LDD demonstrated technical understanding and problem-solving when challenged with weak and highly fractured rock conditions during installation of an oil jacket in the Caribbean.
LDD worked closely with BORCO to understand, develop and provide a bespoke foundation installation service for an oil jacket with loading arms. The challenging geology on-site varied from ‘difficult-to-drill’ hard horizons to highly fractured rock with grout-swallowing voids and installation work was required to be finished before the rapidly approaching hurricane season.
Our project team answered these challenges using bespoke drilling equipment and the first recorded installation of geo-membrane pile ‘socks’ to limit grout loss. The result of the jacket installation proved a real success, with LDD working alongside the client to implement a solution that met client specifications and the LDD site team performed well to complete all works safely and to the client’s deadline.
“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.”
Bahamas Oil Refining Company was expanding its storage terminal and required the installation of a jacket with loading arms. In addition to providing the installation service, our team were able to offer first-hand expert advice to the main contractor, Cal Dive International, about the challenges of piling into the vuggy calcarenite geology containing hard marble horizons and large cavities.
In addition to the ground conditions, the imminent hurricane season provided an additional challenge and the pressure for the installation to be completed on schedule. The main risks were the hard layers could delay the drilling of the four large diameter piles needed to secure the jacket and that excessive quantities of cement and the circulating drilling fluid would be lost to the cavities in the fractured horizons.
Jason Clark, founder of LDD and managing director, stated, “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 the preparations, the LDD team attended the site investigation and observed bores at each pile site. Cal Dive International’s Pacific derrick barge placed the 900t jacket on the seabed. Sister Acteon company, CIS, had pile driving experience in the area and for this project provided an S-150 hydraulic hammer to drive the four 54” piles as part of the permanent works. When driven, these piles ensured the jacket’s short-term storm survival.
The LDD design team also took the time to understand the uniqueness of the project and the specific requirements of the bespoke piling equipment. LDD designed and built a specialist drilling bottom hole assembly, drill-pipe stabiliser and a 49-inch drill bit with hydraulically activated under reamers that opened to 58-inch. This was developed for an oversized hole, required to provide room for manoeuvring the insert pile and to give a large enough grouting annulus.
The biggest challenge was the ‘vuggy’ porosity of the Calcarenite. To mitigate the risk of losing the cuttings flush from the reverse circulation drilling system LDD had a grouting spread standing by. Had LDD experienced loss of fluid circulation, it would have been able to quickly seal the void with cement and continue by drilling through the grouted plug.
LDD’s scope of work was on the project critical path; ensuring completion of the drilling work in the time estimated was vital.
Lee Edwards, Project Manager said: “Some engineers had 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 exactly what we said we would do.”
A second challenge LDD met was relating to the rock’s ultra-high permeability. To prevent excessive loss of cement during grouting, the LDD team proposed placing a geo-membrane ‘sock’ over the piles, which would inflate with grout but prevent it from escaping into the voids. Lee and the team believed this was the first application of geo-membranes for piled jacket foundations.