The Mississippian Barnett Formation is a prolific shale-gas reservoir that was deposited in the Fort Worth Basin, Texas. Many previous studies of the Barnett Formation have been conducted in the main production area; few studies have been made of the Barnett Formation in the southern part of the basin, which is a less productive area. In the present research, several cores from the Barnett Formation in Hamilton County, southeast Fort Worth Basin, are studied in detail. Two vertical, continuous cores from Hamilton County, Texas, were studied to delineate the depositional setting, lithofacies, pore types, and reservoir quality of the Barnett Formation in the area. Five lithofacies were defined by analysis of the two cores: (1) laminated clay-rich silty and skeletal peloidal siliceous mudstone; 2) laminated skeletal silty peloidal siliceous mudstone; 3) nonlaminated silty peloidal calcareous mudstone; 4) laminated and nonlaminated skeletal calcareous mudstone; and 5) skeletal phosphatic packstone to grainstone. As indicated from this study, the dominant organic matter type is a mixture of Type II (major) and Type III (minor) kerogen having a mean TOC content of approximately 4%. Analysis of Rock Eval data shows that most of the interval is within the oil window; calculated Ro is approximately 0.9%. Organic geochemistry shows that the hydrocarbon generation potential of the abundant oil-prone kerogen was excellent. Mineralogical analysis reveals that the two types of siliceous mudstone, which are similar in composition to the siliceous mudstone in the main producing area in the northern Fort Worth Basin, are good for hydraulic fracturing and production, but they are also limited by their marginal thickness. Organic matter pores, which are the dominant pore types in these two cores, are consistent with pore types found in currently producing wells in the Newark East Field. This research also suggests that the deposition of Barnett Formation was controlled largely by basinal geometry, suspension settling, and slope-originated gravity-flow events. Skeletal deposits and carbonate-silt starved ripples suggest gravity-flow deposits and bottom-current reworking during deposition. Redox-sensitive elements and degree of pyritization both indicate anoxic/euxinic conditions during the deposition of the Barnett Formation. / text

Conventional sources of emissions have been a prime target for policymakers in designing pollution control strategies. However, the evolution of shale gas activities is a growing concern over the impact of unconventional sources on urban and regional air quality. Owing to the development of Barnett Shale production, the fast-growing Dallas-Fort Worth (DFW) metroplex has encountered both types of these emissions. Oil and gas activities result in emissions of ozone precursors, notably volatile organic compounds (VOC). The major objective of this study was to evaluate the spatio-temporal distribution of VOC in order to highlight the influence of unconventional emissions. The study utilized measurements from automated gas chromatography (AutoGC) monitors to analyze the patterns of the total non-methane organic compounds (TNMOC) and relative contributions from marker species of traffic versus oil and gas activities. In this study, data from 2001-2014 was obtained from the Texas Commission on Environmental Quality (TCEQ) for fifteen monitoring sites within the North Texas region. With over a thousand wells in a 10 mile radius, two of the rural sites measured twice as much TNMOC as compared to the urban site in Dallas. Source apportionment analysis was conducted using Positive Matrix Factorization (PMF) technique. The target site located in the urban zone resolved an eight factor model. Natural gas signature was the dominant source of emission with a 52% contribution followed by 31% from two separate traffic-related sources. Considering ethane to be the dominant species in oil and gas emissions, it was observed that the rising ethane/NOx ratio correlated with increasing annual average ozone post-2007. In this period, higher concentration of ozone was found to be associated with stronger winds from the Barnett Shale area – a region that did not seem to contribute to high ozone during 2001-2007. With traffic emissions having flattened over the years, the recent increase in oil- and gas-related emissions has a negative impact on the air quality in this area. Results indicate that the area has failed to observe a declining trend in ozone despite effective reductions in NOx and traffic-related VOC emissions. The findings of the study would be helpful in proper evaluation of the ozone-forming potential of unconventional VOC emissions. Although these emissions may not be strong enough to cause harm through direct exposure, underestimating their potential towards ozone formation could hinder the progress in ozone attainment in growing urban areas. After all, a major portion of the study area continues to be in nonattainment of the EPA designated ozone standards. The study therefore draws the attention of policymakers towards the new influx of emissions that have emerged as a powerful source within the DFW metropolitan area.

The effect of shale gas activities on ground-level ozone pollution in the Dallas-Fort Worth area is studied in detail here. Ozone is a highly reactive species with harmful effects on human and environment. Shale gas development, or fracking, involves activities such as hydraulic fracturing, drilling, fluid mixing, and trucks idling that are sources of nitrogen oxides (NOX) and volatile organic compounds (VOC), two of the most important precursors of ozone. In this study two independent approaches have been applied in evaluating the influences on ozone concentrations. In the first approach, the influence of meteorology were removed from ozone time series through the application of Kolmogorov-Zurbenko low-pass filter, logarithmic transformation, and subsequent multi-linear regression. Ozone measurement data were acquired from Texas Commission on Environmental Quality (TCEQ) monitoring stations for 14 years. The comparison between ozone trends in non-shale gas region and shale gas region shows increasing ozone trends at the monitoring stations in close proximity to the Barnett Shale activities. In the second approach, the CAMx photochemical model was used to assess the sensitivity of ozone to the NOX and VOC sources associated with shale oil and gas activities. Brute force method was applied on Barnett Shale and Haynesville Shale emission sources to generate four hypothetical scenarios. Ozone sensitivity analysis was performed for a future year of 2018 and it was based on the photochemical simulation that TCEQ had developed for demonstrating ozone attainment under the State Implementation Plan (SIP). Results showed various level of ozone impact at different locations within the DFW region attributed to area and point sources of emissions in the shale region. Maximum ozone impact due to shale gas activities is expected to be in the order of several parts per billion, while lower impacts on design values were predicted. The results from the photochemical modeling can be used for health impact assessment and air quality management purposes. Both studies in this research show that the impact of shale gas development on local and regional level of ozone is significant, and therefore, it should be considered in the implementation of effective air quality strategies.

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