UTIS as One Example of Standardization of Subsea Intervention Systems
Authors: Hafigen F.G. 
Published: October 2008

The number of diverless subsea intervention has increased dramatically during the tit few years. A number of types of tools and equipment have been designed and used. A typical procedure has been to develop new intervention tools under each new contract based on experience porn the previous project.

This is not at all optimal with regard to project cost and risk, and is no longer acceptable as the oil industry now calls for cost savings within all areas of field development.

One answer to the problem will be to develop universal intervention systems with the capability to perform a range of related tasks, with only minor, planned modifications of the system.

This philosophy will dramatically reduce planning, engineering, construction and interface work related to the intervention operation as the main work will be only to locate a standardized landing facility on the subsea structure. The operating procedures can be taken "off the shelf".

To adapt to this philosophy within the tie-in area, KOS decided to standardize on a Universal Tie-In System (UTIS), which will be included in a Tool Pool for rental world-wide.

This paper describes UTIS as a typical example of standardization of subsea intervention system.

THE TIE-IN SYSTEMS

The number of diverless subsea tie-ins has increased over the last few years. The operations have been performed using a wide range of equipment and tools.

The tie-in methods can be classified in two main categories:

* The ROT-Method, ref. Fig. 1

This method is further divided into two subgroups

ROT/Surface Suspended

This sub group can be characterized as "a semi-automatic robot". One main task is to bring the tool safely to the subsea work site. Once docked, the tool will perform the tie-in operation when the operator "pushes the right buttons" on the surface control panel.

One or more tools may be used for pull-in and connection. Typical tools are:SSP-TOOIS(2 tools), ref. Fig. 2Kvæemer Troll Tool (1 combined pull-in and connection tool)

ROT/ROV Carried

This sub group requires more "manual work" than the surface suspended tools. The operation of the WROV is heavily dependent on the operator's skill.

Two tools are normally used for pull-in and connection. The tools are buoyant and carried by an WROV. Tool control is performed via the WROV umbilical.

Typical tools are:DMaC (Diverless Maintained Cluster Well System) from Costain Eng. & Constr., ref. Fig. 3DFC (Diverless Flowline Connection System), from SonSub.

* The Spool Piece Method, Ref. Fig. 4

This method features a flexible or rigid spool piece lowered from the surface vessel to connect typical satellites to a cluster manifold, The spool piece length is normally shorter than 70 meters, even if rigid spool pieces with lengths up to 180meters have been designed. No dedicated tie-in tools are used for this method.

The ROT-and SPOOL PIECE methods both have their areas of application and both methods can be standardized.

The Layaway method is not regarded as a separate method like the ROT and the SPOOL PIECE methods, as the Layaway includes elements from both these methods (SPOOL PIECE method in the fit end of the pipe).