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what is it? Shale oil, or tight oil, is a type of crude oil that is found in low permeability rock formations such as shale or tight sandstone. The ‘tight’ refers to the fact that the oil is tightly trapped in the rock, unlike conventional oil formations where the oil flows relatively easily. Recent technologies used for shale gas extraction, such as fracking and horizontal drilling, have made it economical to extract shale and tight oil.
how is it extracted?
shale Oil ( Tight oil)
CRUDE OIL FOUND IN SHALE OR OTHER ROCK WHERE IT IS TIGHTLY HELD IN PLACE AND DOES NOT FLOW EASILY. REQUIRES USE OF FRACKING WITH RISK OF WATER POLLUTION AND WORSENS CLIMATE CHANGE.
Shale oil has been known about for a long time, but has only been exploited on a large-scale in the last ten years or so. This has partly been driven by the development of two technologies: horizontal drilling, which opens up deposits inaccessible by conventional vertical drilling, and advanced hydraulic fracturing, or fracking. Fracking is used to free oil or gas trapped in rock by drilling into it and injecting pressurised fluid, creating cracks and releasing the oil or gas. The fracking fluid consists of water, sand and a variety of chemicals which are added to aid the extraction process e.g. by dissolving minerals, killing bacteria that might plug up the well, or reducing friction. The fracking process produces a large volume of waste water, containing a variety of contaminants both from the fracking fluid, and toxic and radioactive materials which are leached out of the rocks. In addition to fracking, acidisation is also sometimes used. This is where the well is pumped with acid to dissolve the rock that is obstructing the flow of oil.
Production from shale oil wells declines very quickly and so new wells must be drilled constantly. This process of continual drilling and fracking means that huge areas of land are covered with well pads where thousands of wells are drilled, with each well requiring millions of litres of water. Shale and tight oil deposits are also highly heterogenous, meaning there is substantial variation within the formation in the qualities of the rock and the oil it contains. Even adjacent wells can have very different production rates. The oil that is extracted from shale is very similar to crude oil from conventional sources and does not require further processing before it can be refined.