Tampnet is the "largest offshore high capacity communication network in the world." It has created off-shore mobile LTE networks in the North Sea and the Gulf of Mexico. In partnership with Tampnet, GigSky offers data plans for use on these networks.
Just use the app (or iPad settings) to select a North Sea plan from those available in "Offshore".
Plastic SIM card
If you do not have an eSIM-compatible device, you can request a plastic SIM card from Tampnet by completing and submitting a form on Tampnet's website here:
The page contains a button labelled "ORDER A SIM CARD" which opens the form to request a SIM card.
Tampnet's website has a page containing coverage maps for their networks in the North Sea and Gulf of Mexico: