- Email: [email protected]
Oil and Gas
Oil and Gas M Downey, Southern Methodist University, University Park, TX, USA ã 2015 Elsevier Inc. All rights reserved.
Origin of Petroleum Multiple Origins of Methane Gas Methane from Petroleum Bacterial Methane Methane Hydrates Town Gas (Manufactured Methane) Costs of Oil and Gas Petroleum Migration and Retention Our Transportation Era Depends on the Petroleum Age
1 1 1 1 1 2 2 2 2
Origin of Petroleum In common English usage, the terms ‘oil and gas’ refer to petroleum and its associated gases. Petroleum, literally ‘rock oil,’ is a mixture of hundreds of types of hydrocarbon molecules, formed by the thermal decomposition of organic matter that has been buried to significant depths and temperatures in the Earth. Living organisms flourish in the upper layers of lakes and seas, extracting energy from sunlight and nutrients from the waters. When these organisms die, their organic matter normally provides a food source for animals burrowing in the bottom sediments. Sometimes, the bottom sediments are sterile, unburrowed, and lacking in oxygen; then, the dead organisms rain to the seafloor and accumulate in thick layers of organic-rich rocks, protected against scavengers while being buried beyond their reach. Continued burial to greater temperatures in the Earth causes the buried organic matter to ‘cook’ and liquefy to petroleum. All petroleum forms in this manner, as does the methane gas generated with the oil.
Multiple Origins of Methane Gas Methane from Petroleum Most of the methane contained in subsurface accumulations of ‘natural gas’ is thermal methane. This particular variety of methane, a product of the thermal decomposition of organic matter, is generally found with its higher homologues, ethane, propane, and butane, and is isotopically ‘heavy,’ compared with methane produced directly by life processes.
Bacterial Methane Methane produced by bacterial decomposition of organic matter is ubiquitous on the Earth and is readily distinguished from thermal methane by bacterial methane’s ‘light’ carbon isotope. Methane is a major by-product of the decomposition of plant material in swamps, oceans, rice fields, and animals and, especially, from cattle. Such bacterial methane can pass directly into the atmosphere. Globally, the agricultural sector is the primary source of methane emissions to the atmosphere. Recovery of methane from large-scale farm manure operations and from organic decay in municipal waste sites provides a modest source of fuel for local electricity generation. Subsurface gas accumulations composed of bacterial methane are common, including the huge gas fields recently discovered under the deep waters of the Mediterranean between Cyprus and Israel. On a pound for pound basis, methane in the atmosphere is over 20 times as effective as carbon dioxide in trapping radiation. Methane is much lighter, however, and has a much shorter residence time in the atmosphere than carbon dioxide.
Methane Hydrates In the presence of water, within a narrow pressure and temperature range, methane forms a solid, icelike substance called methane hydrate. The substance was first recognized by Sir Humphry Davy, and its common appearance in piping has often created flow problems for engineers. In the 1960s, Russian and American scientists discovered that solid methane hydrate occurs widely, abundantly, and naturally in the Earth. It is dominantly of bacterial origin and the hydrate occurs in two settings: at shallow depths in permafrost areas and beneath deep ocean floor sediments.
Reference Module in Earth Systems and Environmental Sciences
http://dx.doi.org/10.1016/B978-0-12-409548-9.09173-9
1
2
Oil and Gas
Enormous quantities of methane hydrate exist in the Earth as a solid, icelike substance, each cubic foot yielding about 0.7 cubic feet of freshwater and 160 cubic feet of methane gas, when decomposed. Worldwide, the quantity of methane held in gas hydrates may exceed all other methane previously discovered. No viable method for commercial production of methane from methane hydrate has ever been established.
Town Gas (Manufactured Methane) London’s streets were lit by methane gaslights in the 1800s. That methane gas was ‘created’ by blowing water over hot carbon; carbon (C) plus water (H2O) gives methane and carbon monoxide and dioxide. The created methane was manufactured locally in many cities and called ‘town gas.’ Since the 1950s, methane gas has been provided more cheaply from underground accumulations of ‘natural gas,’ and the manufacture of ‘town gas’ has ceased. Is methane gas a renewable resource? After all, it can be made from water and hot carbon.
Costs of Oil and Gas Oil and gas costs benefit enormously from the prior energy input by the sun and the Earth. Our sun provided free energy to create organic matter; the Earth’s heat converted organic matter to petroleum; gravity (buoyancy) collected the petroleum into underground deposits of oil and gas. Creation of the Earth’s oil and gas energy is free. Locating the oil and gas and supplying the energy to convenient places, in a useful form, take enormous amounts of money. The energy rivals the agriculture business as the largest business in the world. We will never run out of oil and gas, as long as we can afford oil and gas. Every atom of hydrogen and carbon that was ever present on this Earth is still present and will remain on this Earth. It is child’s play for an able organic chemist to make methane from carbon and hot water or to produce oil and gas from carbon dioxide and water. These processes are well known but are much more expensive than simply extracting petroleum from the Earth. Since oil and gas can be made, worries should focus more on affordability of our future oil and gas and less about ‘running out of oil and gas.’
Petroleum Migration and Retention As petroleum and its associated gases form in the Earth, much of the oil and gas squirts out of the heated organic-rich layers into nearby reservoirs of porous limestones or sandstones, where the petroleum resides until located and produced. Everywhere oil and gas have been found, a look beneath them will recognize the source beds that once generated the petroleum. In the latter part of the twentieth century, geologist recognized that those source beds still contained within them large quantities of petroleum. It has been estimated that these ‘left-behind’ hydrocarbons in source beds are as abundant as all the oil and gas previously discovered. These hydrocarbons are tightly retained in the nanoporosity of the source rocks. To recover these tightly held oil and gas molecules, geologists typically need to drill 5–12 000 ft vertically and then turn the well trajectory horizontally for thousands of feet within the source rock layer. Then, the horizontal portion of the wellbore is injected with a high-pressure mixture of water and sand (hydrofrack) to create hairline fractures in the source rock layer. These created fractures provide flow paths between the nanopores containing petroleum and the horizontal wellbore. The fracture dimensions are controlled by the rock type and the amount of fluid and sand that is injected as a proppant; vertical fracture height is rarely greater than 300 ft; horizontal lengths can be thousands of feet. Within source rocks, the oil and gas molecules move very slowly, feet per year, and commercial recovery depends on the proximity of the newly created fractures to the oil and gas molecules tightly held within the rock. It is the ‘fracture-touched-volume’ that largely determines how much petroleum will be recovered.
Our Transportation Era Depends on the Petroleum Age The use of petroleum fuels has revolutionized transportation and has powered the development of our modern world society. For a million and a half years, humanity relied on muscle power, sometimes aggregated into clans, tribes, and kingships. Four or five thousand years ago, these agglomerations of man power became assisted by horsepower, ox power, and the mechanical advantages of the wheel and the lever. Only three hundred years ago, the development of the English steam engine allowed the Industrial Revolution, with engines powered by coal able to move huge quantities of goods by land and sea. Steam engines brought the benefits of transportation to areas touched by water and the narrow strips of land crossed by railroads.
Oil and Gas
3
Recognizing the limitations imposed by the energy density of coal, in 1915, Winston Churchill saw to the conversion of the British battle fleet from coal-fired steam to petroleum. He saw that much of the capacity of a battleship had been devoted to merely providing space for coal and the coal-handling crew. Petroleum fuels have an extraordinary advantage for personal transportation; they contain enormous energy for little weight. Gasoline, for example, has more energy content, by weight, than the powerful explosive TNT. With the ready accessibility of petroleum provided by the huge early oil fields in Baku, the United States, and the Middle East, the great advantages of energy-dense petroleum fuels became apparent, and our ‘transportation era’ began in the 1920s. Now, for the first time in the history of human society, people can move around the Earth, anytime, anyplace, nearly effortlessly. Petroleum, with its great energy content and low weight, allows rapid transportation of people and products cheaply over long distances. Efforts continue to be made to make transportation more efficient and less costly. These improvements come from vehicle aerodynamics, better engine design, better use of computers to monitor fuel usage, pairing of electric with gasoline engines, and a host of continuing design modifications. Since fuel economy is directly linked to the weight of an automobile, simply making cars 10% lighter improves their gasoline mileage 6–8%. Sometimes, suggestions are heard that we should alter our society to a petroleum and vehicle-free, Eden-like future. Think twice. Few of us would want to live, or could survive, with only those foods, products, and services available within our personal 10 mile day 1 walking range. For better, for worse, for at least another 50 years, our comfortable modern society is firmly coupled to oil and gas and the transportation era.
Origin of Petroleum Multiple Origins of Methane Gas Methane from Petroleum Bacterial Methane Methane Hydrates Town Gas (Manufactured Methane) Costs of Oil and Gas Petroleum Migration and Retention Our Transportation Era Depends on the Petroleum Age
1 1 1 1 1 2 2 2 2
Origin of Petroleum In common English usage, the terms ‘oil and gas’ refer to petroleum and its associated gases. Petroleum, literally ‘rock oil,’ is a mixture of hundreds of types of hydrocarbon molecules, formed by the thermal decomposition of organic matter that has been buried to significant depths and temperatures in the Earth. Living organisms flourish in the upper layers of lakes and seas, extracting energy from sunlight and nutrients from the waters. When these organisms die, their organic matter normally provides a food source for animals burrowing in the bottom sediments. Sometimes, the bottom sediments are sterile, unburrowed, and lacking in oxygen; then, the dead organisms rain to the seafloor and accumulate in thick layers of organic-rich rocks, protected against scavengers while being buried beyond their reach. Continued burial to greater temperatures in the Earth causes the buried organic matter to ‘cook’ and liquefy to petroleum. All petroleum forms in this manner, as does the methane gas generated with the oil.
Multiple Origins of Methane Gas Methane from Petroleum Most of the methane contained in subsurface accumulations of ‘natural gas’ is thermal methane. This particular variety of methane, a product of the thermal decomposition of organic matter, is generally found with its higher homologues, ethane, propane, and butane, and is isotopically ‘heavy,’ compared with methane produced directly by life processes.
Bacterial Methane Methane produced by bacterial decomposition of organic matter is ubiquitous on the Earth and is readily distinguished from thermal methane by bacterial methane’s ‘light’ carbon isotope. Methane is a major by-product of the decomposition of plant material in swamps, oceans, rice fields, and animals and, especially, from cattle. Such bacterial methane can pass directly into the atmosphere. Globally, the agricultural sector is the primary source of methane emissions to the atmosphere. Recovery of methane from large-scale farm manure operations and from organic decay in municipal waste sites provides a modest source of fuel for local electricity generation. Subsurface gas accumulations composed of bacterial methane are common, including the huge gas fields recently discovered under the deep waters of the Mediterranean between Cyprus and Israel. On a pound for pound basis, methane in the atmosphere is over 20 times as effective as carbon dioxide in trapping radiation. Methane is much lighter, however, and has a much shorter residence time in the atmosphere than carbon dioxide.
Methane Hydrates In the presence of water, within a narrow pressure and temperature range, methane forms a solid, icelike substance called methane hydrate. The substance was first recognized by Sir Humphry Davy, and its common appearance in piping has often created flow problems for engineers. In the 1960s, Russian and American scientists discovered that solid methane hydrate occurs widely, abundantly, and naturally in the Earth. It is dominantly of bacterial origin and the hydrate occurs in two settings: at shallow depths in permafrost areas and beneath deep ocean floor sediments.
Reference Module in Earth Systems and Environmental Sciences
http://dx.doi.org/10.1016/B978-0-12-409548-9.09173-9
1
2
Oil and Gas
Enormous quantities of methane hydrate exist in the Earth as a solid, icelike substance, each cubic foot yielding about 0.7 cubic feet of freshwater and 160 cubic feet of methane gas, when decomposed. Worldwide, the quantity of methane held in gas hydrates may exceed all other methane previously discovered. No viable method for commercial production of methane from methane hydrate has ever been established.
Town Gas (Manufactured Methane) London’s streets were lit by methane gaslights in the 1800s. That methane gas was ‘created’ by blowing water over hot carbon; carbon (C) plus water (H2O) gives methane and carbon monoxide and dioxide. The created methane was manufactured locally in many cities and called ‘town gas.’ Since the 1950s, methane gas has been provided more cheaply from underground accumulations of ‘natural gas,’ and the manufacture of ‘town gas’ has ceased. Is methane gas a renewable resource? After all, it can be made from water and hot carbon.
Costs of Oil and Gas Oil and gas costs benefit enormously from the prior energy input by the sun and the Earth. Our sun provided free energy to create organic matter; the Earth’s heat converted organic matter to petroleum; gravity (buoyancy) collected the petroleum into underground deposits of oil and gas. Creation of the Earth’s oil and gas energy is free. Locating the oil and gas and supplying the energy to convenient places, in a useful form, take enormous amounts of money. The energy rivals the agriculture business as the largest business in the world. We will never run out of oil and gas, as long as we can afford oil and gas. Every atom of hydrogen and carbon that was ever present on this Earth is still present and will remain on this Earth. It is child’s play for an able organic chemist to make methane from carbon and hot water or to produce oil and gas from carbon dioxide and water. These processes are well known but are much more expensive than simply extracting petroleum from the Earth. Since oil and gas can be made, worries should focus more on affordability of our future oil and gas and less about ‘running out of oil and gas.’
Petroleum Migration and Retention As petroleum and its associated gases form in the Earth, much of the oil and gas squirts out of the heated organic-rich layers into nearby reservoirs of porous limestones or sandstones, where the petroleum resides until located and produced. Everywhere oil and gas have been found, a look beneath them will recognize the source beds that once generated the petroleum. In the latter part of the twentieth century, geologist recognized that those source beds still contained within them large quantities of petroleum. It has been estimated that these ‘left-behind’ hydrocarbons in source beds are as abundant as all the oil and gas previously discovered. These hydrocarbons are tightly retained in the nanoporosity of the source rocks. To recover these tightly held oil and gas molecules, geologists typically need to drill 5–12 000 ft vertically and then turn the well trajectory horizontally for thousands of feet within the source rock layer. Then, the horizontal portion of the wellbore is injected with a high-pressure mixture of water and sand (hydrofrack) to create hairline fractures in the source rock layer. These created fractures provide flow paths between the nanopores containing petroleum and the horizontal wellbore. The fracture dimensions are controlled by the rock type and the amount of fluid and sand that is injected as a proppant; vertical fracture height is rarely greater than 300 ft; horizontal lengths can be thousands of feet. Within source rocks, the oil and gas molecules move very slowly, feet per year, and commercial recovery depends on the proximity of the newly created fractures to the oil and gas molecules tightly held within the rock. It is the ‘fracture-touched-volume’ that largely determines how much petroleum will be recovered.
Our Transportation Era Depends on the Petroleum Age The use of petroleum fuels has revolutionized transportation and has powered the development of our modern world society. For a million and a half years, humanity relied on muscle power, sometimes aggregated into clans, tribes, and kingships. Four or five thousand years ago, these agglomerations of man power became assisted by horsepower, ox power, and the mechanical advantages of the wheel and the lever. Only three hundred years ago, the development of the English steam engine allowed the Industrial Revolution, with engines powered by coal able to move huge quantities of goods by land and sea. Steam engines brought the benefits of transportation to areas touched by water and the narrow strips of land crossed by railroads.
Oil and Gas
3
Recognizing the limitations imposed by the energy density of coal, in 1915, Winston Churchill saw to the conversion of the British battle fleet from coal-fired steam to petroleum. He saw that much of the capacity of a battleship had been devoted to merely providing space for coal and the coal-handling crew. Petroleum fuels have an extraordinary advantage for personal transportation; they contain enormous energy for little weight. Gasoline, for example, has more energy content, by weight, than the powerful explosive TNT. With the ready accessibility of petroleum provided by the huge early oil fields in Baku, the United States, and the Middle East, the great advantages of energy-dense petroleum fuels became apparent, and our ‘transportation era’ began in the 1920s. Now, for the first time in the history of human society, people can move around the Earth, anytime, anyplace, nearly effortlessly. Petroleum, with its great energy content and low weight, allows rapid transportation of people and products cheaply over long distances. Efforts continue to be made to make transportation more efficient and less costly. These improvements come from vehicle aerodynamics, better engine design, better use of computers to monitor fuel usage, pairing of electric with gasoline engines, and a host of continuing design modifications. Since fuel economy is directly linked to the weight of an automobile, simply making cars 10% lighter improves their gasoline mileage 6–8%. Sometimes, suggestions are heard that we should alter our society to a petroleum and vehicle-free, Eden-like future. Think twice. Few of us would want to live, or could survive, with only those foods, products, and services available within our personal 10 mile day 1 walking range. For better, for worse, for at least another 50 years, our comfortable modern society is firmly coupled to oil and gas and the transportation era.