thanksOil, How is it transported and extracted also what are the problems of extracting it?
Locating the oil field
Nowadays, geologists use seismic surveys to search for geological structures that may form oil reservoirs. The ';classic'; method includes making underground explosion nearby and observing the seismic response that provides information about the geological structures under the ground [1]. However the ';passive'; methods that extract information from naturally-occurring seismic waves are also known [1].
Other instruments such as gravimeters and magnetometers are also sometimes used in the search for petroleum. Generally, the first stage in the extraction of crude oil is to drill a well into the underground reservoir. When an oil bearing structure has been tapped, the wellsite geologist (known on the rig as the ';mudlogger';) will note its presence. Historically, in the USA, some oil fields existed where the oil rose naturally to the surface, but most of these fields have long since been depleted, except for certain remote locations in Alaska. Often many wells (called multilateral wells) are drilled into the same reservoir, to ensure that the extraction rate will be economically viable. Also, some wells (secondary wells) may be used to pump water, steam, acids or various gas mixtures into the reservoir to raise or maintain the reservoir pressure, and so maintain an economic extraction rate.
[edit] Oil extraction and recovery
[edit] Primary recovery
If the underground pressure in the oil reservoir is sufficient, then this pressure will force the oil to the surface. Gaseous fuels, natural gas or water are usually present, which also supply needed underground pressure. In this situation, it is sufficient to place a complex arrangement of valves (the Christmas tree) on the well head to connect the well to a pipeline network for storage and processing.
Usually, about 20% of the oil in a reservoir can be extracted using primary recovery methods.
[edit] Secondary recovery
Over the lifetime of the well the pressure will fall, and at some point there will be insufficient underground pressure to force the oil to the surface. If economical, as often is, the remaining oil in the well is extracted using secondary oil recovery methods (see: energy balance and net energy gain).
Secondary oil recovery uses various techniques to aid in recovering oil from depleted or low-pressure reservoirs. Sometimes pumps, such as beam pumps and electrical submersible pumps (ESPs), are used to bring the oil to the surface. Other secondary recovery techniques increase the reservoir's pressure by water injection, natural gas reinjection and gas lift, which injects air, carbon dioxide or some other gas into the reservoir.
Together, primary and secondary recovery generally allow 25% to 35% of the reservoir's oil to be recovered.
[edit] Tertiary recovery
Tertiary oil recovery reduces the oil's viscosity to increase oil production. Thermally enhanced oil recovery methods (TEOR) are tertiary recovery techniques that heat the oil and make it easier to extract. Steam injection is the most common form of TEOR, and is often done with a cogeneration plant. In this type of cogeneration plant, a gas turbine is used to generate electricity and the waste heat is used to produce steam, which is then injected into the reservoir. This form of recovery is used extensively to increase oil production in the San Joaquin Valley, which has very heavy oil, yet accounts for 10% of the United States' oil production.[citation needed] In-situ burning is another form of TEOR, but instead of steam, some of the oil is burned to heat the surrounding oil. Occasionally, detergents are also used to decrease oil viscosity as a tertiary oil recovery method.
Tertiary recovery allows another 5% to 15% of the reservoir's oil to be recovered.
Tertiary recovery begins when secondary oil recovery techniques are no longer enough to sustain production, but only when the oil can still be extracted profitably. This depends on the cost of the extraction method and the current price of crude oil. When prices are high, previously unprofitable wells are brought back into production and when they are low, production is curtailed.
[edit] Recovery rates
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 production rates.
Alternative methods
As oil prices continue to escalate, other alternatives to producing oil have been gaining importance. The best known such methods involve extracting oil from sources such as oil shale or tar sands. These resources are known to exist in large quantities; however, extracting the oil at low cost without negatively impacting the environment remains a challenge.
It is also possible to transform natural gas or coal into oil (or, more precisely, the various hydrocarbons found in oil). The best-known such method is the Fischer-Tropsch process. It was a concept pioneered in Nazi Germany when imports of petroleum were restricted due to war and Germany found a method to extract oil from coal. It was known as Ersatz (';substitute'; in German), and accounted for nearly half the total oil used in WWII by Germany. However, the process was used only as a last resort as naturally occurring oil was much cheaper. As crude oil prices increase, the cost of coal to oil conversion becomes comparatively cheaper. The method involves converting high ash coal into synthetic oil in a multi-stage process. Ideally, a ton of coal produces nearly 200 liters (1.25 bbl, 52 US gallons) of crude, with by-products ranging from tar to rare chemicals.
Currently, two companies have commercialised their Fischer-Tropsch technology. Shell in Bintulu, Malaysia, uses natural gas as a feedstock, and produces primarily low-sulfur diesel fuels.[8] Sasol[9] in South Africa uses coal as a feedstock, and produces a variety of synthetic petroleum products.
The process is today used in South Africa to produce most of the country's diesel fuel from coal by the company Sasol. The process was used in South Africa to meet its energy needs during its isolation under Apartheid. This process has received renewed attention in the quest to produce low sulfur diesel fuel in order to minimize the environmental impact from the use of diesel engines.
An alternative method of converting coal into petroleum is the Karrick process, which was pioneered in the 1930s in the United States. It uses high temperatures in the absence of ambient air, to distill the short-chain hydrocarbons of petroleum out of coal.
More recently explored is thermal depolymerization (TDP), a process for the reduction of complex organic materials into light crude oil. Using pressure and heat, long chain polymers of hydrogen, oxygen, and carbon decompose into short-chain petroleum hydrocarbons. This mimics the natural geological processes thought to be involved in the production of fossil fuels. In theory, TDP can convert any organic waste into petroleum.
No comments:
Post a Comment