Dual HDD Installs Key to Vineyard Wind One Offshore Wind Farm
Melcar Group recently completed the landfalls for the Vineyard Wind One project in Massachusetts using horizontal directional drilling (HDD). The project involved installing dual 32-in. HDPE outfalls into the Northern Atlantic Ocean as the critical link between land and sea for the Vineyard Wind One Offshore Wind Farm.
Melcar was contracted less than a month before operations began, adding to the risk profile of the already technically challenging installation. To overcome the lack of time between contract and execution, the contractor’s large rig HDD team began the planning, design and preparation phases immediately, working in parallel to maximize efficiencies. Due to the magnitude and importance of this project for the future of the U.S. offshore wind industry, Melcar was committed to ensuring project success by being the key link between onshore and offshore development.
While Vineyard Wind handled the community outreach, operations began with a site survey and the installation of a sound wall to isolate construction noise from the surrounding community. The Covell’s Beach parking lot served as the landfall works package site and as a staging yard for pipe and materials for the onshore duct bank, restricting the working room to 160 ft by 110 ft. The site was outfitted with all-weather sanitation facilities, office containers, frac tanks, light towers and a crew drying cabin. HDD construction began by installing 54-in. surface casings to protect Covell’s Beach, a highly trafficked vacation spot for locals and visitors during the summer. The 54-in. casing was supplied by Trinity Pipe, and installed with a TT Technologies 24-in Taurus hammer.
During casing cleanout, the drill team encountered boulders and cobbles greater than 40 in. in diameter — an indication that the geotechnical reports were inconclusive and the engineered mud plan would need to be re-evaluated. Once the casings were cleaned out, the pilot drill on HDD 1 (East) was completed using a gyroscopic steering tool provided by Brownline. The pilot drill of HDD East exited the seafloor less than 60 in. off target and the BHA was recovered onto the barge deck and removed.
The reaming process started immediately following the successful pilot hole installation. To mitigate the risk for an inadvertent return, the reaming process was highly analyzed and engineered due to the high risks introduced by the abnormally shallow drilling depths required by the project owner. The ground conditions being that of boulders and poorly graded sand, the analysis of the risks of an inadvertent return represented low annular pressure limits. To minimize the annular pressures, a three-stage reaming process was performed. Starting with a 24-in., then 36-in., followed by a 48-in. final ream pass, Melcar’s HDD team enlarged the borehole via forward reaming, with a Tonghand on the barge. A barrel reamer was pulled through the borehole to ensure integrity prior to pulling in the product pipe. The processes employed resulted in an expeditious installation of the bore hole and there were no adverse environmental impacts on the project.
In order to offset schedule impacts due to extreme offshore weather events during the start of the project, Melcar mobilized a second HDD machine and support equipment spread. The second HDD crew began the installation of HDD 2 (West) while HDD East was still in progress. This additional effort advanced the project schedule and ensured the project owner of Melcar’s dedication to completing the project on time and under budget.
HDD West was installed following similar guidelines as HDD East, taking into account the differing ground conditions encountered during the execution. Due to the varying nature of the ground found in the Northeastern United States, Melcar had initially mobilized with appropriate tooling to counteract all ground conditions including rock and mixed-face materials. This ensured that when altering ground conditions were encountered, the HDD team was able to adjust as needed with no down time. Although a boulder bed was encountered during both HDD installations, no inadvertent returns or releases occurred and downhole annular pressures were consistently monitored.
The dual installations were completed using Herrenknecht HK250C and Vermeer D330x500 rigs. Once both HDD installations were complete, demobilization was performed in parallel with conduit proofing, casing extraction and restoration works. The HDD conduits were proofed using a pig launcher attached via an MJ-adapter. The casing annulus was filled with the specified backfill and extracted with a Taurus hammer and extractor kit. The 32-in. HDPE was left 5 ft below ground surface, and the Covell’s Beach parking lot was temporarily restored.
The Vineyard Wind One project is the first commercial-scale offshore wind farm in the United States. Daily project management meetings were held between the contractors and employer to overcome project challenges included scheduling restrictions, inclement winter weather conditions and extremely tight design tolerances for final HDD placement. The project teams worked through the 2021 holiday season and extended hours to meet weather windows for both pipe pull installations. The operational durations per phase were completed in less than half the allotted time per the owner’s schedule.
No safety incidents occurred during the completion of this project. Due to the high level of QA/QC present on all Melcar projects, all teams worked simultaneously. The dual installations were completed with no adverse effects to the shoreline or marine environments.
The success of the HDD landfalls on the Vineyard Wind One project established a standard for all offshore wind and landfall applications in the United States, and sets a precedence of success for efficient, environmentally friendly and safe installation procedures. Once completed, Covell’s Beach will be fully restored, with clean, renewable energy transferring below the shoreline to power over 400,000 homes and businesses across Massachusetts.
James McIntyre is the managing director at Melcar Group.
