There are several different ways to sever a wellhead pipe as part of plug and abandonment project. Some of these include internal pile cutters, portable bandsaws, diamond wire saws, reciprocating pipe cutting saws and water jet cutting.
Below is a brief summary of a case study which can be read in full on our website here Portable band saw used for subsea wellhead removal. You can also download the full details via a pdf download.
Case Study: Subsea Wellhead Removal
A Mirage client was appointed to carry out the challenging task of cutting an X-70, 36” diameter, 2” wall pipe, 3” as part of a wellhead removal project at a subsea depth of 7,000 feet.
Cutting at such a depth requires careful consideration of the best methods as unnecessary trips down to the wellhead and back to the surface have a significant effect on project costs. Mirage diamond wire saws are used successfully in many subsea pipe cutting projects, but in this case, the risk of needing to replace the diamond wire rope part way through the cut was a concern. This would add extra hours onto the project time resulting in additional costs.
Instead, the Mirage team in Houston recommended the Mirage BS3248 heavy duty portable bandsaw adapted for subsea use using purpose designed ancillary equipment. First, a test cut was carried out topside at Mirage Subsea HQ, with thge saw taking just 18 minutes to cut through the 36” X 2” WTH pipe.
The team developed the necessary equipment to convert the band saw for this subsea project and to overcome these challenges:
- Adaptation of the BS3248 for deepwater use, including development of ROV operable ancillary equipment.
- Developing a frame design to facilitate access to the pipe situated underneath the main wellhead assembly.
- All equipment was to be designed to require 100% NDT, Pull Testing.
- The rig was to be tested in water before final delivery to the client.
The items developed for the project included:
- A steel frame to deploy the bandsaw, control panel 12.3 litercompensator and a crash cage. The frame also included a engineered mud mat specific to the site mud conditions and a hot stab holster.
- A cantilever frame, to allow the bandsaw assembly to be mounted to the wellhead underneath the main wellhead structure
- ROV control panel.
- A 4 function hydraulic manifold for the motor, clamp, emergency blade cutter and feed circuits.
- A high volume compensator to accommodatehe 7,000 FSW pressure differential.
The wellhead was removed successfully, with all Mirage equipment performing as expected.
To see Mirage Band saws in action you may wish to view videos below showing various test cuts being made.
To find out more about in-situ machining we recommend you download our case study packs.