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Starting around 2008, there was rapid expansion of oil and natural gas (ONG) production into more heavily populated areas within the Dallas-Fort Worth metroplex in the Barnett Shale region of Texas. This colocation raised concerns regarding the effect of ONG activities on chemical levels in the air. In the current study, we examined the potential impacts of ONG activity on the types and concentrations of chemicals in ambient air in the Barnett Shale. Volatile organic compound (VOC) concentrations from 6-12 years (2008-2019) of hourly ambient air monitoring data from 15 monitors (4 monitors had ≥ 10 years of data) were compared to several metrics of ONG activity (number of active wells, natural gas production, condensate production) within a 2-mile radius of each monitor. Monitoring sites were also classified into urban, suburban, and rural areas as a surrogate for nearby vehicular emission sources. Analyses of this huge dataset showed that both peak and mean chemical concentrations of lighter alkane hydrocarbons (e.g., ethane) were most impacted by the number of gas wells. Levels of heavier alkanes (e.g., pentane) were increased by condensate production and at monitors located in areas with greater urbanicity, and therefore higher vehicular emissions. The levels of unsaturated alkynes (e.g., ethylene) were entirely driven by urbanicity and were unaffected by nearby ONG activity. The same pattern was seen with the ratio of iso:n-pentane, which is contrary to the findings of others and suggests an area for future research. Aromatic hydrocarbons were impacted by multiple emissions sources and did not show the same patterns as non-aromatic VOCs. No VOC concentrations were at levels of concern for human health or odor based on comparison to Texas air monitoring comparison values. Overall, ONG activities impact air quality, but this must be evaluated in the context of other emission sources such as automobiles., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In May 1949, Herman A. Barnett III, a 23-year-old Black veteran, applied to The University of Texas Medical Branch (UTMB) in Galveston. His application occurred in the wake of Black student protests against the segregationist policies of The University of Texas and of judicial victories by the National Association for the Advancement of Colored People (NAACP) to eradicate racial inequalities in state-financed graduate and professional education. Barnett's application prompted the state to fund a medical school at the Texas State University for Negroes, the only time a state ever attempted to thwart desegregation by financing a separate Black medical school. Barnett was clearly qualified for admission to UTMB, and if the school rejected him, he had agreed to be a plaintiff in an NAACP lawsuit. Legal action was not necessary, however. In August 1949 Barnett was accepted into UTMB, thereby becoming the second African American person to desegregate a Southern medical school. Barnett was technically admitted on a contract basis as a student at the Texas State University for Negroes in Houston and was to have transferred there later. The Black medical school was never built and Barnett graduated from UTMB in 1953. This review analyzes the role that Barnett and Black civil rights activists played in the history of medical education in the US and the dismantlement of racially exclusionary policies in medical schools.

Background : This study explores sociodemographic disparities in residential proximity to unconventional gas development (UGD) among pregnant women. Methods : We conducted a secondary analysis using data from a retrospective birth cohort of 164,658 women with a live birth or fetal death from November 2010 to 2012 in the 24-county area comprising the Barnett Shale play, in North Texas. We considered both individual- and census tract-level indicators of sociodemographic status and computed Indexes of Concentration at the Extremes (ICE) to quantify relative neighborhood-level privilege/disadvantage. We used negative binomial regression to investigate the relation between these variables and the count of active UGD wells within 0.8 km of the home during gestation. We calculated count ratios (CR) and 95% confidence intervals (CI) to describe associations. Results : There were fewer wells located near homes of women of color living in low-income areas compared to non-Hispanic white women living in more privileged neighborhoods (ICE race/ethnicity + income: CR = 0.51, 95% CI = 0.48⁻0.55). Conclusions : While these results highlight a potential disparity in residential proximity to UGD in the Barnett Shale, they do not provide evidence of an environmental justice (EJ) issue nor negate findings of environmental injustice in other regions.

In the last decade hydraulic fracturing for natural gas has exploded on the Barnett Shale in Texas. The region is now home to the most intensive hydraulic fracking and gas production activities ever undertaken in densely urbanized areas. Faced with minimal state and federal regulation, Texas cities are on the front line in the effort to figure out how best to balance industry, land use, and environmental concerns. Local governments in Texas, however, do not currently have the regulatory authority, capacity, or the information required to close the regulatory gap. Using the community experience on the Barnett Shale as a case study, this article focuses on the legal and regulatory framework governing air emissions and proposes changes to the current regulatory structure. Under both the state and federal programs, the regulation of hazardous air emissions from gas operations is based largely on questions of cost and available technology. There is no comprehensive cumulative risk assessment to consider the potential impact to public health in urban areas. Drilling operations are being conducted in residential areas. Residents living in close proximity to gas operations on the Barnett Shale have voiced serious concerns for their health, which have yet to be comprehensively evaluated. Given the complexity of the science, and the dearth of clear, transparent, and enforceable standards, inadequate studies and limited statistical analysis have been allowed to provide potentially false assurances. The politically expedient bottom line dominates with little attention paid to the quality of the science or the adequacy of the standards. Determining and applying comprehensive health-based standards for hazardous air pollutants has been largely abandoned at the federal level given uncertainties in the science, difficulties of determining and measuring "safe" levels of toxic pollutants, and the potential for economic disruption. Neither the state nor the federal government has set enforceable ambient standards for hazardous air pollutants. Identifying cumulative air pollution problems that may occur in urban areas, the State of California has called upon local governments to identify "hot spots" and to consider air quality issues in their planning and zoning actions. In Texas, however, preemption discussions dominate the analysis. Any local government regulation that might provide protection from toxic air emissions otherwise regulated by the State must be justified by some other public purpose. Texas should consider authorizing and encouraging local level air quality planning for industrial activities, similar to what California has done. Care should be taken to separate these facilities from sensitive receptors and "hot spots" that may already be burdened with excessive hazardous air emissions. Given the difficulty of the task, there is also an important role for the state and federal governments in working to establish ambient standards for hazardous air pollutants, as well as standards for health based assessment and public communication. The uncertainty inherent in any of these standards should be made clear and accessible to local governments so that it may be considered in making appropriate and protective land use decisions. Texas should consider allowing local governments to have the power to establish ambient air quality standards, emissions limitations, monitoring, reporting, and offsets for hazardous air pollutants, following the model applied to conventional air pollutants pursuant to the federal program. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the Barnett shale completion strategy from 1993 to 2002. It states that Barnett is a black, organic-rich marine deposit with extremely low permeability found in Wise County, Texas. It notes the function of Self Organizing Mapping (SOM) in clustered reservoir and frac data for extracting useful information from the field data. It also presents the geology of Barnett shale, its historical completion practices, data preparation, general comparison and data visualization.

Abstract: We evaluate the economics of drilling new wells in the Barnett Shale, Fort Worth Basin, Texas. The analysis is the most granular public study to date because it is based on 10 productivity tiers and it treats low and high Btu (British thermal unit) segments of the play differently. The study is unique in its use of transient linear drainage production profiles that match the physics of the system and fit the production history in the Barnett very well. Average low Btu wells in the top two tiers are viable at $4/MMBtu, whereas average high Btu wells in the same tiers are economic at $2/MMBtu. Dry gas wells are the most sensitive to fluctuations in the price of natural gas whereas high Btu wells are also sensitive to the prices of oil and natural gas liquids. There is a distribution of productivity within each tier, with better wells requiring a much lower price to be viable than the average well. The granular subdivision of productivity, low versus high Btu, and intra-tier quality variation help to explain historical drilling patterns and also allow us to predict future development patterns in the field accurately as demonstrated for 2011 and 2012 in Browning et al. [4]. [Copyright &y& Elsevier]

Abstract: The organic-rich Barnett Shale is the primary source rock and the main unconventional reservoir in the Fort Worth Basin, Texas. The Early Silurian-Early Devonian Dadas Formation is one of the main source rocks in southeastern Turkey and it is the Turkish equivalent of Silurian hot shales in the Middle East and North Africa. In this study, similarities and differences between the Dadas Formation and the Barnett Shale are presented to indicate the unconventional reservoir potential of the Dadas Formation which covers similar acreage of the Barnett Shale. Main factors that form the basis for comparison are: depositional environment, tectonic setting, thickness, depth, organic geochemical properties and thermal maturity. Both formations have similar depositional environment and they have organic-rich, basal hot shale units indicated by a high gamma-ray log response. Thicknesses of both formations are appropriate to perform horizontal drilling and hydraulic fracturing, however, the Dadas is thicker than the Barnett Shale. Both formations have high Total Organic Carbon (TOC) and Potential Yield (S1 +S2) values. Both formations have gas prone and oil prone regions. However, the gas prone zone of the Barnett is larger. The Dadas Formation is penetrated by only a limited number of wells in comparison to the Barnett Shale. In contrast to the Barnett Shale, which is mainly in the gas zone in the Fort Worth Basin, the Dadas Formation is deeper, and is generally in the oil window. [Copyright &y& Elsevier]

Oil and natural gas operations have continued to expand and move closer to densely populated areas, contributing to growing public concerns regarding exposure to hazardous air pollutants. During the Barnett Shale Coordinated Campaign in October, 2013, ground-based whole air samples collected downwind of oil and gas sites revealed enhancements in several potentially toxic volatile organic compounds (VOCs) when compared to background values. Molar emissions ratios relative to methane were determined for hexane, benzene, toluene, ethylbenzene, and xylene (BTEX compounds). Using methane leak rates measured from the Picarro mobile flux plane (MFP) system and a Barnett Shale regional methane emissions inventory, the rates of emission of these toxic gases were calculated. Benzene emissions ranged between 51 ± 4 and 60 ± 4 kg h-1. Hexane, the most abundantly emitted pollutant, ranged from 642 ± 45 to 1070 ± 340 kg h-1. While observed hydrocarbon enhancements fall below federal workplace standards, results may indicate a link between emissions from oil and natural gas operations and concerns about exposure to hazardous air pollutants. The larger public health risks associated with the production and distribution of natural gas are of particular importance and warrant further investigation, particularly as the use of natural gas increases in the United States and internationally. [ABSTRACT FROM AUTHOR]

Data collected in a general population survey from a random sample of individuals in two counties located in the Barnett Shale region of Texas were used to empirically explore issues associated with public perception of the natural gas industry. Moderate support was found for the hypothesis that individuals residing in places with diverse levels of energy development exhibit dissimilar perceptions of the energy industry. Bivariate and multivariate logistic regression analyses indicate that residents of the county where the natural gas industry is more mature (Wise County) exhibit somewhat more negative perceptions of the energy industry than do residents of the county where natural gas industry is less established (Johnson County). The results also reveal that mineral rights ownership is a relatively strong and consistent factor associated with public perception of the natural gas industry. Possible implications of these findings for the energy industry are proposed, as are suggestions for future research. [ABSTRACT FROM PUBLISHER]

Rapid and extensive development of shale gas resources in the Barnett Shale region of Texas in recent years has created concerns about potential environmental impacts on water and air quality. The purpose of this study was to provide a better understanding of the potential contributions of emissions from gas production operations to population exposure to air toxics in the Barnett Shale region. This goal was approached using a combination of chemical characterization of the volatile organic compound (VOC) emissions from active wells, saturation monitoring for gaseous and particulate pollutants in a residential community located near active gas/oil extraction and processing facilities, source apportionment of VOCs measured in the community using the Chemical Mass Balance (CMB) receptor model, and direct measurements of the pollutant gradient downwind of a gas well with high VOC emissions. Overall, the study results indicate that air quality impacts due to individual gas wells and compressor stations are not likely to be discernible beyond a distance of approximately 100 m in the downwind direction. However, source apportionment results indicate a significant contribution to regional VOCs from gas production sources, particularly for lower-molecular-weight alkanes (

Atmospheric mercury emissions in the Barnett Shale area were studied by employing both stationary measurements and mobile laboratory surveys. Stationary measurements near the Engle Mountain Lake showed that the median mixing ratio of total gaseous mercury (THg) was 138 ppqv (140 ± 29 ppqv for mean ± S.D.) during the June 2011 study period. A distinct diurnal variation pattern was observed in which the highest THg levels appeared near midnight, followed by a monotonic decrease until midafternoon. The influence of oil and gas (ONG) emissions was substantial in this area, as inferred from the i-pentane/n-pentane ratio (1.17). However, few THg plumes were captured by our mobile laboratory during a ~3700 km survey with detailed downwind measurements from 50 ONG facilities. One compressor station and one natural gas condensate processing facility were found to have significant THg emissions, with maximum THg levels of 963 and 392 ppqv, respectively, and the emissions rates were estimated to be 7.9 kg/yr and 0.3 kg/yr, respectively. Our results suggest that the majority of ONG facilities in this area are not significant sources of THg; however, it is highly likely that a small number of these facilities contribute a relatively large amount of emissions in the ONG sector. [ABSTRACT FROM AUTHOR]

Production of natural gas from shale formations is bringing drilling and production operations to regions of the United States that have seen little or no similar activity in the past, which has generated considerable interest in potential environmental impacts. This study focused on the Barnett Shale Fort Worth Basin in Texas, which saw the number of gas-producing wells grow from 726 in 2001 to 15,870 in 2011. This study aimed to measure fence line concentrations of methane and hydrogen sulfide at natural gas production sites (wells, liquid storage tanks, and associated equipment) in the four core counties of the Barnett Shale (Denton, Johnson, Tarrant, and Wise). A mobile measurement survey was conducted in the vicinity of 4788 wells near 401 lease sites, representing 35% of gas production volume, 31% of wells, and 38% of condensate production volume in the four-county core area. Methane and hydrogen sulfide concentrations were measured using a Picarro G2204 cavity ring-down spectrometer (CRDS). Since the research team did not have access to lease site interiors, measurements were made by driving on roads on the exterior of the lease sites. Over 150 hr of data were collected from March to July 2012. During two sets of drive-by measurements, it was found that 66 sites (16.5%) had methane concentrations >3 parts per million (ppm) just beyond the fence line. Thirty-two lease sites (8.0%) had hydrogen sulfide concentrations >4.7 parts per billion (ppb) (odor recognition threshold) just beyond the fence line. Measured concentrations generally did not correlate well with site characteristics (natural gas production volume, number of wells, or condensate production). t tests showed that for two counties, methane concentrations for dry sites were higher than those for wet sites. Follow-up study is recommended to provide more information at sites identified with high levels of methane and hydrogen sulfide.Implications:Information regarding air emissions from shale gas production is important given the recent increase in number of wells in various regions in the United States. Methane, the primary natural gas constituent, is a greenhouse gas; hydrogen sulfide, which can be present in gas condensate, is an odor-causing compound. This study surveyed wells representing one-third of the natural gas production volume in the Texas Barnett Shale and identified the percent of sites that warrant further study due to their fence line methane and hydrogen sulfide concentrations. [ABSTRACT FROM PUBLISHER]

Abstract: Hydrocarbon generation reactions occur within organic-rich shales as a response to thermal maturation. Here, we report observations on samples from the organic-rich Mississippian Barnett shale gas system (Fort Worth Basin, Texas, USA) at varying stages of thermal maturation. A multiscale characterization was achieved using a combination of compositional organic geochemistry and spectromicroscopy techniques, including synchrotron-based scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM). We document the chemical evolution of the macromolecular structure of Barnett Shale kerogen with increasing maturity, from an immature kerogen containing a significant aliphatic component and an important concentration of oxygen and sulfur-containing functional groups to an overmature kerogen dominated by poorly condensed aromatic structures. In addition to the presence of bitumen in samples of oil window maturity, very likely genetically derived from thermally degraded kerogen, the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity, likely resulting from the formation of gaseous hydrocarbons by secondary cracking of bitumen compounds. [Copyright &y& Elsevier]

Accurately estimating total organic carbon (TOC) from suites of well logs is essential as it is too costly and time consuming to take direct measurements from core samples in many wells. Unfortunately, the several methods developed over recent decades, based on various correlations and correlation-based machine learning methods, do not provide universally reliable, accurate or easily auditable TOC predictions. A method is developed and its viability evaluated exploiting a promising correlation-free, data-matching routine. This is applied to published well-log curves, with supporting mineralogical data and measured TOC, for two wells penetrating the Lower Barnett Shale formation at distinct settings within the Fort Worth Basin (Texas, U.S.). The method combines between 5 and 10 well log features and evaluates, on a supervised learning basis, multiple cases for nine distinct models at data- record-sampling densities ranging from one record for every 0.5 ft to one record for every 0.04 ft. At zoomed-in sampling densities the model achieves TOC prediction accuracies for the models combining data from both wells of (RMSE ≤ 0.3% and R2 ≥ 0.955) for models involving 6 and 10 input variables. It is the models involving six input variables that have the potential to be applied in unsupervised circumstances to predict TOC in surrounding wells lacking measured TOC, but that potential requires confirmation in future multi-well studies. [ABSTRACT FROM AUTHOR]

The article discusses Houston, Texas, independent oil prospector George Mitchell and his efforts to drill in the Barnett Shale in north Texas. It states that drilling in the Barnett Shale since 2000 inaugurated a gas boom in the greater Fort Worth, Texas, area as of June 2012. The article also discusses the economic potential presented by shale formations in the U.S. in locations such as Texas, North Dakota, and Pennsylvania, as well as the potential for energy independence. It also examines the environmental concerns over shale drilling.

Abstract: Ethane, propane, and carbon dioxide show reversed carbon isotopic maturity trends in natural gas produced from the Barnett and Fayetteville Shales at thermal maturities greater than ∼1.5% VRE. At this high level of thermal maturity, the iso-butane to n-butane ratio also reverses, suggesting wet gas cracking has occurred, generating more gas molecules in the same volume resulting in overpressure, and increased stabilized production rates in the Barnett. Hydrothermal fluids from the nearby Ouachita Thrust front apparently enhanced the maturity of the Fayetteville and Barnett shales. Water-hydrocarbon reactions at these high maturities may account for the isotopic reversals. [Copyright &y& Elsevier]

Abstract: Chemostratigraphic evidence from the Barnett Formation (Texas, USA) elucidates the restricted nature of the depositional environment in the Fort Worth Basin during the early progression of the late Paleozoic Ouachita Orogeny. In accord with recent lithostratigraphic and petrographic studies, stratigraphic bulk geochemical analyses reveal that the environment of deposition was anoxic to euxinic, sediment-starved, with relatively high rates of organic matter accumulation. Using an environmental proxy developed from the sediment geochemistry of modern anoxic silled basins, the stratigraphic concentrations of total organic carbon (TOC) and molybdenum (Mo) in the Barnett Formation reveal a high degree of subpycnoclinal water mass restriction and an extended timescale of deep-water renewal of at least 8×103 years and potentially as long as 2×104 years. An integrated assessment of elemental concentrations, the degree of pyritization, and TOC–S–Fe relationships reveals that severe Fe limitation controlled pyrite formation and the large excess of sulfide in the overlying water column. Mineralogical and elemental constraints suggest that, following sulfate reduction, less easily bio-extractable Fe(III) was bio-reduced under methanogenic conditions, consequently liberating Fe(II) which was subsequently incorporated into pore-water-formed dolomite (i.e., organogenic dolomite). The preserved Mo–TOC, TOC–S–Fe, and Fe-bearing mineral relationships collectively indicate that the protracted turnover rate and persistent sediment starvation resulted in a biologically inhospitable environment that limited the microbial consumption rate of organic carbon. [Copyright &y& Elsevier]

Horizontal drilling and hydraulic fracturing have enhanced energy production but raised concerns about drinking-water contamination and other environmental impacts. Identifying the sources and mechanisms of contamination can help improve the environmental and economic sustainability of shale-gas extraction. We analyzed 113 and 20 samples from drinking-water wells overlying the Marcellus and Barnett Shales, respectively, examining hydrocarbon abundance and isotopic compositions (e.g., C2H6/CH4, δ(13)C-CH4) and providing, to our knowledge, the first comprehensive analyses of noble gases and their isotopes (e.g., (4)He, (20)Ne, (36)Ar) in groundwater near shale-gas wells. We addressed two questions. (i) Are elevated levels of hydrocarbon gases in drinking-water aquifers near gas wells natural or anthropogenic? (ii) If fugitive gas contamination exists, what mechanisms cause it? Against a backdrop of naturally occurring salt- and gas-rich groundwater, we identified eight discrete clusters of fugitive gas contamination, seven in Pennsylvania and one in Texas that showed increased contamination through time. Where fugitive gas contamination occurred, the relative proportions of thermogenic hydrocarbon gas (e.g., CH4, (4)He) were significantly higher (P < 0.01) and the proportions of atmospheric gases (air-saturated water; e.g., N2, (36)Ar) were significantly lower (P < 0.01) relative to background groundwater. Noble gas isotope and hydrocarbon data link four contamination clusters to gas leakage from intermediate-depth strata through failures of annulus cement, three to target production gases that seem to implicate faulty production casings, and one to an underground gas well failure. Noble gas data appear to rule out gas contamination by upward migration from depth through overlying geological strata triggered by horizontal drilling or hydraulic fracturing.

Shale gas exploration and production (E&P) has experienced substantial growth across the U.S. over the last decade. The Barnett Shale, in north-central Texas, contains one of the largest, most active onshore gas fields in North America, stretching across 5000 square miles and having an estimated 15,870 producing wells as of 2011. Given that these operations may occur in relatively close proximity to populated/urban areas, concerns have been expressed about potential impacts on human health. In response to these concerns, the Texas Commission on Environmental Quality established an extensive air monitoring network in the region. This network provides a unique data set for evaluating the potential impact of shale gas E&P activities on human health. As such, the objective of this study was to evaluate community-wide exposures to volatile organic compounds (VOCs) in the Barnett Shale region. In this current study, more than 4.6 million data points (representing data from seven monitors at six locations, up to 105 VOCs/monitor, and periods of record dating back to 2000) were evaluated. Measured air concentrations were compared to federal and state health-based air comparison values (HBACVs) to assess potential acute and chronic health effects. None of the measured VOC concentrations exceeded applicable acute HBACVs. Only one chemical (1,2-dibromoethane) exceeded its applicable chronic HBACV, but it is not known to be associated with shale gas production activities. Annual average concentrations were also evaluated in deterministic and probabilistic risk assessments and all risks/hazards were below levels of concern. The analyses demonstrate that, for the extensive number of VOCs measured, shale gas production activities have not resulted in community-wide exposures to those VOCs at levels that would pose a health concern. With the high density of active wells in this region, these findings may be useful for understanding potential health risks in other shale play regions., (© 2013. Published by Elsevier B.V. All rights reserved.)

Natural gas from tight shale formations will provide the United States with a major source of energy over the next several decades. Estimates of gas production from these formations have mainly relied on formulas designed for wells with a different geometry. We consider the simplest model of gas production consistent with the basic physics and geometry of the extraction process. In principle, solutions of the model depend upon many parameters, but in practice and within a given gas field, all but two can be fixed at typical values, leading to a nonlinear diffusion problem we solve exactly with a scaling curve. The scaling curve production rate declines as 1 over the square root of time early on, and it later declines exponentially. This simple model provides a surprisingly accurate description of gas extraction from 8,294 wells in the United States' oldest shale play, the Barnett Shale. There is good agreement with the scaling theory for 2,057 horizontal wells in which production started to decline exponentially in less than 10 y. The remaining 6,237 horizontal wells in our analysis are too young for us to predict when exponential decline will set in, but the model can nevertheless be used to establish lower and upper bounds on well lifetime. Finally, we obtain upper and lower bounds on the gas that will be produced by the wells in our sample, individually and in total. The estimated ultimate recovery from our sample of 8,294 wells is between 10 and 20 trillion standard cubic feet.

We monitored the bacterial communities in the gas-water separator and water storage tank of two newly drilled natural gas wells in the Barnett Shale in north central Texas, using a 16S rRNA gene pyrosequencing approach over a period of 6 months. Overall, the communities were composed mainly of moderately halophilic and halotolerant members of the phyla Firmicutes and Proteobacteria (classes Βeta-, Gamma-, and Epsilonproteobacteria) in both wells at all sampling times and locations. Many of the observed lineages were encountered in prior investigations of microbial communities from various fossil fluid formations and production facilities. In all of the samples, multiple HS-producing lineages were encountered; belonging to the sulfate- and sulfur-reducing class Deltaproteobacteria, order Clostridiales, and phylum Synergistetes, as well as the thiosulfate-reducing order Halanaerobiales. The bacterial communities from the separator and tank samples bore little resemblance to the bacterial communities in the drilling mud and hydraulic-fracture waters that were used to drill these wells, suggesting the in situ development of the unique bacterial communities in such well components was in response to the prevalent geochemical conditions present. Conversely, comparison of the bacterial communities on temporal and spatial scales suggested the establishment of a core microbial community in each sampled location. The results provide the first overview of bacterial dynamics and colonization patterns in newly drilled, thermogenic natural gas wells and highlights patterns of spatial and temporal variability observed in bacterial communities in natural gas production facilities. [ABSTRACT FROM AUTHOR]

Between November 2009 and September 2011, temporary seismographs deployed under the EarthScope USArray program were situated on a 70-km grid covering the Barnett Shale in Texas, recording data that allowed sensing and locating regional earthquakes with magnitudes 1.5 and larger. I analyzed these data and located 67 earthquakes, more than eight times as many as reported by the National Earthquake Information Center. All 24 of the most reliably located epicenters occurred in eight groups within 3.2 km of one or more injection wells. These included wells near Dallas-Fort Worth and Cleburne, Texas, where earthquakes near injection wells were reported by the media in 2008 and 2009, as well as wells in six other locations, including several where no earthquakes have been reported previously. This suggests injection-triggered earthquakes are more common than is generally recognized. All the wells nearest to the earthquake groups reported maximum monthly injection rates exceeding 150,000 barrels of water per month (24,000 m3/mo) since October 2006. However, while 9 of 27 such wells in Johnson County were near earthquakes, elsewhere no earthquakes occurred near wells with similar injection rates. A plausible hypothesis to explain these observations is that injection only triggers earthquakes if injected fluids reach and relieve friction on a suitably oriented, nearby fault that is experiencing regional tectonic stress. Testing this hypothesis would require identifying geographic regions where there is interpreted subsurface structure information available to determine whether there are faults near seismically active and seismically quiescent injection wells. [ABSTRACT FROM AUTHOR]

Natural gas has become a leading source of alternative energy with the advent of techniques to economically extract gas reserves from deep shale formations. Here, we present an assessment of private well water quality in aquifers overlying the Barnett Shale formation of North Texas. We evaluated samples from 100 private drinking water wells using analytical chemistry techniques. Analyses revealed that arsenic, selenium, strontium and total dissolved solids (TDS) exceeded the Environmental Protection Agency's Drinking Water Maximum Contaminant Limit (MCL) in some samples from private water wells located within 3 km of active natural gas wells. Lower levels of arsenic, selenium, strontium, and barium were detected at reference sites outside the Barnett Shale region as well as sites within the Barnett Shale region located more than 3 km from active natural gas wells. Methanol and ethanol were also detected in 29% of samples. Samples exceeding MCL levels were randomly distributed within areas of active natural gas extraction, and the spatial patterns in our data suggest that elevated constituent levels could be due to a variety of factors including mobilization of natural constituents, hydrogeochemical changes from lowering of the water table, or industrial accidents such as faulty gas well casings.

The Barnett Shale in north central Texas contains natural gas generated by high temperatures (120 to 150°C) during the Mississippian Period (300 to 350 million years ago). In spite of the thermogenic origin of this gas, biogenic sulfide production and microbiologically induced corrosion have been observed at several natural gas wells in this formation. It was hypothesized that microorganisms in drilling muds were responsible for these deleterious effects. Here we collected drilling water and drilling mud samples from seven wells in the Barnett Shale during the drilling process. Using quantitative real-time PCR and microbial enumerations, we show that the addition of mud components to drilling water increased total bacterial numbers, as well as the numbers of culturable aerobic heterotrophs, acid producers, and sulfate reducers. The addition of sterile drilling muds to microcosms that contained drilling water stimulated sulfide production. Pyrosequencing-based phylogenetic surveys of the microbial communities in drilling waters and drilling muds showed a marked transition from typical freshwater communities to less diverse communities dominated by Firmicutes and Gammaproteobacteria. The community shifts observed reflected changes in temperature, pH, oxygen availability, and concentrations of sulfate, sulfonate, and carbon additives associated with the mud formulation process. Finally, several of the phylotypes observed in drilling muds belonged to lineages that were thought to be indigenous to marine and terrestrial fossil fuel formations. Our results suggest a possible alternative exogenous origin of such phylotypes via enrichment and introduction to oil and natural gas reservoirs during the drilling process.