With research interest mounting in the area of composite coiled tubing, one company has taken the concept of lightweight spoolable tubulars to an extreme. Based on the physics that govern a self-retracting measuring tape, The Centre for Marine Petroleum Technology, working with a company called RolaTube, has developed a bi-stable composite tube that can be spooled flat, but unspools in a open or overlapping tube.
The tube can then be welded with a seam to form a continuous flowline. The key to this development is that the material has two stable states:
- Curvature in the perpendicular direction and lies flat transversely
- Open tube state it forms when unreeled.
RolaTube is shown here as a mast to deliver a camera for nuclear reactor inspection, may offer a compact, lightweight, reelable, composite tubular alternative.
The tube can be open, or designed to overlap. With the correct layup, the wall thickness of the material can be "relatively" thick. In the past, the problem with pipelines, which relied on a continuous weld, was that if the seam split it was impossible to effectively patch or repair it. The goal of bi-stable composite tubes is to produce a tubular that could withstand typical flowline pressures of 30 MPa and temperatures up to 100°C. Aside from the reelable properties of this material it has all the advantages typically associated with composites including light weight, noncorroding, and high insulation properties. Also, according to the CMPT, this material is resistant to ingress of seawater under pressure and will not suffer from delamination. This design does not rely on a specific composite material. The tubes can be manufactured from a wide variety of reinforcing fibers and matrix polymers.
Beyond developing this novel tubular, the project hopes to produce a flowline that can accommodate a continuous welding and deployment system. Because the welding mechanism does not require a hyperbaric enclosure, it lends itself to being deployed subsea. Ultimately, a solution might be engineered to deploy an entire flowline lay system subsea which would not only eliminate the engineering demands of dealing with the loads imposed during the lay, but greatly reduce the requirements for surface support vessels.
Another, even more radical application of this technology would be in the form of casing while drilling. The reel of bi-stable composites would be installed on the seabed to deploy and weld the casing subsea. The designers are looking ahead to the possibility of combining this system with a subsea coiled tubing drilling exploration system, also under development.
To this end, there is a feasibility study underway by the Cambridge University Engineering Department and RolaTube to explore two aspects of the welded seam:
- Overall design of the seam: The primary requirement of the seam is to carry tension from the internal pressure, possibly at elevated temperatures. So this initial part of the study will focus on tension tests of the seam. The tube will be designed with feathered edges that nest together to give a distributed seam when deployed.
- Welding technique: A feasibility study will examine the technique to be used to form the continuous seam. Several technologies that may be suitable for the welding process include hot gas, laser, ultrasonic, microwave, and induction welding. Once the most suitable of these is chosen, then sample welds will be made using a continuous weld and the seam design developed in the first phase of the study.
Deep-draft semi reaches test tank
Technip Geoproduction has announced it will perform tank tests on a novel deep-draft semisubmersible design in a test tank at the Offshore Model Basin in Escondido, California. The TPG 3300 floating platform looks like a conventional semisubmersible on the surface, but has a deep draft caisson made up of three legs, a lattice system, and buoyancy compartment that provide added stability.
The test design will simulate water depths of 1,500 meters with 12 catinary wire chain mooring lines. The three-leg platform will support dry trees and is designed to perform drilling and production operations. The test version will be hooked up to 16 simulated tensioned conductors. Tank tests will take place over a five-week period and studies will focus on the performance of the vessel's hull in conditions typical of the Gulf of Mexico and West Africa.
The goal of these tests is to confirm assumptions made during the design phase, including the wave frequency motions, mean offset, and low frequency motions of the hull. The tests also will allow Technip to calibrate the numerical model used in the design of the hull and define the hydrodynamic aspects such as damping terms, which are difficult to estimate from numerical computations. The effects of the mooring lines and conductors will also be evaluated.
Technip hopes to come away from these tests with information on platform sea keeping, motion RAOs, wave frequency motions, low frequency motions, horizontal offset, total motions, accelerations, damping terms for the six motions, drag loads, stroke of tensionors, sensitivity to different parameters (position of fairleads, drafts, pontoon, hole size, lattice in the legs versus caisson structure), mooring line tensions, and the impact of conductors on platform behavior.
There will be three configurations of the platform tested. The first will be the base model test. This design has the lower part of the platform legs made of triangular lattice and the upper part made of hexagonal buoyancy tanks. This design will be subjected to a variety of environmental conditions. The second configuration will have the buoyancy tank section of the design lowered to the pontoon level, eliminating the lattice structure. Both of these tests will simulate various Gulf of Mexico weather conditions. The final configuration will include the lattice and have the leg lengths center of gravity modified to meet the draft and air gap requirements for West Africa.
ABB makes key acquisition
ABB recently announced the acquisition of CMS Associates of the UK. This provides ABB with key expertise in the engineering of subsea instrumentation and reservoir management for offshore. This small firm has only 20 employees, but is involved in the development of high performance borehole tools for hostile environments. Specifically, CSMA has designed and manufactured electronic and thermal management systems that can operate continuously at high temperatures. Obviously this will take ABB further into the realm of HT/HP engineering. CSMA actually is an offshoot of the Camborne School of Mines, which established it in the late 1980s. Camborne first built the CSMA test facilities in the 1970s to perform geothermal energy research. In 1992, CSMA acquired the site and expanded it to include labs for performing tests and development work including a deep borehole testing facility, engineering and electronic workshops, analytical test laboratories, and a mineral processing pilot plant.
