Why pre-engineering is critical when working off the back of a barge to minimise the critical path.
By working off the back of a barge instead of a drilling rig, Conductor Installation Services Ltd (CIS) estimates it has cut hundreds of thousands of dollars off the cost of a project offshore Malaysia.
A global exploration and production operator commissioned CIS to install conductors for 11 wells. However, to compress the project timeline, the client specified that the procedure should occur before the drilling rig arrived on location. Consequently, all of the work had to be performed from the Castoro Otto, a 190-m barge, instead of from a drilling rig.
“Pre-installing conductors can unlock significant benefits for a project,” explains Andy Penman, group managing director of CIS. “It takes this task off the critical path and means that the rig can begin drilling as soon as it arrives on location. However, although we had proved the procedures for working off the back of a boat or barge, there were substantial challenges involved.”
The main challenge was that, unlike a drilling rig, a barge has no derrick. If the installation does not go according to plan, for instance, a hard formation is unexpectedly hit, there is no intervention capacity available. Pre-engineering, according to Penman, was key to ensuring that the target depth was met when installation commenced.
Here, the pre-engineering took the form of a conductor driveability study. A contractor was hired to run a core drill to obtain a sample of the formation that CIS would be driving through.
CIS then entered details about the rock formation into an advanced computer model for analysis. This analysis revealed information that was vital to the project’s success, including the type of hammer that would be suitable, the depth it would be able to drive the conductor to and how many blows would be necessary. “It is all about determining whether you can meet the target depth without any intervention,” says Penman. “When you are going to be working off the back of barge, you really need to know that.”
Once the driveability study was complete, senior CIS personnel held meetings with the operator’s personnel where they discussed, refined and finalised the procedures and processes.
Working together
Another Acteon company, piledriving specialist MENCK, was also involved in the project offshore Malaysia. Before CIS installed the conductors, MENCK set the jacket on the seabed in May 2011 and drove the four main anchor piles to hold the jacket in place.
Once the jacket had been set, CIS moved in to commence a batch driving operation. To drive the conductors from the back of the barge, an 90-kJ hydraulic hammer was slung from one of the Castoro Otto’s cranes. Within 15 days, CIS had installed all 11 of the 20-in. diameter, 5/8-in. wall-thickness conductors.
“It was an extremely efficient operation,” Penman reflects. “The whole project was completed on time and well within budget. The customer was delighted with the time and cost savings that it realised.
“Working off the back of a barge to pre-install conductors can substantially enhance the economics of a project, but, because there is no drilling package out there, the importance of rigorous pre-engineering and detailed planning cannot be overstated.”