Offshore oil spill prevention and response
Encyclopedia
Offshore oil spill prevention and response is the study and practice of reducing the number of offshore incidents that release oil or hazardous substances into the environment and limiting the amount released during those incidents.
Important aspects of prevention include technological assessment of equipment and procedures, and protocols for training, inspection, and contingency plans for the avoidance, control, and shutdown of offshore operations. Response includes technological assessment of equipment and procedures for cleaning up oil spill
s, and protocols for the detection, monitoring, containment, and removal of oil spills, and the restoration of affected wildlife and habitat.
In the United States, offshore oil spill prevention contingency plans and emergency response plans are federally mandated requirements for all offshore oil facilities in U.S. Federal waters. Currently administered by the Minerals Management Service
(MMS), these regulatory functions were ordered on May 19, 2010 to be transferred to the United States Department of the Interior
's newly-created Bureau of Safety and Environmental Enforcement
. Oil spills in inland waters are the responsibility of the Environmental Protection Agency (EPA), while oil spills in coastal waters and deepwater ports are the responsibility of the U.S. Coast Guard.
Unlike the Best Available Technology
(BAT) criteria stipulated by the Clean Air Act
and the Clean Water Act
, the Outer Continental Shelf Lands Act amendments of 1978 stipulated that offshore drilling and oil spill response practices incorporate the use of Best Available and Safest Technologies (BAST).
While the Technology Assessment and Research (TAR) Program is tasked with research and development
of such technologies through contract projects, human factors
are also highly relevant in preventing oil spills. As William Cook, former chief of the Performance and Safety Branch of Offshore Minerals Management for the MMS, expressed it: "Technology is not enough. Sooner or later, it comes face to face with a human being. What that human being does or does not do, often ensures that the technology works as it was intended--or does not. Technology -- in particular -- new, innovative, cutting edge technology must be integrated with human and organizational factors (HOF) into a system safety management approach."
are blowout preventers (BOPs), which have been used for nearly a century in control of oil well drilling
on land. The BOP equipment technology has been adapted and used in offshore wells
since the 1960s. The inspection and repair of subsea BOPs are much more costly, and the consequences of failure potentially much worse. There are two variations of offshore BOP in use; the sub-sea blowout preventer which sits on the ocean floor, and the surface blowout preventer which sits between the riser
pipe and the drilling platform
. The surface unit is smaller, lighter, less costly, and more easily accessed for routine tests and maintenance. However, it does not prevent blowouts involving a broken riser pipe.
Blowout preventers often contain a stack of independently-operated cutoff mechanisms, so there is redundancy in case of failure, and the ability to work in all normal circumstances with the drill pipe in or out of the wellbore. The BOP used in the Deepwater Horizon
, for example, had five "rams" and two "annular" blowout preventers. The rams were of two types: "pipe rams" and "shear rams". If the drill pipe is in the well, the pipe rams slide perpendicular to the pipe, closing around it to form a tight seal. The annular preventers also close around the pipe, but have more of a vertical motion, so they loosen slightly if the drill pipe is being pushed downward, as might be necessary in a "snubbing" or "well kill" operation. Shear rams may be used as a last resort to cut through the drill pipe and shut off everything, including whatever might be coming up inside the drill pipe.
Studies done for the Minerals Management Service
have questioned the reliability of shear rams in deepwater drilling. Figure 1 shows the result of a 2002 study on offshore oil rigs. This study was designed to answer the question “Can a given rig’s BOP equipment shear the pipe to be used in a given drilling program at the most demanding condition to be expected?” Seven of the fourteen cases in this study opted not to test, another had insufficient data to draw a definitive conclusion, and three failed to shear the pipe under realistic conditions of expected well bore and seawater pressure. In each case of failure, increasing the pressure on the rams above its design value, successfully sheared the pipe. A follow-up study in 2004 confirmed these results with a much larger sample of drill pipes and typical blowout preventers from three different manufacturers.
In addition to insufficient ram pressure, a New York Times investigation
of the Deepwater Horizon oil spill
listed other problem areas for deepwater blowout preventers. If one of the threaded joints between pipe sections is positioned within a shear ram, the ram would probably not cut through it, because the joints are "nearly indestructable". Requiring two shear rams in every blowout preventer may help to avoid this problem and to avoid some types of "single-point failure". Other technologies that might improve the reliability of BOPs include backup systems for sending commands to the BOP and more powerful submersibles that connect to the BOP's hydraulics system.
as in Figure 4. Each section is suspended by a threaded adapter inside the bottom end of the section above. Failure of either the casings or the cement can lead to injection of oil into groundwater layers, flow to the surface far from the well, or a blowout at the wellheaad.
In addition to casings, oil wells usually contain a "production liner" or "production tubing", which is another set of steel pipes suspended inside the casing. The "annulus" between the casing and the production liner is filled with "mud" of a specific density to "balance" the pressure inside the casing with the "pore pressure" of fluids in the surrounding rock "formations".
To ensure that the cement forms a strong, continuous, 360-degree seal between the casing and the borehole, "centralizers" are placed around the casing sections before they are lowered into the borehole. Cement is then injected in the space between the bottom of the new casing section and the bottom of the borehole. The cement flows up around the outside of the casing, replacing the mud in that space with pure, uncontaminated cement. Then the cement is held perfectly still for several hours while it solidifies.
Without centralizers, there is a high risk that a channel of drilling mud or contaminated cement will be left where the casing contacts the borehole. These channels can provide a path for a later blowout. Even a thin crack can be pushed open by the enormous pressure of oil from below. Then erosion of the cement can occur from high-velocity sand particles in the oil. A hairline crack can thus become a wide-open gushing channel.
Another cause of cement failure is not waiting long enough for the cement to solidify. This can be the result of a rushed drilling schedule, or it could happen if there is a leak causing the cement to creep during the time it is supposed to be setting. A "cement evaluation log" can be run after each cement job to provide a detailed, 360-degree check of the integrity of the entire seal. Sometimes these logs are skipped due to schedule pressures.
Cement is also used to form permanent barriers in the annulus outside the production liner, and temporary barriers inside the liner. The temporary barriers are used to "shut in" the well after drilling and before the start of production. Figure 4 shows a barrier being tested by replacing the heavy mud above it with lighter seawater. If the cement plug is able to contain the pressure from the mud below, there will be no upward flow of seawater, and it can be replaced with mud for the final shut in.
There are no cement barriers in the annulus in Figure 4. While there is no requirement for such barriers, adding them can minimize the risk of a blowout through a direct wide-open channel from the reservoir to the surface.
Important aspects of prevention include technological assessment of equipment and procedures, and protocols for training, inspection, and contingency plans for the avoidance, control, and shutdown of offshore operations. Response includes technological assessment of equipment and procedures for cleaning up oil spill
Oil spill
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is mostly used to describe marine oil spills, where oil is released into the ocean or coastal waters...
s, and protocols for the detection, monitoring, containment, and removal of oil spills, and the restoration of affected wildlife and habitat.
In the United States, offshore oil spill prevention contingency plans and emergency response plans are federally mandated requirements for all offshore oil facilities in U.S. Federal waters. Currently administered by the Minerals Management Service
Minerals Management Service
The Bureau of Ocean Energy Management, Regulation and Enforcement , formerly known as the Minerals Management Service , was an agency of the United States Department of the Interior that managed the nation's natural gas, oil and other mineral resources on the outer continental shelf...
(MMS), these regulatory functions were ordered on May 19, 2010 to be transferred to the United States Department of the Interior
United States Department of the Interior
The United States Department of the Interior is the United States federal executive department of the U.S. government responsible for the management and conservation of most federal land and natural resources, and the administration of programs relating to Native Americans, Alaska Natives, Native...
's newly-created Bureau of Safety and Environmental Enforcement
Bureau of Safety and Environmental Enforcement
The Bureau of Safety and Environmental Enforcement is an agency under the United States Department of the Interior, established by Secretarial Order...
. Oil spills in inland waters are the responsibility of the Environmental Protection Agency (EPA), while oil spills in coastal waters and deepwater ports are the responsibility of the U.S. Coast Guard.
Unlike the Best Available Technology
Best Available Technology
Best available technology is a term applied with regulations on limiting pollutant discharges with regard to the abatement strategy. Similar terms are best available techniques , best practicable means or best practicable environmental option...
(BAT) criteria stipulated by the Clean Air Act
Clean Air Act
A Clean Air Act is one of a number of pieces of legislation relating to the reduction of airborne contaminants, smog and air pollution in general. The use by governments to enforce clean air standards has contributed to an improvement in human health and longer life spans...
and the Clean Water Act
Clean Water Act
The Clean Water Act is the primary federal law in the United States governing water pollution. Commonly abbreviated as the CWA, the act established the goals of eliminating releases of high amounts of toxic substances into water, eliminating additional water pollution by 1985, and ensuring that...
, the Outer Continental Shelf Lands Act amendments of 1978 stipulated that offshore drilling and oil spill response practices incorporate the use of Best Available and Safest Technologies (BAST).
While the Technology Assessment and Research (TAR) Program is tasked with research and development
Research and development
The phrase research and development , according to the Organization for Economic Co-operation and Development, refers to "creative work undertaken on a systematic basis in order to increase the stock of knowledge, including knowledge of man, culture and society, and the use of this stock of...
of such technologies through contract projects, human factors
Human factors
Human factors science or human factors technologies is a multidisciplinary field incorporating contributions from psychology, engineering, industrial design, statistics, operations research and anthropometry...
are also highly relevant in preventing oil spills. As William Cook, former chief of the Performance and Safety Branch of Offshore Minerals Management for the MMS, expressed it: "Technology is not enough. Sooner or later, it comes face to face with a human being. What that human being does or does not do, often ensures that the technology works as it was intended--or does not. Technology -- in particular -- new, innovative, cutting edge technology must be integrated with human and organizational factors (HOF) into a system safety management approach."
History
Regulations
Technologies
Hydrocarbon producing wells are designed and managed on the basis of the 'barriers' in place to maintain containment. A 'dual barrier' philosophy is typically used whereby two independently verified barriers to the hydrocarbon reservoir and the environment are required at all times. The failure of a single barrier would not lead to a hydrocarbon release. During the different phases of drilling, production, workover and abandonments, many different pieces of equipment will be used to maintain control of the well fluids and pressures.Drilling blowout preventer
The primary safety control devices for well drillingWell drilling
Well drilling is the process of drilling a hole in the ground for the extraction of a natural resource such as ground water, natural gas, or petroleum...
are blowout preventers (BOPs), which have been used for nearly a century in control of oil well drilling
Blowout (well drilling)
A blowout is the uncontrolled release of crude oil and/or natural gas from an oil well or gas well after pressure control systems have failed....
on land. The BOP equipment technology has been adapted and used in offshore wells
Offshore drilling
Offshore drilling refers to a mechanical process where a wellbore is drilled through the seabed. It is typically carried out in order to explore for and subsequently produce hydrocarbons which lie in rock formations beneath the seabed...
since the 1960s. The inspection and repair of subsea BOPs are much more costly, and the consequences of failure potentially much worse. There are two variations of offshore BOP in use; the sub-sea blowout preventer which sits on the ocean floor, and the surface blowout preventer which sits between the riser
Drilling riser
A drilling riser is a conduit that provides a temporary extension of a subsea oil well to a surface drilling facility. Drilling risers are categorised into two types: marine drilling risers used with subsea blowout preventer and generally used by floating drilling vessels; and tie-back drilling...
pipe and the drilling platform
Oil platform
An oil platform, also referred to as an offshore platform or, somewhat incorrectly, oil rig, is a lаrge structure with facilities to drill wells, to extract and process oil and natural gas, and to temporarily store product until it can be brought to shore for refining and marketing...
. The surface unit is smaller, lighter, less costly, and more easily accessed for routine tests and maintenance. However, it does not prevent blowouts involving a broken riser pipe.
Blowout preventers often contain a stack of independently-operated cutoff mechanisms, so there is redundancy in case of failure, and the ability to work in all normal circumstances with the drill pipe in or out of the wellbore. The BOP used in the Deepwater Horizon
Deepwater Horizon
Deepwater Horizon was an ultra-deepwater, dynamically positioned, semi-submersible offshore oil drilling rig owned by Transocean. Built in 2001 in South Korea by Hyundai Heavy Industries, the rig was commissioned by R&B Falcon, which later became part of Transocean, registered in Majuro, Marshall...
, for example, had five "rams" and two "annular" blowout preventers. The rams were of two types: "pipe rams" and "shear rams". If the drill pipe is in the well, the pipe rams slide perpendicular to the pipe, closing around it to form a tight seal. The annular preventers also close around the pipe, but have more of a vertical motion, so they loosen slightly if the drill pipe is being pushed downward, as might be necessary in a "snubbing" or "well kill" operation. Shear rams may be used as a last resort to cut through the drill pipe and shut off everything, including whatever might be coming up inside the drill pipe.
Studies done for the Minerals Management Service
Minerals Management Service
The Bureau of Ocean Energy Management, Regulation and Enforcement , formerly known as the Minerals Management Service , was an agency of the United States Department of the Interior that managed the nation's natural gas, oil and other mineral resources on the outer continental shelf...
have questioned the reliability of shear rams in deepwater drilling. Figure 1 shows the result of a 2002 study on offshore oil rigs. This study was designed to answer the question “Can a given rig’s BOP equipment shear the pipe to be used in a given drilling program at the most demanding condition to be expected?” Seven of the fourteen cases in this study opted not to test, another had insufficient data to draw a definitive conclusion, and three failed to shear the pipe under realistic conditions of expected well bore and seawater pressure. In each case of failure, increasing the pressure on the rams above its design value, successfully sheared the pipe. A follow-up study in 2004 confirmed these results with a much larger sample of drill pipes and typical blowout preventers from three different manufacturers.
In addition to insufficient ram pressure, a New York Times investigation
of the Deepwater Horizon oil spill
Deepwater Horizon oil spill
The Deepwater Horizon oil spill is an oil spill in the Gulf of Mexico which flowed unabated for three months in 2010, and continues to leak fresh oil. It is the largest accidental marine oil spill in the history of the petroleum industry...
listed other problem areas for deepwater blowout preventers. If one of the threaded joints between pipe sections is positioned within a shear ram, the ram would probably not cut through it, because the joints are "nearly indestructable". Requiring two shear rams in every blowout preventer may help to avoid this problem and to avoid some types of "single-point failure". Other technologies that might improve the reliability of BOPs include backup systems for sending commands to the BOP and more powerful submersibles that connect to the BOP's hydraulics system.
Well casings
Casing of offshore oil wells is done with a set of nested steel pipes, cemented to the rock walls of the boreholeBorehole
A borehole is the generalized term for any narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation, environmental site...
as in Figure 4. Each section is suspended by a threaded adapter inside the bottom end of the section above. Failure of either the casings or the cement can lead to injection of oil into groundwater layers, flow to the surface far from the well, or a blowout at the wellheaad.
In addition to casings, oil wells usually contain a "production liner" or "production tubing", which is another set of steel pipes suspended inside the casing. The "annulus" between the casing and the production liner is filled with "mud" of a specific density to "balance" the pressure inside the casing with the "pore pressure" of fluids in the surrounding rock "formations".
To ensure that the cement forms a strong, continuous, 360-degree seal between the casing and the borehole, "centralizers" are placed around the casing sections before they are lowered into the borehole. Cement is then injected in the space between the bottom of the new casing section and the bottom of the borehole. The cement flows up around the outside of the casing, replacing the mud in that space with pure, uncontaminated cement. Then the cement is held perfectly still for several hours while it solidifies.
Without centralizers, there is a high risk that a channel of drilling mud or contaminated cement will be left where the casing contacts the borehole. These channels can provide a path for a later blowout. Even a thin crack can be pushed open by the enormous pressure of oil from below. Then erosion of the cement can occur from high-velocity sand particles in the oil. A hairline crack can thus become a wide-open gushing channel.
Another cause of cement failure is not waiting long enough for the cement to solidify. This can be the result of a rushed drilling schedule, or it could happen if there is a leak causing the cement to creep during the time it is supposed to be setting. A "cement evaluation log" can be run after each cement job to provide a detailed, 360-degree check of the integrity of the entire seal. Sometimes these logs are skipped due to schedule pressures.
Cement is also used to form permanent barriers in the annulus outside the production liner, and temporary barriers inside the liner. The temporary barriers are used to "shut in" the well after drilling and before the start of production. Figure 4 shows a barrier being tested by replacing the heavy mud above it with lighter seawater. If the cement plug is able to contain the pressure from the mud below, there will be no upward flow of seawater, and it can be replaced with mud for the final shut in.
There are no cement barriers in the annulus in Figure 4. While there is no requirement for such barriers, adding them can minimize the risk of a blowout through a direct wide-open channel from the reservoir to the surface.
Human factors
External links
- U.S. Coast Guard and Environmental Protection AgencyUnited States Environmental Protection AgencyThe U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
, Oil Spill Prevention, Control, & Countermeasure Regulations - American Petroleum InstituteAmerican Petroleum InstituteThe American Petroleum Institute, commonly referred to as API, is the largest U.S trade association for the oil and natural gas industry...
, Oil Spill Prevention and Response - NOAA, 2002. Oil Spill Prevention and Response: A Selected Bibliography on the Exxon Valdez Oil Spill
- Offshore Technology Resource Center. 2001. Comparative Risk Analysis for Deepwater Production Systems
- Oil & Gas UKOil & Gas UK-History:It is a not-for-profit organisation, established in April 2007 on the foundations of the UK Offshore Operators Association Oil & Gas UK is the leading representative body for the UK offshore oil and gas industry that is stretched back over 30 years...
, Oil Spill Prevention and Response Advisory Group (OSPRAG) - International Oil Spill Conference (IOSC), 1969–present. Archives of over 3,000 papers and full-text conference proceedings covering spill prevention, planning, response and restoration processes, protocols and technology.