Experimental ice plugs used to increase gas production

Experimental ice plugs used to increase gas production

As unlikely as it may seem with desert temperatures reaching 45 degrees Celsius, the team succeeded in creating a frozen plug to seal the gas wellhead tree valves, a concept patented by Boots and Coots to increase well control and safety.

Mature wells need regular maintenance work to keep them going as reservoir pressure gradually drops. But there is always a danger of a fatal blowout unless the well is fitted with a double pressure barrier, explained Dan Borling, Resource Manager at BP s Sajaa gas field.

"A lot of the older wells around the world only have a single valve or no barrier at all, which is why it was essential to find a way to make this work," said Borling.

The BP engineers worked with a team from Boots and Coots who had developed the Dynamic Freeze Plug Process (DFPP) in laboratory conditions five years ago, but it had never been tested in the field. Maritime Industrial Services fabricated the parts that would make the process work.

The work was carried out in Sajaa gas field, which has depleted pressure following 20 years of production. After a trial run on a dead well the team tried it out for real on Sajaa 31, an old shut in well, and succeeded in creating the plug using methanol and dry ice.

"Our main concern was that the frozen wellhead tree would be so brittle it would just snap, but we managed to install the tapered velocity strings needed to increase production without incident and then repeated the process on two other wells," said operations engineer Brian Powers who had suggested the solution.

The maintenance well work resulted in adding another 8.5 million cubic feet of gas and nearly 700 barrels of condensate to the field s output.

"The remarkable thing was that no additional remedial work was needed to make the wells flow again. As the plug defrosted there was less than a barrel of fluid lost. More importantly, there were no accidents, no injuries, no harm to the environment, and no damage to the formation," added Borling.

A further set of workovers using DFPP in Sharjah is scheduled for later this year, the Outlook article said. http://www.yb-valve.com/wellhead-equipment/christmas-tree-6288-95.html