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From the previous article.
In the previous article we saw as to what propelled the petroleum companies to seek oil from the ocean beds. We also learnt about the brief history of offshore oil rigs and how the geologists decide as to which surface has subterranean oil streams.
Once a site is decided for drilling, the main thing of exploring and drilling start. Drilling is a very interesting and an arduous process to carry out. We will now learn about this process in detail.
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What is exploratory drill?
Once a site is finalized for drilling, it is checked if it contains a genuine oil source or not. For this reason exploratory drilling is carried out. It is carried out with the sole purpose of getting a sample in order to confirm future actions on the site.
The drilling is carried out either by a drill ship or by a drilling platform that is towed to the site. The exploratory drilling procedure goes for approximately 60-90 days at 4-5 different places on the decided site. Once the site is approved by the geologists with the help of samples taken, it is time to install an exploration platform which will stay there for around 10-15 years, an approximate time for which an oil well lasts. These platforms are fixed to the seabed with the help of metal or concrete foundation. It is of utmost importance that the platform and the drilling structure remains extremely stationary, no matter what the weather condition is or else it will harm the drilling structure and apparatus.
Once the things are set up, its time to gather the riches.
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The drilling process
It’s a difficult process to drill through the tough surface of the ocean beds. So how is this process carried out? You must have sent the normal drilling machine that we use in our houses for drilling holes in the walls. The oil drilling apparatus almost looks the same but have modification made to prevent leaking of oil and for other safety reasons.
The drill consists of a number of drill pipes that are screwed together and which are attached to a drill bit at the other end. The arrangement of the drill pipes attached together is known as drill string. This drill string is rotated and controlled from the platform. The drill bit attached at the other end drills the earth’s surface. The drill bit is formed of either industrial diamonds or steel. This drill string with the drill bit is connected to the platform with the help of a flexible tube known as mariner riser.
To lubricate this drilling bit, something known as drilling mud is used. Drilling mud is a combination of water, clay, lubricating fluids and special chemicals. This drilling clay is sent to the drilling bit through the pores in the drill. It flows in a cyclic process, going back to the platform after lubrication. This drilling mud not only lubricates but also acts like a seal in the well. It also maintains the well’s pressure. It also helps to defend the pressure of the subterranean oil when the drill comes in contact with it. This prevents a blow back or a blow out of oil. There is also a blowout prevention system (BOP) provided , which closes the hydraulically operated valves and rams in case of a blowout.
The size of the drills also changes through out the drilling process. For the first hundred feet, a drill of an 18 inches diameter is used. As the drill goes deeper and deeper, drills with diameter 12-inch and 8-inch are used.
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Deep Challenge: Our Quest for Energy Beneath the Sea by Clyde W. Burleson