An oil rig is a megastructure used to drill a well to explore and extract hydrocarbons from the subsurface formations to surface. Oil rigs also contain primary storage and processing facilities for the explored hydrocarbon. There are numerous kinds of oil rigs available, depending on the location and depth of well to drill.
Broadly, based on the location of a well to be drilled, oil rigs can be classified into two major types. Onshore rigs are used to drill a well in the onshore region, whereas the rigs used to drill wells in the offshore area are known as Offshore rigs.
Onshore Drilling Rigs:
Onshore drilling rigs are used to drill wells on land. The main feature of land rigs is mobility and depth of penetration. Most of the components used to fabricate the structure are present in the form of modules and are skid-mounted to be assembled and reused easily.
Land-based rigs can be further classified into four major types based on the ultimate depth of penetration of well. Although, they look similar to each other but vary in the technical specification.
4 Broad categories are:
Onshore rigs can further be classified based on the mobility of rig. This signifies the ease of portability of a rig when the task at one location is completed, and there is a need to transport the rig at a new location.
Offshore Drilling Rigs:
The exploration for hydrocarbon in oceans started in the early 20th century, which forced engineers to transform the land-based rigs that can suitably be used in marine settings. This gave birth to offshore rigs. Offshore drilling rigs are used to drill wells on marine location. The main feature of marine rigs is movability and sea-bed depth. Most of the components used to fabricate the structure are present in the form of modules and are skid-mounted so that they can easily be transported, assembled, and reused. Mainly offshore rigs are classified into two major types:
Bottom supported units are used for relatively shallower seafloor depth. The part of their structure remains in contact with the sea-bed. The remaining part of the rig is designed in such a way that it can float into water reducing the sheer weight in the contacted part. The rig can float if required during the time of transportation. These are basically of two main types: Submersible and Jack-ups.
Floating units, as the name suggests, are the megastructure which doesn't rest on the ocean floor; instead, they float on the ocean water. Anchors are present to stabilize the rig remains in contact with the seafloor. These units include Drillships, Semi-Submersible, and Barge rigs.