Jacket Pile Installation - Bahamas, Caribbean
LDD, an Acteon company providing near- and offshore specialist drilling and foundation installation services, demonstrated its problem-solving skills when it tackled particularly challenging ground conditions found off Grand Bahama Island in the Caribbean.
LDD was contracted to install foundation piles for an oil jacket with loading arms. The ground contained difficult-to-drill hard horizons and grout-swallowing voids and installation work needed finishing before the rapidly approaching hurricane season. LDD’s answers to these challenges included bespoke drilling equipment and the first-of-its-kind use of pile socks. The work was completed safely and on time.
CLIENT QUOTATION
“It is good to work with professional people who are flexible and have extensive experience,” says Matt Pressel, Project Manager, Cal Dive International. “I have nothing but good things to say about the LDD team members and I look forward to working with them in the future.”
PROJECT STATISTICS
SOW: Jacket Installation Service
No of piles: 4no
Pile diameter: 54-in/ 1372mm
Average length: 32m
Socket depth: 18m
Geology: up to 20 MPa
Duration of pile installation: approx. 14 hours per pile
EQUIPMENT
LD612 Drilling rig;
S-150 Hydraulic hammer;
Drill bit LDD 1245mm to 1550mm Under Reamer;
Specialist grouting equipment
Pile geo-membrane socks;
CHALLENGES
‘vuggy’ ground conditions
excessive loss of cement during grouting
Bahamas Oil Refining Company is expanding its storage terminal and required the installation of a jacket with loading arms. LDD was able to advise the main contractor, Cal Dive International, about the challenges of piling into the vuggy calcarenite ground, which contains hard marble layers and large cavities.
The imminent hurricane season provided additional pressure for the installation to be completed on schedule. The main risks were that the hard layers would delay the drilling of the four large-diameter piles needed to secure the jacket against 100-year storm risks, and that excessive quantities of cement and the circulating drilling fluid would be lost to the cavities.
Jason Clark, LDD managing director, says, “This type of large-diameter drilling was new to Cal Dive International and we had to convince the company that we could complete the work safely and quickly. We promoted the use of reverse circulation drilling as an effective solution to the challenge. It is very gratifying to see that we met their objectives and that that the installation has been completed efficiently.”
As part of its preparations, LDD attended the site investigation and observed bores at each pile site. In May 2011, Cal Dive International’s Pacific derrick barge placed the 900-t jacket on the seabed. LDD’s sister company, CIS, has pile-driving experience in the area and for this project provided an S-150 hydraulic hammer to drive the four 54-in. piles as part of the permanent works. When driven, these piles ensured the jacket’s short-term storm survival.
Lee Edwards, LDD projects manager, takes up the story: “We used our LDD 612 drilling rig, which was affixed to the pile top using our in-house-designed gripper can, to drill 18 m below the pile toe. The project was unique and required specific equipment. We designed and built a special bottom-hole assembly, a drill-pipe stabiliser and a 49-in. drill bit with hydraulically activated side cutters that give a 58-in. under-reaming capacity. An oversized hole was required to provide room for manoeuvring the insert pile and to give a large enough grouting annulus. We have designed, built and operated a wide range of under-reaming systems and consider ourselves to be market leaders in this technology.”
“The single biggest challenge was the ‘vuggy’ ground conditions. We mitigated the risk of losing the cuttings flush from the reverse circulation drilling system by having a grouting spread standing by. Had we experienced loss of fluid circulation, we would have been able to quickly seal the void with cement and continue by drilling through the grouted plug. Our work was on the critical path; everyone was waiting for us, so completing the work in the time we estimated was important.
“Some engineers expressed doubts, based on their experience of this region, as to whether we would be able to drill in such challenging conditions. This made the completion of the first hole in just 14 hours intensely satisfying. We did what we said we would do.”
A second challenge relating to the rock’s ultra-high permeability was to prevent excessive loss of cement during grouting. LDD proposed placing a geo-membrane “sock” over the piles, which would inflate with grout but prevent it from escaping into the voids. Edwards believes that this is the first application of geo-membranes for a jacket installation.