Diverless Flowline Connection System Using ROVs
Authors: Cox David  S. , Gates Stephen  M. 
Published: October 2008

The connection of flowlines to subsea trees hastraditionally been done by divers using a combination of rigging and gantries on the subsea tree structure. As with many aspects of the subsea industry, the use of Remotely Operated Vehicles (ROV?s) is increasing with advantages in cost savings and improved safety.

This paper examines a modular tooling package designed for the diverless connection of flowlines to subsea hardware. This system is known as the Diveriess Flowline Connection System (DFCS) and is capable of completing the tie-in of single and bundled flowline and control umbilical jumped up to 13.5 inches in diameter. It is designed to be used in conjunction with almost any working class ROV and is capable of operating in deepwater environments with currants up to 3 knots.

The system?s main features are its light modular design allowing deployment and use by ROV and in most cases a minimum of permanent subsea hardware and structure requirements.

INTRODUCTION

Flowlines used to connect subsea well completions or manifolds to the production facility are generally deployed to the seafloor independently of other hardware. During the well tie-in phase the flowlines must be pulled from their laydown position to the subsea tree and then connected to the tree. This operation has traditionally been accomplished by divers using a combination of rigging and gantries on the subsea structure, although in deeper water a number of diverless connections have been achieved.

There are three main methods for performing a diverless flowline connection:

1. Surface Connection/Lay Away

The flowlines are passed from the lay vessel to the drill rig and connected to the tree on the surface, and leak tested. The tree is then "run" down the guide wires and established on the wellhead. The lay vessel lays the flowline away from the tree allowing the other end of the flowline to be connected on the surface.

2. Subsea Connection/Lay Away

The tree is established on the wellhead by the drill rig. The flowlines are passed from the lay vessel to the drill rig. The flowline ends are then run down guide wires on the tree to align the pipe flange with the tree flowline connection hubs. A flowline connection running tool is then deployed down the guide wires and operated hydraulically to perform the connection subsea.

(3) Laydown/Subsea Connection

The use of remote pull-in and connection methods to complete the flowline connection. This is generally performed after the flowline has been laid on the seabed.

Methods (1) and (2) have a reasonable track record, however they both suffer the disadvantage of relying upon the drill ship and flowline lay vessel being in position in the field at the same time. For multiple well developments this is generally a cost exposure that is uneconomical. Method (2) also requires a large equipment/support area on the subsea structure which complicates the design and increases costs.

Hence Sonsub decided to build on it?s remote system experience of over a decade and design and manufacture a Diverless Flowline Connection System (DFCS).