Bulletin Article
Organic-carbon–rich shales of the lower Marcellus Formation were deposited at the toe and basinward of a prograding clinothem associated with a Mahantango Formation delta complex centered near Harrisburg, Pennsylvania. Distribution of these organic-carbon–rich shales was influenced by shifts in the delta complex driven by changes in rates of accommodation creation and by a topographically high carbonate bank that formed along the Findlay-Algonquin arch during deposition of the Onondaga Formation. Specifically, we interpret the Union Springs member (Shamokin Member of the Marcellus Formation) and the Onondaga Formation as comprising a single third-order depositional sequence. The Onondaga Formation was deposited in the lowstand to transgressive systems tract, and the Union Springs member was deposited in the transgressive, highstand, and falling-stage systems tract. The regional extent of parasequences, systems tracts, and the interpreted depositional sequence suggest that base-level fluctuations were primarily caused by allogenic forcing—eustasy, climate, or regional thermal uplift or subsidence—instead of basement fault reactivation as argued by previous workers. Paleowater depths in the region of Marcellus Formation black mudrock accumulation were at least 330 ft (100 m) as estimated by differences in strata thickness between the northwestern carbonate bank and basinal facies to the southeast. Geochemical analysis indicates anoxic to euxinic bottom-water conditions. These conditions were supported by a deep, stratified basin with a lack of circulation.
American Association of Petroleum Geologists (AAPG)
Added on 28 February, 2014
Explorer Article
By Sophia Ford
Energy is required to secure, treat and distribute water; conversely, energy production depends on an abundant and reliable source of water.
American Association of Petroleum Geologists (AAPG)
Added on 01 February, 2014
Bulletin Article
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.
American Association of Petroleum Geologists (AAPG)
Added on 31 January, 2014
Explorer Policy Watch
By Edith Allison
The recent National Academies’ Institute of Medicine (IOM) report on its late-April 2012 workshop, “Health Impact Assessment of Shale Gas Extraction,” describes many potential health impacts of shale gas development and identifies the data gaps.
American Association of Petroleum Geologists (AAPG)
Added on 01 January, 2014
Bulletin Article
The Marcellus Shale is considered to be the largest unconventional shale-gas resource in the United States. Two critical factors for unconventional shale reservoirs are the response of a unit to hydraulic fracture stimulation and gas content. The fracture attributes reflect the geomechanical properties of the rocks, which are partly related to rock mineralogy. The natural gas content of a shale reservoir rock is strongly linked to organic matter content, measured by total organic carbon (TOC). A mudstone lithofacies is a vertically and laterally continuous zone with similar mineral composition, rock geomechanical properties, and TOC content. Core, log, and seismic data were used to build a three-dimensional (3-D) mudrock lithofacies model from core to wells and, finally, to regional scale. An artificial neural network was used for lithofacies prediction. Eight petrophysical parameters derived from conventional logs were determined as critical inputs. Advanced logs, such as pulsed neutron spectroscopy, with log-determined mineral composition and TOC data were used to improve and confirm the quantitative relationship between conventional logs and lithofacies. Sequential indicator simulation performed well for 3-D modeling of Marcellus Shale lithofacies. The interplay of dilution by terrigenous detritus, organic matter productivity, and organic matter preservation and decomposition affected the distribution of Marcellus Shale lithofacies distribution, which may be attributed to water depth and the distance to shoreline. The trend of normalized average gas production rate from horizontal wells supported our approach to modeling Marcellus Shale lithofacies. The proposed 3-D modeling approach may be helpful for optimizing the design of horizontal well trajectories and hydraulic fracture stimulation strategies.
American Association of Petroleum Geologists (AAPG)
Added on 30 November, 2013
Explorer Article
The Distinguished Lecture program, funded in part by the AAPG Foundation, is the Association’s flagship initiative for spreading the latest in science, technology and professional information.
American Association of Petroleum Geologists (AAPG)
Added on 01 November, 2013
Explorer Making a Difference
By Christopher Stone
Making a connection: A team of AAPG members spend time with Boy Scouts at this year’s Jamboree, introducing scores of them to the world of geology.
American Association of Petroleum Geologists (AAPG)
Added on 01 November, 2013
Explorer Emphasis Article
By Barry Friedman
Award-winning paper showcases cutting-edge technique that strongly correlates the 2011 Youngstown, Ohio, Earthquake Sequence to wastewater injection.
American Association of Petroleum Geologists (AAPG)
Added on 01 September, 2013