What is Offshore Drilling and Drilling Rigs

Introduction

A mechanical process where a wellbore is drilled through the seabed is referred to as Offshore drilling.
The main purpose of drilling is to explore for and subsequently extract petroleum which lies in rock formations beneath the seabed. Most commonly, the term is used to describe drilling activities on the continental shelf, though the term can also be applied to drilling in lakes, inshore waters and inland seas.

The two factors which present environmental challenges during the offshore drilling operations are:
1. the produced hydrocarbons and
2. the materials used during the drilling operation.

There are many different types of facilities from which offshore drilling operations take place.
These include bottom founded drilling rigs (jackup barges and swamp barges), combined  offshore drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units (MODU) including semi-submersibles and drillships. These are capable of operating in water depths up to 10,000 ft. In shallower waters the mobile units are anchored to the seabed, however in deeper water (>5,000 ft) the semisubmersibles or drillships are maintained at the required drilling location using dynamic positioning.

Offshore drilling jack up rig

WHAT IS OFFSHORE DRILLING RIG

• A offshore drilling rig is a machine which creates holes(usually called wells or boreholes) and/or shafts in the ground.
• Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas wells.
• Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or offshore-based marine units.
• The term “rig” therefore generally refers to the complex of equipment that is used to penetrate the surface of the earth’s crust.

THE OFFSHORE DRILLING CONCEPT

• The offshore drilling concept is to drill a hole in the ground and stabilize it against collapse of its walls.
• The drilling is made using drill bits that penetrate the soil and creates the hole.
• Mud (mixed with cement) is injected in the hole to stabilize the sides and prevent it from collapse.
• The drilling tower (Derrick) is used to handle the pipes and drilling equipment during drilling.
• A blow-out prevention system and/or Christmas Tree is used to cap the well after completing drilling.