GEOL 110 1st Edition Lecture 4Outline of Last Lecture I. Fossil FuelsII. SubsidenceIII. CoalIV. Why We Call Them Fossil FuelsV. Change in Character of CoalVI. Limitations of Coal UseVII. Environmental Impacts of Coal UseVIII. Changes in Coal ProductionOutline of Current Lecture I. Oil ReservesII. Conditions Appropriate for Fossil Fuel FormationIII. Hydrocarbon GenerationIV. Creation of an Oil or Gas ReserveV. After FormationVI. How is Oil Found?VII. Natural GasVIII. Petroleum UsesCurrent LectureI. Oil ReservesA. Definition: an estimate of that part of a total resource that can be extracted and marketed at a profit. They are therefore both economic and political terms.1. Estimates of reserves may change dramatically in response to evolving technologies and economic conditionsB. North America has approximately 6% of the world’s proven reserves of oil, similarto the combined reserves of the Soviet Union, while the Middle east holds approximately 65% of the world’s oil reservesC. Key players in the oil debate1. Geologists: those who think they know where the oil is2. Economists: those who think they know what the price of oil will be in thefutureII. Conditions Appropriate for Fossil Fuel FormationA. Biologically productive environment producing large quantities of organic material – typically shallow water continental marginsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.B. Limited supply of oxygen to bottom waters in contact with sediment limits the biological activity that would act to decompose dead organic materialC. Rapid burial of un-decomposed organic material provides for efficient capture of the organic material in sedimentaty deposits. Burial in sedimentary basins causesthe organic material to be “cooked” to different degrees, thereby producing different type of hydrocarbon materialsD. While coal formation usually involves sedimentary deposits that are terrestrial (formed on land), oil and gas formation is usually in marine sedimentary deposits. Burial and heat in the marine environments result in a progressive change in the organic material, and these changes occur in 3 steps (diagensis, catagenesis, metagenesis)1. Disgenesis: occurs at the surface or under shallow burial depths, and at temperatures generally less than 50 degrees C. Biogenic methane (aka “swamp gas”) forms. The stuff formed here isn’t very valuable.2. Catagenesis: occurs deeper (3-5k) and warmer (80-150 degrees C), so the water is forced out of the rock. The organic material is cooked into a mixture of kerogen (the non-reactive/insoluble part of the organic material) and oil. The breakdown of kerogen results in the formation of natural gas.3. Metagenesis: occurs a depths greater than 5k, and temperatures higher than 150 degrees C. These are essentially the conditions of early metamorphism. Under these conditions, production of natural gas continues from the breakdown of kerogen. Beyond about 300° the remaining kerogen becomes graphite and the formation of natural gas ends. E. Source of carbon for oil and gas formation is primarily the decomposition and ‘cooking’ of plankton and other microorganisms. ‘Cooking’ that happens at higher temperatures results in natural gas, and lower temperatures produces oil. III. Hydrocarbon GenerationA. In order for hydrocarbons to accumulate in a reservoir, there must be a seal to prevent the fluids from flowing back out.B. A seal is rock with low permeability, like shale, salt, and unfractured limestone. Sometimes faults can create seals.IV. Creation of an Oil or Gas Reserve (requires 4 features)A. Source rock: where the hydrocarbons are created; usually a black shale that contains a large quantity of organic materialB. A Migration pathway: something that allows the hydrocarbons to flow upward through the rock formations (pores/fractures)C. Reservoir rock: typically sandstones that are highly porous or fractured (both porous and permeable), so it can hold a large quantity of oil.D. Trap/Seal rocks: keeps the oil or gas in the reservoir. V. After FormationA. After the formation, petroleum is mobile (a liquid or gas), so it must be collected in geologic “traps”1. Anticline trap: seal rock over reservoir rocks2. Fault trap: same as anticline, but with a fault line splitting the sides of sealrock3. Stratigraphic trap: similar to the above, but much smallerB. However, up to 90% of wells are dry and contain little to no oil or gasVI. How is oil found?A. Using sound waves that are drilled into the ground and then picked up by receiversB. Seismic imaging: the exploration for oil and gas done from a ship, or on landVII. Natural GasA. Virtually all geologic systems that produce oil also produce natural gasB. Advantages:1. Minimal processing, burns more cleanly, provides more energy, there’s already extensive infrastructure already in place to handle gas, new technologies might make gas a transportation fuel, extensive reserve gas through frackingC. Disadvantages: methane can leak from pipelines, and it is explosive which can be dangerousVIII. Petroleum UsesA. Petroleum forms from plankton that accumulates in a oxygen poor depositional environment.B. Nearly everything is made from oil, most machinery and nearly all transpotation systems use