 In shallower waters the mobile units are anchored to the seabed, however in deeper water (more than the semi-submersibles or Drillships are maintained at the required drilling location using dynamic positioning.Around 1891, the first submerged oil wells were drilled from platforms built on piles in the fresh waters of the Grand Lake St. Marys in Ohio.The wells were developed by small local companies such as Bryson, Riley Oil, German-American and Banker's Oil.