Traditionally, to complete a subsea well with a vertical Christmas tree, it is necessary to land the tubing hanger and install and pressure test a wireline set tubing hanger plug. Once the plug is tested, the subsea BOP can be removed, the vertical Christmas tree can be installed, and the plug retrieved through the work-over riser before the well is ready for production or injection. This is a time consuming rig operation requiring additional handling of the work-over riser and wireline run, which increases both the HSE and operational risks. With increasing focus being placed on the safety, reliability and cost efficiency of deepwater developments, it is critical that the operational risk and rig time for drilling and completions is reduced.
This paper describes the innovative invention of a shallow set barrier plug – the Disappearing Tubing Hanger Plug (DTHP) – and includes a case study of the first application of the plug on Akpo-214. This ground-breaking solution, based on knowledge of the existing glass barrier plug technology, was developed through a collaboration between Total E&P Nigeria and TCO. The objective of the invention is to provide a more reliable and cost effective solution for deepwater completions offshore of Nigeria.
The application of the DTHP has proven that the disappearing feature of the DTHP with pressure cycling is effective and reliable. The pressure cycle was applied directly from the FPSO, liberating the expensive rig for other purposes. The DTHP also provides improved well integrity by forming an ISO14310 V0 qualified gas-tight barrier. The operator saved rig time for the first installation and the rig time saving is estimated to be mutiple days for an optimized completin sequence on deepwater applications, which directly translates into savings of millions of USD.