Deepwater Challenges For Conductor Installation

Overcoming obstacles through group collaboration.

Several Acteon companies have pooled their expertise and experience to deliver a highly challenging conductor installation project for the Papa Terra oilfield in 1200-m water depths in the southern Campos basin, Brazil. Petrobras operates the Papa Terra concession and has a 62.5% interest; Chevron holds the remaining 37.5%.

In March 2010, Petrobras challenged InterMoor do Brasil to install drilling and production conductors with a tolerance of less than 30 cm off centre using its patented cost-saving conductor installation methodology.

The company was to install the conductors before the arrival of the drilling rig. The key benefits of pre-installation are that it removes this task from the critical field development path and eliminates it from the rig procedures so that lower-cost platforms can be utilised to support the offshore installation. The operator does not have to pay a drilling spread rate for this type of operation, so can realise substantial cost savings.

InterMoor was awarded a contract to manufacture 17 conductors of 36-in. outside diameter, 1½-in. wall thickness and 59-m length, and to install 15 of them in 365 contract days. The pipe supplier was to use 160 of these days to fabricate the pipes in Morgan City, Louisiana, USA, and deliver them. The challenge was further complicated by the turnkey nature of the project: design, fabrication and installation of the conductors to strict inclination, position and height tolerances.

João Ruiz, subsea manager, InterMoor do Brasil, highlighted the importance of Acteon companies working together on this project. “Working together enabled InterMoor, MENCK, 2H Offshore, NCS Survey, Seatronics and Claxton to overcome a series of technical issues and deliver a seamless solution for the project at a reduced cost and within the required time frame.”

Acteon’s involvement began with InterMoor and MENCK performing a high-level installation review focusing on the impact driving of the single-piece conductors. From the soil data provided by the client, it was decided that using the MENCK MHU 270T deepwater hammer spread (MHU 270T MHP DWS) would provide sufficient installation contingency while ensuring structural integrity and minimum induced fatigue to the conductor system.

Acteon’s involvement continued with 2H Offshore performing the engineering critical assessment (ECA), an analysis based on fracture mechanics principles, which Petrobras reviewed and approved.

Milton Pereira, project manager, InterMoor do Brasil, said that one of the main challenges his team faced was getting the welding qualification procedures required approved to DNV standards, which are normally used for the welding qualification of rigid risers. “In addition, the allowable flaw sizes were exceedingly tight,” he says. “These were defined by the ECA and based on critical operational lifetime loads to be induced on the conductors.”

InterMoor manufactured all 17 of the 36-in. conductors and 5 guide templates at its Morgan City facility to the DNV-OS-F101 standard and the client’s specification, whereby the ECA determined whether a given flaw was safe from brittle fracture, fatigue, creep or plastic collapse under the specified installation and service life loads.

Pereira explains: “InterMoor inspected all the conductor welds using X-ray, magnetic particle and automated ultrasonic testing (AUT). AUT is a very sensitive non-destructive testing system and required an equipment configuration specifically designed for this project because of the J-bevel joint profile, the 1½-in. pipe thickness and the allowable flaw sizes, as defined by the ECA study.”

After the 17 conductors and 5 templates had been fabricated, inspected and approved in Morgan City, InterMoor started the highlevel logistics process to transport them safely to Rio de Janeiro, Brazil, using barges for the inland transit from Morgan City to Houston followed by a vessel to Rio de Janeiro. This was equipped with two heavy cranes capable of loading the conductors and templates in Houston and offloading them directly onto barges in Brazil. The offloading was performed in two days after the installation vessel arrived and without incident.

InterMoor’s work offshore commenced in the first quarter of 2012 with template installation using a chartered installation vessel equipped with a 250-t offshore crane with active heave compensation, as one of the main challenges on location concerned the positioning and installation tolerances. These were within 30 cm of the conductor target position, and at less than 1° inclination and ±10-cm stick-up.

For this purpose, InterMoor designed five individual templates in cooperation with Claxton. Each 35-t template measured 24 × 4.5 × 1.5 m and would guide three conductors. The templates were needed in a very short delivery time and their manufacturing required an extraordinary amount of collaboration to ensure that the installation measurements would be accurate. The work included onshore 3D modelling of the templates to provide models for use offshore during quality assurance and control. A further challenge was to devise an appropriate procedure for the vessel to lay the templates in the correct position with minimal iteration.

Acteon’s involvement continued with InterMoor and Seatronics providing survey equipment for the long-baseline survey array, which helped in the control and positioning of the templates. Long-baseline surveyors from NCS Survey worked with InterMoor surveyors during the offshore phase.

To install the conductors, InterMoor applied a technique that had only been used once before in deep water: launching the conductors from an auxiliary barge, the Muliceiro-X, which also transported them to the Papa Terra site, and using special tools. The only other project to use this technique so far was an InterMoor project for Shell Petrobras–ONGC in the Shell-operated BC-10 field in Brazil’s Campos basin in 2008.

The Muliceiro-X was modified by the installation of five rails. Two rails served as the track for a special shuttle system to elevate and transport each conductor to the barge’s side. The other three rails served to support the conductors and to sea fasten them. The conductors, connected by a towline to the installation vessel, were side launched from the barge using the shuttle system, which was operated by on-board InterMoor personnel.

Mobilising the MENCK MHU 270T MHP DWS onto the installation vessel was another challenge owing to the limited deck space. MENCK’s detailed operational procedures for use offshore and the strategic layout of its equipment helped to mitigate the challenges. The company also designed and fabricated a winch frame for the umbilical winch and a chute to deploy the umbilical used to remotely operate the hammer.

Once the Muliceiro-X arrived on location, the five templates being already in position on the seabed, the installation vessel came alongside and began the conductor launching sequence. All 15 conductors were batch set in one field visit, as Michael O’Driscoll, project manager, InterMoor Inc., explains: “Instead of putting one conductor in the mud and then hammering it with the MENCK hammer, we batch set all the conductors. This meant we had all the conductors in the mud in a stable configuration but not yet driven to grade. This helped to minimise the outboard handling of the MENCK hammer. The fewer times you need to handle an 80-t piece of equipment offshore the better!”

He continues, “By batch setting in this way, we only had to launch the hammer once; it drove all 15 conductors and then it was recovered. That was its total use. This approach saved a lot of time offshore and minimised the risks.”

InterMoor used a special suction-to-stability head tool to handle the conductors and safely launch them from the barge into a stable vertical underwater position. This exceptional engineered tool also enables suction to be used to increase the penetration of the conductors beyond their self-weight penetration depths to the minimum allowable depth. Generally, the suction-to-stability heads can increase the penetration depth by up to 5 m.

Installation was completed in April 2012 after template removal and the final as-laid survey. A survey tool specially designed for the final as-laid survey was positioned at the top of each conductor. These confirmed that all the conductors were in their final positions.

“This was a major engineering, procurement, installation and commissioning project that we successfully completed from the financial, logistics, operational, schedule, technical and, particularly, quality, health, safety and environmental aspects,” concludes Ruiz.

Share this content