If you're going to play with oil...we should at least get some basic education of how these come to be. Print it, or read it at your own leasure time.
Exploration for oil and gas is conducted on a worldwide basis, both on land and on the continental shelves. Seismic surveys are conducted in advance of exploratory drilling. These surveys essentially map an area's geology by measuring the reflection of sound waves from the underlying rock strata, in particular looking for traps where petroleum may have accumulated. Seismic surveys provide a remarkably detailed overview of the geologic, structural, and stratigraphic conditions beneath the surface and under exceptional conditions may reveal directly the presence of gas. New technologies, employing lasers and satellites, are also used to detect minute seepages that indicate underlying deposits.
Normally, however, drilling is necessary to confirm the presence or absence of commercially producible amounts of gas and oil. Geologic information is also provided by drilling and is obtained through the use of modern borehole logging techniques. Drilling technology has advanced substantially in recent decades, particularly with respect to the capability of drilling from ships in water as deep as 1,800 m (6000 ft), or from platforms whose legs are anchored to the seafloor. The development of horizontal drilling techniques has increased productivity, allowing producers access to deposits that were previously left untapped.
Drilling
Most wells are now drilled by the rotary method. A steel bit attached to a drill pipe is revolved at the bottom of a hole. This action breaks up the rock by chipping and cutting it. Meanwhile a special mud mixture runs down through the multichannel drill pipe, lubricating the bit, carrying rock cuttings upward to the surface, and creating a pressure that prevents subsurface water from infiltrating the well area. When the drill reaches oil-bearing formations, a casing pipe containing special tubing is lowered into the hole and used to withdraw the fluid. If necessary, explosives or special acid or sand solutions may be injected through the casing pipe to break up the formation and increase the flow of oil and gas. The rate of the flow and the pressure and volume of the well are controlled by special pipings and gate valves--called a "Christmas tree"--installed on the drilling rig above ground.
Once it has been established that a formation contains oil or gas, the precise limits of the field must be delineated through further drilling, since only a portion of any given geological formation will contain petroleum. Production begins once it is known that the extent of the field will allow economical exploitation, and the precise placement of wells is determined after analysis of the size of the field and the geology of the rock.
Drilling continues after a field enters production. Extension wells are drilled to further define the boundaries of the oil, infill drilling is conducted within the field to increase recovery rates, and service wells are used to reopen wells that have become clogged. Additionally, wells are often drilled at the same location but to different depths, to test other geological structures for the presence of petroleum.
The chemistry of the oil, and especially the presence of gas, can require additional aboveground processing equipment. When natural gas is present, it must be separated from the liquid petroleum; lighter liquids like ethane, butane, and propane must be condensed out of the gas, to be sold as fuels or to the petrochemical industry. At gas fields carbon dioxide and sulfur gases may exist as contaminants and are stripped out before the gas is shipped.
Initial production is usually through the mechanism of primary recovery--that is, an initial reliance on the field's own pressure to bring the oil or gas to the surface. As the field ages and pressure drops, however, the oil must be pumped up to maintain production levels. Most fields will yield only one- quarter to one-third of their oil through pumping, depending on the porosity of the rock and the viscosity of the petroleum. The proportion of natural gas recovered is usually much higher, on the order of three-quarters.
Secondary recovery, consisting of the pumped injection of water or gas into the field, is used to restore pressure and increase the proportion of petroleum removed from the field. Tertiary, or enhanced, recovery has also been used on some oil fields. This involves the injection of steam into the well to heat the oil, especially where it is "heavy" and flows poorly. Carbon dioxide or detergents are also used to speed the rate of oil flow. Sometimes more than half of the oil in a deposit may be recovered through these secondary and tertiary methods.
Oil and gas are shipped directly from the wellhead. At small, isolated fields, oil may be stored in tanks and picked up by truck. More often, networks of increasingly larger pipelines bring the production from many fields together at one distribution point.
Offshore Drilling
Approximately one-third of the world's oil is produced from offshore fields, usually from steel drilling platforms set on the ocean floor. In shallow, calm waters, these may be little more than a wellhead and workspace. The larger ocean rigs, however, include not only the well equipment but processing equipment and extensive crew quarters.
Recent developments in ocean drilling include the use of floating tension leg platforms that are tied to the seafloor by giant cables and drill ships, which can hold a steady position above a seafloor well using constant, computer-controlled adjustments. Sub-sea satellite platforms, where all of the necessary equipment is located on the ocean bed at the well site, have been used for small fields located in producing areas. In Arctic areas islands are built from dredged gravel and sand to provide platforms capable of resisting drifting ice fields.
Transportation
Large-scale transport of crude oil, refined petroleum products, and natural gas is usually accomplished by pipelines (see pipe and pipeline) and tankers, while smaller-scale distribution, especially of petroleum products, is carried out by barges, trucks, and rail tank cars.
Pipelines can be used for crude oil and for light oil products, but they are not usually practicable for heavy fuel oil, which does not flow well without being heated. The high capital costs involved in building a pipeline require a large and guaranteed oil-flow volume to be economical. Increasingly, opposition to their passage makes it difficult to build new pipelines, especially in the United States.
Tankers, on the other hand, can be sent to any destination where a port can accommodate them and can be shifted to different routes according to need. Although large tankers are more economical than small ones, the number of ports available to handle the larger vessels is limited. Until the mid-1970s the size of tankers grew significantly, the largest reaching 500,000 deadweight tons, but the fragmentation of the market has meant more numerous, smaller shipments and a resurgence of smaller tankers. The shipment of petroleum products by tanker has become more common; but unlike crude oil from different fields, which can be mixed, petroleum products--gasoline and heating oil, for example--must be kept separate and uncontaminated by each other, requiring that tankers carry only one type of fuel.
Natural gas presents special transport problems. Before World War II its use was limited by the difficulty in transporting it over long distances. The gas found in oil fields was frequently burned off; and unassociated, or dry, gas--that is, the gas found in fields without oil--was usually abandoned. After the war new steel alloys permitted the laying of large-diameter pipes for gas transport in the United States. The discovery of the Groningen field in the Netherlands in the early 1960s and the exploitation of huge deposits in Soviet Siberia in the 1970s and '80s led to a similar expansion of pipelines and natural gas use in Europe.
Because of its lower density natural gas is much more expensive to ship than crude oil. Most natural gas moves by pipeline, but in the late 1960s tanker shipment of cryogenically liquefied natural gas (LNG) began, particularly from the producing nations in the Pacific to Japan. Special alloys are required to prevent the tanks from becoming brittle at the low temperatures (-161 degrees C/-258 degrees F) required to keep the gas liquid.
Refining
Crude oil is rarely used in its raw form but must instead be processed into its various products. Aside from contaminant minerals such as sulfur and small amounts of trace metals--which are removed during refining--petroleum is composed of hydrocarbons, essentially varying combinations of carbon and hydrogen atoms; any hydrocarbon can be converted into any other given the appropriate application of energy, chemistry, and technology. The smaller the molecule and the lower the ratio of carbon to hydrogen, the lighter the hydrocarbon, the lower the evaporation temperature, and, usually, the more valuable the product.
Every crude oil contains a mix of these different hydrocarbons, and the two tasks of a refinery are to separate them out into usable products and to convert the less desirable hydrocarbons into more valuable ones.
The tall metal towers that characterize petroleum refineries are distillation, or fractionating, towers. Distillation is the primary method used to refine petroleum. When the heated crude oil is fed into the lower part of a tower, the lighter oil portions, or fractions, vaporize. Losing temperature as they rise, they condense into liquids, which flow downward into the higher temperatures and are revaporized. This process continues until the various fractions have achieved the appropriate degrees of purity. The lighter fractions, like butane, gasoline, and kerosene, are tapped off from the top; heavier fractions, like fuel and diesel oils, are taken from below.
At more complex refineries the less valuable products of distillation are refined once again through various conversion processes, broadly referred to as "cracking." Through the application of vacuum, heat, and catalysts, larger, heavier molecules are broken down into lighter ones. Thermal cracking, for instance, uses heat and pressure, while catalytic cracking employs a finely powdered catalyst, and hydrocracking involves the addition of hydrogen to produce compounds with lower carbon to hydrogen ratios, such as gasoline. Other processes produce high-octane products for blending with fuels, remove undesirable constituents, or make special petroleum compounds, including lubricants.
Petroleum products are usually distributed from the refinery in the form in which they are to be used. Depending on the geographical location, customer demand, and seasonal needs, refiners can substantially alter their production. In winter, for example, less gasoline and more heating oil is produced.
The chief refinery products are liquefied petroleum gas (LPG); gasoline and jet fuel; petroleum solvents; kerosene; the so-called middle distillates, including heating oil and diesel fuel (known as gasoil outside the United States); residual fuel oil; and asphalts (bitumens), the heaviest fractions. In the United States, with its high demand for gasoline, refineries typically upgrade their products much more than in other areas of the world, where the heavy end products, like residual fuel oil, are used in industry and power generation.
Petroleum products are used to produce petrochemicals, which are the costliest of all petroleum derivatives. In petrochemical production, oil distillation products are broken down by cracking them into light, unsaturated gases, which are then recombined to yield intermediate products, such as ethanol, styrene, ethyl chloride, butadiene, and methanol. These intermediates are used for the manufacture of plastics, synthetic rubbers, synthetic fibers, and other products. There are many advantages to making the first conversion in a refinery, and the oil industry has undertaken chemical manufacture on a large scale (see chemical industry).
The refinery industry originally was concentrated in or near the oil fields, in part because natural gas, which could not then be economically transported long distances, was available to fuel the highly energy-intensive refining process. The combination of cheap oil, larger crude tankers, and concern about refinery security--particularly after the 1951 nationalization in Iran shut down the world's largest refinery at Abadan--led to the shifting of the refining industry to the major consuming nations. After the oil price shocks of the 1970s relatively cheaper natural gas and the exporting nations' desire to export the highest value-added product possible have meant a new movement of the refining industry back to the oil-producing areas |
