introduction to : OFFSHORE OPERATIONdelivered by : Arif Fajar Utomo L2C008118in sharing knowledge classSemarang, April 17th 2012
Presentation Including :• The reason why we need offshore drilling.• Historical review towards offshore drilling.• Steps in Offshore Drilling.• Mobile drilling platforms.• Offshore production platforms.• About Offshore Engineers.
The reason why we need offshore drillingBased on the fact that we consume more than 80 million barrels of oilevery day in 2011 (source: CIA) and it is increasing until now due toeconomic and population growth. In fulfilling this demand, we can’tjust rely on the onshore exploitation of petroleum. And since oceanscover nearly three-quarters of Earth’s surface, so logically there werebigger chance of having reservoirs on the offshore.
Historical review towards offshore drillingThe idea of offshore drilling is already being initiated from many years ago:In 1897, the first platform was constructed at the end of a wharf in California.In 1928, first mobile oil platform for drilling in wetlands is unveiled, the structurewas similar with a barge.In 1947, a consortium of oil companies built the first platform on the ocean, in theGulf of Mexico.And the development continues, as today, oil rigs are truly gigantic structuresemploying and housing hundreds of people. Some rigs, have a 4,000 feet or 1.2 kmin height.
Steps in Offshore DrillingSteps in offshore drilling are including:• Exploration• Own the land• Spud-in• Drilling a hole for second string of casing• Cementing the first two casing sections in place• Connecting BOP and marine riser on top of the wellhead• Drilling the remaining section of the well• Determining if a well has a produceable amount of petroleum (source: www.treesfullofmoney.com)
ExplorationExploration is the first thing we do in order to find the petroleum reservoirs underthe sea. There are many methods that can be used to, one of them is using seismicsurveying or also known as sparking.
ExplorationWe can also implement the magnetic method in the offshore by using sensitivemagnetic survey equipment that is attached on the ship that pass over an area andmap any magnetic anomalies that occur. This method can also give us a decriptionof the underground traps.
Own the landThe petroleum company often don’t own the block especially if the area is ineconomic zone (200 miles from one country), therefore in this case, the petroleumcompany has to obtain a government lease for the block and also for the mineraleither to begin drilling legally, unless the block and the mineral is no one’s.
Spud-inAfter we leased the mineral right and the block, knew the success rates for drilling anoffshore oil well, and have decided on what type of oil rig to use to drill our well, thefirst thing we do then is to spud in.When drilling oil wells in deep water (>1000′), this involves forcing 300-400 feet of 36″diameter metal tubing called “casing” into the ground. This 36″ diameter casing willform the backbone of the well and provide the support we’ll need for the remainingphases in our well construction plan.The 36″ casing is lowered to the seafloor by “drill pipe”. Each section of drill pipe isanywhere from 30-45 feet long and about 6″ in diameter. The drill pipe is connectedend to end and gradually lowered down into the well and back up to the surface asneeded.To help speed up the time connecting hundreds of sections of drill pipe together everytime you want to lower a drill bit, casing, or other piece of equipment into the well, thedrill pipe is stored in the derrick three or for sections at a time. This saves the drillingcompanies time and money.Each section of drill pipe is called a “joint“, and when two or more “joints” connectedand “racked back” in the derrick they are then called a “stand“
Spud-inBut when your seafloor is covered in a deep layer of loose sediment (like whathappened in the Gulf of Mexico), you don’t really need to “drill” the 36″ casing intothe ground. In most cases, pumping sea-water through the end of the casing usingthe ships massive pumps is all you need to do to get the pipe to settle into theground.As the casing gets deeper and deeper into the ground, some rigs use giant“hammers” to pound the casing into the ground to the desired depth.When the 36″ casing is set to the correct depth, we unlatch the drill pipe from it andpull the drill pipe back to the surface so that we can get the next section ofcasing and proceed to step 2 of our well drilling program.
Drilling a hole for second string of casingThe next step in our well drilling plan is to lower a drill bit down inside the 36″casing we just set into the seafloor. Once the drill bit enters inside the 36″ casingwe’ll drill 2000-3000′ into the ground. We need to make sure the bit we are using islarge enough so that we can run our next section of “casing” into the ground(running the casing inside the 36″ casing).
Cementing the first two casing sections in placeOnce the 22″ casing is set inside the 36″ casing, the two different sized casings arecemented in place. This is accomplished by pumping cement down the drill pipe(represented in yellow in the picture below) and out through a special nozzle on the endof the pipe.
Connecting the BOP and marine riser on top of the wellhead
Drilling the remaining section of the wellThe remaining sections of the well are drilled the same way as the 22″ casing wasdrilled in the earlier step only now the cuttings and mud are circulated back up tothe drillship to be processed.The drill crews will drill deeper into the ground so that the next section of casingcan be run and cemented into place. There is no set limit on how long each sectionof casing will be, this decision is left up to the drilling engineers that have closelyanalyzed the survey data and any data from nearby or “offset” wells.As the drill bit continues to make its way towards the oil or “pay zone”, the drillingcrew closely monitors the amount of fluid in the storage tanks as well as thepressure of the formation to ensure that the well is now experiencing a blow-out orkick.If it is determine that the well is experiencing a “blow-out” or kick, the Blow OutPreventer (BOP) control valves are closed off and the drill crew must take measureto stabilize the well. To stabilize a well that has experienced a “kick”, the drill crewis usually able to control it by pumping heavier drilling fluids into the well to“force” the kicked pressure back into the formation.
Determining if a well has a produceable amount of petroleumA series of test called “logs” will be conducted to determine how much oil and gas (ifany) is present in the formation. The process is called logging because the informationis “logged” into a database as it is collected.This is accomplished by sending high tech measurement devices into the hole that candetect various features of the formation.Using a combination of sound wave tools, electrical wave tools, and radiationmeasurement instruments, geologist are able to take readings inside the well which willassist them in determining the presence of oil.However, just because there is oil or gas at the bottom of the well doesn’t always meanit is worthwhile to pump it out. Oil companies must decide whether the amount of oilpresent in the formation is worth investing hundreds of millions of dollars in additionalequipment to pump it out and back to a refinery.In some instances, an oil company may decide to “test flow” a well to help determinehow much oil is there. When test flowing a well, oil is allowed to flow up from the wellinto storage tanks. The pressure is recorded and if it remains at certain levels over acertain amount of time, the oil companies may decide that investing more money to“produce” the well is worth the costs.
Mobile drilling platformsMobile drilling platform is being used in the exploratory drilling, to drill and to findout if there’s oil and then move on to the next site. Mostly, the oil company didn’thave the mobile drilling platforms. Since it is more cost effective to hire expertiseand equipment needed than to keep it under their roof.The expertise in here refers to the drilling contractor and the service company likeTransocean, Schlumberger, Pride, Frontier, and Sea-Drill.There are 5 varieties of mobile drilling platforms: drilling barge, jack-up, semi-submersible rig, submersible rig, and drill ships.
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