BJ Tubular Services has completed a contract for Murphy Sarawak Oil Co. of Malaysia to provide pile-driving services for its jackup-deployed platform installation off the west coast of Borneo.
The project proved to be an engineering and operational challenge, the company said. The four structure support piles – measuring 36 in. x 1.25 in. – 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-in. casing strings, using 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 m below the mudline. Using soil data and drive simulations provided, 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 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. 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, this approach would mitigate internal pile skin friction while driving and allow installation to be achieved with available equipment. BJ settled on 15-mm 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 offshore hydraulic pile driving system.
Murphy Sarawak agreed to the use of the removable composite material insert, and BJ started 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 in. By doing so, the tip of the conductor/structure pipe size is returned to the size of the parent bore. Drilling forward then began for the 3 x 13-3/8 in. casing strings, and was completed on schedule.