Riser and Riserless Subsea Intervention Well Control Package Systems: An Equipment Overview

‍ By Grant Pierce, Intervention Performance Ltd.‍‍ ‍ ‍

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Introduction

Regardless of whether a subsea intervention campaign uses a riser-based or riserless approach, the Well Control Package remains one of the most critical components of the subsea equipment spread. 

Modern subsea intervention systems incorporate sophisticated pressure-control equipment, hydraulic systems, umbilicals, remotely operated functionality, and emergency disconnect capability designed to safely support wireline, coiled tubing, hydraulic stimulation, and abandonment operations. 

Over time, contractors have developed multiple proprietary RLWI (RiserLess Well Intervention) and IRS (Intervention Riser System) configurations with differing bore sizes, pressure ratings, and operational capabilities. 

  1. Well Control Package Fundamentals 

For the Well Control Package and associated equipment, there will typically be: 

  • A Hydraulic Power Unit (HPU) 

  • A Master Control Station (MCS) 

  • A Chemical Injection Unit (CIU) 

The Master Control Station controls all WCP functionality, including: 

  • Opening and closing valves 

  • MEG (Mono Ethylene Glycol) injection to prevent the formation of ice 

  • Shearing functionality 

  • Emergency disconnect operations 

  • System monitoring 

The Well Control Package itself forms the primary subsea pressure-control system during intervention operations. 

2. Umbilicals and Control Systems 

Communication and hydraulic control between the vessel and the WCP are maintained through hydraulic/electrical control umbilicals. 

These umbilicals are typically mounted on powered reels located near the moonpool. 

Where a Module Handling Tower is utilized, guide sheaves route the umbilical upward through the tower and back down through the well center, where it connects to the Umbilical Termination Head on the WCP. 

The umbilical system supports: 

  • Hydraulic actuation 

  • Electrical communication 

  • Fiber optic communication 

  • Data transmission 

  • Emergency response functionality 

Modern systems enable fully remote operation from centralized control cabins on board the vessel. 

3. ROV Integration and Auxiliary Systems 

ROV support forms an essential part of most subsea intervention spreads. 

Most vessels carry at least two Work-Class ROVs used for: 

  • Equipment positioning 

  • Latching operations 

  • Unlatching operations 

  • Visual monitoring 

  • Open-water deployment support 

  • Subsea inspection 

Some vessel configurations position the ROV systems forward of the Module Handling Tower with dedicated: 

  • Moonpools 

  • Launch and Recovery Systems 

  • Over-the-side deployment capability 

In regions such as the UK Continental Shelf, certain vessels also retain saturation diving capability in addition to ROV operations.

 

4. Intervention Riser Stack Architecture 

With a riser-based intervention package, the subsea pressure-control system generally consists of: 

  • Well Control Package (WCP) 

  • Lower Marine Riser Package (LMRP) 

  • Emergency Disconnect Package (EDP) 

  • XT connector 

  • Intervention riser back to surface 

The intervention riser provides a continuous pressure-containing conduit between the vessel and the subsea well. 

This arrangement allows: 

  • Controlled hydrocarbon returns 

  • Large-volume circulation capability 

  • Heavy coiled tubing intervention 

  • Enhanced well control flexibility 

Although lighter and easier to deploy than conventional marine risers, IRS systems still require substantial handling and deployment capability. 

5. RLWI (RiserLess Well Intervention) Stack Architecture 

Riserless Light Well Intervention systems utilize a different pressure-control philosophy. 

A typical RLWI stack may consist of: 

  • Well Control Package (WCP) 

  • XT connector 

  • Lower Lubricator Package (LLP) 

  • Upper Lubricator Package (ULP) 

  • Pressure Control Head (PCH) 

The lubricator sections provide pressure containment for wireline tools during deployment and retrieval. 

It is important to note that RLWI stack terminology varies between contractors. 

For example, the terminology above reflects TechnipFMC Stack #4 nomenclature. Other contractors may refer to similar systems using names such as: 

  • SIL (Subsea Intervention Lubricator) 

  • SILS (Subsea Intervention Lubricator System) 

  • RWIS (Riserless Well Intervention System) 

  • SRIS (Subsea Riserless Intervention System) 

Although terminology differs, the overall operational philosophy remains largely the same. 

6. Current Industry Intervention Systems 

Current industry offerings vary according to: 

  • Nominal bore size 

  • Pressure rating 

  • Water-depth capability 

  • Riser vs riserless functionality 

Examples include: 

AKOFS Offshore 

  • 7 3/8 in. Intervention Riser System with Riserless capability 

  • 10,000 psi rating 

Baker Hughes 

  • 3 1/16 in. Riserless (3.0) 

  • 3 1/16 in. Riserless Lite (3.1) 

  • 4 1/16 in. Riser-based system (4.1) 

  • 7 1/16 in. Riserless (7.0) 

  • 7 3/8 in. Subsea Riserless Intervention System (7.1 & 7.2) 

  • Riser and riserless configurations available 

  • 10,000 psi ratings 

Enovate Systems Ltd 

  • Lightweight P&A intervention systems 

  • Riser and riserless capability 

  • 10,000 psi ratings 

Expro Group 

  • 7 3/8 in. Intervention Riser System 

  • 7 3/8 in. Riserless Well Intervention System 

  • 10,000 psi ratings 

Halliburton 

  • 6 3/8 in. Light Riser Intervention System 

  • Riser and riserless capability 

  • 15,000 psi ratings 

Helix Energy Solutions 

  • 7 3/8 in. Intervention Riser System 

  • 5 1/8 in., 7 1/16 in., and 7 3/8 in. Subsea Intervention Lubricators 

  • 10,000 psi and 15,000 psi ratings 

Oceaneering 

  • 7 1/16 in. Interchangeable Riserless Intervention System 

  • 7 1/16 in. Blue Ocean Riserless Intervention System 

  • 10,000 psi ratings 

Sapura Energy Well Services 

  • 7 3/8 in. Subsea Intervention Device 

  • Riserless system 

  • 10,000 psi ratings 

TechnipFMC 

  • 5 1/8 in. to 7 1/16 in. Completion & Workover Riser 

  • 7 1/16 in. RLWI systems 

  • 10,000 psi and 15,000 psi ratings depending on package 

Trendsetter Engineering 

  • 5 1/8 in., 6 3/8 in., and 7 3/8 in. Trident Intervention Systems 

  • Riser-based and RLWI capability 

  • 10,000 psi, 15,000 psi, and 20,000 psi ratings 

Worldwide Oilfield Machine (WOM) 

  • 6 3/8 in. and 7 3/8 in. Deepwater Riser Systems 

  • 7 3/8 in. RLWI systems 

  • 10,000 psi and 15,000 psi ratings

7. Emergency Quick Disconnect Systems 

Hydraulic intervention operations require Emergency Quick Disconnect systems that can safely disconnect pumping lines during vessel drift-off or drive-off. 

These subsea EQD systems perform a function similar to that of emergency disconnect systems used on stimulation vessels for COFLEX hose operations. 

Both passive and active disconnect systems are available. 

Examples include: 

Blue Logic 

  • Auto Release System 

  • Large Bore Hot Stab 

Flint Subsea Ltd 

  • Mid Line Weak Link EQD 

  • Well Kill Connector 

  • EQD Skid 

SECC Oil & Gas 

  • Hot Make Hot Break Connector 

  • Hot Make Hot Break Gimbal System 

  • Mid Line Weak Link Connector 

Enpro Subsea 

  • Passive Mid Line Weak Link systems 

  • Active and passive EQD systems integrated into Subsea Safety Modules