Oil 2 Essay, Research Paper
Petroleum, or crude oil, naturally occurring oily, bituminous liquid composed of various organic chemicals. It is found in large quantities below the surface of the earth and is used as a fuel and as a raw material in the chemical industry. Modern industrial societies use it primarily to achieve a degree of mobility on land, at sea, and in the air that was barely imaginable less than a hundred years ago. In addition, petroleum and its derivatives are used in the manufacture of medicines and fertilizers, foodstuffs, plastic ware, building materials, paints, and cloth and to generate electricity.
In fact, modern industrial civilization depends on petroleum and its products; the physical structure and way of life of the suburban communities that surround the great cities are the result of an ample and inexpensive supply of petroleum. In addition, the goals of developing countries to exploit their natural resources and to supply foodstuffs for the burgeoning populations are based on the assumption of petroleum availability. In recent years, however, the worldwide availability of petroleum has steadily declined and its relative cost has increased. Petroleum will probably no longer be a common commercial material by the mid-21st century. See Energy Supply, World.
Characteristics
The chemical composition of all petroleum is principally hydrocarbons, although a few sulfur-containing and oxygen-containing compounds are usually present; the sulfur content varies from about 0.1 to 5 percent. Petroleum contains gaseous, liquid, and solid elements. The consistency of petroleum varies from liquid as thin as gasoline to liquid so thick that it will barely pour. Small quantities of gaseous compounds are usually dissolved in the liquid; when larger quantities of these compounds are present, the petroleum deposit is associated with a deposit of natural gas (see Gases, Fuel).
Three broad classes of crude petroleum exist: the paraffin types, the asphaltic types, and the mixed-base types. The paraffin types are composed of molecules in which the number of hydrogen atoms is always two more than twice the number of carbon atoms. The characteristic molecules in the asphaltic types are naphthenes, composed of twice as many hydrogen atoms as carbon atoms. In the mixed-base group are both paraffin hydrocarbons and naphthenes.
See Also Asphalt; Naphtha.
Formation
Petroleum is formed under the earth s surface by the decomposition of marine organisms. The remains of tiny organisms that live in the sea and, to a lesser extent, those of land organisms that are carried down to the sea in rivers and of plants that grow on the ocean bottoms are enmeshed with the fine sands and silts that settle to the bottom in quiet sea basins. Such deposits, which are rich in organic materials, become the source rocks for the generation of crude oil. The process began many millions of years ago with the development of abundant life, and it continues to this day. The sediments grow thicker and sink into the seafloor under their own weight. As additional deposits pile up, the pressure on the ones below increases several thousand times, and the temperature rises by several hundred degrees. The mud and sand harden into shale and sandstone; carbonate precipitates and skeletal shells harden into limestone; and the remains of the dead organisms are transformed into crude oil and natural gas.
Once the petroleum forms, it flows upward in the earth s crust because it has a lower density than the brines that saturate the interstices of the shales, sands, and carbonate rocks that constitute the crust of the earth. The crude oil and natural gas rise into the microscopic pores of the coarser sediments lying above. Frequently, the rising material encounters an impermeable shale or dense layer of rock that prevents further migration; the oil has become trapped, and a reservoir of petroleum is formed. A significant amount of the upward-migrating oil, however, does not encounter impermeable rock but instead flows out at the surface of the earth or onto the ocean floor. Surface deposits also include bituminous lakes and escaping natural gas.
Historical Development
These surface deposits of crude oil have been known to humans for thousands of years. In the areas where they occurred, they were long used for such limited purposes as caulking boats, waterproofing cloth, and fueling torches. By the time of the Renaissance, some surface deposits were being distilled to obtain lubricants and medicinal products, but the real exploitation of crude oil did not begin until the 19th century. The Industrial Revolution had by then brought about a search for new fuels, and the social changes it effected had produced a need for good, cheap oil for lamps; people wished to be able to work and read after dark. Whale oil, however, was available only to the rich, tallow candles had an unpleasant odor, and gas jets were available only in then-modern houses and apartments in metropolitan areas.
The search for a better lamp fuel led to a great demand for rock oil that is, crude oil and various scientists in the mid-19th century were developing processes to make commercial use of it. Thus James Young of England, with others, began to manufacture various products from crude oil, but he later turned to coal distillation and the exploitation of oil shales. The Canadian physician and geologist Abraham Gessner in 1852 obtained a patent for producing from crude oil a relatively clean-burning, affordable lamp fuel called kerosine; and in 1855 an American chemist, Benjamin Silliman, published a report indicating the wide range of useful products that could be derived through the distillation of petroleum.
Thus the quest for greater supplies of crude oil began. For several years people had known that wells drilled for water and salt were occasionally infiltrated by petroleum, so the concept of drilling for crude oil itself soon followed. The first such wells were dug in Germany in 1857-59, but the event that gained world fame was the drilling of an oil well near Oil Creek, Pennsylvania, by Colonel Edwin L. Drake in 1859. Drake, contracted by the American industrialist George H. Bissell who had also supplied Silliman with rock-oil samples for producing his report drilled to find the supposed mother pool from which the oil seeps of western Pennsylvania were assumed to be emanating. The reservoir Drake tapped was shallow only 21.2 m (69.5 ft) deep and the petroleum was a paraffin type that flowed readily and was easy to distill.
Drake s success marked the beginning of the rapid growth of the modern petroleum industry. Soon petroleum received the attention of the scientific community, and coherent hypotheses were developed for its formation, migration upward through the earth, and entrapment. With the invention of the automobile and the energy needs brought on by World War I, the petroleum industry became one of the foundations of industrial society.
Exploration
In order to find crude oil underground, geologists must search for a sedimentary basin in which shales rich in organic material have been buried for a sufficiently long time for petroleum to have formed. The petroleum must also have had an opportunity to migrate into porous traps that are capable of holding large amounts of fluid. The occurrence of crude oil in the earth s crust is limited both by these conditions, which must be met simultaneously, and by the time span of tens of millions to a hundred million years required for the oil s formation. Petroleum geologists and geophysicists, however, have many tools at their disposal to assist in identifying potential areas for drilling. Thus, surface mapping of outcrops of sedimentary beds makes possible the interpretation of subsurface features, which can then be supplemented with information obtained by drilling into the crust and retrieving cores or samples of the rock layers encountered. In addition, increasingly sophisticated seismic techniques the reflection and refraction of sound waves propagated through the earth reveal details of the structure and interrelationship of various layers in the subsurface. Ultimately, however, the only way to prove that oil is present in the subsurface is to drill a well. In fact, most of the oil provinces in the world have initially been identified by the presence of surface seeps, and most of the actual reservoirs have been discovered by so-called wildcatters who relied perhaps as much on intuition as on science. (The term wildcatter comes from West Texas, where in the early 1920s drilling crews encountered many wildcats as they cleared locations for exploratory wells. Shot wildcats were hung on the oil derricks, and the wells became known as wildcat wells.)
An oil field, once found, may comprise more than one reservoir, that is, more than one single, continuous, bounded accumulation of oil. Indeed, several reservoirs may be stacked one above the other, isolated by intervening shales and impervious rock strata. Such reservoirs may vary in size from a few tens of hectares to tens of square kilometers, and from a few meters in thickness to several hundred or more. Most of the oil that has been discovered and exploited in the world has been found in a relatively few large reservoirs. In the U.S., for example, 60 of approximately 10,000 oil fields have accounted for half of the productive capacity and reserves.
Primary Production
Most oil wells in the U.S. are drilled by the rotary method that was first described in a British patent in 1844 assigned to R. Beart. In rotary drilling, the drill string, a series of connected pipes, is supported by a derrick. The string is rotated by being coupled to the rotating table on the derrick floor. The drill bit at the end of the string is generally designed with three cone-shaped wheels tipped with hardened teeth. Drill cuttings are lifted continually to the surface by a circulating-fluid system driven by a pump.
Trapped crude oil is under pressure; were it not trapped by impermeable rock it would have continued to migrate upward, because of the pressure differential caused by its buoyancy, until it escaped at the surface of the earth. Thus, when a well bore is drilled into this pressured accumulation of oil, the oil expands into the low-pressure sink created by the well bore in communication with the earth s surface. As the well fills up with fluid, however, a back pressure is exerted on the reservoir, and the flow of additional fluid into the well bore would soon stop, were no other conditions involved. Most crude oils, however, contain a significant amount of natural gas in solution, and this gas is kept in solution by the high pressure in the reservoir. The gas comes out of solution when the low pressure in the well bore is encountered and the gas, once liberated, immediately begins to expand. This expansion, together with the dilution of the column of oil by the less dense gas, results in the propulsion of oil up to the earth s surface.
Nevertheless, as fluid withdrawal continues from the reservoir, the pressure within the reservoir gradually decreases, and the amount of gas in solution decreases. As a result, the flow rate of fluid into the well bore decreases, and less gas is liberated. The fluid may not reach the surface, so that a pump (artificial lift) must be installed in the well bore to continue producing the crude oil.
Eventually, the flow rate of the crude oil becomes so small, and the cost of lifting the oil to the surface becomes so great, that the well costs more to operate than the revenues that can be gained from selling the crude oil (after discounting the price for operating costs, taxes, insurance, and return on capital). The well s economic limit has then been reached and it is abandoned.
Enhanced Oil Recovery
The foregoing has described the cycle of primary production by solution gas expansion. No extraneous energy is added to the reservoir other than that required for lifting fluids from the producing wells. As stated, however, most reservoirs are developed by numerous wells; and as primary production approaches its economic limit, perhaps only a few percent and no more than about 25 percent of the crude oil has been withdrawn from a given reservoir. The oil industry, therefore, has developed schemes for supplementing the production of crude oil that can be obtained mostly by taking advantage of the natural reservoir energy. Such supplementary schemes, collectively known as enhanced oil recovery technology, can increase the recovery of crude oil, but only at the additional cost of supplying extraneous energy to the reservoir. In this way, the recovery of crude oil has been increased to an overall average of 33 percent of the original oil. Two successful supplementary schemes are in use at this time: water injection and steam injection.
Water Injection
In a completely developed oil field, the wells may be drilled anywhere from 60 to 600 m (200 to 2000 ft) from one another, depending on the nature of the reservoir. If water is pumped into alternate wells in such a field, the pressure in the reservoir as a whole can be maintained or even increased. In this way the rate of production of the crude oil also can be increased; in addition, the water physically displaces the oil, thus increasing the recovery efficiency. In some reservoirs with a high degree of uniformity and little clay content, water flooding may increase the recovery efficiency to as much as 60 percent or more of the original oil in place. Water flooding was first introduced in the Pennsylvania oil fields, more or less accidentally, in the late 19th century, and it has since spread throughout the world.
Steam Injection
Steam injection is used in reservoirs that contain very viscous oils, those that are thick and flow slowly. The steam not only provides a source of energy to displace the oil, it also causes a marked reduction in viscosity (by raising the temperature of the reservoir), so that the crude oil flows faster under any given pressure differential. This scheme has been used extensively in the states of California, in the United States, and of Zulia, in Venezuela, where large reservoirs exist that contain viscous oil. Experiments are also under way to attempt to prove the usefulness of this technology in recovering the vast accumulations of viscous crude oil (bitumens) along the Athabasca River in north central Alberta, Canada, and along the Orinoco River in eastern Venezuela. If success is encountered in these trials, the age of petroleum dominance may be extended by several decades.
Offshore Drilling
Another method to increase oil-field production and one of the most exciting engineering achievements in recent decades has been the construction and operation of offshore drilling rigs. The drilling rigs are installed, operated, and serviced on an offshore platform in water up to a depth of several hundred meters; the platform may either float or sit on legs planted on the ocean floor, where it is capable of resisting waves, wind, and in Arctic regions ice floes.
As in traditional rigs, the derrick is basically a device for suspending and rotating the drill pipe, to the end of which is attached the drill bit. Additional lengths of drill pipe are added to the drill string as the bit penetrates farther and farther into the earth s crust. The force required for cutting into the earth comes from the weight of the drill pipe itself. To facilitate the removal of the cuttings, mud is constantly circulated down through the drill pipe, out through nozzles in the drill bit, and then up to the surface through the space between the drill pipe and the bore through the earth (the diameter of the bit is somewhat greater than that of the pipe). Successful bore holes have been drilled right on target, in this way, to depths of more than 6.4 km (more than 4 mi) from the surface of the ocean. Offshore drilling has resulted in the development of a significant additional reserve of petroleum in the U.S., about 5 percent of the total reserves.
Refining
Once oil has been produced from an oil field, it is treated with chemicals and heat to remove water and solids, and the natural gas is separated. The oil is then stored in a tank, or battery of tanks, and later transported to a refinery by truck, railroad tank car, barge, or pipeline. Large oil fields all have direct outlets to major, common-carrier pipelines.
Basic Distillation
The basic refining tool is the distillation unit. In the U.S., after the Civil War, more than 100 still refineries were already in operation. Crude oil begins to vaporize at a temperature somewhat less than that required to boil water. Hydrocarbons with the lowest molecular weight vaporize at the lowest temperatures, whereas successively higher temperatures are required to distill larger molecules. The first material to be distilled from crude oil is the gasoline fraction, followed in turn by naphtha and then by kerosine. The residue in the kettle, in the old still refineries, was then treated with caustic and sulfuric acid, and finally steam distilled thereafter. Lubricants and distillate fuel oils were obtained from the upper regions and waxes and asphalt from the lower regions of the distillation apparatus. In the later 19th century the gasoline and naphtha fractions were actually considered a nuisance because little need for them existed, and the demand for kerosine also began to decline because of the growing production of electricity and the use of electric lights. With the introduction of the automobile, however, the demand for gasoline suddenly burgeoned, and the need for greater supplies of crude oil increased accordingly.