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Bulletin Article

5776
 

The origin of thermogenic natural gas in the shallow stratigraphy of northeastern Pennsylvania is associated, in part, with interbedded coal identified in numerous outcrops of the Upper Devonian Catskill and Lock Haven Formations. Historically documented and newly identified locations of Upper Devonian coal stringers are shown to be widespread, both laterally across the region and vertically throughout the stratigraphic section of the Catskill and Lock Haven Formations. Coal samples exhibited considerable gas source potential with total organic carbon as high as 44.40% by weight, with a mean of 13.66% for 23 sample locations analyzed. Upper Devonian coal is thermogenically mature; calculated vitrinite reflectances range from 1.25% to 2.89%, with most samples falling within the dry-gas window. Source potential is further supported by gas shows observed while drilling through shallow, identifiable coal horizons, which are at times located within fresh groundwater aquifers. Thermogenic gas detected in area water wells during predrill baseline sampling is determined not only to be naturally occurring, but also common in the region.

5687
 

Using diverse geologic and geophysical data from recent exploration and development, and experimental results of analysis of gas content, gas capacity, and gas composition, this article discusses how geologic, structural, and hydrological factors determine the heterogeneous distribution of gas in the Weibei coalbed methane (CBM) field.

The coal rank of the Pennsylvanian no. 5 coal seam is mainly low-volatile bituminous and semianthracite. The total gas content is 2.69 to 16.15 m3/t (95.00–570.33 scf/t), and gas saturation is 26.0% to 93.2%. Burial coalification followed by tectonically driven hydrothermal activity controls not only thermal maturity, but also the quality and quantity of thermogenic gas generated from the coal.

Gas composition indicates that the CBM is dry and of dominantly thermogenic origin. The thermogenic gases have been altered by fractionation that may be related to subsurface water movement in the southern part of the study area.

Three gas accumulation models are identified: (1) gas diffusion and long-distance migration of thermogenic gases to no-flow boundaries for sorption and minor conventional trapping, (2) hydrodynamic trapping of gas in structural lows, and (3) gas loss by hydrodynamic flushing. The first two models are applicable for the formation of two CBM enrichment areas in blocks B3 and B4, whereas the last model explains extremely low gas content and gas saturation in block B5. The variable gas content, saturation, and accumulation characteristics are mainly controlled by these gas accumulation models.

3688
 
Characterization of oil shale kerogen and organic residues remaining in postpyrolysis spent shale is critical to the understanding of the oil generation process and approaches to dealing with issues related to spent shale. The chemical structure of organic matter in raw oil shale and spent shale samples was examined in this study using advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Oil shale was collected from Mahogany zone outcrops in the Piceance Basin. Five samples were analyzed: (1) raw oil shale, (2) isolated kerogen, (3) oil shale extracted with chloroform, (4) oil shale retorted in an open system at 500degC to mimic surface retorting, and (5) oil shale retorted in a closed system at 360degC to simulate in-situ retorting. The NMR methods applied included quantitative direct polarization with magic-angle spinning at 13 kHz, cross polarization with total sideband suppression, dipolar dephasing, CHn selection, 13C chemical shift anisotropy filtering, and 1H-13C long-range recoupled dipolar dephasing. The NMR results showed that, relative to the raw oil shale, (1) bitumen extraction and kerogen isolation by demineralization removed some oxygen-containing and alkyl moieties; (2) unpyrolyzed samples had low aromatic condensation; (3) oil shale pyrolysis removed aliphatic moieties, leaving behind residues enriched in aromatic carbon; and (4) oil shale retorted in an open system at 500degC contained larger aromatic clusters and more protonated aromatic moieties than oil shale retorted in a closed system at 360degC, which contained more total aromatic carbon with a wide range of cluster sizes.

Explorer Article

2228
 

A Fairway to paradise? Nova Scotia’s offshore energy industry is in the global spotlight after an enticing assessment of resources in the Scotian Basin.

2725
 

Renaissance era: Geoscience research – often more practical than theoretical – is enjoying a strong revival.

Explorer Emphasis

2351
 

Scientific knowledge about the origins of oil in the Gulf of Mexico Basin and the resulting impact on oil quality has evolved over a long period of time.

2179
 

Oil and liquids-rich gas deposits are hot targets today among prospectors and operators – and the action in the self-sourced Niobrara shale play in the Rocky Mountain region is about as fired up as it can be.

2931
 

Kinetics and hieroglyphics and pyrolysis! Oh my! Following the traditional method of determining kerogen kinetics is slow and expensive and yields little kinetic data. The new method of one-run kinetics proves to save both time and money while acquiring more data.

Explorer Regions and Sections

2665
 

Concepts and technologies developed for liquid-rich unconventional plays in North America are on the verge of being exported worldwide.

Explorer Spotlight On…

2340
 

A multi-disciplinary team of geoscientists has developed a new framework for the north Red Sea region – and their findings may cause a new reassessment of the area’s resource potential.

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