Deepwater safety challenges to consider in a fast-paced development environment

An FPSO is the most common floating production system.

Rules development, modification, and improvement are required to maintain the regulatory framework up to date with the most recent technologies in spars, tension leg platforms, semisubmersibles, jackups, and other floating structures. This normally occurs in a proactive or corrective form.

Proactive action

Classification societies act proactively to understand the new concepts, to identify risks associated with these and to develop specific guidelines that eliminate or mitigate the risks.

The following are examples of proactive action taken by the American Bureau of Shipping (ABS) to improve the standards:

• The Guide for Building and Classing Floating Productions Installations (ABS FPI Guide) was first published in 2000.

In 2004 the ABS FPI Guide was revised, introducing specific requirements for TLPs and spars. These requirements addressed safety concerns related to the unique characteristics of these types of floaters, such as the stability requirements for multiple compartment flooding and development of large heel angles on a spar under design conditions.

In September 2007, the ABS FPI Guide incorporated new stability requirements, among other changes. The most recent updates include requirements for wet tow and installation. The Guide can be viewed athttp://www.eagle.org/absdownloads/index.cfm, and click on publication No. 82.

• The search for oil and gas in deeper waters introduced a major challenge: the mooring system of a floating facility. Mooring an offshore platform in deepwater requires long mooring lines. Therefore, the weight of the mooring hardware is substantially increased.

The additional weight decreases the payload capacity, thereby reducing drilling or production capacity. This constraint proportioned the application of synthetic ropes on mooring systems in lieu of the traditional wire rope. The main advantage is the weight savings due to the neutrally buoyant characteristics of the synthetic ropes. Safety challenges associated with the synthetic rope include: the need for additional care during installation to avoid damage, the stretching characteristics of the ropes requiring pre-loading and pre-stretching, and the absolute requirement to keep the rope off the seabed, which causes sand grains and other solid particles to penetrate the windings and consequently damage the yarn.

On a proactive action to regulate the use of synthetic materials on mooring systems, ABS issued Guidance Notes on the Application of Synthetic Ropes for Offshore Mooring in 1999, consolidating requirements on the application of this technology.

• In line with the need to reduce weight dictated by deeper waters, another technology has emerged in the last decade: the use of non-metallic materials. These lighter, corrosion resistant materials are employed on gratings for decks, platforms and walkways, cable trays, and piping.

The industry developed an array of materials to suit the offshore applications, which brings an inherited safety challenge related to the fire endurance characteristics. Regulatory bodies and classification societies analyzed the risks associated with non-metallic materials and the result was the ABS Guide for Certification of FRP Hydrocarbon Production Piping Systems in 2005. Requirements for the use of non-metallic gratings have been published on the ABS Guide for Building and Classing Facilities on Offshore Installations, 2000.

• The harsh marine environment heavily impacts offshore structures that remain stationary, moored to the seafloor even during the strongest storms. The additional fatigue penalty caused by the exposure of these structures to the elements needed to be specifically addressed with sound engineering methods and requirements. In 2003, ABS published the Guide for the Fatigue Assessment of Offshore Structures, addressing specific requirements for designers and fabricators to improve the fatigue life of the steel structures.

Corrective action

As part of continuous improvement, rules and guides are revised periodically and are updated to consider the lessons learned from design, construction, and operation.

Classification societies and government agencies react whenever a casualty occurs. By investigating the causes and consequences of the events, areas of improvement for the current body of rules and guidelines are identified, leading to rules changes and improvements. The following describes some examples of casualties with semisubmersibles and jackups that led to major improvements to the existing body of design and/or operation rules and guidelines:

Semisubmersible

Ocean Ranger

TheOcean Ranger was one of the largest semisubmersible MODUs in the early 1980s. It sank in Canadian waters on Feb. 15, 1982, with 84 crew members on board. There were no survivors.

On Feb. 14, 1982, a major Atlantic cyclone hit theOcean Ranger. Radio transmissions were heard from the unit, describing a broken port light (a porthole window), water in the ballast control room, noting that valves on the Ocean Ranger’s ballast control panel appeared to be opening and closing on their own accord, severe weather of 100 knot winds and waves up to 65 ft (20 m) and a MAYDAY call noting a severe list to port.

Semisubmersibles can be used for drilling or production.

The accident was investigated by the US Coast Guard Marine Board of Investigation and by a Commission formed by the Canadian government. The Canadian Royal Commission (CRC) spent two years looking into the disaster. Among the Commission conclusions were thatOcean Ranger had design and construction flaws, particularly in the ballast control room, and that the crew lacked proper safety training (e.g. failure of the operating personnel to secure the deadlight covers for the port lights in preparation for the forecasted heavy weather condition), survival suits, and equipment.

As a result of the investigation, USCG issued 26 recommendations to improve maritime safety. The CRC’s final report contained 136 recommendations and was signed in August 1984.

Major revisions were made to the ABS MODU Rules in the stability and ballasting sections following theOcean Ranger accident. Significant changes were implemented to the bilge and ballast system in the 1985 rules. Stability criteria were extensively modified in the 1991 rules. The following are some of the improvements brought to the ABS rules:

• Ballast system capacity enhancement
• Ballast system redundancy
• Ballast control room above damage waterline
• No portholes on columns
• Ballast system harmonized
• Residual stability enhancement.

Jackups

Ocean Express

On April 15, 1976, the self-elevating drilling unitOcean Express capsized in high winds and heavy seas and sank in the Gulf of Mexico 40 mi (64 km) off Texas at Mustang Island. The marine casualty report issued by the US Coast Guard Marine Board of Investigation says the accident happened when the rig was under tow from one drilling site to another. The primary cause of the capsize was the loss of directional control resulting from the loss of one of the tug boat’s engines and the breaking of the towline of another tug boat at a time when the weather conditions were worsening. This allowed the Ocean Express to drift broadside to the boarding seas.

Bohai 2

TheBohai 2 was a self-elevating drilling unit that sank under tow in heavy weather on Nov. 25, 1979, in the Gulf of Bohai between China and Korea. During tow, the rig encountered force 10 wind. Waves running over deck sheared off a pump room ventilator on port deck. The pump room flooded, and the rig toppled over and sank. Two of 74 workers survived.

West Gamma

In August 1990, theWest Gamma sank during tow in the North Sea. The weather was winds to 90 mph (145 kph) and waves up to 12 m (39 ft). The tow line was lost, causing the rig to drift towards the German coast.

Bad weather, loss of the towline, structural failure, and flooding all contributed to the sinking of theWest Gamma.

A jackup is a self-contained combination of drilling rig and floating barge.

One common factor onOcean Express, Bohai 2, and West Gamma is loss of the units during wet tow in heavy weather. In fact, the history of jackup losses suggests that this type of unit is vulnerable during wet tow. According to “Marine Casualties,” 25 accidents with jackups during wet tow were registered in 42 years (from December 1956 to June 1998).

During recent years, regulatory bodies and the industry investigated the causes of the loss of jackups and suggested preventive measures. The following organizations had significant contribution in this research:

• American Bureau of Shipping (ABS)
• International Association of Drilling Contractors (IADC)
• United States Coast Guard (USCG)
• UK Health and Safety Executive (UK HSE)
• UK Offshore Operators Association (UKOOA).

Investigations showed most jackup losses during transit occurred after minor damage was followed by a long period of progressive flooding. The sequence of events below form a common pattern:

1. Towline failure due to heavy weather leads to loss of control of heading
2. Green water on the deck because of jackup’s relatively low freeboard
3. Severe motion and wave impact on deck equipment and cargo damages on hatches, vents, companionways, and ventilation trunks
4. Loss of watertight integrity leads to multiple compartment flooding
5. Evacuation of the crew
6. Capsizing and sinking of the jackup.

Corrective actions resulted from the aforementioned investigations. The implementation of operational procedures that addressed the root causes of many accidents seems to be successful since no major accident on jackups during transit has been reported since. Following are some of the publications issued in consequence of the investigations that provide guidelines for the wet tow of self-elevating drilling units:

• General Ocean Tow recommendations published by IADC and dated Feb. 13, 1991
• Navigation and Vessel Inspection Circular No.11-91 (NVIC 11-91) published by USCG and dated July 16, 1991, which endorses the IADC recommendation above
• Safe movement of self-elevating offshore installations (jackups) published by UKOOA on April 1995.

The following are some recommendations presented in the guidelines:

• Development of a towing loading plan
• Detailed planning of the tow routing including ports of refuge and required entry data
• Improved weather forecast
• Deck cargo to be minimized and properly lashed
• Towing vessels to be equipped with emergency tow line
• Priority on communication between the rig and the towing vessels
• Watertight integrity monitoring and control, testing of the bilge/ballast service pump; deck openings to be protected from damage
• Rig to be equipped with damage control inventory
• Crew to be briefed on responsibilities during tow.

The UK HSE technical work group “Jackups Safety in Transit” (JSIT) published several reports from its investigation. Among the conclusions was that the damage stability criteria for jackups adopted by the industry at the time might not be adequate in certain environmental conditions; this inadequacy could lead to insufficient or inadequate compartmental subdivision.

ABS took the initiative to address the JSIT concerns and formed an ad hoc committee to revamp the regulations. The ad hoc committee of designers, builders, regulators, drilling contractors, and others outlined the requirements for new damage stability criteria.

The research culminated a new residual damage stability criteria for SEDUs which resulted in an improvement of rig subdivision. The new criteria were enforced from Jan. 1, 2005, and were incorporated to the ABS MODU Rules in 2006.

Acknowledgements

The authors thank ABS engineers Joseph Rousseau, J. Andrew Breuer, and Kenneth Huang for the support and information provided.

Worldwide energy demand is growing at an average rate of 1.6% annually, driving the need to find and develop new oil and gas sources. Deepwater fields constitute one of the few remaining untapped sources for new oil and gas production. In consequence, over the past 30 years floating production has evolved to a mature technology that opens for development of oil and gas reservoirs that would be otherwise unreachable and unprofitable. The advancement of offshore E&P technology has extended capabilities and reduced cost, enabling drilling and production far beyond the depth constraints of fixed platforms, making possible the operation in severe environments, and providing a flexible solution for the development of short-lived fields and exploitation of marginal fields.