Introduction CHAPTER 8 Oil The terms oil and petroleum have been used interchangeably by industry since the early 1900s. However, there are some who refer to petroleum as the crude oil prior to any treatment/refinery, with oil reserved as the definition of “any of the various kinds of greasy, combustible substances obtained from animal, vegetable, and mineral sources, and liquid at ordinary temperature.” The viscosity of the oil in these formations may be as thin as gasoline or as thick as tar. CHAPTER 8 Oil Introduction Oil is an entirely separate substance from the rock in which it was formed. Oil, in its liquid form, is very mobile and tends to move upward as the heat in the Earth’s crust causes it to expand. Rising oil frequently penetrates surrounding rock formations and continues its upward journey until it meets a layer of rock that is so tightly compressed that passage is not possible. Introduction Because the gases are lighter than the oil, they gradually separate and gather at the top of the oil reservoir. Similarly, oil is lighter than water and will float into the pore spaces above it. However, in most oilfields, there is not enough space for all three substances as they expand in the high temperatures deep within the Earth’s crust. This explains why pressure builds up and drives oil to the surface when a well is drilled. Oil, like coal, is a fossil hydrocarbon fuel. The combination of hydrogen and carbon determines whether the fuel takes the solid form of coal or the liquid form of oil or the gaseous form of natural gas. Availability/Distribution Regarding availability/distribution, every estimate of oil reserves represents and is based on current knowledge. It is possible to increase reserves by new discoveries and by enhanced recovery methods. However, oil is a nonrenewable resource, the end of the age of oil may be reached sooner rather than later. Regarding distribution, individuals and companies called jobbers handle the wholesale distribution of oil. Approximately 15,000 jobbers in the United States handle orders for petroleum products from gasoline stations, industries, utility companies, farmers, and other consumers of oil. The last step involves a retailer. A retailer may be a gasoline station or a home heating oil company. Characterization Regarding fuel oil characterization, fuel oils contain virtually all petroleum products that are less volatile than gasoline. They range from light oils, suitable for use in internal combustion or turbine engines, to heavy oils requiring heating. The heavier fuels are primarily suited for steam generation boilers. The ASTM specifications for fuel oil properties are given in Table 8.1. Fuel oils can be divided into two classes: distillate and residual. Distillate fuels are those that are vaporized in a petroleum refining operation. They are typically clean, essentially free of sediment and ash, and relatively low in viscosity. The residual fuel oils are those that are not vaporized by heating. They contain virtually all the inorganic constituents present in the crude oil. Frequently, residual oils are black, high-viscosity fluids that require heating for proper handling and combustion. Characterization A typical analysis of a fuel oil provides the following information: 1. Ultimate analysis 2. API gravity 3. Heating value 4. Viscosity 5. Pour point 6. Flash point 7. Water and sediment Details for each are provided below. Characterization 1.Ultimate analysis. The ultimate analysis for an oil is like that for a coal. The results indicate the quantities of sulfur, hydrogen, carbon, nitrogen, oxygen, and ash. 2. API gravity. The petroleum industry uses the API gravity scale to determine the relative density of oil. Characterization 3. Heating value . The heating value of a liquid fuel indicates the heat released by the complete combustion of one unit mass of fuel (pound or kilogram). 4. Viscosity. The viscosity of a liquid is the measure of its internal resistance to flow. 5. Pour point. The pour point is the lowest temperature at which a liquid fuel flows under standardized conditions. 6. Flash point . The flash point is the temperature to which a liquid must be heated to produce vapors that flash but do not burn continuously when ignited. Characterization There are two instruments used to determine the flash point: the Pensky– Martens or closed cup flash tester, and the Cleveland or open cup tester. The closed cup tester indicates a lower flash point because it retains light vapors that are lost by the open cup unit. Characterization 7. Water and sediment. The water and sediment level, also called bottom sediment and water, is a measure of the contaminants in a liquid fuel. The sediment normally consists of calcium, sodium, magnesium, and iron compounds. For heavy fuels, the sediment may also contain carbon. Characterization The basic analyses described above are important in designing oil-fired boilers. The HHV determines the quantity of fuel required to reach a given heat input. The ultimate analysis determines the theoretical air required for complete combustion and, therefore, indicates the size of the burner throat. Also available from the ultimate analysis is the carbon/hydrogen ratio, which shows the ease with which a fuel burns. This ratio also indicates the expected level of carbon dioxide emissions. Compared to coal, fuel oils are relatively easy to handle and burn. There is less bulk ash to dispose of and the ash discharged is correspondingly small. Extraction Companies today searching for oil use many methods to investigate possible sites before drilling even begins. Underground rock formations are carefully surveyed to determine the best place to explore. 1- Variations in the Earth’s natural magnetism which can provide a clue to the type and thickness of rock that will be found below the surface. Underground rocks containing iron cause a distortion in the Earth’s magnetic pull, which can be recorded on very sensitive instruments. However, the influence of these rocks deep in the Earth’s crust is reduced if they are covered by thick layers of nonmagnetic, oil-bearing rocks. Possible oilfields can therefore be detected by measuring the distortions in magnetic pull caused by the rock pattern, a job usually carried out by aircraft equipped with devices that can quickly record magnetic variations over large areas. Extraction 2- Seismic surveying A more detailed picture can be obtained by setting off a small explosion at or just below ground level and recording the time the shock waves take to bounce off the deep rock layers and return to a series of sensing devices strung out along the ground at regular intervals. This method is known as seismic surveying. The speed at which the shock waves travel back varies according to the type and thickness of the underlying rocks. The echoes that return to the surface are recorded by the sensing devices and the information is fed into a computer to produce a picture, known as a seismograph, which indicates possible oil reservoirs. CHAPTER 8 Oil Extraction 3- Drilling Drilling techniques have advanced a long way since the early days of oil prospecting. The natural pressure that causes oil to gush to the surface will normally keep an oilfield flowing for months or even years after the first well has been drilled. But eventually, the pressure will drop to a level where it is no longer sufficient to produce a flow, and at this stage up to three-quarters of the total volume of oil may remain in the rocks. When this happens, the flow of oil can be boosted by reproducing the natural pressure of the water and gas between which it is sandwiched. Extra wells can be drilled to inject water into the zone below the oil, or gas into the area above. The gas can be collected at the surface after bubbling out with the oil and compressed to boost its pressure before being returned to the natural underground reservoir. Water injection, however, demands a ready supply of pure water, which may be difficult to obtain at oilfields in the desert or other arid zones. CHAPTER 8 Oil Oil exploration at sea During the last few decades new techniques have been developed to tackle oil exploration at sea. 1- One of the earliest was the jack-up rig. It gets its name from a set of steel legs that rest on the seabed and can be extended to jack up the drilling platform above the reach of the waves. The legs can also be raised through the deck so that the platform can be towed to another location. Jack-up rigs can also operate in deep water. 2- Another drilling rig has been specially designed for exploration in deeper water. This has huge buoyancy tanks that enable it to float out to the drilling site. There, the tanks are partly filled with water, making the rig sink lower in the sea and giving it more stability in stormy weather. Anchors are also used to keep it in place above the well. This type of rig, known as a semisubmersible rig, allows exploration in water depths of more than a thousand feet. CHAPTER 8 Oil Processing Distillation may be defined as the separation of the components of a liquid feed mixture by a process involving partial vaporization through the application of heat. In general, the vapor evolved is recovered in liquid form by condensation. In continuous distillation, a feed mixture is introduced to a column where vapor rising up the column is contacted with liquid flowing downward (which is provided by condensing the vapor at the top of the column). This process removes or absorbs the less volatile (heavier) components from the vapor, thus effectively enriching the vapor with the more volatile (lighter) components. CHAPTER 8 Oil CHAPTER 8 Oil In order to provide fuels, crude oil must be refined. It is the distillation column that is the workhorse of this process. As portrayed in Figure 8.2, the liquid is first boiled to turn it into a light vapor, which is passed into a tower where it rises and cools. Each of the components of crude oil has a different boiling point, so at each stage of the cooling a different liquid, or fraction, can be drawn off at different heights in the column. Parts of the mixture that are not fully vaporized at first will be collected as a liquid at the bottom of the tower and recirculated. At the end of this stage, known as fractional distillation, the crude oil mixture will have been separated into several distinct substances. CHAPTER 8 Oil CHAPTER 8 Oil Transportation/Transmission Pipelines are the safest and cheapest way to move large quantities of either crude oil or refined petroleum across land. Other transport methods include ships (and barges) and trains. Details follow: 1- Pipelines - Oil (and natural gas) can be transported in their natural states through pipelines buried underground or even on the seabed. - Some of the earliest pipelines used to move fuel were made from wood. - Main distribution lines for crude oil (and gas) are nowadays almost always made of steel. - Most land pipelines are buried at least 3 feet underground - Underwater pipelines may also be buried in a trench on the seabed. - All oil and gas pipelines are coated with a layer of bitumen or fiberglass to prevent corrosion while underwater pipelines have an additional coating of concrete for extra protection against the effects of seawater. CHAPTER 8 Oil 2- Ships Much of the world’s oil comes from areas such as the Middle East that are too distant from the main markets to make transport by pipeline either eco- nomic or practicable. Oil from these regions is shipped to North America, Europe, and Japan in specially built tankers. The first oil tanker, the Glückauf, launched in 1866, could carry just 300 tons of oil, but modern vessels can carry 500,000 tons. These supertankers are more than 1,300 feet long and hide their bulk beneath the surface like icebergs. 3- rains Oil is transported by train in small quantities, usually across short distances. This mode is employed when the receiver is not near pipelines or major terminals. As noted earlier, jobbers handle the wholesale distribution of most petroleum products. The retailer—a gasoline station or a home heating oil company—then receives the product. The last stage is when a car receives gasoline and/or the home receives fuel oil for heating purposes. CHAPTER 8 Oil Environmental Issues As with coal, environmental concerns will continue to exist for the petroleum industry. • Drilling for and transporting oil can endanger wildlife and the environment if it spills into rivers or oceans. • Leaking underground storage tanks can pollute groundwater and create noxious fumes. • Processing oil at the refinery can contribute to air and water pollution. • Burning gasoline to fuel cars contributes to air pollution. • Even the careless disposal of waste oil drained from a car can pollute rivers, lakes, and estuaries. • Power plants burning all the various grades of oil produce SO2. The combustion of any carbon- bearing compound also produces CO2, a gas that may contribute to global warming. CHAPTER 8 Oil Future Prospects and Concerns The increasing dependence on petroleum presents a continuing challenge for the future. This dependence must be balanced by the growing demand for petroleum products, increased costs, the depletion of this resource, and the protection of the environment. Dependence on imported petroleum is a major problem that reduces not only energy security and the ability to withstand the disruption of oil supplies, but also economic stability and national security. These factors need, therefore, to be considered when developing an energy management policy that heavily relies on oil. There are steps that need to be taken in the future to help ensure oil energy resources and reduce high oil prices. Some believe the most important step is to decrease demand for oil through increased conservation (e.g., reducing the oil used by increasing the efficiency of vehicles and transportation).
