Trace Gas Emissions from Oil and Gas Operations Considerations for Atmospheric Researchers NASA AQAST Meeting June 17, 2014 Cambridge, MA
• Numerous studies of emissions from oil and gas production, gathering systems, and gas processing. Some address criteria pollutants or HAPs, but majority focused on methane emissions. • Some of these studies, coupled with agency programs such as EPA’s GHG Reporting Rule, have increased understanding of sector emissions. Many other studies have just raised more questions. • Challenge for researchers measuring atmospheric concentrations and estimating mass fluxes is accounting for the unique operating characteristics of the oil and gas sector. 2
Industry Characteristic: Variability of Gas Composition • Composition of hydrocarbons in the reservoir is a key factor in VOC and GHG emissions – Widely variable – spans entire range of hydrocarbons (think pure methane to tar). There is no “mean composition”. – Also drives what equipment and processing are necessary • Hydrocarbon composition of a “gas well” typically has 2 phases: gas and condensate (liquids) – Species partitioning between gas and liquids depends on the initial composition, and the T and P at which gas and liquids are separated. Emissions speciation also depends on the T and P of the process – Different speciation profiles on a single well-pad (e.g., tank flashing, dehydrator overhead, raw gas) – A single surface well can access multiple subsurface reservoirs with different compositions 3
Example Well Pad* Sales gas Dry Gas to Sales Produced gas Wellheads or “raw gas” Dehydrator vent gas Gas, Produced Water, and Condensate Wet Gas Dehydrator Skid Separator Flash gas Produced Water Condensate Tank vapors may be recovered or combusted Combustor or Flare Produced Water Condensate 4 *Simplified diagram for illustrative purposes – one of many possible well configurations
Emission Em ons com ompos osition on v varies a acros oss t the well pad Example Speciation Profile Produced Gas v. Flash Gas Mole Percent Produced Gas Flash Gas Methane 84.98% 34.40% Ethane 6.81% 13.74% Propane 3.17% 18.28% i-Butane 0.64% 6.79% n-Butane 0.71% 9.12% 4.27% i-Pentane 0.24% n-Pentane 0.20% 3.71% Benzene 0.01% 0.30% Toluene 0.02% 0.38% CO2 2.73% 2.86% 5
Comp mpositions are n not c consistent by f forma mation type Example Sales Gas Compositions* % Ethane % Methane % CO 2 No. of Data Formation Type Region Ave Ave Ave Low High Points High Permeability Gas North East 83 70 98 10 0.07 878 Gulf Coast 86 54 98 5 1.20 727 Rocky 93 90 94 3 2.72 3848 Shale Gas North East 85 69 98 9 0.12 2584 Gulf Coast 92 75 98 3 3.20 414 Other Tight Reservoir North East 87 74 98 8 0.08 862 Rock Gulf Coast 87 59 96 5 0.92 808 Rocky 86 82 89 7 2.01 1129 Oil North East 77 70 83 15 0.10 129 Gulf Coast 80 66 92 9 1.08 2028 Coal Seam Rocky 88 NA NA 2 8.26 30 Gulf Coast 89 77 94 4 0.21 14 *Compositions are taken from random industry data and do not represent overall formation averages 6
Comp mpositions are n not c consistent within a a single ba basin in Example Sales Gas Compositions Appalachia Basin – Shale Gas Mole % Methane Ethane Propane Butanes Pentanes Hexanes CO2 Dataset 1 68.75 19.28 8.44 2.35 0.53 0.22 0.09 Dataset 2 69.36 19.31 7.69 1.97 0.44 0.18 0.06 Dataset 3 73.76 15.83 6.58 1.92 0.53 0.25 0.08 Dataset 4 73.80 16.69 6.23 1.83 0.48 0.22 0.08 Dataset 5 74.15 14.95 6.59 1.98 0.54 0.29 0.09 Dataset 6 75.90 13.49 6.22 1.74 0.43 0.22 0.07 Dataset 7 76.59 14.33 5.47 1.87 0.55 0.31 0.10 Dataset 8 76.61 13.20 6.11 1.48 0.30 0.11 0.07 Dataset 9 76.85 12.65 5.70 1.69 0.46 0.29 0.19 Dataset 10 77.89 13.55 5.37 1.61 0.44 0.21 0.10 Dataset 11 78.06 10.65 5.32 1.77 0.51 0.24 0.05 Dataset 12 78.40 13.54 4.63 1.58 0.50 0.29 0.11 Dataset 13 78.69 12.03 4.87 1.35 0.34 0.17 0.05 Dataset 14 87.09 8.97 2.36 0.70 0.20 0.11 0.07 Dataset 15 90.54 4.92 1.91 1.06 0.39 0.22 0.01 7
Composit itio ions drive ive equip quipment a and p processin ing Example VOC Emissions Breakdown for Two Basins 1 Other Venting - Other Venting - Compressor Categories recompletions Categories initial Engines Compressor 8% 0.5% 3% completions 2% engines Drill rigs Pneumatic 1% 27% 1% Devices 20% Oil Tank Pneumatic 2% devices Drill rigs 17% 2% Condensate tank Pneumatic Venting - Oil Well Truck 33% pumps initial Loading 6% completions 6% 5% Dehydrator Fugitives Venting - 6% 24% Miscellaneous Fugitives recompletions Dehydrator Artificial Lift engines 14% 7% 10% 2% 3% Southwest Wyoming Basin Powder River Basin VOC emissions sources vary significantly from basin to basin – tank flashing, dehydration and pneumatic devices are consistently large source categories in most basins, but for coal bed methane (CBM) dominant basins other categories are significant 1 from October 21, 2013 presentation by Tom Moore, WRAP/Westar, Air Quality and Oil & Gas Development in the Rocky 8 Mountain Region, Boulder, CO. Data are for 2008 WRAP inventory.
Industry Characteristic: Temporal Variability Another consideration: Some emissions typically occur during daylight hours, such as truck loading emissions Some examples. Along with frequency, the magnitude of these emissions will also vary with production, load, etc. Periodic or Intermittent Emissions Episodic Emissions • Well venting for liquids unloading (wide frequency • Engine emissions during drilling, completion, range: 1/day to less frequent than 1/year or never) and workovers • Truck loading • Maintenance blowdowns • Tank flashing (depends on separator dump frequency Continuous Emissions to storage tanks) Glycol dehydrators • • Pneumatic pumps and intermittent vent controllers • Equipment fugitives • Intermittent fired heaters/boilers • Compressor engines/turbines • Continuous fired heaters/boilers • Continuous bleed pneumatic controllers 9 Tank working/breathing (non-flash) losses •
Industry Characteristic: Production Decline Example for Western US – Tight Sands Gas Well 3,000 3,000 2,500 2,500 2,000 2,000 MSCF/Day 1,500 1,000 MSCF/Day 1,500 500 - 0.00 20.00 40.00 60.00 80.00 100.00 1,000 Days From Initial Prod 500 - 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 10 Days From Initial Prod.
Accounting for Background and Non- Oil and Gas Sources Enteric Fermentation 2012 CH4 Emissions, MMT CO2e Non-oil and gas 12.8 Landfills 7.4 5.7 sources, which may be 15.3 12 co-located in Other Oil and Gas production areas, are a Oil and Gas Production 141 significant portion of 52.9 Coal Mining US methane emissions. Manure Management Is it reasonable for 55.8 studies to attribute any Forest Land Remaining Forest Land “gap” between study Wastewater Treatment estimated methane flux 102.8 Rice Cultivation and bottom-up 73 inventory estimates Stationary Combustion solely to the oil and gas 88.6 Other sector? From EPA 2012 National GHG Inventory Methane from natural geologic seeps can be significant. Geological sources have been From EPA 2012 National GHG Inventory estimated to account for 7-14% 1 of global methane emissions, with some researchers suggesting that the contribution could be as much as 30% 2 . 11 1 Etiope, G., 2012. Methane Uncovered. Nature Geoscience 5, 373-374; 2 http://newsinfo.iu.edu/news-archive/24236.html
Considerations for Experimental Design Many emission sources from oil and gas production are not at steady-state, and there is a tremendous amount of variability depending on hydrocarbon composition, site-specific geology, and operational practices Uncertainty in flux calculations coupled with variability in emissions lead to non-trivial uncertainties – experiments must be carefully designed Background and non-oil and gas emission sources should be considered Close collaboration with industry could help to design experiments to capture a full range of emissions, which will allow more quantitative comparisons with inventories 12
API Efforts Under Consideration – Methane Emissions Workshop focused on major methane-producing industries (oil and gas, agriculture, landfills, etc.) and exploration of how to fill research gaps Guidance Manual on Methane Emissions Sources - Encompass production, gathering and collection, and processing sectors - Address minimization and control of methane emissions 13
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