scholarly journals Detecting and explaining why aquifers occasionally become degraded near hydraulically fractured shale gas wells

2018 ◽  
Vol 115 (49) ◽  
pp. 12349-12358 ◽  
Author(s):  
Josh Woda ◽  
Tao Wen ◽  
David Oakley ◽  
David Yoxtheimer ◽  
Terry Engelder ◽  
...  
Keyword(s):  
Natural Gas ◽  
Shale Gas ◽  
Noble Gas ◽  
Marcellus Shale ◽  
Temporal Trends ◽  
Gas Wells ◽  
Domestic Water ◽  
Upward Migration ◽  
Water Wells ◽  
Marcellus Formation

Extensive development of shale gas has generated some concerns about environmental impacts such as the migration of natural gas into water resources. We studied high gas concentrations in waters at a site near Marcellus Shale gas wells to determine the geological explanations and geochemical implications. The local geology may explain why methane has discharged for 7 years into groundwater, a stream, and the atmosphere. Gas may migrate easily near the gas wells in this location where the Marcellus Shale dips significantly, is shallow (∼1 km), and is more fractured. Methane and ethane concentrations in local water wells increased after gas development compared with predrilling concentrations reported in the region. Noble gas and isotopic evidence are consistent with the upward migration of gas from the Marcellus Formation in a free-gas phase. This upflow results in microbially mediated oxidation near the surface. Iron concentrations also increased following the increase of natural gas concentrations in domestic water wells. After several months, both iron and SO42− concentrations dropped. These observations are attributed to iron and SO42− reduction associated with newly elevated concentrations of methane. These temporal trends, as well as data from other areas with reported leaks, document a way to distinguish newly migrated methane from preexisting sources of gas. This study thus documents both geologically risky areas and geochemical signatures of iron and SO42− that could distinguish newly leaked methane from older methane sources in aquifers.

scholarly journals Evaluating a groundwater supply contamination incident attributed to Marcellus Shale gas development

2015 ◽  
Vol 112 (20) ◽  
pp. 6325-6330 ◽  
Author(s):  
Garth T. Llewellyn ◽  
Frank Dorman ◽  
J. L. Westland ◽  
D. Yoxtheimer ◽  
Paul Grieve ◽  
...  
Keyword(s):  
Natural Gas ◽  
Shale Gas ◽  
Management Practices ◽  
Marcellus Shale ◽  
Complex Mixture ◽  
Oil And Gas Industry ◽  
Gas Wells ◽  
Gas Industry ◽  
Gas Drilling ◽  
Groundwater Supply

High-volume hydraulic fracturing (HVHF) has revolutionized the oil and gas industry worldwide but has been accompanied by highly controversial incidents of reported water contamination. For example, groundwater contamination by stray natural gas and spillage of brine and other gas drilling-related fluids is known to occur. However, contamination of shallow potable aquifers by HVHF at depth has never been fully documented. We investigated a case where Marcellus Shale gas wells in Pennsylvania caused inundation of natural gas and foam in initially potable groundwater used by several households. With comprehensive 2D gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS), an unresolved complex mixture of organic compounds was identified in the aquifer. Similar signatures were also observed in flowback from Marcellus Shale gas wells. A compound identified in flowback, 2-n-Butoxyethanol, was also positively identified in one of the foaming drinking water wells at nanogram-per-liter concentrations. The most likely explanation of the incident is that stray natural gas and drilling or HF compounds were driven ∼1–3 km along shallow to intermediate depth fractures to the aquifer used as a potable water source. Part of the problem may have been wastewaters from a pit leak reported at the nearest gas well pad—the only nearby pad where wells were hydraulically fractured before the contamination incident. If samples of drilling, pit, and HVHF fluids had been available, GCxGC-TOFMS might have fingerprinted the contamination source. Such evaluations would contribute significantly to better management practices as the shale gas industry expands worldwide.

Quantitative Prediction of Radon Concentration at Wellhead in Shale Gas Development

SPE Journal ◽  
2016 ◽  
Vol 22 (01) ◽  
pp. 235-243 ◽  
Author(s):  
Wei Tian ◽  
Xingru Wu ◽  
Tong Shen ◽  
Zhenyu Zhang ◽  
Sumeer Kalra
Keyword(s):  
Natural Gas ◽  
Numerical Simulations ◽  
Shale Gas ◽  
Radon Concentration ◽  
Marcellus Shale ◽  
Gas Production ◽  
Influential Factors ◽  
Natural Fracture ◽  
Quantitative Prediction ◽  
Radon Gas

Summary Hydraulic fracturing has been applied as an effective method to increase gas production from shale formations; however, this method has also raised concerns about its adverse impacts on environment. For example, in the Marcellus shale formation, some measured radon-gas concentrations exceeded the safe standard. Therefore, it is important to quantitatively evaluate radon concentration from fractured wells. However, existing researches have not successfully conducted a systematic and predictive study on the relationship between shale gas production and radon concentration at the wellhead of a hydraulically fractured well. To address this issue and quantitatively determine the radon concentration, we present the mechanisms of radon-gas generation and releasing, and conducted numerical simulations on its transport process in the subsurface formation system. The concentration of radon in produced gas is related with the original sources where the natural gas is extracted. Radon, generated from the radium alpha decay process, is trapped in pore spaces before the reservoir development. With the fluid flowing through the subsurface network, released radon will move to surface with the produced streams such as natural gas and flowback water. Our study shows that the radon concentration at wellhead could be significant. Influential factors such as natural-fracture-network properties, formation petrophysical parameters, and fracture dimension are investigated with sensitivity studies through numerical simulations. Analysis results suggest that radon wellhead concentration is strongly related with production rate. Thus, careful production design and protection are necessary to reduce radon hazard regarding the public and environmental impact.

scholarly journals Methane in groundwater before, during, and after hydraulic fracturing of the Marcellus Shale

2018 ◽  
Vol 115 (27) ◽  
pp. 6970-6975 ◽  
Author(s):  
E. Barth-Naftilan ◽  
J. Sohng ◽  
J. E. Saiers
Keyword(s):  
Groundwater Quality ◽  
Shale Gas ◽  
Marcellus Shale ◽  
Gas Wells ◽  
Local Flow ◽  
Gas Well ◽  
Monitoring Wells ◽  
Regional Flow ◽  
Flow Systems ◽  
Methane Concentrations

Concern persists over the potential for unconventional oil and gas development to contaminate groundwater with methane and other chemicals. These concerns motivated our 2-year prospective study of groundwater quality within the Marcellus Shale. We installed eight multilevel monitoring wells within bedrock aquifers of a 25-km2 area targeted for shale gas development (SGD). Twenty-four isolated intervals within these wells were sampled monthly over 2 years and groundwater pressures were recorded before, during, and after seven shale gas wells were drilled, hydraulically fractured, and placed into production. Perturbations in groundwater pressures were detected at hilltop monitoring wells during drilling of nearby gas wells and during a gas well casing breach. In both instances, pressure changes were ephemeral (<24 hours) and no lasting impact on groundwater quality was observed. Overall, methane concentrations ([CH4]) ranged from detection limit to 70 mg/L, increased with aquifer depth, and, at several sites, exhibited considerable temporal variability. Methane concentrations in valley monitoring wells located above gas well laterals increased in conjunction with SGD, but CH4 isotopic composition and hydrocarbon composition (CH4/C2H6) are inconsistent with Marcellus origins for this gas. Further, salinity increased concurrently with [CH4], which rules out contamination by gas phase migration of fugitive methane from structurally compromised gas wells. Collectively, our observations suggest that SGD was an unlikely source of methane in our valley wells, and that naturally occurring methane in valley settings, where regional flow systems interact with local flow systems, is more variable in concentration and composition both temporally and spatially than previously understood.

Temporal Changes in Microbial Ecology and Geochemistry in Produced Water from Hydraulically Fractured Marcellus Shale Gas Wells

2014 ◽  
Vol 48 (11) ◽  
pp. 6508-6517 ◽  
Author(s):  
Maryam A. Cluff ◽  
Angela Hartsock ◽  
Jean D. MacRae ◽  
Kimberly Carter ◽  
Paula J. Mouser
Keyword(s):  
Microbial Ecology ◽  
Shale Gas ◽  
Produced Water ◽  
Marcellus Shale ◽  
Temporal Changes ◽  
Gas Wells

Geochemical and isotopic evolution of water produced from Middle Devonian Marcellus shale gas wells, Appalachian basin, Pennsylvania

AAPG Bulletin ◽  
2015 ◽  
Vol 99 (02) ◽  
pp. 181-206 ◽  
Author(s):  
Elisabeth L. Rowen ◽  
Mark A. Engle ◽  
Thomas F. Kraemer ◽  
Karl T. Schroeder ◽  
Richard W. Hammack ◽  
...  
Keyword(s):  
Shale Gas ◽  
Middle Devonian ◽  
Marcellus Shale ◽  
Appalachian Basin ◽  
Gas Wells ◽  
Isotopic Evolution

scholarly journals Factors Affecting Shale Gas Chemistry and Stable Isotope and Noble Gas Isotope Composition and Distribution: A Case Study of Lower Silurian Longmaxi Shale Gas, Sichuan Basin

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5981
Author(s):  
Chunhui Cao ◽  
Liwu Li ◽  
Yuhu Liu ◽  
Li Du ◽  
Zhongping Li ◽  
...  
Keyword(s):  
Natural Gas ◽  
Isotopic Composition ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Noble Gas ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
The Sichuan Basin ◽  
Gas Fields ◽  
Cracking Gas

The Weiyuan (WY) and Changning (CN) fields are the largest shale gas fields in the Sichuan Basin. Though the shale gases in both fields are sourced from the Longmaxi Formation, this study found notable differences between them in molecular composition, carbon isotopic composition, and noble gas abundance and isotopic composition. CO2 (av. 0.52%) and N2 (av. 0.94%) were higher in Weiyuan than in Changning by an average of 0.45% and 0.70%, respectively. The δ13C1 (−26.9% to −29.7%) and δ13C2 (−32.0% to −34.9%) ratios in the Changning shale gases were about 8% and 6% heavier than those in Weiyuan, respectively. Both shale gases had similar 3He/4He ratios but different 40Ar/36Ar ratios. These geochemical differences indicated complex geological conditions and shed light on the evolution of the Lonmaxi shale gas in the Sichuan Basin. In this study, we highlight the possible impacts on the geochemical characteristics of gas due to tectonic activity, thermal evolution, and migration. By combining previous gas geochemical data and the geological background of these natural gas fields, we concluded that four factors account for the differences in the Longmaxi Formation shale gas in the Sichuan Basin: a) A different ratio of oil cracking gas and kerogen cracking gas mixed in the closed system at the high over-mature stage. b) The Longmaxi shales in WY and CN have had differential geothermal histories, especially in terms of the effects from the Emeishan Large Igneous Province (LIP), which have led to the discrepancy in evolution of the shales in the two areas. c) The heterogeneity of the Lower Silurian Longmaxi shales is another important factor, according to the noble gas data. d) Although shale gas is generated in closed systems, natural gas loss throughout geological history cannot be avoided, which also accounts for gas geochemical differences. This research offers some useful information regarding the theory of shale gas generation and evolution.

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