Oil and petroleum

Summary: Oil and petroleum are nonrenewable combustible liquids that can be refined into gasoline or petrol, diesel fuel, motor oil, and many other compounds.

Crude oil, a naturally occurring, flammable fossil fuel, is a mixture of various hydrocarbons and other chemical compounds. Crude oil, also called petroleum, is one of the world’s most important energy sources, producing gasoline, kerosene, and heating fuel, among other products. However, there is increasing debate on how long the production of crude oil can continue and whether it will be able to meet market demand.

Unrefined Petroleum

Crude oil—that is, unrefined petroleum—is a flammable fossil fuel in a mixture of up to 17,000 substances in variable compounds, including diverse hydrocarbons, such as alkanes (paraffins), cycloalkanes (naphthenes), aromatic hydrocarbons, and asphaltenes, which bind nitrogen, oxygen, and sulfur and form compounds such as thioether, alcohols, and resins. Also, metals, such as iron, copper, vanadium, and nickel, may be found in crude oil. Not only does the chemical composition of crude oil vary, so do its physical properties, including color and viscosity, from transparent, light yellow and thin fluid to deep black and viscous, depending on its source. Its density ranges from 0.82 to 0.94 gram per cubic centimeter. Crude oil containing only little sulfur is referred to as “sweet,” while crude oil relatively rich in sulfur is called “sour.” The latter has an unpleasant odor. Low density refers to light oil, and high density refers to heavy oil. Crude oil is not soluble in water or ethanol, but it is soluble in ether, benzene, and tetrachloromethane.

Crude oil has long been one of the most important fuels of modern industrialized societies. Aside from fuels, oil has also been used in industrial chemical processes to produce pharmaceuticals, fertilizers, foods, plastics, paints, textiles, and construction materials. Many industrially developed countries have largely remained highly dependent on petroleum. Most chemical products can be synthesized from about 300 bulk chemicals based on natural gas and petroleum, including ethane (or ethylene), propene, benzene, toluol, and xylol, avoiding expensive alternative methods. Much oil is burned as fuel in power plants and engines. In 2023, worldwide consumption of petroleum and other liquid fuels was approximately 101.8 million barrels per day, according to the US Energy Information Administration.

Global processes of exploration, extraction, refining, transporting (by means of both supertankers and pipelines), and marketing of petroleum products are major areas of the oil industry. Until 1985, global oil prices followed a pricing system administered by the Organization of Petroleum Exporting Countries (OPEC). After this system collapsed, oil-exporting countries adopted a market-linked pricing mechanism for international crude oil trade.

Like with all fossil fuels, petroleum fuels, when combusted, pose environmental risks, mainly with respect to exhaust products. Too little oxygen during combustion yields carbon monoxide. Exhaust gases from car engines include nitrogen oxides, which cause photochemical smog.

History

In a technical sense, petroleum refers only to crude oil, but in a broader sense it describes all liquid, gaseous, and solid hydrocarbons. Petroleum means literally “rock oil” (from the Latin oleum petrae). Its density is lower than that of water, so it wells up to the Earth’s surface through vugs (cavities) in sediments of shale, sand, or carbonate. Crude oil at the Earth’s surface, mostly in the form of bitumen due to a reaction with oxygen, was known 12,000 years ago in Mesopotamia.

The ancient Babylonians used bitumen to pave for roads, seal ship planks, and impregnate textiles. Naphtha can be traced back to the Babylonian word naptu, which means “to glow.” The first known public regulation of oil respective of bitumen was written by Hammurabi, first king of the Babylonian Empire, in 1875 BCE. The Roman army probably used crude oil as lubricant for axes and wheels. In early medieval Byzantium, bitumen was used for flamethrowers during battles, and in the Renaissance so-called St. Quirin oil was sold by German monks as a medicine. The Pechelbronn oil field in Alsace was the site of the first European oil well, productive from 1498 until 1970.

In 1854, the Canadian physician and geologist Abraham P. Gesner obtained his first US patent for the synthesis of kerosene from coal and petroleum, providing the initial impetus for the oil industry. The development of kerosene was motivated by the search for a reasonable alternative to train oil (from whales), at that time the common lamp fuel. Only a few years later, in 1859, Colonel Edwin L. Drake drilled for oil in Pennsylvania and found a big deposit only 70 feet (21.2 meters) underground. In the same year, the first oil refinery was established, soon followed by many others. After the introduction of electric lighting, oil lost its attraction for a while, only to return in the form of benzine, or petroleum ether. Henry Ford considered ethanol as fuel for his automobiles, but John D. Rockefeller, founder of Standard Oil Company, used benzine as motor fuel. It was Standard Oil of California that discovered the first oil deposit in Saudi Arabia close to Dammam in 1938. Since then, giant amounts of crude oil have been used as motor fuels.

Geophysical Prospection

Precise maps provide fundamental information prior to geophysical prospection (or geophysical surveys), a systematic search for oil in place. In certain areas, such as Iran, deposits can be identified by means of aerial photographs. In cases where there are rocks at the surface that are typical for oil in place, samples are taken.

During prospection, physical properties, such as magnetism, density, sonic speed, electrical resistance, and radioactivity, are measured. The most often applied method is seismic reflection. To receive computable data, a controlled seismic source, such as an artificially induced dynamite explosion, an air gun, or a seismic vibrator, is required; these methods produce acoustic waves that propagate in the Earth’s crust. The waves need different times to pass different rock formations, and reflect at the border of two formations. Reflected waves are received by sensitive geophones or hydrophones and are logged in a seismogram. The result is an image of the underground, providing information about existent trap structures.

Based on seismic data, sample drills are done. In a next step, three-dimensional measurements are taken in selected areas. In combination with geophysical measures at the borehole, a quantitative model of oil or natural gas deposits, as well as plans for further boreholes and production, can be prepared.

Production

When oil occurs subaerially (at or near the Earth’s surface), it can be recovered by means of opencast mining. For deeper deposits, boreholes are drilled to recover the oil. Deposits under the sea are recovered by means of offshore drilling. At a water depth of up to 328 feet (100 meters), the oil platforms stand on stilts. Another type of drilling platform is called semisubmersible floating platform, carrying heavy ballast weights to stabilize the platform. The deepest successful offshore wells have been drilled at depths of several thousand feet below sea level. Drillships can even drill in depths of up to 12,000 feet (more than 3,600 meters). The installation of a permanent drilling platform costs several billion dollars. However, offshore drilling has made enormous additional oil reservoirs available.

Traditional oil drilling is done using the rotary drilling technique. Steel drilling rods hang at the oil derrick and are attached at the rotary table at the bottom of the derrick. Scavenging pumps flush water into the borehole, forcing the drilling cuttings through the hollow spaces between rods and borehole to the surface. The mixture of water and cuttings covers the borehole wall, preventing it from collapsing and thus making extremely deep boreholes possible. Once the drill reaches the oil reservoir, pressure can be so high that the oil rockets upwards like a fountain.

Commonly the recovery of conventional crude oil takes place in three stages. The natural reservoir pressure is exploited for the primary oil recovery. Natural gas in the reservoir enables an eruptive recovery of about 10 to 30 percent of the oil available in that reservoir. For the second oil recovery phase, two primary methods are used to boost production: the water flood method, which is the injection of water into the reservoir to increase pressure, and the thermal flood method, which is injection of steam (primarily used to give very viscous oil a lower viscosity and thus force the oil to the borehole). Because water is denser than oil, it sinks beneath it, filling up the reservoir from the bottom without mixing with the oil. More specialized methods include the injection of solvents via the chemical flood technique. These methods enable the recovery of 10 to 30 percent more oil, so that altogether 20 to 60 percent of the available oil can be recovered.

In the final, third stage of recovery, complex substances such as polymeres, carbon dioxide, and mircoorganisms are injected to increase the capacity of the well again. High prices and global market dynamics can intensify efforts at this tertiary stage of oil recovery, not only at currently producing reservoirs but also at old reservoirs. Usually, the cost of recovering oil increases as the amount available at the well decreases until production becomes too expensive and the borehole is shut down. However, as world reserves decline and the price of oil rises, the economics of oil recovery may change to encourage more recovery at later stages.

When crude oil is found in semisolid form mixed with sand and water, it is also called crude bitumen, or oil sand. There are abundant reservoirs known in Canada, the Athabasca oil sands, and in Venezuela, the Orinoco oil sands. These sands are considered unconventional oil sources because the oil cannot be recovered by means of traditional drilling methods. In addition, oil shales represent an indirect source of oil. These rocks contain the waxy, high-carbon substance called kerogen. Using heat and high pressure, the process that leads to the geological formation of crude oil can be simulated, converting the trapped kerogen into oil. This method it not a modern discovery but has been known for centuries. It was even patented in 1694 under British Crown Patent No. 330. An advanced version known as hydraulic fracturing, or fracking, became increasingly prevalent in the twenty-first century.

Factors for the classification of crude oil, conducted by the oil industry, are the geographic location of its source, the API gravity (a measure, devised by the American Petroleum Institute, of the density of a petroleum liquid compared to water), and the sulfur content. The geographic location determines transportation costs to the refinery. Lighter grades of crude oil are more eligible than heavier grades because, upon refining, they produce more gasoline. Also, sweet oil is traded at higher prices than sour oil because it causes less environmental problems. Refineries have to meet strict sulfur standards, just as fuels for consumption must. The specific molecular characteristics of the different crude oil grades are listed in crude oil assay analysis, used in petroleum laboratories.

Processing

First the recovered crude oil is separated into oil, natural gas, and saltwater by means of a gas separator. When the gas is completely escaped, oil and saltwater can be separated by density separation.

Petroleum refineries then decompose crude oil into light and heavy components, such as heating oil, kerosene, jet fuel, and gasoline, by means of distillation columns, called fractional distillation or rectification. Because of these distillates’ different boiling points, they can be fractionated into boiling ranges. During this first distillation, fractioned gases, such as methane, ethane, propane, and butane, are important heating fuels. Light and heavy petrols (with boiling points of 30–180 degrees Celsius) are used as gasoline for cars. The medium distillate (180–250 degrees Celsius) is used as lamp oil or is processed into jet fuel. In a subsequent vacuum distillation of the residue, additional important petroleum products are produced, such as lubricants, used to grease engines, and bitumen, used to pave roads. The heavy fuel oil fuels power plants and ship’s engines. Special refineries recycle waste oil.

The amounts of naphtha produced directly from crude oil per fractional distillation are not sufficient to cover the market. However, a process that takes place at high temperatures, called catalytic cracking, cracks long-chain alkanes into short-chain alkanes. With this method, petrol can be produced from paraffin oil. For example, decane cracks up into propene and heptane. A trap inside the reactor separates the cracking products from the spent catalyst. Again, the cracked hydrocarbons become fractionated in a subsequent distillation. At the surface, the catalyst segregates carbon, making the catalyst ineffective. Upon mixing with hot air, the carbons burn up, regenerating the catalyst. This process is also used to crack heavy crude oil because it often contains too much carbon and too little hydrogen.

Gasoline (Petrol) Production

The compression and heat in the cylinders of a gasoline engine may cause untimely spontaneous combustion of the gasoline-air mixture, resulting in engine knocking. Unramified hydrocarbons tend toward untimely ignitions, while unsaturated, ramified hydrocarbons are relatively knockproof. The antiknock rating is indicated by an octane number. The higher the octane number is, the more knockproof the gasoline is. Pure isooctane would have an octane number 100, while pure n-heptane would have an octane number of 0. Common octane numbers for gasoline are 87, 95, and 98, and the higher the antiknock rating of the gasoline used, the longer the life of an engine. Therefore, naphtha is converted into gasoline with high antiknock ratings by means of a platinum catalyst in a process called platinum reforming. By-products of this process are hydrogen and gaseous alkanes. Prior to reforming, the naphtha needs to be desulfurized, releasing hydrogen sulfide, because sulfur would destroy the catalyst.

Desulfurization, Hydrofining, and the Claus Method

After fractional distillation, heating fuel and lubricants still contain much sulfur, leading to toxic sulfur dioxide exhaust upon combustion; these emissions lead to environmental degradation in the form of acid rain and forest decline. In a process called hydrofining, the oil is mixed with hydrogen and heated. Then the hydrogen in the hot mixture reacts in a catalytic reaction with the contained sulfur to form hydrogen sulfide. Subsequently, the hydrogen sulfide is burned in the Claus desulfurization process, forming sulfur and water, as follows:

6H₂S + 3O₂ g 6S + 6H₂OH = -664 kJ/mol

Synthesis Gas

Other residues from fractional distillation are used to produce synthesis gas. That is a mixture of carbon monoxide and hydrogen, used to produce many other, organic compounds, such as ammonia and methanol. Synthesis gas production from methane occurs as follows:

CH₄ + H₂O g CO + 3H₂ (endothermic)

The carbon monoxide can be converted with water vapor into hydrogen and carbon dioxide, which can be washed out with water. The carbonized water is sold to the soft-drink industry. The pure gases nitrogen and hydrogen are left over as chemical precursors for other products.

Another refining process is called pyrolysis, used to crack light gasoline at very high temperatures into ethene, acetylene, and propene. A mixture of methane and oxygen is heated to 2,500 degrees Celsius. When the light gasoline is conveyed into this mixture, it cracks. For example, pyrolysis for n-heptane occurs as follows:

n-heptane g ethene + acetylene + propene + hydrogen

Ethene and propene are important key precursors for the production of plastics. Compared to catalytic cracking, pyrolysis takes place at much higher temperatures and without a catalyst.

Global Resources, Production, and Consumption

The question of how long global oil resources will be able to cover the world’s consumption has been debated. In the late twentieth and early twenty-first centuries, many forecasters began to warn that "peak oil" was imminent based on ever-increasing consumption and limited known reserves. Many scientists agreed that peak of oil discoveries was reached in 1965, and from 1980 oil consumption typically exceeded oil discoveries each year. However, the discovery of some new reserves and especially improvements in extraction methods such as fracking allowed further growth in production into the 2020s, exceeding some estimates. Optimistic observers, including some in the oil industry, asserted that with modern technology, prospected areas, and consumption, Earth’s oil resources would cover the world’s consumption for at least another century; this prediction assumes that only 10 percent of all liquid oil resources have been recovered. Still, even the most staunch supporters of the oil industry acknowledge that oil is a finite, nonrenewable resource. Key publications, such as the International Energy Agency (IEA)’s annual World Energy Outlook, present different outlooks based on potential scenarios for the global energy landscape.

The most important oil producing countries in 2023 included the United States, Saudi Arabia, Russia, Canada, China, and Iraq. The United States, China, India, Russia, Saudi Arabia, and Japan were some of the biggest consumers of oil in 2022. The annual consumption in the United States was about 20.01 million barrels per day (mBPD), representing 20 percent of the global total, while China consumed 15.15 mBPD, or 15 percent of the global share.

Worldwide Oil Prices

Prices for all types of crude oils fluctuate according to various market factors. The importance of oil to global energy production means that oil prices have a major impact on the world economy, as well as the economies of individual countries. Periods of significantly elevated or depressed oil prices can have widespread effects, which are often most visible to average citizens in the price of gasoline for automobiles. Gasoline prices themselves have been correlated to consumer habits, notably including a tendency to purchase large and less fuel-efficient vehicles when prices are low and, conversely, favoring smaller, more efficient vehicles when prices are high.

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