Downhole database analysis improves safety valve performance

The mean time failure for SCSSVs improved over the four phase of IKU's SCSSV database development (WR = wireline retrievable valves, TR = tubing retrievable valves. A significant improvement in downhole safety has taken place thanks to the surface controlled subsurface safety valve (SCSSV) and Wellmaster databases run on behalf of the SINTEF group by its research company IKU Petroleum Research.

A significant improvement in downhole safety has taken place thanks to the surface controlled subsurface safety valve (SCSSV) and Wellmaster databases run on behalf of the SINTEF group by its research company IKU Petroleum Research.

Wellmaster incorporates information on the reliability of downhole components, in terms of both failure rate and failure mode. It was established in 1993 to continue and expand the work of the SCSSV database, which itself was set up in 1983.

The feedback provided by these two reliability databases has led to a clear improvement in the performance of many components, according to Einar Molnes, IKU's department manager for drilling and well technology.

This is particularly evident in the case of downhole safety valves, for which the mean time to failure has quadrupled to about 10.5 years since data reporting began.

This is not to say that other factors such as technological development would not have improved performance levels. But Molnes is confident of Wellmaster's contribution. "From the feedback we get from the industry, we can see that we are acting as a catalyst for this process," he says.

The basic data comes in the form of failure reports from the participating oil companies, supplemented by information from the supplier on the cause of each failure. A windows-type program developed by IKU/SINTEF is used for handling and analyzing the data.

Companies are provided with full information on their own failures, as well as information on other companies' failures presented in an anonymous form. Suppliers receive a report on failures involving their own equipment.

The information can be analyzed in various ways - for example, failures relating to a particular item, or a particular supplier - and to benchmark the performance, for instance, of operators or of types of component.

"The oil companies benefit from getting a decision basis for designing well completions and selecting the most reliable components," says Molnes, "While manufacturers get feedback on the performance of their equipment."

There is also the substantial benefit for oil companies of reducing costly well shutdowns and interventions brought about by equipment failure.

Wellmaster is now into its third phase, with a budget of some NKr 4 million and the participation of 13 oil companies - Amerada Hess Norge, BHP Petroleum, BP Exploration, British Gas, Conoco Norway, Enterprise Oil, Mobil Norway, Norsk Agip, Norsk Hydro, Norske Shell, Saga Petroleum, Statoil and Total Norge.

Phase two, which ran from 1993 to 1996, covered 985 completions representing 851 wells. More than 4,000 completion-years of service history was recorded, with a total of 30,000 equipment items represented.

Altogether some 380 failures were reported, with SCSSVs, tubing, travel joints, tubing hangers and production packers, in that order, being the most common failure causes in the generic part of completions.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.

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