Under the extended deal, JDR will deliver pre-commissioning, testing and termination services for the project.
JDR is also responsible for providing onshore planning and procedures, project management, mechanical installation, cable containment, termination, test, modification and reporting.
Siem Offshore chief operating officer Günther Bakker said: "We brought JDR into the Baltic 2 project due to their full support team capability and extensive experience in offshore power cable operations.
"In field, their work has been professional with on-time delivery. We are delighted to extend their role in the project."
The Baltic 2 wind farm is expected to generate 1,200 gigawatt hours of electricity per year for about 340,000 homes and save 900,000 tons of CO2.
