How is crude oil extracted?

Image Source: RachenStocker, Shutterstock.com

Summary

  • The earliest known oil wells were drilled in ancient China around 200-300 A.D.
  • John D. Rockefeller, the first billionaire of the modern world, earned his fortune through the oil business.
  • Oil and gas exploration uses modern and state-of-the-art technology to detect the presence of crude oil deep down the Earth’s surface.

Crude oil is hydrocarbon trapped in rock pores beneath the Earth’s surface. Being said so, oil and gas are found in very few geographical areas on the Earth, and out of all, only a few of them are economically viable to produce.

So how it started in the first place?

Crude oil history dates back to 200-300 AD when China discovered its existence and usefulness in everyday life. The Chinese are even considered the pioneers for building the world’s first pipeline using bamboos to transport crude oil.

Image source: Anan Kaewkhammul, Shutterstock

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The first modern oil well was drilled in Titusville, Pennsylvania, back in 1859 by Edwin Drake. There are references to the commercial production of oil in various parts of the world during the same period, but Titusville is the first one.

During the initial days, oil producers used to look out for seepages and start digging pits to extract oil. Soon it was realised that they could not dig deep with shovels and need something to dig dip. As a result, oil drilling rigs came into existence.  

How do you know oil is in the subsurface?

Early drillers used to drill at the location of seepages, and the success rate was pretty low. Soon they realised that oil is not below the seepages or oil showings, rather it is at a different location, and they need to trace the origin.

This led to an evolution in petroleum geology and geophysics, and many breakthrough technologies were developed to scan the subsurface for oil.

Gravity and magnetic survey technologies were developed to identify the prospective areas that can have the highest probability of holding hydrocarbon. Most of crude oil is found in basins.  

Beginning of exploration phase (Image source: Copyright © 2021 Kalkine Media) 

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Basins, spread in thousands of square kilometres in area, form due to tectonic activities, and over time, sediments laden with organic remains of plants and animals get deposited in the basins. Over the next millions of years, river or wind bring more sediments, which keep depositing in the basins. The enormous pressure and temperature exerted by the sediment layers convert the organic remains into hydrocarbon.

Coal, crude oil, and gas form through the same process but under different burial conditions, which result in their physical and chemical properties.

Now you have the basin, the next thing you need to figure out whether it contains enough crude oil to be produced economically. The gravity and magnetic anomaly in a basin can point at the presence of crude oil. But there are other deposits like salt domes that can give same gravity and magnetic signature as crude oil. Geophysicists have to factor in all possibilities before reaching to a conclusion.

Geochemical studies could be used to supplement geophysical findings. Seismic surveys are conducted in 2D or 3D arrays to know the subsurface structure. Numerous studies are conducted, and instruments are used to detect the presence of oil and gas.

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You have all the data and survey results; what now?

Drilling is the only practical way to know the presence of oil or gas. The geologist team uses the plethora of data and interpretation to decide on the location of a well where there is probability to hit oil.

The technology used in the oil industry is only second to that used in deep space exploration.  Still, the success of hitting oil is only 30% in the case of wildcat wells.

Drilling rigs in action (Image source: © Jimsphotos  Megapixl.com)

The first well drilled in any new field or basin is referred as a wildcat, as there is very little data available to know what will come next under the drill bit. Drillers do not have any idea what kind of pressure they will encounter in the well. Most of the ‘blowouts’ occur in wildcats.

Drilling is one of the most cost expensive operations in the oil and gas business. Whether the bit hits a pay zone or a reservoir filled with oil, further wells are drilled to study the subsurface conditions and occurrence of hydrocarbons.

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Technologies like logging while drilling (LWD) and measurement while drilling (MWD) are employed on the drill string to have the real-time data of formation parameters. Once a section of the well is drilled, it is cased and cemented to provide a permanent support wall to drill further and keep the hole from collapsing.

Once the well has been drilled to a pay zone, logging tools in a device called Sonde are placed inside the well to measure radioactivity, resistivity of formation water, diameter of the hole being drilled, and several other parameters.

Logging gives the exact depth from which oil could be produced efficiently. Once the depth is known, a perforation team will come and lower a perforating gun laden with explosive charges into the well. A controlled blast is done to create holes in the casing and cement layer in order to connect the reservoir with the hole.

In ideal conditions, the reservoir pressure will gush oil into the well. Also, a production tubing is installed prior to commencing production otherwise sulphur content in crude oil could corrode the walls of the casing and may damage the well.   

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