FLOATING TECHNOLOGY: Tanker lightering, transport leaks carry highest risk in FPSO operations

Risk comparable to pipeline transport

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Th 6011osfps02
Graphic provided by the U.S. Department of the Intererior Minerals Management Service - Gulf of Mexico OCS Region.
Click here to enlarge image

The highest crude oil spill risks in floating production, storage, and offloading (FPSO) vessel operations in deepwater come from the transport function, not the production function. Excluding conven-tional offloading and shuttle tanker spills, FPSO-unique spill risks comprise only 5% of total risk, claims the US Minerals Management Service, which conducted a risk analysis for a draft Environmental Impact Statement (EIS).

The remaining 95% of oil spills are not FPSO related and are equally likely to occur with a tension leg platform or other deepwater production solution, which are already in operation in the Gulf.

Risk analysis shows that only 1.8% of crude oil volumes lost during all phases of FPSO operations would take place during the transfer of oil from the vessel to the shuttle tanker. The volumes would involve spills smaller than 1,000 bbl. A slightly lesser volume, 1.2%, would involve collisions between FPSOs and passing merchant vessels.

The largest crude oil volume, 94.4%, would involve pure transfer operations in two areas: during FPSO-to-tanker transfers and tanker-to-shore transfers. A smaller volume, 53.6%, of FPSO-type spills would be lost from shuttle tankers near port, and 39.0% would be lost from shuttle tankers in transit to port.

"Eight hundred oil spills in the Gulf were within 10 miles of the Texas coastline, which are under the GLO (Texas General Land Office) domain," Robert J. Siddall told an audience during a recent hearing on FPSO safety. "I believe there is tremendous potential (for FPSO deployment), but our concerns are traffic, transfers, and oil spills from transfers," Siddall said.

Spill history

In the draft EIS, the history of low spill frequency and small spill volumes during tanker lightering operations in the Gulf of Mexico is similar to oil-spill risks during FPSO offloading to shuttle tankers.

When compared to spills transported from offshore pipelines, there will likely be "1.32 spills with volumes greater than 1,000 bbls for every billion bbls transported, and for tanker transport, there will be 1.21 spills with volumes greater than 1,000 bbls for every billion bbls transported. Therefore, the oil spill risk for shuttle tanker transport is comparable to and slightly less than that of pipeline transport," the study staes.

The Gulf of Mexico has had six spills greater than 1,000 bbl from oil pipelines since 1981. Information drawn from the database contains incidents dating back to the 1970s.

Peder E. Farmen, President of Navion, Inc. in Houston, said human error is probably the biggest factor in oil spills. Officers have undergone training every year in the North Sea for the past 20 years, and that experience could be brought into the Gulf of Mexico if the FPSO vessels are approved. Navion has performed more than 10,000 loading and unloading operations over the past 20 years in the North Sea. The total volume spilled was 283 bbl. The firm has transported 8 billion and experienced three spills of more than 1 bbl.

Other experiences

Skaugen Petro Trans, a lightering company working with Navion, has performed more than 8,350 lightering operations in the Gulf of Mexico with two recorded spills. Total volume was 851 bbl.

"FPSOs have been operating in the North Sea a long time, and (North Sea) environmental regulations and regulators are pretty tough. We feel we have operated successfully for a year in the North Sea, so we should be okay in operating in the Gulf of Mexico," Peter Lovie, Business Development Manager for Bluewater Offshore Production System, Ltd., said.

He explained that the best way to prevent future spills is to carefully examine tanker operating procedures and experience, and ultimately have the right to reject using tankers that don't meet certain standards.

SBM-Imodco president Louis Smulders said oil-spill statistics for their company is less per bbl produced than the statistics presented in the informational brochure distributed by the MMS for the Gulf of Mexico. The firm's sister company, SBM Production Contractors, is operating 11 FPSOs and FSOs on lease contracts around the world. These units have an accumulated experience of 50 years in the field. Today, the total production of all units combined exceeds 450 million bbl of oil and LPG.

According to one FPSO company, large spills can be prevented by using a breakaway coupling device. However, the device is sometimes too costly for smaller companies, so they cut back on the extra precaution, hoping that an accident will not occur.

Also at the hearing, John Gunning, President of Texas State Pilots Association, said his organization is concerned with the safe movement to and from the port and ships carrying dangerous cargo. "Don't leave the mother-ship without a pilot," he warned.

Collision with other vessels accounts for 1.2% of all FPSO risks because of potentially larger oil-spill volumes. Process releases are the single largest risk hazard for releases oboard the FPSOs.

Statistical evaluation

Statistics used in the study were derived from 20 operations representing a total of 119 years of FPSO service and 1.6 billion bbl of oil produced. The vessels reported a total of 206 oil spills, which averaged 4,641 bbl of oil. Total spills equaled 2.9 bbl spilled for every 1 million bbl produced. The largest reported oil spill was 3,900 bbl. In the Gulf of Mexico, operators have produced approximately 5.5 billion bbl of crude oil, with about one bbl spilled for every 89,500 bbl produced, since 1980.

Currently, operators depend on pipelines to bring oil and gas to shore. As development reaches out to deeper water and the cost of installing pipelines beyond 3,000-4,000 ft becomes too expensive, FPSOs are one of very few choices left. The final EIS draft is scheduled for release in January 2001 and a general decision on FPSOs is due February 2001.

FPSO advantages and disadvantages in US Gulf


  • Cheaper than deepwater pipelines.
  • Development will take place earlier.
  • Render some fields commercial that are not developable due to infrastructure access or other transport limitations.
  • Balance competition for smaller producers with larger producers.
  • Able to store tons of fluid.
  • Generally insensitive to depth, so can work in deepwater.
  • Contractors can lease the vessel.
  • Is gradually becoming a commodity as mobile service offshore.
  • Pipeline contractors still competitive because increased number of fields made commercial in deepwater and ultra-deepwater by the FPSO option.
  • Comply with Jones Act.
  • Vessel can connect to pipeline almost anywhere.


  • Takes 1-2 years to convert or build.
  • Companies compete with own pipeline infra-structure.
  • Companies must conduct timely and costly environmental study for a specific field once accepted.

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