How exactly is petroleum formed?

i’ve been looking around and i know about coal and all that stuff, but is there any difference in the formation of petroleum and coal, besides their height in the earth’s crust?

4 Responses to “How exactly is petroleum formed?”

  1. carbonates Says:

    First of all, petroleum and natural gas share very little in common with the formation of coal. Yes, both processes involve burial, preservation of organic matter, and pressure and heat, but they are very different. Coal is formed from plants that are preserved in shallow waters under anoxic water conditions. Burial compaction can reduce anywhere from 10 ft to 30 ft of plant material into 1 ft of bituminous coal. Oil and natural gas are deposited in dispersed conditions, often as little as 1% of the rock. Natural gas is often formed by bacteria that live in the subsurface.

    Oil and natural gas are formed by the deposition and preservation of the remains of plankton, both phytoplankton (microscopic plants) and zooplankton (microscopic animals). Few macro-size organisms make up the source for oil and natural gas. Most planktonic sources of oil were marine in origin. Some were lacustrine (fresh water) and these often have some input from woody sources.

    Fine grained sediments that eventually become shale are a common source rock for oil and gas. Carbonate rocks often source oils as well where the rock contains high volumes of organic matter left behind by algae and other marine organisms that either helped build the carbonate rocks (limestone and dolomite) or lived in the same environment. If the bottom waters had conditions of low oxygen or no oxygen, which is a common thing in the world’s oceans, the organic remains of these microscopic organisms are preserved and not eaten or oxidized. We can see evidence of these organisms in things called biomarkers that can be seen with a microscope in crude oil as well as remaining compounds formed by living organisms that are found in crude oil. As time goes by, these sediments are buried by depositional processes such as river deltas until they begin to reach depths where geothermal heat from the Earth’s interior begins to warm them. Once the temperature reaches a level of around 100 degrees C (212 F.) the organic remains convert to oil. This is the temperature at about the typical peak of the oil generation window. As temperatures rise to nearly 140 degrees C, the organic material begins to form natural gas, and at those levels some of the oil will convert to natural gas. At even higher temperatures it becomes "dry gas" meaning the oil component has completely cracked to natural gas. Some natural gas is actually formed by bacteria, so catagenic (heat-formed) natural gas is only part of the source.

    The process is not slow, at least not in geologic time. Deposits of oil have been found that are less than 1,000 years old in areas where there is a high geothermal heat gradient. This means that the commonly held conception that it takes millions of years to form oil is actually misrepresentation of reality. The process that takes millions of years is most often the burial of the sediment to depths where it begins to "cook" to oil. Biogenic natural gas can be formed almost as fast as it comes out of the well in some cases, but even where it is in an accumulation is often rather recently formed.

    Once oil and natural gas has formed it may ‘migrate’, or move out of the rock where it was deposited and migrate upward or laterally until it reaches a rock where there is open space known as porosity, and some sort of boundary above it that traps it, and prevents it from continuing its upward migration. If there is no trap, the oil and natural gas will make its way to the surface. More oil and gas has migrated completely out of the ground and evaporated into the atmosphere over geologic history than all the oil and gas that has been trapped. Oil seeps are common in many parts of the world and evidence of huge natural oil spills can be found in the geologic record. Oil and natural gas accumulations can be detected with chemical analysis of the surface soil, as some oil and natural gas almost always comes to the surface.

    One change in geologic thinking that has come about in the past decade is changing the amount of oil and natural gas that we believe exists in the world very dramatically. It is slowly being realized that much of the oil and gas never migrated out of the source rocks where it was created. With new drilling techniques created in the past decade, it has been proven that huge amounts of natural gas and oil are remaining in rocks that ten or twenty years ago were not believed to have significance. This is the gas shale revolution. Twice the energy equivalent of all the oil in Saudi Arabia has been found within gas shales in the United States in only the past five to ten years. The implications of this for oil are just beginning to be understood.

  2. Celaw Joseph Says:

    petroleum is formed by processes similar to those which yielded coal but it is more of sea animals than plants

  3. QueryJ Says:

    Answers found on Yahoo Answers:

    Coal contains larger hydrocarbon molecules on the average) than does petroleum. Coal contains more elemental carbon. For a given amount of energy produced, coal puts out more carbon dioxide.

    Coal, Oil or Petroleum, and Natural Gas are considered the three, basic fossil fuels. Carbon in it’s pure form is coal, and petroleum and natural gas are hydrocarbons formed during the decaying process. The only difference between natural gas and petroleum is their relative sizes. Since the natural gasses tend to be much smaller molecules, they are lighter, and exist in a gaseous state at room temperature, whereas petroleum molecules are heavier, and are liquid at room temperature.

    Answers found on EHow:

    Natural Gas
    •Natural gas accounts for almost a quarter of the energy used in the United States, according to the Energy Information Administration. Natural gas in its purest form is pure methane but before it is refined, it also contains varying amount of ethane, propane, butane and carbon dioxide. When refined, it is colorless and odorless but can be burned to release large amounts of energy.
    •Coal also accounts for about 23 percent of the energy usage in the United States. Coal releases large amounts of energy when it is burned because of the density of hydrocarbons in the material. Coal is formed by dead plants being put under significant pressure and temperature for millions of years. There are four grades of coal: lignite, subbituminous, bituminous coal and anthracite. Bituminous coal is the best for releasing energy and is the most commonly mined type of coal in the United States.
    •Petroleum is used to generate about 40 percent of energy in the United States. Petroleum is formed from the compression of animal and plant remains over millions of years. Petroleum has to be drilled for because it is usually located deep below the earth’s surface and is then refined to produce a number of different products including gasoline, heavy fuel oil and diesel fuel.

  4. Raheem Taylor Says:

    From decayed plant/animal material