Multi-Service Vessel Well Intervention With New SILS
Authors: Hewlett Clyde , Clegg Bill , Thorne Don , Newman Peg 
Published: October 2008

This paper introduces a new Subsea Intervention Lubricator System (SILS) that utilizes remotely operated vehicle (ROV) technology and a MSV to safely perform wireline well intervention on subsea completions, in water depths ranging from 300fsw to ultimately 10,000fsw. Operators employing this simplified system can consequently lower their associated costs.

Introduction

Demand for hydrocarbons continues to expand and subsea developments in deepwater arenas such as the Gulf of Mexico, West Africa and Brazil are projected to grow considerably.

(Figure 1) To improve production, wireline intervention services for simple mechanical manipulations, component changes, downhole surveys, etc. will be required. The concept of utilizing a wireline intervention system is not new. Best known for use in surface deployed applications, the wireline lubricator, when used in the subsea environment allows access to the well bore without the need for a drilling rig and aworkover riser. Historically, operators have utilized a drilling rig or a dedicated vessel and divers to perform most wireline operations on subsea wells. Now, increasing numbers of subsea developments installed in deepwater beyond the range of divers are causing operators to seek containment of project costs by searching for innovative techniques that will challenge the traditional drilling rig/diver-based intervention model. Independent of water depth, the SILS/MSV/ROV combination can lower the cost of well interventions for tasks including wireline and P&A operations. (Figure 2)

As subsea wells become a more commonly employed field development solution, a safe, rapidly deployed and costeffective intervention method will be required. The SILS/MSV/ROV equipment combination offers a diverless/rigless first step solution toward lowering the life cycle costs for subsea wells at any depth.

Definitions

BOP - Blow Out Preventor DP - Dynamic Positioning MUX E/H - Multi-phased Electro-hydraulic HAZID - Hazard Identification HAZOP - Hazardous Operation HPU - Hydraulic Power Unit MSV - Multi-Service Vessel OEM - Original Equipment Manufacturer P&A - Plug and Abandonment ROV - Remotely Operated Vehicle (work class) SILS - Subsea Intervention Lubricator System SSSCV - Surface Controlled Subsurface Control Valve

Design Approach

The new SILS design began with the simple objective to reduce the cost of wireline intervention on subsea completions. As many of the other technical barriers to subsea production have been overcome, downhole intervention costs remain the largest disadvantage to the complete subsea solution. Without the ability to cost-effectively re-enter the well bore, valuable reserves are often left in the ground for want of a simple downhole manipulation. The concept of subsea wirelining is by no means new. It has been employed for years in the North Sea, in relatively shallow waters, from dedicated vessels, relying heavily on diver assist. To be most cost-effective in arenas such as the Gulf of Mexico, the new SILS design would have to be fully diverless in operation and be capable of being extended into water depths up to 10,000fsw.

Investigating a possible SILS solution began with a Gulf of Mexico market review of existing subsea installations where dynamically positioned MSV's already perform a multitude of other well services.