby, especially since the degree of habituation to the noise by the mammals in the area is unknown. Sometimes this can lead to seals and sea lions abandoning their pups and not returning when they are disturbed by noise by their rookeries (WCOEEAP, 1986; Petro Canada, 1995, Richardson et al. 1985a, 1985b, Payne et al., 1983, Watkins and Moore, 1983, Leatherwood et al., 1982, all in JWEL 2001; Richardson et al., 1995). Again, studies into the effects of airborne noise on marine mammals of the area should be initiated.

Vessels are a major contributor to background noise, although data are lacking on the character of noise from different types of vessels (Richardson et al., 1995). Ross (1976 in Richardson et al., 1995) found that supertanker noise was audible up to 463 km away. Bain and Dahlheim (1994) found that vessel noise impairs killer whale hearing. Richardson et al. (1995) stated that impacts on marine mammals from marine vessel noise are most likely negligible. However, Richardson et al. (1995) also cautioned the data are insufficient to reach firm conclusions. It is not known how other marine life may be affected by vessel noise.

There has been some concern that birds can be attracted to or confused by lights from offshore structures. Suggestions such as the use of strobe lighting and masking lights to minimize outward illumination have been made, but may not be safety conscious (WCOEEAP, 1986). Rig lights are designed for the safety of those working on and near the rig in mind and alternative lighting would only be acceptable if worker safety would not be jeopardized (COGLA and BCMEMPR, 1988). Lighting must also conform to marine navigation and communication regulations for ocean vessels and structures.

Production (Extracts from SFU, 2004)

Produced water (water from wells drilled) contains constituents characteristic of the geology of the formation as well as those added during different stages of drilling and extraction. Typical geological constituents can include hydrocarbons and heavy metals while various chemical additives include corrosion inhibitors, polymers, descalers, biocides, dispersants and emulsion breakers among others (Kenchington, 1997). In addition, produced water frequently contains high levels of naphthalenes, as well as NORMs such as radium-226 and radium-228 (Patin, 1999). Produced water is often not saline, is at a higher temperature and a different pH (acidity) than the surrounding seawater (JWEL, 2001; Kenchington, 1997).

Produced water discharged to the marine environment disperses and dilutes rapidly. At its point of release, produced water discharges may be hot enough to cause thermal shock in some organisms. However, Husky (in JWEL, 2001) suggested that water temperature should return to ambient levels within 50 m of discharge points. Acute toxicity is only expected in the immediate vicinity of outlets (Nihoul and Ducrotoy, 1994) and is considered negligible greater than two km away (Kenchington, 1997; Stroemgren et al., 1995). Both Kenchington (1997) and GESAMP (1993) concluded that impacts should be marginal beyond half a kilometer from discharge points in most oceanic waters. In contrast, others argued that contamination and impact may be occurring at distances from discharge points much further than commonly thought (Lee, 2003; GESAMP, 1993; Kingston, 1992). Some contaminants—such as heavy metals—appear to bioaccumulate (Canada, 1999), and the long-term impacts of chronic discharges of produced water are poorly understood (Strong et al., 2002).

Nonetheless, dilute concentrations of produced water impact marine life. Sessile organisms are the most likely to be impacted from chronic discharges, though mobile species may also be affected. Studies have indicated that produced water impacts benthic organisms (Din and Abu, 1992; Krause et al., 1992; Osenburg et al., 1992; Rabalais et al., 1992; Raimondi and Schmitt 1992 in JWEL 2001), kelp (Reed, Lewis, and Anghera, 1994), sea urchins (Cherr and Fan, 1997; Krause, 1994), mussels (Cherr and Fan, 1997), and the eggs and larvae of haddock, lobster and scallop (Cranford et al. 1998 in Canada, 1999).

Another environmental risk in production occurs during the course of transporting oil and/or gas from the rig, certainly in terms of severity though not necessarily in terms of potential probability. Tanker spills have had devastating impacts around the world and the offshore industry has continually sought to reduce petroleum inputs into the marine environment over the past several decades. This is addressed in a specific section on spills and blowouts.

Miscellaneous (Extracts from SFU, 2004)

Numerous other potential pollutants are created during various stages of offshore oil and gas production. Fluid discharges include wash and drainage water, sewage and sanitary waste, losses from process equipment, minor spills and leaks—including fuels, lubricants, hydrocarbons and other chemicals on board—water from fire hoses, platform run-off, fire-fighting foam, well work-over fluids, well-bore fluids, well-treatment fluids, desalinator brine, ballast, chlorinated and high temperature cooling water, sludge from mud treatment, hypochlorite, glycols, cementing discharge, cement and other dusts, antifouling compounds, and other miscellaneous pollutants (Patin, 1999). Sewage will undergo primary treatment before it and the grey water are discharged overboard. The volume would be fairly small when compared to what is discharged from municipalities in the surrounding area.

Combustible garbage can be incinerated on the drilling rig while noncombustible waste will need to be transported to shore for disposal. The disposal of this waste is unlikely to cause environmental degradation provided that all wastes are disposed of according to regulation.

Offshore oil and gas operations must also be monitored for air pollution. Sources include engine combustion (such as generators, ships and production facilities), well fluid burning during production tests and clean-ups, as well as flaring and gas venting during production, treatment, transportation and storage (JWEL, 2001). Air pollutants include nitrogen oxides, sulfur oxides, carbon monoxide, carbon dioxide, particulate matter, unburned hydrocarbons, volatile organic compounds and hydrogen sulfide (JWEL, 2001; Patin, 1999). In 1998, almost 25 million tonnes of air pollutants were released by U.K. offshore and associated onshore facilities and equipment. Flared gases from oil and gas production facilities provide roughly 30% of the gross world production of gaseous hydrocarbons and are one of the major sources of atmospheric emissions in the world (Patin, 1999).

Decommissioning

During decommissioning, impact is limited to the vicinity of structures being removed. Sometimes explosives may be used and small fish mortality may result. Where facilities are either sunken or sub sea portions of structures are left in place, the remaining “artificial reef” maintains the ecological community that has developed during operations. These structures are often marked by buoys or other means to prevent future accidents involving other vessel traffic.

 

Some credit from above text to Review of Offshore Oil and Gas Development by Simon Fraser University, 2004 and Royal Roads University: BC Offshore Oil and Gas Socio-Economic Papers, 2004

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