Controls on Methane Occurrences in Shallow Aquifers Overlying the Haynesville Shale Gas Field, East Texas

Abstract

Understanding the source of dissolved methane in drinking-water aquifers is critical for assessing potential contributions from hydraulic fracturing in shale plays. Shallow groundwater in the Texas portion of the Haynesville Shale area (13,000 km ) was sampled (70 samples) for methane and other dissolved light alkanes. Most samples were derived from the fresh water bearing Wilcox formations and show little methane except in a localized cluster of 12 water wells (17% of total) in a approximately 30 × 30 km area in Southern Panola County with dissolved methane concentrations less than 10 mg/L. This zone of elevated methane is spatially associated with the termination of an active fault system affecting the entire sedimentary section, including the Haynesville Shale at a depth more than 3.5 km, and with shallow lignite seams of Lower Wilcox age at a depth of 100 to 230 m. The lignite spatial extension overlaps with the cluster. Gas wetness and methane isotope compositions suggest a mixed microbial and thermogenic origin with contribution from lignite beds and from deep thermogenic reservoirs that produce condensate in most of the cluster area. The pathway for methane from the lignite and deeper reservoirs is then provided by the fault system.

Trace Element Behavior in Methane‐Rich and Methane‐Free Groundwater in North and East Texas

“…A total of 17 (8.2%) and 10 (24%) samples have dissolved methane concentrations >10 mg/L and concentrations of 152 (73%) and 24 (57%) samples are <1 mg/L, respectively. Results previously published by Nicot et al (, ) clearly indicate the presence of thermogenic methane. This is particularly evident in the Barnett counties with high C1/C2 + C3 ratios and heavy carbon isotope ratios.…”

Global Isotope Hydrogeology―Review

“…Unlike groundwater δ 18 O, δ 2 H, and 3 H measurements, groundwater carbon isotope data provide information about sources and processes governing gas and solute concentrations in groundwater, rather than information about water molecules. Groundwater carbon isotope compositions have been analyzed for gaseous and dissolved phases for many different molecular species, including total dissolved inorganic carbon, total dissolved organic carbon, methane, and other hydrocarbons (e.g., Aravena et al, ; Barker & Fritz, ; Bates et al, ; Cheung et al, ; Deines et al, ; Etiope et al, ; Genereux et al, ; Humez et al, ; Hunkeler et al, ; Hunkeler & Aravena, ; Jackson et al, ; Li et al, ; McIntosh et al, ; Meckenstock et al, ; Meredith et al, ; Münnich & Vogel, ; Nicot et al, ; Osborn et al, ; Révész et al, ; Schlegel et al, ; Vinson et al, ; Vogel, ; Vogel, Lerman & Mook, ; Vogel & Ehhalt, ; Walvoord et al, ).…”

Numerical Modeling of Methane Leakage from a Faulty Natural Gas Well into Fractured Tight Formations

“…Significant progress has been made in collecting data in advance of drilling for shale gas and in developing more robust geochemical and hydrogeological approaches to evaluating the source and the occurrences of methane in shallow aquifers (Darrah et al 2015a(Darrah et al , 2015bHarkness et al 2017;Heilweil et al 2015Heilweil et al , 2016Humez et al 2016;Jackson et al 2013a;Moritz et al, 2015;Nicot et al, 2017aNicot et al, , 2017bSiegel et al 2015;Vengosh et al 2014;Warner et al 2012aWarner et al , 2012bWarner et al , 2014). Yet, there is a need for modeling approaches to constrain the pathways, timing, and mechanisms of hydrocarbon migration to and within shallow aquifers (Schwartz 2013).…”

“…Yet, there is a need for modeling approaches to constrain the pathways, timing, and mechanisms of hydrocarbon migration to and within shallow aquifers (Schwartz 2013). For example, aquifers rarely can be characterized as homogenous porous media (Gorody 2012;Darrah et al 2015a;Nicot et al 2017aNicot et al , 2017b. Modeling gas transport in shallow aquifers overlying unconventional hydrocarbon reservoirs is complicated by complexities in the physical setting.…”