Extraction of petroleum

Petroleum is a fossil fuel that can be drawn from beneath the Earth's surface. Reservoirs of petroleum are formed through the mixture of plants, algae, and sediments in shallow seas under high pressure. Petroleum is mostly recovered from oil drilling. Seismic surveys and other methods are used to locate oil reservoirs. Oil rigs and oil platforms are used to drill long holes into the earth to create an oil well and extract petroleum. After extraction, oil is refined to make gasoline and other products such as tires and refrigerators. Extraction of petroleum can be dangerous and have led to oil spills.^[1]

"Oil extraction" redirects here. For the 1907 Azerbaijani film, see Oil Extraction (film).

Locating the oil field[edit]

Geologists and geophysicists use seismic surveys to search for geological structures that may form oil reservoirs. The "classic" method includes making an underground explosion nearby and observing the seismic response, which provides information about the geological structures underground. However, "passive" methods that extract information from naturally occurring seismic waves are also used.^[2]

Other instruments such as gravimeters and magnetometers are also used in the search for petroleum. Extracting crude oil normally starts with drilling wells into an underground reservoir. When an oil well has been tapped, a geologist (known on the rig as the "mudlogger") will note its presence.

Historically in the United States, in some oil fields the oil rose naturally to the surface, but most of these fields have long since been used up, except in parts of Alaska. Often many wells (called multilateral wells) are drilled into the same reservoir, to an economically viable extraction rate. Some wells (secondary wells) may pump water, steam, acids or various gas mixtures into the reservoir to raise or maintain the reservoir pressure and economical extraction

Oil extraction and recovery[edit]

Primary recovery[edit]

During the primary recovery stage, reservoir drive comes from a number of natural mechanisms:

of the rock

permeability

strength of natural drives (the associated gas present, pressure from adjacent water or gravity)

of the reservoir rock, i.e. the rock storage capacity

porosity

viscosity of the oil

The amount of recoverable oil is determined by a number of factors:

When the reservoir rocks are "tight", as in shale, oil generally cannot flow through, but when they are permeable, as in sandstone, oil flows freely.

Estimated ultimate recovery[edit]

Although recovery of a well cannot be known with certainty until the well ceases production, petroleum engineers often determine an estimated ultimate recovery (EUR) based on decline rate projections years into the future. Various models, mathematical techniques, and approximations are used.

Shale gas EUR is difficult to predict, and it is possible to choose recovery methods that tend to underestimate decline of the well beyond that which is reasonable.