An innovative subsea installation technique developed by InterMoor has helped Shell Brasil Ltda to prove a new technology for conductor installation.
The scope of work performed by InterMoor in the Parque das Conchas fields in Brazil’s Espirito Santo basin included installing eleven 36-in × 50-m drilling conductors, two templates, a guide for the caissons and a foundation for the artificial gas lift manifold at water depths of 1600–1800 m. Six 48-in. × 60-m caissons were installed and driven through the template.
InterMoor’s work involved welding the conductor sections and using a transport-and-launch barge to carry the conductors out to the site. This was a bespoke barge manufactured to a tight timescale and included an InterMoor designed conductor side-launch system for keelhauling the conductors to the anchor-handling vessel (AHV).
To maximise control during the installation of the conductors from the AHV, InterMoor applied its compensated anchor handler subsea installation method (CASIM). This included performing dynamic lowering analyses on the conductors and the hammer to be used, and conductor driving analysis and procedures.
As part of the CASIM service package, InterMoor also supplied two of its 6-m heave-compensation devices: single-unit cylinders that act as shock absorbers. These reduce motion and line tension spikes by behaving as soft, dampened springs applied in series with the much stiffer wire lowering system.
For the hammer, InterMoor turned to MENCK, as it is the only supplier of deepwater hammer systems. The company selected the MHU-270T deepwater hydraulic hammer, which has a driving energy of 270 kJ (at a water depth of 1000 m) combined with MENCK’s girdle-type electrohydraulic power pack. Generating hydraulic power at depth, rather than at the surface, helps to minimise the hydraulic hose length and reduces energy losses. This is the only practical method at these water depths. It also reduces environmental risks, as hydraulic fluids do not have to be pumped over long distances. In addition, the system ran on just 1400 L of a synthetic oil that biodegrades within 14 days.
The project was a major undertaking with many unknowns at the outset. The combination of onshore requirements before the offshore operations could start proved to be the biggest hurdle. However, the offshore phase was a success: all the conductors and the two templates for the gas lift manifold were installed from the AHV between Q4 2007 and Q1 2008.
John Cook, drilling manager, Shell Brasil, says, “The subsea hammering concept was particularly beneficial for the 48-in. caissons in the gas-lift-manifold templates. There was really no other installation method available that would give us the accuracies needed for the final conductor height.”
John Riggs, managing director, InterMoor do Brasil, points out that InterMoor’s novel approach created valuable project management benefits: “By using an AHV, we were able to keep the conductor installation activity off the schedule of the drilling rig. In addition, it meant that Shell knew the exact positions of the wells before the rig’s arrival so that the detailed rigid jumper and flowline work could be performed in advance.”
The concept of pre-installing conductors off the drilling rig’s critical path, although not problem free, was demonstrated to be feasible in water depths in excess of 1800 m. The main obstacle to the project was weather related downtime in deploying the subsea hammer and the remotely operated vehicle, which was essential for the hammer deployment and installation process. The lengthy mobilisation and demobilisation times required for the hammer and its associated equipment were also major contributors to the overall project time.
This was a concept-proving project that showed the technique to have merit and one that could benefit larger-scale projects in less onerous operating conditions.