How oil and gas are extracted

Oil and natural gas are created when rotting plants and microorganisms are caught in sedimentary layers and – for many millions of years – are buried deep down within the ground, where high temperatures and pressure mould them into essential hydrocarbons, like oil and natural gas.

The rock layer in which hydrocarbons are formed is called source rock. High underground pressure tends to squeeze hydrocarbons from source rock into what is called reservoir rock. This is a rock, like sandstone, which has pores large enough to allow liquids such as oil, natural gas, and water to pass through it. Because oil and natural gas are not as dense as water, they will rise up to the surface. If there is nothing to prevent this migration, oil and natural gas can reach the surface through what is called surface seepage.

However, more often, upward hydrocarbon pathways are blocked by opaque rock layers, such as shale, or by several other geological formations. This traps oil and natural gas, either in underground bags or in reservoir rock layers, so it can be recovered only by drilling wells.

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Extracting oil and natural gas from a deep underground deposit is not as easy as just drilling and completing a well. A number of factors in the underground environment – including rock porosity and deposit viscosity – can inhibit the free flow of products into the well. Until technology advanced, it was usual to only be able to remove 10% of the oil because the tools to recover the rest weren’t available. Today, advanced technology enables the production of around 60 percent of the available resources from a formation.

The first primary recovery depends on underground pressure to push the liquid to the surface. When pressure drops, artificial lifting technology, such as pumps, is used to help bring more liquid to the surface. In some cases, natural gas is sent back to the wells under the oil. The gas then expands, which pushes the oil up to the surface. This method of lifting gas is commonly used in facilities that are offshore.

Water is produced and then separated from the oil during the first phase of drilling, it is then injected back into the area containing the oil with the effect of to bringing more oil up to the surface. In addition to increasing oil recovery, it also removes wastewater, returning it to its original place. This can bring an additional 20 percent of the oil on the surface. For a supplier of Industrial Valves, so important in the oil and gas industry, contact

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Next, a more advanced form of recovery is undertaken to reach the remaining oil. There are 3 common approaches: by gas injection, thermal recovery or flooding with chemicals.

The thermal method requires a steam injection into the oil seam. Heat from steam makes the flow of oil easier, and the pressure increases to the surface.

Gas injection uses gas that is mixed or not mixed. Soluble gas dissolves CO2, propane, methane or other gases in oil to reduce its viscosity and increase flow. Unmixed gas does not mix with oil, but increases the pressure in the “gas cap” in the reservoir to push additional oil into the wellbore.

Chemical floods involve mixing solid polymers that dissolve in water with water and inject the mixture into the field. Water pushes oil out of the formation and into the wellbore.

Enhanced recovery techniques are used to bring as much as 60 percent of the reserves to the surface.


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