Subsea Wellhead Retrieval Tool Uses New Technologies to Successfully and Efficiently Complete Abandonment Operations

Abstract

The objective of the campaign was to safely and efficiently complete a plug-and-abandonment (P&A) operation in a harsh Norwegian North Sea well using a high-performance conductor-recovery tool. The operation used the newly reinvented, second generation mechanical, outside-latch, single trip (MOST) tool system. Along with recovering the subsea wellhead, the associated casing strings and conductor were to be cut and retrieved.

The standard MOST tool is a field-proven system, which latches externally to the wellhead, then cuts and recovers subsea wellheads. The newly released second generation system is a reinvented P&A tool that includes several innovative technologies to increase tool capabilities and performance. The latest release of the MOST tool includes a newly designed tension-cut mandrel, nonrotating flexible stabilizer (NRFS), large-diameter cutter, and high-angle knives. The system confirms the cut without the need for tripping, easily latches and releases to inspect the cutting knives, and does not cause damage to the internal wellhead sealing profile. Furthermore, the external-latch mechanism helps to prevent swarf buildup by allowing more flow area in the high-pressure wellhead, which permits the cuttings to easily exit. The latch and unlatch function can also be visually confirmed using a remotely operated vehicle (ROV) on the seafloor. External latching provides superior lateral support for the wellhead assembly to eliminate any lateral whipping that might impede cutting. The second-generation design of the MOST tool, with the tension-cut mandrel, provides pulling capabilities up to 1,000,000 lb (453,592 kg) and fail-safe features, which enable the outside latch to be released by the ROV, if needed.

The newly deployed system successfully recovered multiple subsea wellheads in Norway and demonstrated its operational effectiveness with reduced cutting times compared to traditional cut-and-pull operations. With advanced features, the subsea wellhead-retrieval system reduces rig time by cutting and retrieving multiple cemented or uncemented strings in a single trip. The NRFS and large-diameter cutter increase stabilization and minimize vibration during cutting, and the high-angle knives increase cutting efficiency when compared to traditional retrieval systems. The MOST system supports quick wellhead recovery, minimizes operational expenditure, and reduces rig time.

The new developments to the next generation MOST tool system give the customer several additional application choices. The various interchangeable components allow for a wide range of cutting options including abrasive cutting, tension cut, motor cut, and umbilical support for laser cutting.