Slugging, pulsating gas and liquid flow are familiar problems for oil wells with seabed pipelines. Slugging frequently causes trouble in the process plant on the platform and reduces the amount of oil that can be recovered from a well or pipeline.
A subsea installation, the K-frame, is situated 14 kilometers south of the Hydro-operated Oseberg Sor platform in the North Sea. This is linked to the Oseberg Sor platform by a seabed cable, the K-cable. Since start-up in the autumn of 2000, the K-frame has produced 20,000 barrels of oil a day. This is all very well, but the pressure conditions from the well to the platform indicate that a higher daily production level should be possible. The problem was that a higher flow rate only produced fluid slugs and unacceptable operational conditions in the process plant on the platform.
Hydro's production engineers on Oseberg Sor were not, however, willing to accept this situation. Over the last six months, a number of tests have been carried out to find ways of better handling slugs and stabilizing the flow through the seabed pipeline, and the results are promising.
During the course of three exciting days this summer, the pressure conditions in the pipeline were changed in a particular way, giving an increase in production of over 15 percent.
This is approximately equivalent to an additional 3000 barrels of oil a day, or around NOK 200 million per year.
"In simple terms we have managed to establish short, stable fluid slugs in parts of the pipeline that run downhill. These prevent the formation of the large fluid slugs that cause problems for the process plant on Oseberg South," explains production engineer Ole Harald Utvik.
"Studying the flow conditions in the pipeline has made it possible for us to prevent the formation of large slugs, which means we are now able to maintain a higher production rate. We can also optimize the flow from the two wells that is tapped into the pipeline.
"We can envisage the possibility of getting even more out of the K-frame and are testing different ways of further increasing the production rate. We are also working on improving regulation to reduce the extra capacity that the small slugs now take up in the process plant," explains Utvik.
"This knowledge will also be important for the operation of the seabed pipeline from the satellite development on the Oseberg J-structure, which will start up in about an year," he adds.
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