Objective
The aim of the project is to identify a system, for the cutting of subsea well structural members and conductors to be used in a versatile and flexible way in the various situations which may arise when the removal of offshore structures is required.
The research project will identify a system which foresees the use of equipment which, supported by a conventional ROV already on the market, is capable of operating one or more cutting tools and/or setting blasting charges.
Cutting tools already used in normal underwater operations carried out by divers will be taken into consideration, with special reference to the Abrasive Water Jet (AWJ) and explosives.
The market created by the requirement to remove offshore installations has been analyzed in detail investigating the applicable rules, the expectations of the operators and possible scenarios. The complexity and cost of a removal operation are defined by platform size, water depth and available means for lifting/transportation. Existing technology (based on explosives and pile cutting by internal AWJ tools) is satisfactory for water depth not exceeding 75 m and platform weight within 2000 t.
A new approach is required for larger structures that have to be split in sections by cutting structural beams at different levels. The cutting system is required to be flexible such as, in the same dive, it can cut a number of beams with different orientation, diameter and thickness. The AWJ cutting tool, operated through an ROV manipulator, does respond to this requirement and has been chosen for lab and pool trials.
Laboratory tests have been conducted to verify configuration of cutting tool holder (a trolley grasped by the manipulator end-effector) by in-air testing with a 180 bar AWJ equipment. Smooth and continuous cuts have been obtained on flat plates and tubular elements demonstrating the validity of the system that has been able to achieve satisfactory cutting velocity (typ. 20 mm/s on 20 mm thick steel).
Integration of the cutting equipment with the complete Supervisory Control Telemanipulation System (in turn integrated with a commercial ROV) has been completed to conduct pool trials. The underwater cutting tests gave, with respect to air tests, further information on the performance of the entire ROV/skid + manipulator + cutting equipment, namely:
- the capability to perform complete 360 deg. cuts on cylindrical elements;
- good performance of the abrasive water jet system also in water;
- inspection of the cut, made possible through a camera which allows vision of jet direction during cutting.
On the basis of tests data a time of about 4 hours can be extrapolated for the performance of cuts similar to the one tested, i.e.:
- steel tubular 20 mm thick, 700 mm diameter
- "square wave" cutting pattern alternating segments on the circumference and parallel to axis
- AWJ equipment pressure 180 bar
This estimate takes into account the time required for the necessary positioning of manipulator and ROV around elements to cut under operating conditions.
The project is divided into activities according to content and subdivision as shown below :
A100 "State of the art": Already existing subsea cutting systems are studied in order to identify the more promising ones for this particular application.
Typologies of the platform for platforms for possible removal are identified.
B100 "Regulation and market analysis": Already existing rules and future tendencies are analysed. The potential market for the most important geographical areas is estimated.
C100 "Design premises": Premises are defined in terms of water depth, cutting tickness, platform typologies, etc...
D100 "System configuration": The configuration of the cutting system is established and operational procedure identified.
E100 "Marine operations": Procedure regarding the cutting, removal and transportation of the structures are defined.
F100 "Design of the Cutting Underwater Module (CUM)": The preliminary design of the CUM is carried out taking into account problems relatedto tool manipulation. Techniques for the reconstruction of thr operation scenario are studied and experimented on the basis of the use of the TV-trackmeter.
Experimental cutting tests are performed in the work-shop and in a pool simulating a real operational situation and carrying out cutting operations with an AWJ operated by an ROV.
G100 "Support equipment design": The criteria and guide lines for the design and operation of support systems as well as for the transportation of the cut structures are studied.
I100 "Safety analysis": Safety problems related to the operational procedure are studied.
L100 "Cost analysis": Costs related to the utilization of the selected system are examined.
M100 "Project review": A critical review of the project, after completion of the cutting system design, is performed also to take into account any remarks by potential users of the system.
N100 "Development plan": A detailed plan is drawn up outlining the activities that would characterise a hypothetical phase 2 of the project for the construction of an enhanced prototype and subsequent related tests.
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DEM - Demonstration contractsCoordinator
30124 VENEZIA
Italy