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Organic Petrology

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Monday, December 29, 2014

Thermal maturity of Tasmanites microfossils from confocal laser scanning fluorescence microscopy

Outside Publication: Fuel
We report here, for the first time, spectral properties of Tasmanites microfossils determined by confocal laser scanning fluorescence microscopy (CLSM, using Ar 458 nm excitation). The Tasmanites occur in a well-characterized natural maturation sequence (Ro 0.48–0.74%) of Devonian shale (n = 3 samples) from the Appalachian Basin...


Friday, August 29, 2014

Standardization of reflectance measurements in dispersed organic matter: Results of an exercise to improve interlaboratory agreement

Outside Publication: Marine and Petroleum Geology
Vitrinite reflectance generally is considered the most robust thermal maturity parameter available for application to hydrocarbon exploration and petroleum system evaluation. However, until 2011 there was no standardized methodology available to provide guidelines for vitrinite reflectance measurements in shale...

Tuesday, August 05, 2014

Reprint of "Organic petrology of the Aptian-age section in the downdip Mississippi Interior Salt Basin, Mississippi, USA: Observations and preliminary implications for thermal maturation history"

Outside Publication: International Journal of Coal Geology
This study identifies a thermal maturity anomaly within the downdip Mississippi Interior Salt Basin (MISB) of southern Mississippi, USA, through examination of bitumen reflectance data from Aptian-age strata (Sligo Formation, Pine Island Shale, James Limestone, and Rodessa Formation)...

Thursday, July 31, 2014

Petrographic maturity parameters of a Devonian shale maturation series, Appalachian Basin, USA. ICCP Thermal Indices Working Group interlaboratory exercise

Outside Publication: International Journal of Coal Geology
This paper presents results of an interlaboratory exercise on organic matter optical maturity parameters using a natural maturation series comprised by three Devonian shale samples (Huron Member, Ohio Shale) from the Appalachian Basin, USA. This work was conducted by the Thermal Indices Working Group of the International Committee for Coal and Organic Petrology (ICCP) Commission II (Geological Applications of Organic Petrology).

Sunday, June 15, 2014

The use of solvent extractions and solubility theory to discern hydrocarbon associations in coal, with application to the coal–supercritical CO2 system

Outside Publication: Organic Geochemistry
Samples of three high volatile bituminous coals were subjected to parallel sets of extractions involving solvents dichloromethane (DCM), carbon disulfide (CS2), and supercritical carbon dioxide (CO2) (40 °C, 100 bar) to study processes affecting coal–solvent interactions. Recoveries of perdeuterated surrogate compounds, n-hexadecane-d34 and four polycyclic aromatic hydrocarbons (PAHs), added as a spike prior to extraction, provided further insight into these processes.

Friday, May 23, 2014

Organic substances in produced and formation water from unconventional natural gas extraction in coal and shale

Outside Publication: International Journal of Coal Geology
Organic substances in produced and formation water from coalbed methane (CBM) and gas shale plays from across the USA were examined in this study. Results from five CBM plays and two gas shale plays (including the Marcellus Shale) show a myriad of organic chemicals present in the produced and formation water. Organic compound...

Monday, January 13, 2014

Differentiation of pre-existing trapped methane from thermogenic methane in an igneous-intruded coal by hydrous pyrolysis

Outside Publication: Organic Geochemistry
The gas released from coals under hydrous pyrolysis conditions represents a quantifiable mixture of ancient (270 Ma) methane (likely microbial) that was generated in situ and trapped within the rock during the rapid heating by the dike, and modern (laboratory) thermogenic methane that was generated from the indigenous organic matter due to thermal maturation induced by hydrous pyrolysis conditions. These findings provide...

Thursday, January 09, 2014

Rock-Eval pyrolysis and vitrinite reflectance results from the Sheep Creek 1 well

Susitna basin, south-central Alaska

USGS Publication: Open-File Report 2013–1307
We used Rock-Eval pyrolysis and vitrinite reflectance to examine the petroleum source potential of rock samples from the Sheep Creek 1 well in the Susitna basin of south-central Alaska. The results show that Miocene nonmarine coal, carbonaceous shale, and mudstone are potential sources of hydrocarbons and are thermally immature with respect to the oil window.

Monday, February 04, 2013

New vitrinite reflectance data for the Wind River Basin, Wyoming

USGS Publication: Open-File Report 2013–1002
The Wind River Basin is a large Laramide (Late Cretaceous through Eocene) structural and sedimentary basin that encompasses about 7,400 square miles in central Wyoming. The basin is bounded by the Washakie Range and Owl Creek and southern Bighorn Mountains on the north, the Casper arch on the east and northeast, and the Granite Mountains on the south, and Wind River Range on the west. The purpose of this report is to present new vitrinite reflectance data collected mainly from Cretaceous marine shales in the Wind River Basin to better characterize their thermal maturity and hydrocarbon potential.



Photomicrograph of coal from the Trinity Group in Bradley County, Arkansas.
Photo: Photomicrograph of coal from
the Trinity Group in Bradley County,
Arkansas. The image contains a
mix of huminite, liptinite and
inertinite macerals.

Organic petrology is the comprehensive investigation of organic materials occurring in sedimentary rocks; in particular, coal and petroleum source rocks. Organic petrology also includes study of the utilization products of coal and petroleum source rocks, for instance, coke, fly ash, and liquefaction residue. Studies of the origin, occurrence, structure, and history of sedimentary organic matter typically are pursued through techniques of optical microscopy. Complementary geochemical methods of investigation include pyrolysis, gas and liquid chromatography, solvent extraction, and mass spectroscopy.

Organic petrology research is used to understand and predict the behavior of coal in utilization and/or thermal maturity of petroleum source rocks, and to understand and predict hydrocarbon generation. Other important themes of organic petrology research include the impact of coal composition on coalbed gas generation and storage. Research in the USGS Organic Petrology Laboratory at the National Center in Reston includes all of these themes.

Paul Hackley
Project Chief


Coal Petrology
Coal Petrology

Coal Petrology

The individual organic components of coal are termed “macerals,” similar to “minerals” in rock. Macerals are divided into three broad groups: vitrinite, inertinite, and liptinite. Vitrinites are the coalified remains of humic plant substances, primarily lignin and cellulose. In most cases, inertinites consist of the same original plant material as vitrinite but have been altered by charring or oxidation prior to coalification... [+]

In most cases, inertinites consist of the same original plant material as vitrinite but have been altered by charring or oxidation prior to coalification. Inertinites can also include fungal bodies. Liptinites are the remains of hydrogen-rich plant materials such as cutins, resins, fats, waxes, andsporopollenin (the outer cell walls of spores and pollen). The maceral content of coal is determined with a reflected light microscope (light is reflected from the sample towards the analyst) at magnifications of about 500x, using tungsten filament and gas arc light sources. Photomicrographs of USGS coal samples are contained in the organic petrology photomicrograph atlas.

Stanton, R.W., Warwick, P.D., and Swanson, S.M., 2005, Tar yields from low-temperature carbonization of coal facies from the Powder River Basin, Wyoming, USA: International Journal of Coal Geology, v. 63, p. 13-26.

Hackley, P.C., Warwick, P.D., and Gonzáles, E., 2005, Petrology, mineralogy, and geochemistry of mined coals, western Venezuela: International Journal of Coal Geology, v. 63, p. 68-97.

Maturation Studies
Maturation Studies

Maturation Studies

Measurement of the reflectance of the maceral vitrinite is a commonly performed analysis that is used to establish the rank of coals or the thermal maturity of petroleum source rocks. A well-established correlation exists between vitrinite reflectance and rank due to increases in the refractive and adsorption indices of vitrinite with increasing aromatization. Coal or source rocks samples are prepared in polished briquettes... [+]

which are then compared to the reflectance of calibrated glass standards on a reflected light microscope. The USGS is currently involved in maturation studies of coals and rock in support of coalbed methane exploration in Louisiana, Arkansas, and Texas.

Hackley, P.C., Guevara, E. H., Hentz, T.F., and Hook, R.W., 2009, Thermal maturity and organic composition of Pennsylvanian coals and carbonaceous shales, north-central Texas: implications for coalbed gas potential: International Journal of Coal Geology, v. 77, p. 294-309, doi:10.1016/j.coal.2008.05.006.

Coalbed Methane Organic Petrology
Coalbed Methane
Organic Petrology

Coalbed Methane Organic Petrology

The maceral composition of coals may impact the ability of coal to generate and/or store natural gases, primarily methane. The USGS is actively pursuing studies to elucidate the role of maceral content on gas generation and storage, primarily in the Gulf Coast region of the United States. Coal samples from coalbed methane test wells are desorbed to measure actual stored gas content, microscopically analyzed for organic... [+]

content, and subjected to adsorption isotherm analyses to measure the coal’s ability to store gas. These comparative studies allow predictions of the role of maceral content on gas storage and may help in understanding gas generation. For more information pertaining to coalbed methane, please visit the "Oil and Gas" section of this website.

Hackley, P.C., Warwick, P.D., and Breland, F.C., Jr., 2007, Organic petrology and coalbed gas content, Wilcox Group, northern Louisiana: International Journal of Coal Geology, v. 71, p. 54-71, doi:10.1016/j.coal.2006.05.009.

Warwick, P.D., Breland, F.C., Jr., and Hackley, P.C., 2008, Biogenic origin of coalbed gas in the northern Gulf of Mexico Coastal Plain, USA: International Journal of Coal Geology, v. 76, p. 119-137, doi:10.1016/j.coal.2008.05.009.

Paleoenvironmental Studies
Paleoenvironmental Studies

Paleoenvironmental Studies

The types and amounts of organic material preserved in coal beds are indicators of the environmental processes that operated in the original peat mires. In conjunction with other types of analytical and geologic data, the organic content of coals can be used to infer moisture stress (frequency and degree of fluctuations in the water table), depositional environment (acidity, mechanical stress), types and relative amounts of original plant... [+]

vegetation, tectonic environment (subsidence), and climateThe USGS Organic Petrology Laboratory is involved in a number of national and international projects which characterize paleoenvironments through organic petrology.

Hackley, P.C., and Martínez, M., 2007, Organic petrology of Paleocene Marcelina Formation coals, Paso Diablo mine, western Venezuela: Tectonic controls on coal type: International Journal of Coal Geology, v. 71, p. 505-526, doi:10.1016/j.coal.2006.05.002.

Hackley, P.C., SanFilipo, J.R., Azizi, G.P., Davis, P.A., and Starratt, S.W., 2010, Organic petrology of subbituminous carbonaceous shale samples from Chalâw, Kabul Province, Afghanistan: speculations on paleoenvironment and energy resource potential: International Journal of Coal Geology, v. 81, p. 269-280, doi:10.1016/j.coal.2009.12.007.

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Page Last Modified: Wednesday, December 03, 2014



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