Crude Oil Production

Crude oil production involves the processes of exploration or location of oil filed, drilling and extraction of the crude. Now, let’s briefly look at each of the processes involve in crude oil production:

Exploration of crude oil

Geologist use seismic surveys to explore crude oil.  Seismic survey is used to search for geological structures that may form oil reservoirs. This can be done by two methods known as ‘classic’ and ‘passive’ method. The classic method include making an underground explosion nearby and observing the seismic response that provides information about the geological structures under the ground while passive methods involves extracting information from naturally-occurring seismic waves.

Other instruments such as gravimeters and magnetometers are also used to explore crude oil.

Drilling Crude oil wells

After exploration and discovery of crude oil, the next step in crude oil production is drilling wells into the underground reservoir. Drilling crew sets up and start the drilling operations and this is done by first, from the starter hole, they drill a surface hole down to a pre-set depth, somewhere the oil trap is located.

Once the pre-set depth is reached, they must place casing-pipe sections into the hole to prevent it from collapsing in on itself. The casing pipe has spacers around the outside to keep it centered in the hole. The crew completes the well to allow oil to flow into the casing in a controlled manner once the have reached the final depth. Finally, a collection of valves called a “Christmas Tree” is fitted to the top to regulate pressure and control flows.

Extraction of crude oil

Once the crude oil is flowing, the next step in crude oil production is to remove the oil rig from site and set up production equipment to extract the oil from the well. This is done by placing a pump at the well head. The pump system comprises a gear box driven by an electric motor to move a lever. The lever pushes and pulls a polishing rod up and down. The polishing rod is attached to a sucker rod, which is attached to a pump. This system forces the pump up and down, creating a suction that draws oil up through the well.

In cases where the oil is too heavy to flow, a second hole is drilled into the reservoir and steam is injected under pressure. The heat from the steam thins the oil in the reservoir, and the pressure helps push it up the well. This process is called enhanced oil recovery.

The amount of oil that is recoverable is determined by a number of factors including the permeability of the rocks, the strength of natural drives (the gas present, pressure from adjacent water or gravity), and the viscosity of the oil. When the reservoir rocks are "tight" such as shale, oil generally cannot flow through but when they are permeable such as in sandstone, oil flows freely. The flow of oil is often helped by natural pressures surrounding the reservoir rocks including natural gas that may be dissolved in the oil, natural gas present above the oil, water below the oil and the strength of gravity. 

Oils tend to span a large range of viscosity from liquids as light as gasoline to heavy as tar. The lightest forms tend to result in higher extraction rates.