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The Nature of Oil and Gas. Oil and gas are naturally occurring hydrocarbons. Two elements, hydrogen and carbon make up a hydrocarbon. Hydrocarbons (i.e. oil and gas) can exist as solid, liquid or gas.
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The Nature of Oil and Gas. • Oil and gas are naturally occurring hydrocarbons. Two elements, hydrogen and carbon make up a hydrocarbon. Hydrocarbons (i.e. oil and gas) can exist as solid, liquid or gas. • In our text, Petroleum is defined as liquid crude oil and natural gas liquids as well as the common fuels propane and butane; including gasoline, kerosene, heating oil and diesel fuel. • The oil industry processes and refines hydrocarbons such as natural gas, liquefied petroleum gas (LPG), and gasoline from natural and crude hydrocarbons that occur in the earth.
Natural Gas. The simplest hydrocarbon is methane. Under normal temperature and pressure, methane is a gas. Methane is the main component of natural gas. Natural gas occurs naturally in the earth, usually mixed with other hydrocarbon gasses and non hydrocarbon gasses such as carbon dioxide. After Natural gas is produced, a processing facility removes such impurities before it reaches the consumer.
Liquid Petroleum Gas (LPG). LPG is mainly propane and butane. When propane and butane are compressed a little at normal temperature, they liquefy. When the pressure is released, the liquid turns back into gas. This is why LPG is used as a portable fuel. It is transported in a portable pressurized container as a liquid. When the container is connected to a stove’s burner, for example, the LPG changes into gas when the burner is turned on and the pressure is released.
Other Hydrocarbons. Other hydrocarbons may be liquid or solid under normal conditions. Pentane, hexane, heptane, and octane, for example are liquid under normal conditions. Gasoline is a mixture, or blend of several hydrocarbons that are liquid under normal conditions. CRUDE OIL, TAR & ASPHALT Crude oil is also a mixture and usually occurs as a liquid. Tars and asphalts are solid hydrocarbons under normal conditions. Raising the temperature liquefies them. When a roofer heats tar, for example, it liquefies and binds gravel or other roofing materials into a spreadable mixture. When it cools back to normal temperature, it solidifies to form a hard waterproof surface.
Characteristics of Reservoir Rocks. Reservoir rocks must be porous; i.e., they must posses many, many tiny holes through which oil can flow. Reservoir rocks must also be permeable; i.e., the pores must be connected. A suitable reservoir rock must be porous, permeable, and contain enough hydrocarbons to make it economically feasible for the oil company to drill for and produce it.
Origin and Accumulation of oil and gas Millions of years ago, vast numbers of small organisms lived in the sea. When these organisms died, they settled to the sea bottom. Over the years, enormous quantities of this organic sediment accumulate on the sea floor. The organic material mixes with the mud and sand at the bottom. Over many million years, many layers of sediment build up and become thousands of feet thick. Pressure and heat change the deep layers into rock. At the same time, heat, pressure, and other forces change the dead organic material in the layers into oil and gas.
Origin and Accumulation of oil and gas Geological action creates cracks or faults in the earth’s crust. Earth movements fold rock upward and downward. Molten rock thrusts upward, altering the shape of the surrounding beds. Disturbances in the earth shove great blocks of land upward, downward and sideways. Wind and water erode formations, earthquakes burry them, and new sediments fall on them. In short, geological forces slowly but constantly alter the shape of the earth. These alterations in the layers of rock are important because under the right conditions they can trap hydrocarbons.
Petroleum Traps. • Two types of traps; (1) Structural traps and (2) Stratigraphic traps. • Structural traps form due to the deformation in the rock layer that contains the hydrocarbons. Two examples of structural traps are Fault traps and Anticlinal traps. A fault trap occurs when formations on either side of the fault move. The formations come to rest in such a way that when hydrocarbons migrate into one of the formations they become trapped. An anticline is an upward fold in the rock layers, much like an arch in a building. • Stratigraphic traps form when other beds seal a reservoir bed, or when the permeability changes within the reservoir bed itself.
History of Oil Production in the US. One Sunday afternoon in 1859, William Smith (Uncle Billy) decided to inspect a well he was drilling near Oil Creek, just outside Titusville, PA. Uncle Bill was drilling the well for a former railroad engineer named Edwin Drake (Colonel Drake). Uncle Bill peered into the pipe that enclosed the top of the hole and saw it was full of Crude oil. Uncle Bill’s discovery marks the beginning of oil drilling and production in the US.
History of Oil Production in the US. Pennsylvania’s oil fields were short lived; but oil was also found in Ohio, Indiana, California and Texas. In 1862, 3 million barrels of oil was produced from 75 wells in Pennsylvania. By 1909, the United States was producing 500,000 barrels per day. The oil produced in the beginning was refined to produce kerosene for heating, cooking and lighting. When electric lights came to replace kerosene lamps, oil production could have declined; but just then, the automobile was replacing horses and a larger market for oil emerged.
Petroleum Refining. The primary process in oil refinery is fractional distillation. Crude oil is vaporized by heating to 400oC; the vapors then enter at the bottom of a fractional distillation column. The vapors condense at various collection points going up the tower as the temperature for condensation decreases (fig. 2.4 of text). Table 2.3 shows some of the products of the fractional distillation of crude oil. There is usually a deficiency in the lighter hydrocarbon molecules needed in gasoline; for example in table 2.3, C6H14, C7H16 and C8H18 molecules are all missing. There is usually an excess in the heavy molecules of paraffin and tar (C20-up).
Petroleum Refining 2. The excess heavy molecules can be broken into the lighter molecules needed in gasoline. Thermal cracking (using high temperatures and pressures) is the oldest method used to break the heavier molecules into lighter ones. A more efficient method is catalytic conversion, a process in which petroleum vapor is passed over alumina-silica mixture or certain types of clay that act as catalysts in bringing about a chemical reaction. The reverse process of joining light hydrocarbon molecules together to form heavier ones is called polymerization. Natural gas and other gases from the cracking process are made into high octane fluids by polymerization.
Natural Gas (NG). Natural gas (CH4, 80%-95%; C2H6; with trace amounts of heavier hydrocarbons) has become a favorite fossil fuel in recent years with great prospects of filling our energy needs in the near future. Several reasons for the possible increase in our use of natural gas: • Improvements in technology for exploration and production, and increase in resource base. • Compared to other fossil fuels, NG releases less harmful combustion products per unit energy produced. • New applications of NG such as motor fuel for transportation. • Compared to oil and electric energy, NG is a less costly source of energy (see example 2.1).
Natural Gas (NG). Example 2.1 shows that in applications where heat is the main goal, NG obviously offers an advantage. It is less expensive to operate appliances such as clothes driers, water heaters, ovens, furnaces, etc., using NG rather than electricity. History of Natural Gas. NG was discovered in China and used in China and Japan in the 16th century BC. The gas was transported in bamboo pipes and used for lighting fixtures. In the US, widespread use began in Fredonia, NY in 1821. Abundant sources were discovered later in Kansas and Texas but their development was held back for many years because no system of pipelines were in place to deliver the gas from source to consumer.
History of Natural Gas. By 1923 annual use of NG in the US was only 1x1012 ft3 (=1tcf = 1trillion cubic feet); much of the NG emerging from oil wells was wasted be venting it to the atmosphere or faring it at the source due to lack of delivery. During and soon after WWII a rapid expansion of the NG industry took place in the US. Extensive pipeline system was laid from the Texas panhandle to northeastern US and later extended to the West coast. Development in large diameter welded steel pipes and improved pipe laying techniques made the rapid expansion possible. • The economic advantage, as well as its convenience and cleanliness, drove the widespread adoption of natural gas. Oil, coal and coal gas (manufactured gas) are at a disadvantage relative to NG.
Advantages of using Natural Gas. • In recent years, falling market prices for NG and increased concerns about air pollution from coal have made NG the fuel of choice for many new electric plants. • About half of the new power plants being built will use NG as a boiler fuel to produce steam to drive turbines. • Newer types of gas turbines are able to use the combustion of NG to drive the turbines directly, without the need for a steam producing burner. • Steam driven power plants have about 35% efficiency for converting the energy in the fuel to electricity; a gas turbine system has about 45% or higher efficiency.
Advantages of using Natural Gas 2. • Gas turbine plants cost about half as much to build as conventional coal-fired plant equipped with pollution control devices. • Air pollution due to sulfur and particulates is entirely avoided in the use of NG as fuel in power plants. • NG is also coming into common use as a motor fuel in cars, trucks, and buses. For this use, the gas must be compressed under pressure in the vehicle’s fuel tank in order to get sufficient range. Estimates show that as many as four million vehicles powered by compressed NG will be operating in the US by this year, 2005!
Formation of Coal • Coal originates from abundant plants that started to grow over 350 million years ago. • Then, there were Huge swamps with giant ferns, shrubs, vines, trees, and algae that grew and then fell into decay. • The carbon in the organic material accumulated in layers at the bottom of the swamp • The dead plant material in the top layers are decomposed by aerobic (oxygen-rich) bacteria, yielding CO2, CH4 and other gasses. The material in the deeper layers decay by anaerobic (oxygen deficient) action and turn into peat.
Coal formation Stages &Types of Coal • Peat is the first stage in coal formation. It is the lowest grade of coal-like material. • Lignite is the next grade of coal above peat. It contains up to about 50% Carbon and it is about 150 million years old. • Bituminous coal is about 300 million years old and contains about 50%-80% Carbon. • Anthracite is the oldest form of coal. It is the hardest and cleanest burning with carbon content of up to 95%. Peat provides low quality fuel in many parts of the world; gardeners also use peat as organic material. Largest deposits of peat in the US are found in Wyoming, North and south Dakota, Montana and New Mexico.
Coal Resources • Size of the coal resource is more easily determined than for oil and gas because coal beds are close to the surface and cover large areas. • In US significant amounts of coal are found in three major regions: (1) The Appalachian Basin (parts of WV, PA, OH, and eastern KY). (2) The Illinois Basin (IL, western KY, and IN). (3) Northern Great Plains and Rocky Mountain Region (MN, WY, CO, ND, and NM). Minable coal in the US is 71% bituminous and sub-bituminous, 28% lignite, and 1% anthracite. Almost all the anthracite coal is found in Pennsylvania.
Coal Resources 2. • There are environmental concerns with regards to the surface mining of coal. Among these concerns are the effect of CO2 emissions on global climate, and the health effects of SO2 and particulate emissions. The only known practical way to reduce CO2 emissions is by reducing the rate of burning carbon based fuels. • SO2 is perhaps the pollutant of most concern that results from burning coal in electric power plants. • Vast amounts of coal in the world; about 20% of the world’s resources is located in the US.
Shale Oil • The Green River Formation is the most extensive deposit of oil shale in the US. Two large tropical lakes covered the area about 50 million years ago. Organic matter from the surrounding hills was deposited on the lake bottom along with sedimentary material. The deposits grew to about 3000ft over many million years. The combined materials from plants and some aquatic animals formed a carbon-bearing mudstone, or marlstone on the bottom of the lakes. This is the source of shale oil. • Shale oil or marlstone contains an organic substance called kerogene. Kerogen is solid a hydrocarbon.
Tar Sands • Tar sands contain thick tar-like hydrocarbon substance which is a very viscous crude oil called bitumen. Tar sands are mined as a solid material and transported to a processing plant where the bitumen is extracted by steam or hot water. Using a centrifuge, the bitumen is broken down (cracked) into naphtha, kerosene, and heavy fuel oil. Two tons of tar sand produces one barrel of oil; thus the energy density is very low.
