Design, operational standards
Given the extensive damage to offshore infrastructure from hurricanes Ivan, Katrina, and Rita, the oil and gas industry, led by the MMS, appears to be speeding up efforts to address and implement any necessary modifications to standards in place for structural design and operations.
In May, more than seven months after Hurricane Ivan struck the GoM’s oil and gas production facilities, the MMS allocated over $600,000 worth of contracts to study the impact of the storm.
“These studies will address short- and long-term adjustments in the MMS’s technical, engineering, and geological standards and regulations to ensure that offshore oil and gas production remains safe, environmentally friendly, and less susceptible to interruption,” said Johnnie Burton, director of the MMS. “Studies like these will help the MMS continue to ensure that the safe, clean operation of the offshore industry will be able to withstand even hurricanes like Ivan,” added Burton.
A majority of the studies will be finalized by 2Q 2006. Latest figures from the MMS indicated 348 bcf of natural gas and 68 MMbbl of oil were lost due to shut-ins from Katrina and Rita.
MMS statistics also revealed that of the 2,900 platforms located along the paths of Katrina and Rita, 52 of them were severely damaged and 113 were destroyed. The hurricanes damaged 98 pipelines as well. The government agency added that a staggering number of rigs were impacted by the storms. A total of 46 rigs were damaged; 19 were severely impacted, 8 destroyed, and 19 were set adrift.
“Those offshore facilities that withstood the storms best were those constructed to the 1988 MMS upgraded design standards,” said Gale Norton, US Department of Interior Secretary. “Of all the facilities constructed after the 1988 upgraded standards, only one platform was significantly damaged. We are currently working to determine whether that damage was a result of the storm itself or whether another facility collided with it.”
The MMS indicated that it plans to hold a half-day Structural Assessment Process Dissemination Meeting on the proposed American Petroleum Institute (API) Structural Integrity Management Recommended Practice. A task group has been working on updating Section 17 of the API RP 2A and developing a stand-alone Recommended Practice (RP) for the Structural Integrity Management (SIM) of Existing Offshore Platforms. The MMS is holding the meeting to discuss the status of the two items.
API weighs in
The American Petroleum Institute (API) has been taking its share of heat lately, given the structural damage to the offshore infrastructure from the latest hurricanes.
The API standards are reviewed every five years, and some of the more widely used standards are updated more frequently.
API says existing platforms in the GoM are structurally designed to the meet the requirements of API RP 2A,Planning, Designing and Constructing Fixed Offshore Platforms - the industry standard for designing and building offshore platforms. The API RP 2A, first published in 1969, is currently in its twenty-first edition, and is referenced in the regulations of the MMS for use in US offshore waters.
According to the API, the standards outlined in API RP 2T,Planning, Designing and Constructing Tension Leg Platforms (second edition, 1997), and API RP 2FPS, Planning, Designing and Constructing Floating Production Systems Platforms (first edition, 2001), are used to design and build some of the structures used in deepwater (over 1,500 ft) and are also referenced in MMS regulations.
The basic design methodology used for deepwater structures is similar to that for fixed offshore platforms, and industry groups are currently working to create updated versions of these standards.
Design criteria
According to the API, the main factors considered include a combination of wind, waves, tides, currents, and movement of the seafloor, during both normal and extreme conditions. Standards within API RP 2A recommend that GoM platform designers use the 100-year design criteria.
API defines the 100-year design criteria “as a set of environmental conditions that will produce a total force on the platform, due to the combination of waves, wind, and current, that has a 1% probability of occurrence per year at that specific location. (The 1 in 100 chance of occurrence in a year is the origin of the term ‘100-year design criteria’). These criteria are determined based on statistics compiled from all historical hurricanes and other storms in the GoM.”
W&T-operated platform in Vermilion block 226 was damaged by the hurricanes. The platform was installed in 1981 and is set in 122 ft of water.
For the majority of the Gulf, the 100-year design criteria are described as a wave measuring approximately 70 ft high, an 80-knot wind, and a 2.1-knot current. The specified criteria are re-assessed whenever new hurricane data and other relevant experience become available.
As a result, the API is currently assessing wind, wave, current data, and platform response from hurricanes Ivan, Katrina, and Rita, which may lead to changes in the design criteria for new platforms.
According to the API, platforms in the GoM are designed by applying the 100-year design criteria wave, current, and wind conditions together with a safety margin of 1.5 or greater. The API explains that inclusion of this safety margin means that the platform can actually withstand forces significantly beyond those defined by the 100-year design criteria (forces with a significantly smaller probability of occurrence than 1% per year).
The net result is that well-designed platforms are typically capable of surviving wave, wind, and current criteria producing a total force with a 0.1% probability of occurrence per year at a specific location. The good performance of recently designed offshore platforms in extreme environments caused by Ivan, Katrina and Rita demonstrates this point. For platforms or platform components for which current or wind forces could be more dominant than wave forces, a number of different combinations of wave, wind, and current are checked as part of the design.
Action items
According to the API, as a result of Hurricane Ivan, the industry began exploring the notion of revising certain standards, including the 100-year design criteria, and the mooring design criteria for drilling units (currently covered by API RP 2SK,Design and Analysis of Stationkeeping Systems for Floating Structures, second edition, December 1996).
The API adds that these items are currently being reviewed and studied by industry and regulatory agencies, and final recommendations on proposed standard revisions are likely in the near future.•
