A pioneering operation that uses fluid cryogenics as a freeze plug barrier has been tested in a tie up between specialists at Wild Well Global and Saudi Aramco.
The use of a cryogenic freeze plug as a barrier is used when conventional methods are not possible.
Saudi Aramco was looking for a seal so that dual shutoffs would be available prior to removing the production tree.
The process requires two independent shutoff barriers to be in place for the tubing and tubing casing annulus prior to the decompletion of wells that contain downhole packers.
Additionally, the shutoffs must operate independently of each other and be pressure tested separately.
Under normal operations, tubing plugs and tubing hanger back pressure valves are capable of providing dual shutoffs. But when the operator prepared to remove the production tree, crews discovered that the production tubing had collapsed and parted, leaving the kill fluid column as the only annular barrier.
The process presents a “tested, proven alternative method” for a successful secondary annular barrier with the presence of a kill fluid column in the annulus.
Wild Well Control general manager of special services, Carlo Mazzella, has published the results in a paper that appears in the Spring 2016 Saudi Aramco Journal of Technology.
Mazzella also discussed the techniques at the SPE/IADC Middle East Drilling Technology Conference in January.
To create the plug, the temperature surrounding the casing is dropped to a range of 0 to −80°F by installing a metal container around the pipe and filling it with liquid nitrogen.
The kill fluid inside the pipe freezes as a result of the surrounding temperature, creating an effective barrier capable of being pressure tested.
Independent tests and research have been conducted to determine the effects of subjecting API grades of tubing and casing to liquid nitrogen temperatures.
The freeze plug does not affect the exposed area of casings or wellhead equipment integrity.
“Our clients have become receptive to new isolation techniques as case history in the region is becoming more common,” Mazzella said.
Freeze services are used to place a temporary barrier (ice plug) in a tubular or vessel to maintain pressure control while safe mechanical repairs are carried out.