Methane Concentrations in Water Wells Unrelated to Proximity to Existing Oil and Gas Wells in Northeastern Pennsylvania

Siegel, Donald I.; Azzolina, Nicholas A.; Smith, Bert J.; Perry, Ann E.; Bothun, R.

doi:10.1021/es505775c

Cited by 113 publications

(154 citation statements)

References 8 publications

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“…To unambiguously address such concerns, it is essential to assess the natural occurrence of methane and its spatial distribution, the variability of methane concentrations and the sources of methane in shallow groundwater prior to unconventional energy development to establish a baseline. In the last 5 years, an increasing number of publications have addressed the questions of occurrence and sources of methane in shallow groundwater in natural gas producing regions (Osborn et al, 2011a, b;Warner et al, 2013;Darrah et al, 2012Darrah et al, , 2014Molofsky et al, 2013;Siegel et al, 2015;Vengosh et al, 2013;Brantley et al, 2014;Baldassare et al, 2014;McPhilips et al, 2014;McIntosh et al, 2014;Vidic et al, 2013;Hamilton et al, 2015). These studies have contributed a wealth of baseline data for gas occurrences in shallow groundwater in many regions of North America.…”

Section: Introductionmentioning

confidence: 99%

Redox controls on methane formation, migration and fate in shallow aquifers

Humez¹,

Mayer²,

Nightingale³

et al. 2016

Hydrol. Earth Syst. Sci.

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Abstract. Development of unconventional energy resources such as shale gas and coalbed methane has generated some public concern with regard to the protection of groundwater and surface water resources from leakage of stray gas from the deep subsurface. In terms of environmental impact to and risk assessment of shallow groundwater resources, the ultimate challenge is to distinguish (a) natural in situ production of biogenic methane, (b) biogenic or thermogenic methane migration into shallow aquifers due to natural causes, and (c) thermogenic methane migration from deep sources due to human activities associated with the exploitation of conventional or unconventional oil and gas resources. This study combines aqueous and gas (dissolved and free) geochemical and isotope data from 372 groundwater samples obtained from 186 monitoring wells of the provincial Groundwater Observation Well Network (GOWN) in Alberta (Canada), a province with a long record of conventional and unconventional hydrocarbon exploration. We investigated whether methane occurring in shallow groundwater formed in situ, or whether it migrated into the shallow aquifers from elsewhere in the stratigraphic column. It was found that methane is ubiquitous in groundwater in Alberta and is predominantly of biogenic origin. The highest concentrations of biogenic methane ( > 0.01 mM or > 0.2 mg L −1 ), characterized by δ 13 C CH 4 values < −55 ‰, occurred in anoxic Na-Cl, Na-HCO 3 , and Na-HCO 3 -Cl type groundwaters with negligible concentrations of nitrate and sulfate suggesting that methane was formed in situ under methanogenic conditions for 39.1 % of the samples. In only a few cases (3.7 %) was methane of biogenic origin found in more oxidizing shallow aquifer portions suggesting limited upward migration from deeper methanogenic aquifers. Of the samples, 14.1 % contained methane with δ 13 C CH 4 values > −54 ‰, potentially suggesting a thermogenic origin, but aqueous and isotope geochemistry data revealed that the elevated δ 13 C CH 4 values were caused by microbial oxidation of biogenic methane or postsampling degradation of low CH 4 content samples rather than migration of deep thermogenic gas. A significant number of samples (39.2 %) contained methane with predominantly biogenic C isotope ratios (δ 13 C CH 4 < −55 ‰) accompanied by elevated concentrations of ethane and sometimes trace concentrations of propane. These gases, observed in 28.1 % of the samples, bearing both biogenic (δ 13 C) and thermogenic (presence of C 3 ) characteristics, are most likely derived from shallow coal seams that are prevalent in the Cretaceous Horseshoe Canyon and neighboring formations in which some of the groundwater wells are completed. The remaining 3.7 % of samples were not assigned because of conflicting parameters in the data sets or between replicates samples. Hence, despite quite variable gas concentrations and a wide range of δ 13 C CH 4 values in baseline groundwater samples, we found no conclusive evidence for deep thermogenic gas migration into shallow aqu...

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Section: Introductionmentioning

confidence: 99%

Redox controls on methane formation, migration and fate in shallow aquifers

Humez¹,

Mayer²,

Nightingale³

et al. 2016

Hydrol. Earth Syst. Sci.

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“…Some investigations have shown geochemical evidence for the migration of fluids (especially methane) from gas-bearing formations towards surficial aquifers through natural or wellrelated pathways (Jackson et al 2013;Warner et al 2012;Darrah et al 2014) but were partly refuted by others (Engelder et al 2014;Siegel et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Numerical modeling of fracking fluid migration through fault zones and fractures in the North German Basin

2016

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Gas production from shale formations by hydraulic fracturing has raised concerns about the effects on the quality of fresh groundwater. The migration of injected fracking fluids towards the surface was investigated in the North German Basin, based on the known standard lithology. This included cases with natural preferential pathways such as permeable fault zones and fracture networks. Conservative assumptions were applied in the simulation of flow and mass transport triggered by a high pressure boundary of up to 50 MPa excess pressure. The results show no significant fluid migration for a case with undisturbed cap rocks and a maximum of 41 m vertical transport within a permeable fault zone during the pressurization. Open fractures, if present, strongly control the flow field and migration; here vertical transport of fracking fluids reaches up to 200 m during hydraulic fracturing simulation. Long-term transport of the injected water was simulated for 300 years. The fracking fluid rises vertically within the fault zone up to 485 m due to buoyancy. Progressively, it is transported horizontally into sandstone layers, following the natural groundwater flow direction. In the long-term, the injected fluids are diluted to minor concentrations. Despite the presence of permeable pathways, the injected fracking fluids in the reported model did not reach near-surface aquifers, either during the hydraulic fracturing or in the long term. Therefore, the probability of impacts on shallow groundwater by the rise of fracking fluids from a deep shale-gas formation through the geological underground to the surface is small.

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“…After the CIC released documents in Feb ruary revealing Soon's industry ties, the journal amended the study to clarify his funding. In another case, hydrologist Donald Siegel of Syracuse University in New York came under fire for a study 5 that concluded that naturalgas production had not contaminated groundwa ter in an area of Pennsylvania dominated by …”

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confidence: 99%

Earth science wrestles with conflict-of-interest policies

Tollefson¹

2015

Nature

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Methane Concentrations in Water Wells Unrelated to Proximity to Existing Oil and Gas Wells in Northeastern Pennsylvania

Cited by 113 publications

References 8 publications

Redox controls on methane formation, migration and fate in shallow aquifers

Redox controls on methane formation, migration and fate in shallow aquifers

Numerical modeling of fracking fluid migration through fault zones and fractures in the North German Basin

Earth science wrestles with conflict-of-interest policies

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