New Data Show Methane in Pennsylvania Water Wells Unrelated to Hydraulic Fracturing Lisa Molofsky, John Connor, Shahla Farhat GSI Environmental Inc. Albert S. Wylie, Tom Wagner Cabot Oil and Gas Corporation GSI ENVIRONMENTAL INC. Houston and Austin, TX (713) 522-6300 CABOT OIL & GAS Pittsburgh, PA
Overview: Susquehanna County Nature of Methane Impacts on GW Pre-Drill Methane Survey: Susquehanna County Geologic and Historical Background Overview: Osborn et al. (2011) PNAS Study Susquehanna County Pennsylvania Isotopic Signatures of Source and Impact Gases in Susquehanna County
Methane Impacts on GW in Northeastern Pennsylvania: Regional Survey of Pre-Drill Methane in Water Wells Pre-Drill Methane in >1700 Water Wells, 2008-2011 FINDINGS 78% of water wells contain methane Higher concentrations in valleys vs. uplands No correlation with gas production areas
Underlying Geology of Northeastern PA Key Strata Geologic Cross Section: Susquehanna County Glacial Till: Contains Microbial Gas Catskill & Lockhaven Formations: Thermogenic gascharged sandstone deposits (contain extensive fracture networks) Marcellus shale: Gas at ~6000 ft below surface.
Underlying Geology of Northeastern PA Key Point Organic seams in Catskill formation are potential source of thermogenic gas
Historical Locations of Gas Shows: 200 years Key Point Shrewsbury Gas Field, 1969 Lovelton Gas Field, 1965 Salt Springs, pre-1800 Shallow gas shows observed in water and gas wells for over 200 years Harveys Lake Gas Field, 1956
PNAS Osborn et al. 2011 Study (Duke University) Objective: Comparison of Water Quality in Active vs. Non-Active Gas Extraction Areas Study Area New York and Northeastern Pennsylvania Susquehanna County, Dimock Township Data Set Otsego Bradford Susquehanna 60 Water Wells Sampled for Dissolved Gas Concentrations & Stable Isotopic Signatures
Osborn et al. Study: Conclusions Re. Methane Impacts on GW Methane Concentration (mg/ch 4 /L) Active Extraction Areas Non-Active Extraction Area Findings by Osborn et al., 2011 Higher methane in water wells in gas prod. zones. Methane in gas prod. zones = thermogenic (deep shale gas). Methane in non-production zones = microbial or microbial/ thermogenic mix. Distance to Nearest Gas Well (m) FINDINGS Gas drilling and hydraulic fracturing activities are impacting water wells across region
Oil and Gas Journal Article: Isotopic Analyses of Source Gases vs. Methane in Water Wells DATA SET Dimock 14 Water Wells 1 Salt Spring 4 Gas Wells (sampled at multiple intervals) LOCATION Susquehanna County, Dimock Township
Isotope Analyses: Source Gases Identified by Pennsylvania DEP and Cabot Upper and Middle Devonian Gases Above Marcellus Marcellus Shale Gas Source Gases Marcellus Production Gas (PA DEP & Cabot) CO 2 Reduction Microbial Gas Thermogenic Gas Fermentation Upper / Middle Devonian Gas Above Marcellus (PA DEP) Dissolved Gas Identified as Upper/Middle Devonian (PA DEP) KEY POINT: Although similar, in many cases local Marcellus shale gas can be distinguished from shallower thermogenic gases.
Isotope Analyses: Water Well Gases Sampled by Pennsylvania DEP and Cabot CO 2 Reduction Upper and Middle Devonian Gases Above Marcellus Thermogenic Gas Marcellus Shale Gas Water Samples Dissolved Gas Sampled from Local Water Wells (PA DEP & Cabot) Microbial Gas Fermentation Spring: Salt Springs State Park (Cabot) KEY POINT: Signatures of dissolved gases from local water wells are consistent with microbial or shallow thermogenic sources.
Isotope Analyses: Water Well Gases Sampled by Osborn et al. CO 2 Reduction Upper and Middle Devonian Gases Above Marcellus Thermogenic Gas Marcellus Shale Gas Osborn Water Samples Osborn Study: Dissolved Gas Sampled from Local Water Wells Microbial Gas Fermentation KEY POINT: Water well gases sampled by Osborn appear generally consistent with gases from Upper and Middle Devonian strata.
Relationship of Gas Source to Water Well Depth Cabot Post-Drill Sampling of 3 Water Wells Thermogenic Gas Microbial Gas/ Mix Gas Well Pad CH 4 = 26.1 ppm CH 4 = 28 ppm 30 ft CH 4 = 13 ppm 175 ft 120 ft Deep Water Wells in Catskill Formation = Thermogenic Gas Shallow Water Wells in Glacial Till = Microbial Gas / Mixture
Nature of Methane Impacts on GW: Key Findings Majority of water wells contain methane Elevated methane found in valleys vs. uplands Geological and historical evidence of shallow gas Most water wells and all gas wells penetrate Catskill formation (well construction issues) Isotopic signature of gas in water wells is consistent with: 1. Thermogenic gas from shallow Upper/Middle Devonian Formations 2. Microbial gas KEY POINT: No clear evidence of impacts by Marcellus gas or the hydraulic fracturing process.
RPSEA Proposal 2012: Stray Gas Investigation Protocol: Incentive: Variable results in recent gas sourcing studies due to use of different analytical suites, sampling methodologies, and consideration of different lines of evidence. Key Research Issues: 1. Compile pre-drill water sample database 2. Develop isotopic database of source gases 3. Evaluate Temporal Variability of dissolved and free gas 4. Evaluate Sampling Methods
OBJECTIVE: Need for Effective Approaches to the Investigation of Stray Gas Incidents Credit: Bennett V/Flickr