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Organic-rich sedimentary rocks
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<p>Organic-rich sedimentary rocks are a specific type of <a href="/facts/Sedimentary_rock/HQDCjrco">sedimentary rock</a> that contains significant amounts (>3%) of <a href="/facts/Organic_matter/t17tVCvk">organic</a> carbon. The most common types include <a href="/facts/Coal/83kV3qxg">coal</a>, <a href="/facts/Lignite/pGFaDtFa">lignite</a>, <a href="/facts/Oil_shale/WSREUH8t">oil shale</a>, or black <a href="/facts/Shale/bsIhqY5F">shale</a>. The organic material may be disseminated throughout the rock giving it a uniform dark color, and/or it may be present as discrete occurrences of <a href="/facts/Tar/E4tVbqyq">tar</a>, <a href="/facts/Bitumen/tW6EqphW">bitumen</a>, asphalt, <a href="/facts/Petroleum/IQV0bHVd">petroleum</a>, <a href="/facts/Coal/83kV3qxg">coal</a> or <a href="/facts/Carbon/ukrgQexo">carbonaceous</a> material. Organic-rich sedimentary rocks may act as <a href="/facts/Source_rock/4GHJwIYJ">source rocks</a> which generate hydrocarbons that accumulate in other sedimentary "reservoir" rocks (see <a href="/facts/Oil_sands/ewYn43lb">oil sands</a> and <a href="/facts/Petroleum_geology/jMPyPVmN">petroleum geology</a>). Potential source rocks are any type of sedimentary rock that the ability to dispel available carbon from within it (<a href="/facts/Limestone/8ntvtFnR">limestone</a> is a classic example of a source rock). Good reservoir rocks are any sedimentary rock that has high pore-space availability. This allows the hydrocarbons to accumulate within the rock and be stored for long periods of time (a <a href="/facts/Sandstone/RP8B6fqL">sandstone</a> commonly makes a good source rock). Highly permeable reservoir rocks are also of interest to industry professionals, as they allow for the easy extraction of the hydrocarbons within. The hydrocarbon reservoir system is not complete however without a "cap rock". Cap rocks are rock units which have very low porosity and permeability, which trap the hydrocarbons within the units below as they try to migrate upwards. </p>