Subsea Decommissioning Technologies

‍ By Grant Pierce, Intervention Performance Ltd.‍‍ ‍ ‍

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Introduction

The offshore industry continues focusing on reducing the cost, operational complexity, and environmental footprint associated with subsea decommissioning. 

As operators evaluate aging subsea assets globally, there is increasing emphasis on technologies that reduce reliance on conventional drilling rigs while maintaining long-term barrier integrity and regulatory compliance. 

Advances in: 

  • Wireline intervention 

  • Alloy barrier systems 

  • Thermite technologies 

  • Vessel-based cutting systems 

  • Automated deployment systems 

  • Single-trip retrieval systems 

continue expanding the amount of decommissioning work that can be performed from lighter intervention assets. 

The long-term industry direction is clearly toward increasingly rigless abandonment and decommissioning operations. 

  1. Wireline-Based Abandonment Technologies 

One of the more significant developments in subsea abandonment is the emergence of wireline-based technologies that can reduce or eliminate the need to retrieve tubing. 

These systems are designed to establish permanent barriers without requiring extensive workover operations. 

In certain applications, the objective is to leave tubing in place where complete removal is not operationally necessary. 

This significantly reduces: 

  • Intervention complexity 

  • Vessel time 

  • Equipment spread 

  • Personnel exposure 

  • Overall abandonment cost

2. Emerging Barrier Technologies 

Several specialized companies are developing thermite and alloy fusion technologies for subsea abandonment applications. 

Examples include: 

BISN - Perf & Melt technology 

Isol8 - Fusion Tubing Plug and Fusion Annulus Barrier 

Interwell - RockSolid barrier systems 

WellStrøm - Bismuth alloy barrier technology 

These systems aim to establish permanent well barriers using alternative materials and deployment philosophies compared to conventional cement-based methods. 

3. Wireline-Only Multi-Zone Abandonment 

Additional developments include systems designed to perform multi-zone abandonment entirely through wireline operations. 

An example is the Wireline Abandonment Tool (K-WAT system) from Wireline Abandonment and Completion Corp (WACORP). 

The K-WAT system allows: 

  • Simultaneous bridge plug setting 

  • Pressure testing on wireline 

  • Elimination of dedicated tubing runs 

This approach significantly improves abandonment efficiency while reducing operational complexity. 

4. Vessel-Based Cut-and-Retrieve Philosophy 

Cut-and-retrieve operations traditionally required drilling rigs and drillpipe deployment systems. 

More recent developments now allow many of these operations to be performed directly from intervention vessels utilizing single-trip systems. 

The primary objective of these systems is to: 

  • Reduce offshore time 

  • Simplify deployment 

  • Minimize personnel exposure 

  • Eliminate rig dependency 

  • Improve decommissioning efficiency 

The most advanced systems are capable of: 

  • Cutting multiple casing strings 

  • Retrieving wellheads in a single deployment 

  • Operating from vessel-based intervention spreads 

5. Mechanical vs Abrasive Waterjet Cutting 

Modern subsea cutting systems generally utilize one of two primary cutting methodologies. 

Mechanical Cutting 

Mechanical cutting systems typically utilize: 

  • Hydraulic motors 

  • Mechanical cutter assemblies 

  • Rotational cutting mechanisms 

Advantages include: 

  • Compact equipment footprint 

  • Rapid mobilization 

  • Minimal deck spread 

  • Simpler support requirements 

Abrasive Waterjet Cutting 

Abrasive waterjet systems utilize: 

  • High-pressure water 

  • Entrained abrasive media 

  • Internal multistring cutting tools 

Advantages include: 

  • Multi-string cutting capability 

  • Effective cutting across varying metallurgy 

  • Large casing-range flexibility 

  • Single-pass cutting efficiency 

Both methodologies continue to be widely used, depending on project requirements. 

6. Future Direction of Subsea Intervention and Decommissioning 

The offshore industry continues moving toward greater utilization of lighter intervention assets for both production enhancement and abandonment operations. 

As intervention and decommissioning technologies continue maturing, operators increasingly recognize the advantages of: 

  • Reduced vessel footprint 

  • Lower emissions 

  • Reduced mobilization time 

  • Increased operational agility 

  • Lower overall cost 

At the same time, improvements in: 

  • Automated handling systems 

  • Remote operations 

  • Wireline abandonment technologies 

  • Hydraulic intervention systems 

  • Riserless coiled tubing 

  • Vessel-based retrieval systems 

continue expanding the capability envelope of LWIV and WIU assets. 

Considering the value of well intervention and hydraulic stimulation compared to drilling new wells, combined with the increasing ability to perform abandonment operations from lighter assets, continued growth across the subsea intervention and decommissioning sector appears inevitable.