A drilling rig is any system set up for drilling wells, to get resources from the subsurface of the earth, this could be oil, water or any other natural resources. The rig refers to complex equipment used to drill the earth’s surface. Drilling rigs vary in a lot of ways, some are large structures set up permanently on land or marine based oil platforms called offshore oil rigs containing complex and advanced technology equipment used to drill oil wells or natural gas extraction wells, while some are mobile equipment mounted on trucks, trailers or tracks used for drilling water boreholes, mineral exploration, blast holes and environmental investigations; some are small enough to be moved by one person, these are called augers.
They can also be used to sample underground mineral deposits, test rock, soil and groundwater physical properties; to install underground structures like wells and tunnels.
These are drilling sites that are located on dry land, because of the ease of access compared to offshore oil reserves, onshore drilling accounts for 70% of the world’s oil production.
Just like offshore drilling, onshore oil production requires drilling deep beneath the earth’s surface but without the hindrance of deep water between the platform and oil; since the ground offers a solid base, the drilling structures and storage areas are built directly on the soil.
In onshore drilling, the crew first drills below the water table to prevent contamination, then the hole is encased in cement to prevent oil from leaking into the soil or groundwater when extraction starts. Drilling continues until they reach the depth of the oil trap in the area, then liquids are pumped into the ground at high pressure to push the oil out to the surface.
An off shore rig or offshore oil platform is a massive structure constructed on water bodies (river, sea, ocean, lakes) with facilities for exploration, extraction, storage and processing of petroleum and natural gas products that lie under the seabed. Most offshore rigs activities are done on continental shelves but can also be used on rivers, lakes and inland seas; the rig could be fixed to the ocean floor, floating or on an artificial island.
A lot of the world’s oil reserves lie under the sea and through technological advancements like advanced drilling techniques the hydrocarbon industry have been able to find and produce oil and gas successfully, execute projects quickly and control environmental impacts.
Offshore and onshore rigs are similar in the techniques and equipment used; they are different in the arrangement of the drilling rig and equipment and some methods of operation, and offshore rigs cost higher to operate because some operations have to adapt to the requirements dictated by extreme environmental conditions.
Off shore rigs have to create the same working conditions as onshore rigs so they can move from one point to the other and other features to help adaptation to the marine environment like:
Heliport: a very important feature since this is often the primary means of transportation.
Living quarters: comprising of bedrooms, dining hall, recreation room, office space and an infirmary
Cranes: used to move equipment from workboats to the rig or transport load around the rig
Risers: used to extend the wellhead from the mudline to the surface.
Off shore rigs can be divided into two main categories depending on water depth
Bottom supported drilling rigs and floating drilling rigs.
In bottom supported drilling rigs, the drilling operations are similar to that of onshore oil platforms. The ordinary Blow-out preventers (BOPs) are located permanently above sea levels and are accessible from the supporting structure. Bottom supported rigs include:
Barge rig: designed to work in shallow water of less than 20 ft. it is floated to the site where the lower hull is sunk to the bottom, the large surface area of the lower hull prevents the rig from sinking into the soft sea bed and keeps the platform stable.
Submersibles: this is a barge that is designed to work in deeper water of up to 50 ft. It is fitted with extensions that allow it to raise its upper hull above the water level.
Platforms: a steel tubular framework called jacket is anchored to the sea bed to support surface production equipment.
Multiple directional wells are drilled from the platform by using a rig with a movable substructure. The rig is positioned over preset wellheads by jacking across on skid beams. After all the wells are drilled, the rig and quarters are removed from the platform.
Jack-ups: these are similar to platforms only that the support legs are not permanently attached to the sea bed. the rig’s weight is sufficient to keep rig’s lrgs on the seafloor and they can be jacked down to drill and jacked up to move to a new location
These are offshore rigs that are not permanently fixed or resting on the sea bed, they can drill in waters with depths deeper than jack-ups and platforms can.
They are fixed to the location by anchors or dynamic positioning, motion compensators are used to isolate the drill string and risers from wave motion; The wellheads and BOPs are on the ocean floor and are connected to the rig by a riser to allow circulation of drilling mud.
The two categories of floaters are semisubmersibles and drill ships.
Semisubmersibles: they are usually anchored in place. Some have mechanisms to move to drill sites by themselves but most require towing. The drilling apparatus is located in the center where wave motion is minimal. Semis are flooded to a drilling draft where the lower pontoons are below the active wave base, thereby stabilizing the motion.
Drill ships: drill ships can work in waters too deep for anchors and can be turned into oncoming winds and currents for stability. On drill ships, the drilling apparatus is mounted in the center of the ship over a moon pool- a reinforced hole in the bottom of the ship through which the drill string is raised and lowered.
7 Job and Positions / Salaries in the Oil Rig Jobs
Oil rig workers generally earn good wages as the job requires them to spend long time away from home and is also physically and mentally challenging. These are seven oil rig jobs and and their salaries according to offshore-technology.com:
A lot of equipment are involved in the drilling of oil, technological advanced and sophisticated equipment; and some of them are used simultaneously in complicated sequences. Some of these equipment include:
An assembly of sheaves or pulleys mounted on beams at the top of the derric. The drilling line is run over the sheaves down to the hoisting drum.
Structural framework erected near the top of the derrick for lifting material.
A hoisting line reeved on sheaves of the crown block and travelling block. It’s purpose is to hoist or lower drill pipes or casing from or into a well.
An arrangement of pulleys or sheaves through which drilling cable is reeved, which moves up or down in the derrick or mast
The top drive rotates the drill sring end bit without the use of a Kelly and rotary blade.
Heavy seamless tubing used to rotate the bit and circulate the drilling fluid
A small enclosure on the rig floor used as an office for the driller or as a storehouse for small objects.
Valves installed at the wellhead to prevent the escape of the pressure either in the annular space between the casing and the drill pipe or in open hole during drilling or completion operations.
It is used to store water that is used for mud mixing, cementing and rig cleaning.
Other oil rig equipment include:
Offshore Oil Rig Disasters
Oil drilling is a very dangerous exercise as they deal with very volatile materials and any mistake could lead to accident of disastrous proportions so oil companies and rig workers must take extreme caution when carrying out all drilling processes to avoid disaster. They must avoid cutting corners to save time and money in other not to put the lives of workers at risk.
The most devastating accidents that happen on oil rigs are fire and explosions, injuries gotten from oil rig accidents can have dire and long term consequences for workers and their family.
Some of the worst oil rig disasters to ever happen include:
Alexander L Kielland, North Sea, Norway
Seacrest Drillship disaster, South China Sea, Thailand
Ocean Ranger oil rig disaster, Canada.
Glomar Java Sea Drillship disaster, South China Sea.
Bohai 2 oil rig disaster, China.