Shallow water hazards

Elaine Maslin

May 1, 2015

Protecting, inspecting and repairing pipelines in the shallow waters of the Middle East isn’t as easy as it sounds. Elaine Maslin reports.

McDermott’s DP2 offshore construction support vessel Thedbaud Sea in the Middle East. Photos from McDermott International.

The Middle East region is home to around 85,000km of pipelines, or about 2.5% of the global total pipeline assets, representing, theoretically, a relatively small issue to deal with when it comes to pipeline inspection and maintenance.

However, it is not the reality in the area, as Manoj Kulshrestha, McDermott Middle East, explained at Subsea Expo held in Aberdeen earlier this year.

Pipelines in the region are predominantly in shallow waters and prone to damage. The seabed is also quite hard, making burial costly and often uneconomical on projects.

Earlier development of fields in the regions has not been systematically planned and coordinated, often with multiple operators following an individual design approach, creating a “spaghetti of pipelines, cables and umbilical in the field, crisscrossing each other.”

Statutory guidelines regarding movement of marine traffic around pipelines, vessel anchorage and loading areas are not well established. There is no well-defined protection philosophy. Some of the unburied pipelines are even sometimes without concrete coating.

Fishing activities in the region are not fully controlled — fish traps can often be found on pipelines and cables — and there are no concrete abandonments plans, which means non-operational pipelines are also left in-situ, unpreserved. Environmental guidelines are still immature, Kulshrestha says.

More than 50% of pipeline damage is caused by anchoring (21%) or impact from anchor or dropped objects (30%) while a large proportion of the remainder damages is the result of corrosion (26%), according to a probability analysis of damage to offshore pipelines by ship factors, by Liu, Hu and Zhang, presented to the Transportation Research Board annual meeting in 2013.

In the Middle East, the causes are no different, Kulshrestha says. The damage is caused by anchor handling tugs, drilling rigs, construction vessels and accommodation barge activities, as well as heavy oil and LNG tanker traffic, and fishing activities, which mainly cause cable or umbilical damage.

To prevent damage, operating companies are looking for security shields in the form of radar surveillance around critical offshore assets. Satellite surveillance of vessel operations and information sharing between operators is also prevalent in the region.

Manoj Kulshrestha

“In spite of all preventive measures in place, any damage to subsea pipeline is distinctive and requires a careful engineering assessment prior to any major intervention,” Kulshrestha says. “Absence of advanced engineering evaluation may lead to unwarranted repairs and production delays.” Kulshrestha says a majority of companies in the region do not employ resources and software to perform such advanced analyses, nor do they have contractual provisions to engage consultants instantly.

McDermott is promoting emergency preparedness, including performing emergency pipelines repair system (EPRS) studies and maintaining repair equipment. Further, Kulshrestha recommends sharing such assets, under an emergency pipelines repair system club, and having long-term contracts for use of vessels to mobilize the EPRS equipment.

Kulshrestha says an EPRS should target for total preparedness and comprise of; detailed emergency response manual, procedures, installation engineering, repair spread, repair ancillaries, and installation aids.

McDermott led an EPRS study for one of the major operators in North Field offshore Qatar. It is the world’s third largest non-associated gas reservoir, discovered in 1971, with some 885 Tcf, he says.

In order to assess repair requirements, types of non-corrosive damages are categorized as: gouges; gouge on weld; dent; gouge in dent; dent in weld; abrasion; anchor drag (i.e. displacement); displacement with dent and gouge; crack and crack-like flaws.

To create the repair mythologies for the manual, an assessment of all the possible damage scenarios for all distinctive sections of pipelines is performed, with acceptance limits for dents and gouges created. Anchor dragging (the most prominent damage cause) is simulated using finite element analysis tools and all the results knitted into a decision making process through a flow chart.

A decision making tree is then adopted to aid an operator’s decision making on intervention or continuing operation, with time frames included for repair to reduce any loss in production.

While the EPRS offers a framework for emergency pipeline repairs, it does have limitations, however, Kulshrestha says. Primarily, this is based on generalized parameters, while in reality each damage occurrence is unique and can be impacted by the specific location or environment it is in. Some damage therefore requires sensitivity checks and explicit analysis before any intervention.

The industry also lacks codes and practices for EPRS he says, something which need to be developed in the future.