Study could reduce chances of offshore oil leaks

Researchers at the University of Missouri-Rolla (UMR) hope to reduce the occurrence of offshore oil leaks by analysing current methods for detecting such leaks in the Gulf of Mexico.

Through funding from the US Department of the Interior's Minerals Management Service, UMR researchers are examining the way the oil and gas industries monitor their Gulf pipelines for possible leaks or line breaks.

The monitoring methods involve electronic sensors that detect sudden drops in pressure and warn engineers of a potential problem, said Dr. Shari Dunn-Norman, associate professor of geological and petroleum engineering at UMR and the principal investigator of this project.

'The pipelines are monitored for leaks, and one of the methods is to monitor the pressure of the line,' said Dunn-Norman. 'But this method of leak detection may not be as accurate as it should be. False alarms do occur.'

Dunn-Norman is working with Dr. Kelvin T. Erickson, professor of electrical engineering; Dr. E. Keith Stanek, professor and chair of electrical and computer engineering; and Dr. Ann Miller, the Cynthia Tang Missouri Distinguished Professor of computer engineering.

The current research builds on the group's earlier study of the oil industry's supervisory, control and data acquisition systems (SCADA systems). The earlier study helped the researchers better understand how often line failures might occur, the probability of a release, and the probable failure rate for the systems that monitor oil and gas pressure in offshore pipelines.

'Virtually all pipelines in the Gulf of Mexico employ SCADA systems that monitor and record data from the pipeline operations,' Dunn-Norman said.

According to Dunn-Norman, there are some 32,000 miles of offshore pipelines in the Gulf of Mexico. Those lines supplied the US with 1.3 million barrels of oil and 13.9 billion standard cubic feet of natural gas daily in 1999, accounting for about 20 percent of the nation's domestic oil production and 27 percent of its domestic natural gas production.

The Minerals Management Service estimates Gulf of Mexico oil production to increase to 1.8 million barrels a day by the end of 2001, Dunn-Norman said.

These offshore pipelines operate at designated pressures, which are continuously recorded and monitored as a means of determining leaks, Dunn-Norman said.

Whenever the pressure in a pipeline drops below a pre-set amount, the sensors set off an alarm known as a pressure safety low (or PSL). This alarm indicates a possible leak or break in the pipe, Dunn-Norman said.

'Pressure monitoring is a reasonable method of detecting leaks,' she added, 'because wall failure of a pipeline under pressure is a sudden event, and the fluid loss produces a sudden pressure disturbance within the pipeline.'

But the alarms don't always indicate a leak. 'Sometimes the pressure drops, especially in two-phase flow lines' that carry both oil and natural gas, Dunn-Norman noted. 'There may be a slugging or a surge effect when both liquid and gas are moving through the same lines. That is just part of the flow phenomena.'

The UMR researchers plan to analyse the reliability of PSL alarms in detecting actual pipeline releases, and then submit their recommendations for improving the monitoring system's reliability. The results, Dunn-Norman said, should help the oil and gas industry improve the monitoring of undersea pipeline operations.

The outer continental shelf surrounding the US contains about 15 percent of the nations proven oil reserves and 19 percent of the nation's proven natural gas reserves, Dunn-Norman said. But petroleum experts estimate that the outer continental shelf contains more than 50 percent of the nation's remaining undiscovered natural gas and oil resources, Dunn-Norman said.