Glossary of Terms Applicable to Petroleum Geochemistry
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Glossary of Terms Applicable to Petroleum Geochemistry Frederik W. Vlierboom Occidental Petroleum Corporation BakersFeld, California, U.S.A. Note: Terms denoted by asterisks (*) are defined as entries to black streak. It is practically insoluble in carbon elsewhere in the Glossary. disulfide but partly soluble in turpentine; decom- poses prior to fusion. ABNORMAL PRESSURE: Any departure from hydro- static pressure. Overpressures generally range ALCOHOLS: A class of oxygen-containing organic above 12 kPa/m (0.53 psi/ft) and underpressures compounds having the structure R--OH, where R is range below 9.8 kPa/m (0.43psi/ft). a hydrocarbon radical. ABSORPTION: Penetration of a substance into the ALGAE: General biological term for a large group of body of another (includes dissolution). lower plants of single cell or cell aggregates, the majority living in water and containing chlorophyll* ACIDIFICATION: The process by which most of the (autotroph). In geology, generally designating all inorganic mineral matrix of a rock is destroyed with phytoplankton, e.g., diatoms,* dinoflagellates, and acid to release the insoluble organic matter (kerogen) seaweed. for further study. Hydrochloric acid (HC1) is used to destroy carbonates; hydrofluoric acid (HF) is used to ALGINITE: The coal maceral* of the exinite* group destroy the silicates. formed from algal remains. It is rare in humic coal* but is the principal constituent of the sapropelic* ACTIVATION ENERGY: The extra amount of energy a Boghead coal.* molecule must have before it can participate in a certain reaction (E in the Arrhenius equation*). ALICYCLIC: Referring to saturated cyclic hydrocar- bons. ACYCLIC: Having no rings. ALIPHATIC: Referring to all organic compounds char- ADSORPTION: The adhesion of a thin layer of acterized by open-chain structures. molecules of gases, liquids, or dissolved substances to the surface of solids. ALKANES: Saturated* hydrocarbons with either straight or branched (by not cyclic) chains of carbon AEROBE: A bacterium that utilizes molecular oxygen atoms. Alkanes have the general formula CnH2n+2, for its metabolic processes. e.g., phytane; C20H42. AEROBIC: A term applied to bacteria or other microor- n-ALKANES: Alkanes having a continuous, ganisms living or active only in the presence of unbranched, noncyclic chain of carbon atoms. Also molecular oxygen. called straight-chain alkanes or normal alkanes. AIR SPACE: Synonym for headspace.* ALKENE: An unsaturated hydrocarbon with at least one carbon-carbon double bond present. ALBERTITE: An asphaltite* with specific gravity of 1.07-1.10 and 2550% fixed carbon; having brilliant ALKYL: The adjective form of alkane, made by luster, conchoidal fracture, hardness 1-2, and brown dropping -ane and adding -yl. The same substitu- Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3837691/9781629811208_backmatter.pdf by guest on 24 September 2021 160 Vlierboom tion can be made to convert the names for specific API GRAVITY: An arbitrary scale known as the API alkanes (such as propane) to names for attached degree used for reporting the gravity or the density groups (propyl). of a petroleum product. The degree API is related to the specific gravity scale (6OoF/60"F)by the formula: ALLOCHTHONOUS: Originating elsewhere. Contrast with autochthonous.* 141.5 Degree API = -131.5 Specific gravity at 60°F ALPHA: A designation meaning that the indicated group in a polycyclic compound is attached below the plan of the beta ring. AROMATICS: Hydrocarbons derived from or related to benzene,' C6&. The benzene nucleus is the origin AMINO ACIDS: Amino acids are compounds having of a group of characteristic chemical properties both amino (-NH) and carboxylic acid (--COOH) known as the aromatic character of the molecule. groups. They occur in nature in the free state and in Only one hydrogen atom is bound to each carbon proteins: which are condensation products of amino atom of the ring; they may be replaced by various acids. Most natural acids can be represented by types of side chains. Typical aromatics are benzene, toluene, and xylene. The general structure is shown here. c 4 \ H-C C-H in which R represents an aliphatic, aromatic, or hetero- I II cyclic group. H-$, ,c-H AMORPHOUS ORGANIC MATTER: Kerogen F particles exhibiting no distinctive morphology. Some amorphous organic material is apparently of AROMATIZATION: The process of converting an algal origin; other examples represent highly alicyclic system to an aromatic one. Aromatization is degraded material of uncertain or perhaps eclectic an oxidative process that occurs during catagenesis origin. and metagenesis. AMU: See Atomic mass unit.* ARRHENIUS EQUATION: k = Ae-E/RT,where k is the rate constant, A is the frequency factor, E is the acti- ANAEROBE: A microorganism that functions under vation energy,* R is the universal gas constant, and T anaerobic conditions. is the absolute temperature. ANAEROBIC: A term applied to bacteria or other ASH: Inorganic residue obtained after combustion of microorganisms that live and grow in the absence of fuels or caustobiolites.* molecular oxygen. ASPHALT: A term applied to both native asphalt* and ANCHIMETAMORPHISM: Meaning high-age meta- pyrogenous asphalts (i.e., man-made asphalt from morphism and applied in those instances where thermal treatment of residual oils). They are reactions are interpreted as essentially governed by generally hard, dark-colored, nonvolatile materials time. It is not recommended to use this term in with low fusing points, low specific gravities connection with organic metamorphism.* (1.0-1.1), and low fixed-carbon values (4-20%). They are generally soluble in carbon disulfide, but are ANOXIC: Conditions where Q is absent or where the soluble only to the extend of 10-70°h in petroleum concentration of 02is very low (less than 0.1 mL/L naphtha. water). ASPHALTENES: The portion of petroleum and of ANTHRACITE: See Coal rank.* other bitumen that is soluble in solvents such as benzene, chloroform, and carbon disulfide (hence, ANTHRAXOLITE: A coal-like, lustrous, probably soluble or extractable bitumen), but which is highly coalified asphaltite* rich in carbon (8595%); insoluble in low-boiling (C3-7) alkanes. They hardness 3-4, specific gravity near 2; insoluble in generally contain more than 40 carbon atoms per organic solvents, practically infusible. molecule. Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3837691/9781629811208_backmatter.pdf by guest on 24 September 2021 Glossa y of Terms Applicable to Petroleum Geochemistry 161 ASPHALTIC CRUDE OILS: Crude oils with a high (cycloparaffins). A naphthenic-base crude contains content of asphaltenes, and often also of vanadium predominantly naphthene hydrocarbons. An and sulfur, and with API gravities below about 35. asphalt-base crude is one containing a relatively high They can be classified as asphaltic-paraffinic crudes proportion of nonhydrocarbon constituents such as or as asphaltic-naphtheniccrudes. nitrogen, sulfur, and oxygen compounds. The term aromatic base is not used because there are no oils ASPHALTIC ROCK: Predominantly sedimentary known to contain predominantly aromatic hydrocar- rocks containing in their porous space native bons. asphalt.* An asphaltic sandstone is very often, but incorrectly, called a tar sand; asphaltic limestone is BENZENE: See Aromatics.* generally, but inadequately, called bituminous limestone. BICYCLANES: Saturated compounds having two condensed rings in their molecules. ASPHALTITE: A group name embracing solid forms of native naphthabitumens7 which are harder and BIOCHEMICAL PHASE: See Organic metamorphism.' less fusible than true asphalt*. They are composed principally of hydrocarbons (substantially free from BIODEGRADATION: The alteration of organic matter, oxygenated bodies and crystallizable alkanes), either including oils, by microbes (bacteria); in the case of pure or associated with mineral matter. Asphaltites oils, usually producing poorer quality oils depleted are derived either from naphthabitumen* or in normal paraffins and with added sulfur. kerogen* and altered during or after migration.* They are usually found in veins and fissures. BIOGENIC: Formed biologically by an organism or According to their solubility in carbon disulfide and within an organism. benzene, they are divided into two groups: (1) largely soluble: gilsonite,* glance pitch,* and BIOGENIC GAS: (1) Natural gas, virtually all methane, grahamite*; and (2) largely insoluble: elaterite,* produced by microbes (bacteria) in shallow rocks. wurtzilite,* albertite,* impsonite,* and anthraxolite.* Biogenic methane can be recognized by its relative It is possible that elaterite and wurtzilite represent abundance of the 12C isotope; also called marsh gas. immature kerogenous material; if so, they should be Hydrogen sulfide is also a biogenic gas. (2) Dry gas treated as sapropelites*. Albertite, impsonite, and (virtually pure methane) formed by anaerobic anthraxolite may be asphaltites with a high microorganisms called methanogens. maturity* acquired after migration. BIOLOGICAL MARKERS: Organic compounds whose ASSAY: See Fischer assay.* carbon structure, or skeleton, is formed by living organisms and is sufficiently stable to be recognized ATOMIC MASS UNIT (AMU): A mass approximately in crude oil or the organic matter of ancient equal to that of one neutron, used in describing the sediments. Typical markers are the porphyrins, masses of atoms, molecules, or ions. pristane, phytane, steranes, carotenes, and penta-