The project proved to be a real engineering and operational challenge. The four structure support piles – measuring 36in. x 1.25in. – would also be used as conductors for the Production A Platform in West Patricia Field. Each of the four structure piles – or conductors – were to contain 3 x 13-3/8" casing strings, utilizing AB- STL flush connections depending on pipe weight. This configuration would serve as the basis of a 12-well platform. The four piles were made up using internally-externally flush Oil States Puma connections.
Murphy Oil Engineering determined that the required depth – or penetration - of the 36-in. piles would be from 72 to 75 meters below mudline. Using soil data provided and drive simulations, BJ proposed to use a reduced (ID) drive shoe to reduce the potential for washing out the casing during driving to reach the required pile penetration. This type of drive shoe is normally constructed from steel and remains inside the tip of the pile after it is successfully driven into place.
However, due to the risk of connection interference and/or hang-up at the pile tip, Murphy Sarawak wanted a drillable drive shoe to avoid a permanent reduction in pile I.D. As an alternative to conventional approaches, BJ proposed using an insert made of material other than steel that would perform the same function as a traditional drive shoe, but could be removed after pile driving was completed. Called the Composite Drillable Drive Shoe system (CDDS), this approach would mitigate internal pile skin friction while driving and allow installation to be achieved with currently available equipment. BJ considered several different materials and methods of installation, finally settling on 15mm thick composite material sheets formed to suit the I.D. of the pipe in question, which were then bonded to the inner bore of the parent pipe.
BJ designed inserts and constructed scale models before testing them to destruction to determine the shear potential of the bonding material. Once testing was completed, BJ proposed the new system plans to Murphy Sarawak. The presentation included pile-driving simulations to demonstrate the performance of the composite material insert in conjunction with BJ's specialised Offshore Hydraulic Pile Driving System.
Murphy Sarawak agreed to the use of the removable composite material insert, and BJ commenced with fabrication and subsequent installation of the inserts. The approach involved removing the insert after pile driving had been completed during the first pass of drill bit, while the combined structure pile/conductor string was cleaned out to a point located just past the shoe. A watermelon mill was located above the bit and set to the I.D. of the pipe at 33.5". By doing so, the tip of the conductor/structure pipe size is returned to the size of the parent bore. Drilling forward then commenced for the 3 x 13-3/8in. casing strings, and was successfully completed on schedule.
"The greatest challenge for us was to devise an easily extractable drive shoe that would deliver the same performance as the standard steel unit, but could then be removed permanently from the pile tip. The composite material insert performed well, as indicated in our field testing and pile driving simulations," said Doug Bell, area manager – Asia Pacific for BJ Tubular Services. "The primary benefit of this approach is that when we remove the drive shoe, we lower the risk of possible connection problems and complications at the pile tip sometimes caused by permanently reducing the pile I.D. By preventing these problems, the overall operation is likely to run more efficiently. In the long-run it will be less costly," he added.
BJ has successfully carried out several pile driving operations in Malaysia using the CDDS. Looking ahead, BJ will be carrying further similar procedures for operators in Malaysia and Vietnam.
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