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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Source rock</span></span>

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<p>In <a href="Petroleum_geology" title="Petroleum geology">petroleum geology</a>, <b>source rock</b> is a sedimentary rock which has generated <a href="Hydrocarbons" class="mw-redirect" title="Hydrocarbons">hydrocarbons</a> or which has the potential to generate hydrocarbons.<sup id="cite_ref-:0_1-0" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Source rocks are one of the necessary elements of a working <a href="Petroleum_system" class="mw-redirect" title="Petroleum system">petroleum system</a>. They are organic-rich sediments that may have been deposited in a variety of <a href="Sedimentary_depositional_environment" class="mw-redirect" title="Sedimentary depositional environment">environments</a> including deep water <a href="Marine_biology" title="Marine biology">marine</a>, <a href="Lake" title="Lake">lacustrine</a> and <a href="River_delta" title="River delta">deltaic</a>. <a href="Oil_shale" title="Oil shale">Oil shale</a> can be regarded as an organic-rich but immature source rock from which little or no oil has been generated and expelled.<sup id="cite_ref-Hyne_2-0" class="reference"><a href="#cite_note-Hyne-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> Subsurface source rock mapping methodologies make it possible to identify likely zones of petroleum occurrence in sedimentary basins as well as <a href="Shale_gas" title="Shale gas">shale gas</a> plays.

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<div class="mw-heading mw-heading2"><h2 id="Types_of_source_rocks">Types of source rocks</h2></div>

<p>Source rocks are classified from the types of <a href="Kerogen" title="Kerogen">kerogen</a> that they contain, which in turn governs the type of hydrocarbons that will be generated:<sup id="cite_ref-:0_1-1" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

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<ul><li>Type I source rocks are formed from algal remains deposited under <a href="Anoxic_waters" title="Anoxic waters">anoxic</a> conditions in deep lakes: they tend to generate waxy <a href="Petroleum" title="Petroleum">crude oils</a> when submitted to <a href="Thermal_stress" title="Thermal stress">thermal stress</a> during deep burial.</li>

<li>Type II source rocks are formed from marine <a href="Plankton" title="Plankton">planktonic</a> and bacterial remains preserved under anoxic conditions in marine environments: they produce both oil and gas when <a href="Thermal_cracking" class="mw-redirect" title="Thermal cracking">thermally cracked</a> during deep burial.</li>

<li>Type III source rocks are formed from terrestrial plant material that has been decomposed by <a href="Bacteria" title="Bacteria">bacteria</a> and <a href="Fungi" class="mw-redirect" title="Fungi">fungi</a> under oxic or sub-oxic conditions: they tend to generate mostly gas with associated light oils when thermally cracked during deep burial. Most coals and coaly shales are generally Type III source rocks.</li></ul>

<div class="mw-heading mw-heading2"><h2 id="Maturation_and_expulsion">Maturation and expulsion</h2></div>

<p>With increasing depth of burial by sediments or dead organic matters and increase in temperature, the kerogen within the rock begins to break down. This <a href="Thermal_decomposition" title="Thermal decomposition">thermal degradation</a> or <a href="Cracking_(chemistry)" title="Cracking (chemistry)">cracking</a> releases shorter chain hydrocarbons from the original large and complex <a href="Molecules" class="mw-redirect" title="Molecules">molecules</a> occurring in the kerogen.<sup id="cite_ref-:0_1-2" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p><p>The hydrocarbons generated from thermally mature source rock are first expelled, along with other pore fluids, due to the effects of internal source rock over-pressuring caused by hydrocarbon generation as well as by <a href="Compaction_(geology)" title="Compaction (geology)">compaction</a>. Once released into porous and permeable <a href="Carrier_(disambiguation)" class="mw-redirect mw-disambig" title="Carrier (disambiguation)">carrier</a> beds or into <a href="Fault_(geology)" title="Fault (geology)">faults planes</a>, oil and gas then move upwards towards the surface in an overall buoyancy-driven process known as <i>secondary migration</i>.

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<div class="mw-heading mw-heading2"><h2 id="Mapping_source_rocks_in_sedimentary_basins">Mapping source rocks in sedimentary basins</h2></div>

<p>Areas underlain by thermally mature generative source rocks in a <a href="Sedimentary_basin" title="Sedimentary basin">sedimentary basin</a> are called <i>generative basins or depressions</i> or else <i>hydrocarbon kitchens</i>. Mapping those regional oil and gas generative "hydrocarbon kitchens" is feasible by integrating the existing source rock data into seismic depth maps that structurally follow the source horizon(s). It has been statistically observed at a world scale<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> that zones of high success ratios in finding oil and gas generally correlate in most basin types (such as intracratonic or <a href="Rift" title="Rift">rift basins</a>) with the mapped "generative depressions". Cases of long distance oil migration into shallow traps away from the "generative depressions" are usually found in <a href="Foreland_basin" title="Foreland basin">foreland basins</a>.

</p><p>Besides pointing to zones of high petroleum potential within a sedimentary basin, subsurface mapping of a source rock's degree of <a href="Maturity_(geology)" title="Maturity (geology)">thermal maturity</a> is also the basic tool to identify and broadly delineate <a href="Shale_gas" title="Shale gas">shale gas</a> plays.

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<div class="mw-heading mw-heading2"><h2 id="World_class_source_rocks">World class source rocks</h2></div>

<p>Certain source rocks are referred to as "world class", meaning that they are not only of very high quality but are also thick and of wide geographical distribution. Examples include:

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<ul><li><a href="Middle_Devonian" title="Middle Devonian">Middle Devonian</a> to <a href="Mississippian_(geology)" title="Mississippian (geology)">lower Mississippian</a> widespread marine <a href="Hypoxia_(environmental)" title="Hypoxia (environmental)">anoxic</a> oil and gas source beds in the <a href="Mid-Continent" class="mw-redirect" title="Mid-Continent">Mid-Continent</a> and <a href="Appalachia" title="Appalachia">Appalachia</a> areas of North America: (e.g. the <a href="Bakken_Formation" class="mw-redirect" title="Bakken Formation">Bakken Formation</a> of the <a href="Williston_Basin" title="Williston Basin">Williston Basin</a>, the <a href="Antrim_Shale" title="Antrim Shale">Antrim Shale</a> of the <a href="Michigan_Basin" title="Michigan Basin">Michigan Basin</a>, the <a href="Marcellus_Shale" class="mw-redirect" title="Marcellus Shale">Marcellus Shale</a> of the <a href="Appalachian_Basin" class="mw-redirect" title="Appalachian Basin">Appalachian Basin</a>).</li>

<li><a href="Kimmeridge_Clay" title="Kimmeridge Clay">Kimmeridge Clay</a> – This <a href="Late_Jurassic" title="Late Jurassic">upper Jurassic</a> marine <a href="Mudstone" title="Mudstone">mudstone</a> or its stratigraphic equivalents generated most of the oil found in the <a href="North_Sea" title="North Sea">North Sea</a> and the <a href="Norwegian_Sea" title="Norwegian Sea">Norwegian Sea</a>.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup></li>

<li>La Luna Formation – This <a href="Late_Cretaceous" title="Late Cretaceous">Late Cretaceous</a> (mostly <a href="Turonian" title="Turonian">Turonian</a>) formation generated most of the oil in northwestern <a href="Venezuela" title="Venezuela">Venezuela</a>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></li>

<li><a href="Late_Carboniferous" class="mw-redirect" title="Late Carboniferous">Late Carboniferous</a> <a href="Coal" title="Coal">coals</a> – Coals of this age generated most of the gas in the southern North Sea, the Netherlands Basin and the northwest German Basin.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup></li>

<li>Hanifa Formation – This upper Jurassic laminated carbonate-rich unit has sourced the oil in the giant <a href="Ghawar" class="mw-redirect" title="Ghawar">Ghawar</a> field in <a href="Saudi_Arabia" title="Saudi Arabia">Saudi Arabia</a>.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup></li></ul>

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<ul><li><a href="Basin_modelling" title="Basin modelling">Basin modelling</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFFerridayMontenari2016" class="citation journal cs1">Ferriday, Tim; Montenari, Michael (2016). <span class="id-lock-subscription" title="Paid subscription required"><a rel="nofollow" class="external text" href="https://www.sciencedirect.com/science/article/abs/pii/S2468517816300053">"Chemostratigraphy and Chemofacies of Source Rock Analogues: A High-Resolution Analysis of Black Shale Successions from the Lower Silurian Formigoso Formation (Cantabrian Mountains, NW Spain)"</a></span>. <i>Stratigraphy & Timescales</i>. <b>1</b>: <span class="nowrap">123–</span>255. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1016%2Fbs.sats.2016.10.004">10.1016/bs.sats.2016.10.004</a> – via <a href="Elsevier_Science_Direct" class="mw-redirect" title="Elsevier Science Direct">Elsevier Science Direct</a>.</cite></span>

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<li id="cite_note-Hyne-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-Hyne_2-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFHyne_N.J.2001" class="citation book cs1">Hyne N.J. (2001). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=D4I-G0DcTcUC&dq=oil+shale+immature+source&pg=PA164"><i>Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production</i></a>. <a href="PennWell_Books" class="mw-redirect" title="PennWell Books">PennWell Books</a>. p. 164. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9780878148233</bdi>.</cite></span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text">Gerard Demaison: "The Generative Basin Concept" in: American Association of Petroleum Geologists (AAPG) Memoir #35 : "Petroleum Geochemistry and Basin Evaluation", 1984, Edited by Gerard Demaison and Roelof J. Murris, <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-89181-312-8</bdi></span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://pubs.usgs.gov/bul/2204/c/pdf/B2204C.pdf">Kimmeridgian Shales Total Petroleum System of the North Sea Graben Province – USGS Bulletin</a></span>

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<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.doi.org/10.1111/j.1747-5457.2000.tb00488.x">James, K.H. 2000. The Venezuelan hydrocarbon habitat, Part 2: hydrocarbon occurrences and generated-accumulated volumes. Journal of Petroleum Geology, 23, 133–164</a></span>

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<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://pubs.usgs.gov/bul/b2211/b2211.html">Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary – USGS Bulletin</a></span>

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<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://pubs.usgs.gov/bul/b2202-h/b2202-h-508.pdf">Total Petroleum Systems of the Paleozoic and Jurassic, Greater Ghawar Uplift and Adjoining Provinces of Central Saudi Arabia and Northern Arabian-Persian Gulf – USGS Bulletin</a></span>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="https://portal.ga.gov.au/persona/sra">Australian Source Rock and Fluid Atlas</a></li>

<li><a rel="nofollow" class="external text" href="http://www.aapg.org/science/discipline/geochemistry-and-basin-modeling/source-rock#4339479-new-publications">Source rock publications</a></li></ul></div><div><div class="zim-footer">

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