Offshore drilling refers to the act of extracting crude oil which lie underwater near the shoreline in the oilfield . Offshore drilling is used to describe oil extraction off the coasts of continents.
The first offshore drilling was done at the end of the 19th century in Baku at the Bibi-Eibat field.[citation needed] In 1896 oil companies began drilling from wharves built out over the Pacific Ocean at Summerland field, California.
This is how offshore drilling done in detail preparation:
The crew makes the rig ready and starts the drilling perations. From the first hole, they drill a surface hole down to a pre-set depth, which is above where the oil trap is placed. There are five sequences to drilling the well:
1. Put the drill bit, collar and drill pipe in the hole.
2. Mount the kelly and turntable and begin drilling.
3. As drilling runs, circulate mud through the pipe and out of the bit to float the rock cuttings out of the hole.
4. Add new sections (joints) of drill pipes as the hole gets deeper.
5. Remove (trip out) the drill pipe, collar and bit when the pre-set depth (anywhere from a few hundred to a couple-thousand feet) is reached.
when they reach the depth they are expected, they operate and cement the casing -- put casing-pipe sections into the hole to avoid it from collapsing in on itself. The casing pipe has spacers around the outside to make the pipe keep staying in the center of the hole.
The crew installes the casing pipe in the hole. The cement crew pumps cement down the casing pipe using a bottom plug, a cement slurry, a top plug and drill mud. The pressure from the drill mud causes the cement slurry to flow through the casing and fill the space between the outside of the casing and the hole.
You might interested to read about the types to do offshore drilling and where is it done??
Wednesday, March 25, 2009
Offshore Drilling In Detailed
Monday, March 23, 2009
How Difficult Is Offshore Drilling?
Offshore drilling in the oilfield can be done with 3 types of "vehicles" or Oil Drilling Rig, depending on the depth of water
1. Offshore drilling For depth of 7 - 15 ft (shallow sea) is often used type of oil rig "Swamp Barge." How to mobilize the oil rig to the location of the wells? after the rig was drowned by filling the tanks Ballast with water. After the rig sitting on the base and the Spud Can be fixed into its sea floor, we can start the offshore drilling. To prevent the oil rig from the sea flow , The oil rig is stabilized first by attaching it to the poles. If they are not stable and the position of rig is moving, there will be a serious problem, especially the well.
2. Offshore drilling for depth 15 - 250 ft, is usually used jack-up rig (typically 3 or 4 feet, and the independent legs with spud legs on its leg. There is also a non-independent leg with type "mat foundation" . The oil riglegs with a mat foundation is usually used in the sea that have soft seabed .
Jack-up oil rig can be used to drill exploration wells in the oilfield . The most critical time is when moving the oil rig aproaching to the platform, because the rig should be close to a certain distance from the platform. It should be done carefully, The oil rig might hit the platform and can cause significant damage. The distance between the oil rig and platform has been determined according to the design,so oil rig floor and derrick located on the cantilever on the deck that can moved so those all can reach the well slots on the platform . One platform can contain 4, 6, 9, 12 or more slots depending on the size of the well platform. Platform for approaching oil rig is guided by 2 or 3 towing boats, and supported by 2 or 4 anchors in the rig. After the rig in the final locked position, the rig legs are given the initial burden with water. The Oil Rig hull is increased slightly above sea surface until the rig legs is not going down at 100% preload. Usually after the oil rig is stable for three hours the "initial burden" is removed and the rig can be jacked up to the height of a certain mode position for Drilling on the platform. That's how the offshore drilling done for water depth 15 - 250 ft.
3. Offshore drilling for depth (> 250 ft), used drillships (floater) or semi-submersible.
This Floater Drilling Rig is usually used for drilling well since this type can be attached to developments wells.This type of oil rig is usually equipped with 8 anchors, which are spread around the rig. After the rig is in the position of the wells, all anchors are deployed and given tension (pretension) to 300000lbs for each anchor. Similar to 'preloading' in type jack-up oil rig, 'pretension' during mooring operations is very important to be done to floaters oil rig ,so it can be stable at the Drilling mode. In addition, the rig is also equipped with "motion compensator" system to overcome the problem heave, pitch and roll, so the relative position of the hole is stable all the times. After all these steps are done,we are ready to do offshore drilling. That's how the offshore drilling done for water depth more than 250 ft
Friday, March 20, 2009
Huge Oil Rig Is Floating In The Ocean??
Oil rig is one of modern technology in oilfield history. It is used to drill exploration wells to look for oil. And oil rigs are used to drill into an oil field to extract the oil. There are several different types of oil rig and oil rig.
1. Fixed oil rig
This type of oil rig is built on concrete and fixed directly onto the seabed, a wide deck with space for drilling rigs, production facilities and workers facilities. an oil rig is built for long term use. Usually the structure is made of steel , concrete , floating steel or floating concrete. Steel structures are the vertical sections made of tubular steel members, mounded into the seabed. Concrete structuresare for the tanks below the sea surface and these tanks fuction is for flotation capability. This type of oil rig is economically sufficient for water depths up to 520m.
2. Compliant towers oil rig
Compliant tower is fixed oil rig structure. This oil rig has slim compliant towers structures with a foundation for deck drilling operation . It is specially designed to maintain lateral deflection and force. This type of rig structure can be configured to adapt to existing fabrication and installation equipment. This flexibility makes this oil rig can be operated in depper water since, this rig can abbsorb the pressure from the wind and sea.
3. Semi-submersible oil rig
Semi Submersible oil rig is moving oil rig structure. It can be moved from one location to another location. The hulls system of these oil rigs make buoyancy. It makes the structure floating. It's balanced by weight, so the structure keep upright. It can be ballasted up or down by altering the amount of flooding in buoyancy tanks. Semi-submersibles can be used in water depths 180m to more than 10,600 m
Thursday, March 19, 2009
Oil Rig : Huge Structure in The Middle of Ocean
An offshore oil rig, is a huge structure used for oilfield operation. An oil rig become one of the most important elements needed in oilfield industry. By using this oil rig, oil can be extracted from the layer of the earth and ship them to shore. An oil rig can be fixed to the surface of the earth it's built on the artificial land. Another kind of oil rig is floating rig. All are depends on the situation.
Most oil rigs are still located on the continental shelf, since the cost for the structure cheaper and easier. But today oil companies with their advances in technology build oil rig in the deeper water.A typical oil rig has around thirty wellheads located on the oil rig and directional drilling allows reservoirs to be accessed at both different depths from the oil rig.
The first modern oil rig structure had ever been built is The Thames Sea Forts . It was pre-constructed in a very short time. It's floating oil rig. In 1938 it was placed on the shallow bottom of Thames Estuary. But the period where it is accepted as offshore oil era is in 1947 when Kerr-Mc Gee Company producing oil rig out of sight of land.
An oil rig structure is equipped with many equipments needed for processing oil, transporting oil by pipelines or tanker. The elements including wellhead, manifold, gas compressor,pump and still many things that support production and transportation. An oil rig is equipped also with workers facilities such as housing, electricity generator, water and etc.
The world tallest oil rig can be as tall as an television and radio broadcasting tower. Here are the examples of The tallest oil rig structures
* Petronius oil rig, 610 meters (2,000 ft)
* Baldpate oil rig, 579.1 meters (1,900 ft)
* Bullwinkle oil rig, 529.1 meters (1,736 ft)
The widest oil rig in the world is The Hibernia oil rig located in the Atlantic ocean with 364 feet high and storage capacity 1.3 million barrels.
Read also the article about many different kinds of huge oil rig
Tuesday, March 17, 2009
About Oilfield
An oilfield is an area with a big potential of petroleum or crude oil below the ground. an area of oilfield usually extend over a big area, possibly around hundred kilometres across. There might be several wells scaterred in that oilfield area . An oilfield is equipped with oil rig / oil platform, support facilities such as transportation, employer housing,electricity and still many things.
There are more than 40,000 oilfields of all sizes in the world.However, 94% of known oil is concentrated in fewer than 1500 giant oilfield. We can say it is a giant oilfield area if it has potential with 500 million barrels of recoverable oil. And these all 1500 giant oilfields are believed contains 40 percent of the world's petroleum . They are scattered in 27 regions of the world, with the largest is in the Persian Gulf,the Burgan OilField in Kuwait and Zagheh Oli Field in Iran .
There are several oilfield companies specialize in providing specialized service to operate an oilfield. They build a large scale infrastructure such as drilling rig, pipelines to transport the oil elsewhere to do the exploration. Schlumberger Limited, Baker Hughes and Halliburton are oilfield company who provide this service.
In this century, oilfield become something attracting for every country in the worlds. Oil is still our main energy,people say "oil is black gold". The profit from oil industry is still promissing. No wonder, whereever the location of oilfield with proven oil reserves is there,there always come with geopolitical conflicts.