Misplaced Pages

#251748

62-560: The upper Akata Formation is cited to be a primary source rock, providing Type II/III kerogen , and a potential target in deep water offshore and possibly beneath currently producing intervals onshore. The clays are typically over-pressured due to the absence of enough porous sediments during compaction and are about 9,000 feet vertical depth below mean sea level. The Agbada Formation has intervals that contain organic-carbon contents sufficient to be considered good source rocks. The intervals, however, rarely reach thickness sufficient to produce

124-419: A molality , the proportionality constant is known as the cryoscopic constant ( K f ) and is characteristic for each solvent. If w represents the mass fraction of the solute in solution, and assuming no dissociation of the solute, the molar mass is given by The boiling point of a solution of an involatile solute is higher than that of the pure solvent , and the boiling-point elevation ( Δ T )

186-409: A compound in g/mol thus is equal to the mass of this number of molecules of the compound in grams. The molar mass of atoms of an element is given by the relative atomic mass of the element multiplied by the molar mass constant , M u  ≈  1.000 000 × 10  kg/mol = 1 g/mol. For normal samples from earth with typical isotope composition, the atomic weight can be approximated by

248-408: A particular rock formation depends on the type of organic material that was originally present. Kerogen can be classified by these origins: lacustrine (e.g., algal ), marine (e.g., planktonic ), and terrestrial (e.g., pollen and spores ). The type of kerogen depends also on the degree of heat and pressure it has been subjected to, and the length of time the geological processes ran. The result

310-420: A precision of a few parts per million . This is accurate enough to directly determine the chemical formula of a molecule. The term formula weight has a specific meaning when used in the context of DNA synthesis: whereas an individual phosphoramidite nucleobase to be added to a DNA polymer has protecting groups and has its molecular weight quoted including these groups, the amount of molecular weight that

372-475: A revival of research into the composition, structure, and properties of kerogen. Many studies have documented dramatic and systematic changes in kerogen composition across the range of thermal maturity relevant to the oil and gas industry. Analyses of kerogen are generally performed on samples prepared by acid demineralization with critical point drying , which isolates kerogen from the rock matrix without altering its chemical composition or microstructure. Kerogen

434-414: A sample which has been distilled will be enriched in the lighter isotopes of all the elements present. This complicates the calculation of the standard uncertainty in the molar mass. A useful convention for normal laboratory work is to quote molar masses to two decimal places for all calculations. This is more accurate than is usually required, but avoids rounding errors during calculations. When

496-523: A shortening of carbon-carbon distances in covalently bonded carbons (related to the transition from primarily aliphatic to primarily aromatic bonding) but a lengthening of carbon-carbon distances in carbons at greater bond separations (related to the formation of kerogen-hosted porosity). This evolution is attributed to the formation of kerogen-hosted pores left behind as segments of the kerogen molecule are cracked off during thermal maturation. These changes in composition and microstructure result in changes in

558-514: A specific chemical formula . Upon heating, kerogen converts in part to liquid and gaseous hydrocarbons. Petroleum and natural gas form from kerogen. The name "kerogen" was introduced by the Scottish organic chemist Alexander Crum Brown in 1906, derived from the Greek for "wax birth" (Greek: κηρός "wax" and -gen, γένεση "birth"). The increased production of hydrocarbons from shale has motivated

620-554: A world-classoil province and are immature in various parts of the delta. The Akata shale is present in large volumes beneath the Agbada Formation and is at least volumetrically sufficient to generate enough oil for a world class oil province such as the Niger Delta. Based on organic-matter content and type. This Nigeria location article is a stub . You can help Misplaced Pages by expanding it . Kerogen Kerogen

682-555: Is Raman spectroscopy . Raman scattering is characteristic of, and can be used to identify, specific vibrational modes and symmetries of molecular bonds. The first-order Raman spectra of kerogen comprises two principal peaks; a so-called G band ("graphitic") attributed to in-plane vibrational modes of well-ordered sp carbon and a so-called D band ("disordered") from symmetric vibrational modes of sp carbon associated with lattice defects and discontinuities. The relative spectral position (Raman shift) and intensity of these carbon species

SECTION 10

#1732872727252

744-400: Is a bulk, not molecular, property of a substance. The molar mass is an average of many instances of the compound, which often vary in mass due to the presence of isotopes . Most commonly, the molar mass is computed from the standard atomic weights and is thus a terrestrial average and a function of the relative abundance of the isotopes of the constituent atoms on Earth. The molar mass

806-506: Is a complex mixture of organic chemical compounds that make up the most abundant fraction of organic matter in sedimentary rocks . As kerogen is a mixture of organic materials, it is not defined by a single chemical formula. Its chemical composition varies substantially between and even within sedimentary formations. For example, kerogen from the Green River Formation oil shale deposit of western North America contains elements in

868-400: Is appropriate for converting between the mass of a substance and the amount of a substance for bulk quantities. The molecular mass (for molecular compounds) and formula mass (for non-molecular compounds, such as ionic salts ) are commonly used as synonyms of molar mass, differing only in units ( daltons vs g/mol); however, the most authoritative sources define it differently. The difference

930-451: Is distinct but related to the molar mass, which is a measure of the average molecular mass of all the molecules in a sample and is usually the more appropriate measure when dealing with macroscopic (weigh-able) quantities of a substance. Molecular masses are calculated from the atomic masses of each nuclide , while molar masses are calculated from the standard atomic weights of each element . The standard atomic weight takes into account

992-403: Is formed during sedimentary diagenesis from the degradation of living matter. The original organic matter can comprise lacustrine and marine algae and plankton and terrestrial higher-order plants. During diagenesis, large biopolymers from, e.g., proteins , lipids , and carbohydrates in the original organic matter, decompose partially or completely. This breakdown process can be viewed as

1054-662: Is generally higher than in other kerogen types, and sulfur is found in substantial amounts in the associated bitumen. Although pyrolysis of type II kerogen yields less oil than type I, the amount yielded is still sufficient for type II-bearing sedimentary deposits to be petroleum source rocks. Similar to type II but with high sulfur content. Type III kerogens are characterized by low initial H/C ratios and high initial O/C ratios. Type III kerogens are derived from terrestrial plant matter, specifically from precursor compounds including cellulose , lignin (a non-carbohydrate polymer formed from phenyl-propane units that binds

1116-405: Is given by Combining these two equations gives an expression for the molar mass in terms of the vapour density for conditions of known pressure and temperature : The freezing point of a solution is lower than that of the pure solvent , and the freezing-point depression ( Δ T ) is directly proportional to the amount concentration for dilute solutions. When the composition is expressed as

1178-436: Is limited by the knowledge of the isotopic distribution of the element. If a more accurate value of the molar mass is required, it is necessary to determine the isotopic distribution of the sample in question, which may be different from the standard distribution used to calculate the standard atomic mass. The isotopic distributions of the different elements in a sample are not necessarily independent of one another: for example,

1240-461: Is particularly important in polymer science , where there is usually a molar mass distribution of non-uniform polymers so that different polymer molecules contain different numbers of monomer units. The average molar mass of mixtures M ¯ {\displaystyle {\overline {M}}} can be calculated from the mole fractions x i of the components and their molar masses M i : It can also be calculated from

1302-740: Is sensitive to sulfur-containing functional groups such as sulfides , thiophenes , and sulfoxides . Sulfur content in kerogen generally decreases with thermal maturity, and sulfur speciation includes a mix of sulfides and thiophenes at low thermal maturities and is further enriched in thiophenes at high maturities. Overall, changes in kerogen composition with respect to heteroatom chemistry occur predominantly at low thermal maturities (bitumen and oil windows), while changes with respect to carbon chemistry occur predominantly at high thermal maturities (oil and gas windows). The microstructure of kerogen also evolves during thermal maturation, as has been inferred by scanning electron microscopy (SEM) imaging showing

SECTION 20

#1732872727252

1364-412: Is shown to correlate to thermal maturity, with kerogens of higher thermal maturity having higher abundance of graphitic/ordered aromatic carbons. Complementary and consistent results have been obtained with infrared (IR) spectroscopy , which show that kerogen has higher fraction of aromatic carbon and shorter lengths of aliphatic chains at higher thermal maturities. These results can be explained by

1426-466: Is solid, insoluble organic matter in sedimentary rocks . It consists of a variety of organic materials, including dead plants, algae, and other microorganisms, that have been compressed and heated by geological processes. All the kerogen on earth is estimated to contain 10 tons of carbon. This makes it the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. The type of kerogen present in

1488-441: Is that a complex mixture of organic compounds reside in sedimentary rocks, serving as the precursor for the formation of hydrocarbons such as oil and gas. In short, kerogen amounts to fossilized organic matter that has been buried and subjected to high temperatures and pressures over millions of years, resulting in various chemical reactions and transformations. Kerogen is insoluble in normal organic solvents and it does not have

1550-498: Is that molecular mass is the mass of one specific particle or molecule, while the molar mass is an average over many particles or molecules. The molar mass is an intensive property of the substance, that does not depend on the size of the sample. In the International System of Units (SI), the coherent unit of molar mass is kg/mol. However, for historical reasons, molar masses are almost always expressed in g/mol. The mole

1612-538: Is the mass of one molecule (of any single isotopic composition), and to the atomic mass , which is the mass of one atom (of any single isotope). The dalton , symbol Da, is also sometimes used as a unit of molar mass, especially in biochemistry , with the definition 1 Da = 1 g/mol, despite the fact that it is strictly a unit of mass (1 Da = 1 u = 1.660 539 068 92 (52) × 10  kg , as of 2022 CODATA recommended values). Obsolete terms for molar mass include gram atomic mass for

1674-397: Is the molar mass of the atoms multiplied by the number of atoms in each molecule: The molar mass of a compound is given by the sum of the relative atomic mass A r of the atoms which form the compound multiplied by the molar mass constant M u ≈ 1  g/mol {\displaystyle M_{u}\approx 1{\text{ g/mol}}} : Here, M r

1736-1312: Is the relative molar mass, also called formula weight. For normal samples from earth with typical isotope composition, the standard atomic weight or the conventional atomic weight can be used as an approximation of the relative atomic mass of the sample. Examples are: M ( NaCl ) = [ 22.98976928 ( 2 ) + 35.453 ( 2 ) ] × 1  g/mol = 58.443 ( 2 )  g/mol M ( C 12 H 22 O 11 ) = [ 12 × 12.0107 ( 8 ) + 22 × 1.00794 ( 7 ) + 11 × 15.9994 ( 3 ) ] × 1  g/mol = 342.297 ( 14 )  g/mol {\displaystyle {\begin{array}{ll}M({\ce {NaCl}})&={\bigl [}22.98976928(2)+35.453(2){\bigr ]}\times 1{\text{ g/mol}}\\&=58.443(2){\text{ g/mol}}\\[4pt]M({\ce {C12H22O11}})&={\bigl [}12\times 12.0107(8)+22\times 1.00794(7)+11\times 15.9994(3){\bigr ]}\times 1{\text{ g/mol}}\\&=342.297(14){\text{ g/mol}}\end{array}}} An average molar mass may be defined for mixtures of compounds. This

1798-737: Is thought to have formed the terrestrial planets . Kerogenous materials have been detected also in interstellar clouds and dust around stars . The Curiosity rover has detected organic deposits similar to kerogen in mudstone samples in Gale Crater on Mars using a revised drilling technique. The presence of benzene and propane also indicates the possible presence of kerogen-like materials, from which hydrocarbons are derived. Helgeson, H.C.et al. (2009). "A chemical and thermodynamic model of oil generation in hydrocarbon source rocks". Geochim. Cosmochim. Acta. 73 , 594–695. Marakushev, S.A.; Belonogova, O.V. (2021), "An inorganic origin of

1860-454: Is ultimately added by this nucleobase to a DNA polymer is referred to as the nucleobase's formula weight (i.e., the molecular weight of this nucleobase within the DNA polymer, minus protecting groups). The precision to which a molar mass is known depends on the precision of the atomic masses from which it was calculated (and very slightly on the value of the molar mass constant , which depends on

1922-487: The isotopic distribution of the element in a given sample (usually assumed to be "normal"). For example, water has a molar mass of 18.0153(3) g/mol , but individual water molecules have molecular masses which range between 18.010 564 6863 (15) Da ( H 2 O ) and 22.027 7364 (9) Da ( H 2 O ). The distinction between molar mass and molecular mass is important because relative molecular masses can be measured directly by mass spectrometry , often to

Akata Formation - Misplaced Pages Continue

1984-411: The mass fractions w i of the components: As an example, the average molar mass of dry air is 28.96 g/mol. Molar mass is closely related to the relative molar mass ( M r ) of a compound and to the standard atomic weights of its constituent elements. However, it should be distinguished from the molecular mass (which is confusingly also sometimes known as molecular weight), which

2046-422: The relative molar mass ( M r ). This is a dimensionless quantity (i.e., a pure number, without units) equal to the molar mass divided by the molar mass constant . The molecular mass ( m ) is the mass of a given molecule: it is usually measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. This

2108-448: The amount of substance that has as many constituent particles as there are atoms in 12 grams of carbon-12 . During that period, the molar mass of carbon-12 was thus exactly 12 g/mol, by definition. Since 2019, a mole of any substance has been redefined in the SI as the amount of that substance containing an exactly defined number of particles, 6.022 140 76 × 10 . The molar mass of

2170-564: The conversion of aliphatic bonds (such as alicyclic rings) to aromatic bonds. IR spectroscopy is sensitive to carbon-oxygen bonds such as quinones , ketones , and esters , so the technique can also be used to investigate oxygen speciation. It is found that the oxygen content of kerogen decreases during thermal maturation (as has also been observed by elemental analysis), with relatively little observable change in oxygen speciation. Similarly, sulfur speciation can be investigated with X-ray absorption near edge structure (XANES) spectroscopy, which

2232-435: The core out of chlorin -based compounds such as the magnesium in chlorophyll and replace it with their vanadium center in order to attach and harvest energy via light-harvesting complexes . It is theorized that the bacteria contained in worm castings, Rhodopseudomonas palustris , do this during its photoautotrophism mode of metabolism. Over time colonies of light harvesting bacteria solidify, forming kerogen . Kerogen

2294-438: The different components of kerogen can be identified by microscopic inspection and are classified as macerals . This classification was developed originally for coal (a sedimentary rock that is rich in organic matter of terrestrial origin) but is now applied to the study of other kerogen-rich sedimentary deposits. The Van Krevelen diagram is one method of classifying kerogen by "types", where kerogens form distinct groups when

2356-702: The formation and/or sedimentation of one or more mineral components resulting in a sedimentary rock like oil shale . When kerogen is contemporaneously deposited with geologic material, subsequent sedimentation and progressive burial or overburden provide elevated pressure and temperature owing to lithostatic and geothermal gradients in Earth's crust. Resulting changes in the burial temperatures and pressures lead to further changes in kerogen composition including loss of hydrogen , oxygen , nitrogen , sulfur , and their associated functional groups , and subsequent isomerization and aromatization Such changes are indicative of

2418-406: The kerogen-rich source rock (i.e. the source rock is also the reservoir rock). Much of the porosity in these shales is found to be hosted within the kerogen, rather than between mineral grains as occurs in conventional reservoir rocks. Thus, kerogen controls much of the storage and transport of oil and gas in shale. Another possible method of formation is that vanabin -containing organisms cleave

2480-484: The largest quantity of hydrocarbons upon pyrolysis . Hence, from the theoretical view, shales containing type I kerogen are the most promising deposits in terms of conventional oil retorting. Type II kerogens are characterized by intermediate initial H/C ratios and intermediate initial O/C ratios. Type II kerogen is principally derived from marine organic materials, which are deposited in reducing sedimentary environments. The sulfur content of type II kerogen

2542-412: The mass, in grams, of one mole of atoms of an element, and gram molecular mass for the mass, in grams, of one mole of molecules of a compound. The gram-atom is a former term for a mole of atoms, and gram-molecule for a mole of molecules. Molecular weight (M.W.) (for molecular compounds) and formula weight (F.W.) (for non-molecular compounds), are older terms for what is now more correctly called

Akata Formation - Misplaced Pages Continue

2604-428: The measured value of the dalton ). Most atomic masses are known to a precision of at least one part in ten-thousand, often much better (the atomic mass of lithium is a notable, and serious, exception). This is adequate for almost all normal uses in chemistry: it is more precise than most chemical analyses , and exceeds the purity of most laboratory reagents. The precision of atomic masses, and hence of molar masses,

2666-703: The molar mass is greater than 1000 g/mol, it is rarely appropriate to use more than one decimal place. These conventions are followed in most tabulated values of molar masses. Molar masses are almost never measured directly. They may be calculated from standard atomic masses, and are often listed in chemical catalogues and on safety data sheets (SDS). Molar masses typically vary between: While molar masses are almost always, in practice, calculated from atomic weights, they can also be measured in certain cases. Such measurements are much less precise than modern mass spectrometric measurements of atomic weights and molecular masses, and are of mostly historical interest. All of

2728-411: The molar mass of water is about 18.0153 g/mol. For chemical elements without isolated molecules, such as carbon and metals, the molar mass is computed dividing by the number of moles of atoms instead. Thus, for example, the molar mass of iron is about 55.845 g/mol. Since 1971, SI defined the "amount of substance" as a separate dimension of measurement . Until 2019, the mole was defined as

2790-1141: The nature of the minerals surrounding different particles. Measurements performed with atomic force microscopy coupled to infrared spectroscopy (AFM-IR) and correlated with organic petrography have analyzed the evolution of the chemical composition and mechanical properties of individual macerals of kerogen with thermal maturation at the nanoscale. These results indicate that all macerals decrease in oxygen content and increase in aromaticity (decrease in aliphalicity) during thermal maturation, but some macerals undergo large changes while other macerals undergo relatively small changes. In addition, macerals that are richer in aromatic carbon are mechanically stiffer than macerals that are richer in aliphatic carbon, as expected because highly aromatic forms of carbon (such as graphite) are stiffer than highly aliphatic forms of carbon (such as wax). Labile kerogen breaks down to generate principally liquid hydrocarbons (i.e., oil ), refractory kerogen breaks down to generate principally gaseous hydrocarbons, and inert kerogen generates no hydrocarbons but forms graphite . In organic petrography,

2852-412: The nature of the product, with lower thermal maturities yielding mainly bitumen/oil and higher thermal maturities yielding gas. These generated species are partially expelled from the kerogen-rich source rock and in some cases can charge into a reservoir rock. Kerogen takes on additional importance in unconventional resources , particularly shale. In these formations, oil and gas are produced directly from

2914-444: The preferential removal of aliphatic carbons by cracking reactions during pyrolysis, where the cracking typically occurs at weak C–C bonds beta to aromatic rings and results in the replacement of a long aliphatic chain with a methyl group. At higher maturities, when all labile aliphatic carbons have already been removed—in other words, when the kerogen has no remaining oil-generation potential—further increase in aromaticity can occur from

2976-412: The presence of abundant internal pore networks within the lattice of thermally mature kerogen. Analysis by gas sorption demonstrated that the internal specific surface area of kerogen increases by an order of magnitude (~ 40 to 400 m /g) during thermal maturation. X-ray and neutron diffraction studies have examined the spacing between carbon atoms in kerogen, revealing during thermal maturation

3038-443: The procedures rely on colligative properties , and any dissociation of the compound must be taken into account. The measurement of molar mass by vapour density relies on the principle, first enunciated by Amedeo Avogadro , that equal volumes of gases under identical conditions contain equal numbers of particles. This principle is included in the ideal gas equation : where n is the amount of substance . The vapour density ( ρ )

3100-471: The properties of kerogen. For example, the skeletal density of kerogen increases from approximately 1.1 g/ml at low thermal maturity to 1.7 g/ml at high thermal maturity. This evolution is consistent with the change in carbon speciation from predominantly aliphatic (similar to wax, density < 1 g/ml) to predominantly aromatic (similar to graphite, density > 2 g/ml) with increasing thermal maturity. Additional studies have explored

3162-447: The proportions carbon 215 : hydrogen 330 : oxygen 12 : nitrogen 5 : sulfur 1. Kerogen is insoluble in normal organic solvents in part because of the high molecular weight of its component compounds. The soluble portion is known as bitumen . When heated to the right temperatures in the earth's crust , ( oil window c. 50–150  °C , gas window c. 150–200 °C, both depending on how quickly

SECTION 50

#1732872727252

3224-406: The ratios of hydrogen to carbon and oxygen to carbon are compared. Type I kerogens are characterized by high initial hydrogen-to-carbon (H/C) ratios and low initial oxygen-to-carbon (O/C) ratios. This kerogen is rich in lipid-derived material and is commonly, but not always, from algal organic matter in lacustrine (freshwater) environments. On a mass basis, rocks containing type I kerogen yield

3286-414: The reverse of photosynthesis . These resulting units can then polycondense to form geopolymers . The formation of geopolymers in this way accounts for the large molecular weights and diverse chemical compositions associated with kerogen. The smallest units are the fulvic acids , the medium units are the humic acids , and the largest units are the humins . This polymerization usually happens alongside

3348-496: The right shows the organic carbon cycle with the flow of kerogen (black solid lines) and the flow of biospheric carbon (green solid lines), showing both the fixation of atmospheric CO 2 by terrestrial and marine primary productivity . The combined flux of reworked kerogen and biospheric carbon into ocean sediments constitutes total organic carbon burial entering the endogenous kerogen pool. Carbonaceous chondrite meteorites contain kerogen-like components. Such material

3410-560: The source rock is heated) some types of kerogen release crude oil or natural gas , collectively known as hydrocarbons ( fossil fuels ). When such kerogens are present in high concentration in rocks such as organic-rich mudrocks shale , they form possible source rocks . Shales that are rich in kerogen but have not been heated to required temperature to generate hydrocarbons instead may form oil shale deposits. The chemical composition of kerogen has been analyzed by several forms of solid state spectroscopy. These experiments typically measure

3472-490: The spatial heterogeneity of kerogen at small length scales. Individual particles of kerogen arising from different inputs are identified and assigned as different macerals . This variation in starting material may lead to variations in composition between different kerogen particles, leading to spatial heterogeneity in kerogen composition at the micron length scale. Heterogeneity between kerogen particles may also arise from local variations in catalysis of pyrolysis reactions due to

3534-432: The speciations (bonding environments) of different types of atoms in kerogen. One technique is C NMR spectroscopy , which measures carbon speciation. NMR experiments have found that carbon in kerogen can range from almost entirely aliphatic ( sp hybridized ) to almost entirely aromatic ( sp hybridized ), with kerogens of higher thermal maturity typically having higher abundance of aromatic carbon. Another technique

3596-486: The standard atomic weight or the conventional atomic weight. Multiplying by the molar mass constant ensures that the calculation is dimensionally correct: standard relative atomic masses are dimensionless quantities (i.e., pure numbers) whereas molar masses have units (in this case, grams per mole). Some elements are usually encountered as molecules , e.g. hydrogen ( H 2 ), sulfur ( S 8 ), chlorine ( Cl 2 ). The molar mass of molecules of these elements

3658-428: The strings of cellulose together); terpenes and phenols . Coal is an organic-rich sedimentary rock that is composed predominantly of this kerogen type. On a mass basis, type III kerogens generate the lowest oil yield of principal kerogen types. Type IV kerogen comprises mostly inert organic matter in the form of polycyclic aromatic hydrocarbons . They have no potential to produce hydrocarbons. The diagram on

3720-549: The thermal maturity state of kerogen. Aromatization allows for molecular stacking in sheets, which in turn drives changes in physical characteristics of kerogen, such as increasing molecular density, vitrinite reflectance , and spore coloration (yellow to orange to brown to black with increasing depth/thermal maturity). During the process of thermal maturation , kerogen breaks down in high-temperature pyrolysis reactions to form lower-molecular-weight products including bitumen, oil, and gas. The extent of thermal maturation controls

3782-416: The “oil-source” rocks carbon substance". Georesursy = Georesources. 23 , 164–176. Molecular weight In chemistry , the molar mass ( M ) (sometimes called molecular weight or formula weight , but see related quantities for usage) of a chemical compound is defined as the ratio between the mass and the amount of substance (measured in moles ) of any sample of the compound. The molar mass

SECTION 60

#1732872727252

3844-418: Was defined in such a way that the molar mass of a compound, in g/mol, is numerically equal to the average mass of one molecule or formula unit, in daltons. It was exactly equal before the redefinition of the mole in 2019 , and is now only approximately equal, but the difference is negligible for all practical purposes. Thus, for example, the average mass of a molecule of water is about 18.0153 daltons, and

#251748