Hammer technology swings into offshore construction

Two recent operations point to the complexity of today’s construction demands and the manner in which service companies are using engineering expertise and custom fabrication to create safe foundations for oil and gas facilities around the world.

Safe haven in ‘Iceburg Alley’
Service companies face several challenges when operating off the coast of eastern Canada including icebergs, frigid seas, major storms, and strong currents.

The S-200 Hydrohammer system and deployment frame sit on the deck of the DSV Well Servicer during the installation in Iceburg Alley. (Images courtesy of BJ Services)

BJ Services recently carried out a variety of services in association with a contract awarded by installation contractor Technip as part of an engineering, procurement, construction, and installation contract. The development consisted of a series of tieback satellites to a floating production, storage, and offloading vessel about 300 miles (483 km) offshore St. John’s, Newfoundland, in water depths to 510 ft (155 m) in an area known as “Iceberg Alley.”

The goal was to install pin and foundation piles for two manifold support frames and one subsea distribution unit, running S-200 Hydrohammer equipment from Technip’s Wellservicer support vessel during a short weather window between June and July 2009. Construction was unusual because of the difficult environment and because the “top-of-the-seabed” equipment was being placed in pre-excavated glory holes 10 ft (3 m) below the surrounding seabed to protect against iceberg scour.

The environmental conditions presented several challenges. The first was how to stabilize the hammer onboard the dynamically positioned support vessel to ensure safe operations in high seas. In the Gulf of Mexico and other relatively calm environments, hammers are laid on the deck of the vessel and can be picked up safely by a crane or an A-frame for operations. For this operation, however, BJ Services designed and fabricated a large hammer-upending frame that would minimize the hammer’s tendency to swing when lifted, thereby widening the operating envelope in the expected sea states. It would also help to keep the hammer securely in place when it was not being used.

The S-150 Hydrohammer system drove the pile sections to final depth before placing the topsides onto the piles.

A number of customized items also were developed for this operation, including weatherized control and compressor rooms, a hydraulically powered supply reel connected to the hammer, a soundproofed P-750L diesel hydraulic power pack, chaser subs for the 24-in. piles, and ancillary equipment.

Based on a drivability analysis for operations, engineers chose to use the S-200 hammer system because of its maximum energy potential of 147,000 ft-lb (200 kNm). Two hammers were supplied, with one serving as the primary pile installation tool and the other as a backup.

The modified internal lifting tool is set in the pin of a “weight set” connector. Four freestanding piles with connectors can be seen in the background.

To ensure safe, efficient operations, safety and operational planning meetings were held at the St. John’s operations base and in Lafayette, La., where the equipment was being designed and fabricated. Following a final installation test (FIT) in Lafayette, all equipment was mobilized to St. John’s, where the upending frame was welded to the deck of the Wellservicer and all other equipment installed for the operation.

Overcoming the current
Operations on the 24-in. piles began in mid-June, when the hammer system was raised on the frame and then lowered into the water for placement onto the pile on the seabed. The vessel’s thrusters were used to maneuver the vessel and position the free-hanging hammer as the crane stabbed the chaser sub into the pile. Remotely operated vehicles provided underwater video to guide this operation (although the rough weather did churn the seabed at times, obscuring the images on surface).

By monitoring the video and analyzing data generated by the hammer system, the crew was able to adjust the blow count while driving the piles. During the 37-day operation, the crew drove fifteen 24-in. piles and six 36-in. piles about 43 ft (13 m) below the mudline. Each 24-in. pile was driven to depth with an average of 24 blows (0.8 ft/0.25 m), while the 36-in. piles required an average of 65 blows (0.8 ft/0.25 m).

Although the offshore operation progressed without incident, it was not without challenges. Due to unexpectedly strong currents while driving the 24-in. piles, the crew struggled to keep the hammer upright. This problem was solved by increasing the length of the mule shoe on the chaser. In addition, a stabbing guide was welded onto the 36-in. drive sleeve to make it easier to stab the hammer onto the pile.

Another hurdle was inclement weather. On one occasion, while recovering the hammer system from the seafloor, stormy seas made it unsafe to lift the heavy weight onboard and place it in the frame. The system was wet-stored in the water for 14 hours until the weather calmed, making it safe to retrieve.

Careful attention to design, pre-planning, fabrication, and completion of the FIT before beginning the job contributed to its success. In spite of challenges posed by extreme conditions, this complex subsea pile-driving operation was completed according to plan.

Safe platform construction
In its most recent operation, BJ Services completed a platform pile-installation operation for NuCoastal (Thailand) Ltd. in Block G5/43 in the Gulf of Thailand. Custom-engineered internal lifting tools that cater to the nonlinear (upset) internal bore of pipe ends were used to handle and drive jacket leg piles joined with externally flush and internally upset weight set connectors, rather than employing traditional welding methods. This was necessary to save time on location (these connectors can be made up in 10 to 12 minutes as opposed to four to six hours or longer to weld manually) and to eliminate the need for welding platforms on the free-standing pile sections that had already been driven.

BJ Services worked with equipment designer IHC Handling Systems to convert BJ’s internal lifting and handling tool to allow for the pickup, deployment, assembly, and remote release of eight multisection 36-in. diameter, 2-in. wall thickness jacket leg piles. These piles are the foundation of a linked pair of offshore production structures scheduled for installation in 65 ft (20 m) water depth. Installation was carried out from the Lewek Champion heavy-lift accommodation and pipelay vessel.

To complete the jacket pile installation equipment package, BJ Services analyzed site-specific soil information, seafloor conditions, pile configurations, borehole logs, and other data in a driveability analysis to select a 110,000-ft-lb (150-kNm) S-150 hammer system for the operation. Two hammers were on location to ensure reliable operation and to eliminate the possibility of nonproductive time.

With pile installation operations for both jacket structures carried out around the clock, all piles were installed in five days. The piles were driven to target depths of 222 ft (68 m) below the mudline for the wellhead platform and 150 ft (46 m) below the mudline for the production platform, within the predicted number of blow counts. All equipment operated as planned during the leg pile pickup, installation, driving, and pipe add-on phases. The scope of work was supported by personnel at BJ Services’ regional technical hub in Singapore and operations base in Songkhla.