Subsea 7's Mooring Suction Anchor Installation
Brazil's Barracuda - Caratinga field is situated in the Campos Basin in water depths ranging from 2,493 to 3,608 feet (760 to 1,100m). A total of 52 subsea wells will produce from reserves of 1.229 million barrels of oil and 14.7 billion cubic meters of gas.

The main field development contract was awarded to Kellogg Brown & Root, who sub-contracted the subsea installation scope of work to Subsea 7. The project's work scope comprised the installation of all subsea hardware, including suction anchors for the floating, production, storage, and offloading (FPSO) vessel's mooring and riser anchoring.

The installation raised various engineering challenges related to the 5m-diameter, 90-ton mooring suction anchors. Subsea 7 answered the challenges by building an ROV-based suction skid system, orienting the pile heading, and overcoming the potential resonance in the lift lines.

Suction anchors are cylindrical steel tubes, open at the lower end and closed at the top. Installation involves lowering the anchor to the seabed at the correct location, where it sinks into the seabed a certain distance (self-penetration).

The water inside the anchor is then pumped out by an ROV fitted with a special pumping skid, causing the anchor to be sucked down into the seabed to the required depth. Once in position, lines are attached to the anchors used to moor the FPSO or the flowline risers.

Each anchor has an internal volume of 325 cubic meters that must be displaced during installation. An efficient suction skid is required to drive it to the correct depth in an acceptable time.

Subsea 7 built two suction skids that were fitted underneath and powered by a work class ROV. Careful interfacing of the skids allowed unhindered operations of other ROV functions.

Prior to self-penetration of the anchors, their heading must be oriented to ensure the correct direction of the mooring line attachment point. This is achieved using a specially developed system onboard the ROV that uses an onboard gyrocompass heading sensor.

Dynamic analysis related to the installation of the suction anchors highlighted the possibility of resonance in the lift line, potentially leading to unacceptable crane tip loads of over 300 tons. This phenomenon is attributed to the mass of seawater inside the anchor and the stiffness of the crane wire when operating in unfavorable weather conditions.

To solve this problem, a nylon "stretcher" was incorporated into the lifting string to increase the natural period above that of the vessel, combined with specific installation procedures developed to take into account wave conditions, vessel heading, and water depth.

Other challenges faced during the installation included hook-up of the heavy 150-ton SWL rigging to the anchors on deck, maneuvering them overboard, and setting up the crane heave compensation system. Continuous recording of critical parameters such as sea-state, wave period, vessel pitch and roll periods, crane tip loads, vessels motions, speeds and accelerations and pile motions is performed to gain a comprehensive understanding of system resonance. To date, more than 70 suction anchors have have been installed successfully using Subsea 7's ROV-based suction skids and stretcher system, with no evidence of the resonance phenomenon.

Specialty Offshore Stops Gas Leak
Specialty Offshore (Hammond, Louisiana) was recently contracted by ATP Oil and Gas (Houston) to locate and stop a natural gas leak in a subsea tree at Vermillion Block 260. The leak had been caused by damage due to contact. Specialty's project manager worked closely with ATP personnel in the planning phase to minimize rig downtime at the location and lower the cost of the project.

A video inspection of the wellhead and net guard began the on-site operations. After the inspection, a crane line was put into the water to reach the net guard and free it from the wellhead. The net guard was then removed from the water and transferred to the vessel.

The vessel, utilizing sonar, was then positioned over the wellhead so the team could start the repair process.

Upon the diver's inspection of the wellhead, all flange bolts appeared to be tight. The underwater burning equipment was prepared and a downline was established to the wellhead. The diver removed four bolts on the wellhead, allowing the cap to be removed. A drillstring was attached and the rig crew, instructed by the dive crew, performed down-hole wireline operations. The diver was unable to attach Hytorc due to the configuration of the subsea tree. The bolts were then hammered and tightened.

Next, the wing valve and master valve guards had to be repaired and checked for leaks. The valves were operated and no leaks were visible. The diver operated a three-way valve, and no movement was detected.

The upper master valve was then manually overridden, and a leak was detected from the flange. The team commenced Hytorcing on the flange bolts. A bolt-on clamp was installed to stop the leak.

Sandbags were placed on the base of net guard. The net guard was then placed on the bottom next to wellhead, and the diver opened the hydraulic and crown valves.

The diver cleared debris from the old annulus valve, and replaced it with a new valve. The crane line was reattached to net guard, which replaced it over the wellhead. All valves were then closed. At that point, the platform crew began operating the tree. All repairs were successful and no leaks were present. Specialty Offshore had stopped the leak quickly and had the operation back up and running sooner than expected.

Specialty Offshore specializes in marine construction, fabrication, maintenance, repair, inspection, and underwater survey. Their commercial dive teams are ADC-certified, trained in Haz-Mat and First Aid, and meet the high standards set by the company's own safety and drug policies.

For more, visit www.sdive.com.

Integra's SeaStallion
Nowhere in the world is there a more hostile and dangerous work environment than under the surface of the ocean. The pressure is on contractors to provide zero-defect solutions that protect workers and the environment, while ensuring uninterrupted production whenever possible.

The new SeaStallion High Performance Hydraulic Nuts from Integra Technologies (Houston) were developed to meet the challenges of subsea leak prevention. The SeaStallion nuts provide a safer and faster installation than traditional assembly methods using impact tools, hydraulic torque wrenches, and even hydraulic stud tensioning.

To understand how this is done, one must first underscore the importance of controlling non-conformances in subsea work. As big as the offshore oil and gas market is, so is the potential for non-conformance leading to incidents affecting safety, environment and production. Hydraulic nuts provide the control required, while simultaneous multi-stud tightening ensures the quickest and most accurate method of flange assembly.

Recognizing the risk inherent in offshore oil and gas production, the US congress issued a moratorium on granting of drilling leases.

Further, the Outer Continental Shelf (OCS) Lands Act specifies that the best available and safest technologies that are economically feasible shall be used on all exploration, development, and production equipment.

SeaStallion High Performance Hydraulic Nuts have been proven in refining, petrochemical and nuclear power plants, and now new designs are available for the OCS market. The SeaStallion is a self-tightening solution, completely eliminating the need for conventional tools.

A hydraulic nut is installed by screwing onto the bolt until the base is hand-tight against the working face of the flange. Hydraulic pressure is then applied by a pump that remains top side and is connected via a downline to the nipple fitting on the top of the nut body and into the sealed chamber. Hydraulic pressure forces the piston and nut body apart, thus stretching and tensioning the bolt through the flange joint. The threaded locking collar mounted on the nut body is then screwed back and hand-tightened with a small hand-held tommy bar, thus retaining the induced tension in the stud. The pressure is then simply released and the hydraulic hose removed from the nipple fitting, completing the operation.

Each stud in the flange is fitted with a hydraulic nut and tensioned simultaneously, providing an extremely fast and accurate procedure for flange assembly.

The bolt load is achieved simply by the hydraulic pressure exerting force across an accurately defined area. A simple preset pressure generated by the topside hydraulic pump achieves a powerful, accurate and known preload to each of the studs simultaneously.

Throughout the installation, the diver's hands are free while the studs in the flange are being simultaneously tightened. This eliminates errors due to friction and the pinch points associated with torquing.

Bolt load accuracies of 95 percent are typical with hydraulic nuts, far greater than those of torquing and tensioning. Removing the hydraulic nut is accomplished by reapplying pressure through the nipple fitting to unload the locking collar. The internal pressure is then relieved and the hydraulic nut can be easily removed with a small hand-held tommy bar.

No major physical force, large wrenches, or torque tools are required to correctly fit and remove the SeaStallion nuts. The diver simply needs a small C-wrench or tommy-bar in the palm of his hand to do the job.

Hydraulic nuts have revolutionized the make-up and disassembly of critical flanges. The many advantages of using hydraulic nuts for subsea applications include:

• A typical reduction in installation and removal time of 90 percent or more. A large flange can be completely tightened in less than an hour.
• Quick payback in time and manpower. The operation takes minutes instead of hours or days.
• Elimination of the need for conventional tools. The only tightening tool needed can be strapped to a diver's wrist.
• The ability to tighten all studs in a single operation, accurately achieving identical clamping pressure on each and every bolt.
• The delivery of exceptionally powerful bolt loads, ensuring superior gasket sealing.
• Compactness in constricted areas. The hydraulic nuts can often be installed on a component topside and lowered with the bolts or flange assembly.
• Hydraulic nuts are versatile and can be used on virtually any bolted flange component, making the existing nut and tightening method obsolete.

One potential application for the Integra Technologies SeaStallion is a hot tap clamp used for making on-bottom subsea lateral tie-ins without welding and without interrupting product flow through the line being tapped.

Platform Decommisioning with Circle Technical Services
During the early years of platform installation little consideration was given to the future problem of how to decommission them. But times have changed dramatically. Engineers who were once involved with the design and installation process are now turning their skills to decommissioning and disposal.

Although decommissioning timescales are being extended by as much as 15 years, there comes a point where the decline of production, compared to the on-going maintenance costs, no longer justifies a platform's continued operation. Against this must be balanced the enormous costs of removing them.

In these environmentally aware times, decommissioning has become a much more complex operation, involving much more than the simple the logistics of lifting the redundant jacket off the seabed.

"Whether it is in the Gulf of Mexico, the North Sea, or any other offshore province," says Circle Technical Services' Managing Director David Dent, "the requirement is to safely disconnect all the conductors, pipelines and templates to remove any obstructions from the seabed."

He goes on to point out that the cost implications involved can be effectively reduced. "Experience shows us that this can be achieved not by cost cutting and reducing equipment day rates, but by effective pre-planning."

Dent believes that early involvement of contractors can pay dividends in cost savings. Circle Technical's experience in tackling such projects can help in the design and implementation of cost-effective solutions. These can include full mock-up onshore trials, before offshore deployment, to reduce the estimated project duration and reduce costs on vessels, equipment, and man-hours.

Environmental considerations and security conditions have made the use of explosives less acceptable, putting the focus on underwater high-pressure, water-abrasive cold cutting. Circle Technical Services has been one of the companies to see business growth as a result. Lessons learned during their 12 years' experience in the North Sea are now being put to use internationally.

"One of the main advantages of water-abrasive cutting systems is their versatility," points out Harry Ashton, Operations Director at Circle Technical Services. "We can cut through almost any material. When you consider the range of coatings and materials we may have to deal with - from concrete to plastics - that ability is very important."

Another advantage of water-abrasive cutting is it produces a very clean cut. The cutting head is precisely positioned in a manipulator, either on the outside or the inside of the pipe being cut. These manipulators are designed at Circle Technical's premises in Aberdeen, and can be deployed from a topside platform, dive support vessel, or heavy-lift barge.

Cold cutting can also be carried out in water depths down to 1,640 feet (500m). In the Norwegian sector a Circle Technical team recently carried out remote cutting of a 16-inch plastic coated steel pipe at 1,132 feet (345m).

A four-year contract with Technip-Coflexip, completed last year, involved Circle Technical cutting and removing seabed conductors, risers, and pipelines on the Maureen Alpha Complex in North Sea block 16/29a.

The project demonstrated the value of involving the cutting contractor early on. Planning began in 1998 and much of the work was carried out before the Maureen platform was refloated in June 2001. "As the first deepwater decommissioning in the North Sea, the Maureen project posed particular challenges for everyone involved," says Ashton. "Careful and methodical planning proved invaluable to the successful re-float."

The expertise developed in the North Sea by Circle Technical Services is now being applied in the Gulf of Mexico. Working out of its new Houston base, the company has so far worked on 20 decommissioning projects in its first year of operations in the area. The company has six more large contracts in the Gulf already in the book.

Success for SRD's Pipe Lay Support System
Sonar Research and Development (SRD)'s Pipe Lay Support (PLS) system is installed on Coflexip Stena Offshore's (CSO) CSO Deep Blue, proving very successful in the field and generating substantial operational savings. The system was fully commissioned in the Gulf of Mexico and is now in its second year of operation. Pipeline catenary and touchdown monitoring in real-time operational conditions has produced exceptional results down to 4,264 feet (1,300m) on a number of pipelay projects. The system is rated to 7,872 feet (2,400m) working depth.

SRD's PLS system is a bespoke package that provides a flexible approach to sonar visualization. Sensors are mounted on the ROV garage, which is suspended in the water column. From this relatively noise-free platform, a range of specialized sonar beams illuminate both the pipeline catenary astern of the vessel and the seabed vertically below. Acoustic returns are obtained from various regularly-spaced features on the pipeline assembly itself, rather than from any dedicated retrofitted targets.

The system software can track the progress of contacts on the pipe catenary down to seabed touchdown. Whole Field Modelling (WFM) techniques give the operator a real-time 3D presentation of the pipeline being laid from the moving vessel, including ROV position and seabed terrain, all in their accurate dynamic spatial relationship. As with many other SRD software, the benefit to the operator is an immediate understanding of complex underwater operations in real time.

The PLS derives a touchdown point that is continuously updated as the pipelay operation progresses. The accuracy of the information received has significant advantages during the laying operation and integrates information on the three principal aspects of the process: vessel position and bathymetric data (i.e., start and end point of the lay model) and catenary position. Stress data can be included. For J-lay operations, SRD's Pipeline Exit Monitoring system (PEMS) is also employed, whereby a network of transducers installed in the walls of the moonpool tracks the exit point of the pipe from the vessel. Information influencing lateral movement of the catenary, such as vessel movement, wave height and current profile in the water column, can also be accepted. The three-dimensional catenary model derived from field measurements is continuously cross-checked with the theoretical catenary shape.

The accuracy and flexibility of the PLS system offer a cost-effective monitoring and recording package. The information supplied by the system is used during the laying operation, but also has wider advantages.

The data acquired by PLS accurately replicates the relative positions of pipeline, seabed, and any other in-water systems or vessels as required. The real-time touchdown information display to the barge helmsman can be tailored to individual requirements, and can incorporate 3D, plan, and longitudinal section displays. The WFM capability of the system will enable the displayed information to be readily assimilated for a full understanding of ongoing operations. The x, y, & z position of the touchdown point is logged against kilometer post. Absolute position and deviations from the planned route can also be identified. All such as-laid information is stored as a separate database, which can be augmented with stress-related data.

A data replay option is available in the field, and for later review back onshore. It provides real-time evidence of the actual pipelaying operation which can be presented or archived by the contractor. The system can also provide a valuable resource for pipe lay simulation or rehearsal.

The PLS system can be installed in J-lay and S-lay vessels, eliminating the need for support vessels used in monitoring roles and offering significant cost savings.

Thales GeoSolutions Mexicana
With geophysical and geotechnical investigations over the last three years in approximately 50 different locations in the Gulf of Mexico and offshore Mexico, Thales has demonstrated considerable expertise in this important segment of the world's oil industry.

Primarily focused on the installation of fixed and jack-up platforms and submarine pipeline construction, Thales GeoSolutions Mexicana provides geoscience services to the region's oil companies. Most of these fields are located approximately 60 miles northeast of Carmen Island in the bay of Campeche, with the others situated along the coast of the Mexican states of Tabasco, Veracruz, and Tamaulipas. The majority of the studies over the last three years was to detect potential hazards, define the most adequate area for the future installation of marine structures, and determine the best position for geotechnical boreholes.

The geophysical surveys were carried out using the latest technology available and installed on the MV Shin Nichi Maru. The geoscience experts aboard the vessel use SkyFix, the Differential Global Positioning System (DGPS) for precise positioning, together with the GNS II navigation software interfaced with the MultiFix system, both developed by Thales GeoSolutions.

While gathering analog and digital data based on the reflective and acoustic behavior of both the water column and the subsea strata, relevant information and events (such as mapping the seabed's geological faults, gas instructions, and calcareous formations) may be identified and stored for analysis later.

Data processing and interpretation is performed onshore at the Thales GeoSolutions laboratories in Carmen, Mexico. The results from the data gathered are then produced as engineering drawings, charts, profiles and technical reports. Based on this information, the oil company experts are able to design accurate underwater structures or pipeline routes, define the coordinates of where geotechnical borehole operations will be carried out, and specify exactly where fixed platforms will be established.

Thales GeoSolutions Mexicana field investigations help determine the physical conditions of the soil and subsoil, and develop the static and dynamic criteria that will be used for the assessment and design of the foundations for fixed jacket platforms using tubular steel piles.

A program of geotechnical investigations completed at the beginning of this year was carried out onboard Thales's DSV Pacific Retriever. The DP vessel, using DGPS SkyFix positioning, is fitted with one of Thales GeoSolutions' SMR-series drilling rigs installed on a cantilever platform over the side of the vessel. The drilling system features full heave-motion compensation, wireline sampling and testing and a combined water-depth-plus-borehole-depth drilling capacity in excess of 1,000 feet (300m) designed specifically for geotechnical fieldwork.

In this most recent survey, "undisturbed" soil samples were obtained at the same time as the in-situ testing, such as piezo cone penetration testing and Thales remote vane testing. Having completed the borehole, the samples were classified and sent to an onshore laboratory for analysis and static and dynamic soil mechanics testing. For this purpose specialist laboratories were employed in Mexico City and Northway, with all of the testing under the direct control and supervision of Thales GeoSolutions' expert personnel. This ensured that all the laboratory testing was conducted under the strictest quality-controlled conditions to comply with the standards and procedures required for this work. This field and laboratory information was analyzed and processed using specialist software to produce a final engineering report which will provide the basis for any structural design.

Thales GeoSolutions Mexicana has cultivated a reputation for excellence in its geophysical and geotechnical investigation services. This is borne out by the company's continued and significant participation in the sustained development of the Mexican petroleum industry.

The Thales GeoSolutions Group employs more than 2,000 people around the world, and provides precise positioning, integrated geosciences, ROV manufacture and operation, vessel and vehicle tracking, environmental and data management services, and saturation and air diving services.

Fugro and RD Instruments Measure Surface Currents from Drillships
Strong currents throughout the deepwater column have a significant impact on exploration activities. These currents are often strongest in the surface layers, and the influence of a dynamically-positioned (DP) platform on surface currents and the noise from its thrusters have restricted the collection of key data.

Until now.

Surface current velocities at distances of up to 820 feet (250m) from a DP drillship were recently measured in the deepwater Gulf of Mexico. Fugro GEOS and RD Instruments (RDI) have deployed a new horizontal acoustic Doppler current profiler to overcome past restrictions. Courtesy of BHP Billiton, the two companies operated from the Global Marine drillship, CR Luigs, in over 6,560-foot (2,000m) water depths in the Gulf of Mexico.

"The results were remarkable," said Fugro GEOS's Caroline Nicholas. "Despite the drillship's thruster noise, the new instrument was able to detect and display - in real time - currents up to 250m away in the upper 65 feet (20m) of the water column. We could clearly see wave-generated currents and the vortices from the thrusters."

This means that it is now possible to measure not only the currents influenced by the platform and its thrusters, but also the "true" currents outside the platform's influence.

"And we can do this right up to the sea surface," Nicholas added. "Previously, the noise problem restricted us to data from below about 164 (50m) from the surface. But it is in that top layer that the currents are often strongest and where operators need the most information."