Colorado State University



Texas Oil and Gas Area Source Emissions Inventory DevelopmentThe Texas Commission on Environmental Quality (TCEQ) develops the Texas oil and gas area source (non-point) emissions inventory using a set of Excel spreadsheet calculators originally developed by Eastern Research Group, Inc. (ERG) in the 2010 study Characterization of Oil and Gas Production Equipment and Develop a Methodology to Estimate Statewide Emissions, available at . The Appendix D calculator is used to estimate compressor engine emissions, and the Appendix E calculator is used to estimate all of the other stationary oil and gas emissions.The calculators use oil and gas activity data from the Railroad Commission of Texas (RRC), such as the number of oil and gas wells, the amount of oil, condensate, and gas production, and the amount of drilling activity. The county-level activity data is combined with source-specific emission factors and equipment profiles to estimate county-level emissions by type of source. Emissions are estimated for a variety of sources, including but not limited to: compressor engines, condensate and crude oil storage tanks, equipment leak fugitives, pneumatic devices, and loading losses.The calculators estimate total oil and gas emissions at the county-level. Point source emissions are summed by county and source type and subtracted from the applicable total county-level emissions to arrive at the final area source emissions estimates.The TCEQ continually works to improve the emissions estimates, with an emphasis on developing and updating oil and gas basin and shale specific emission factors and equipment profiles. There are seven oil and gas basins in Texas along with a number of shale plays. Updated emission factors and equipment profiles are developed by TCEQ-contracted studies as well as TCEQ staff projects. Updates include:Produced water storage tanks: State-wide VOC factor of 0.01 lb/bbl of produced water taken from the 2010 study Emission Factor Determination for Produced Water Storage Tanks, available at .Condensate storage tanks: ERG developed region-specific emission factors and control factors for eight geographic regions in Texas in the 2012 study Condensate Tank Oil and Gas Activities, available at .Heaters: ERG developed region-specific heater and boiler equipment profiles for eight geographic regions in Texas as well as an updated nitrogen oxides (NOx) emission factor for these source types in the 2013 study Upstream Oil and Gas Heaters and Boilers, available at .Compressor engines: TCEQ conducted the Barnett Shale Special Inventory in 2011, obtaining data from over 8,000 sites that operated in the Barnett Shale in 2009, including information from over 1,850 compressor engines. This compressor engine data was combined with control requirements from the TCEQ Chapter 117 NOx rules to develop updated compressor engine profiles and emission factors for the DFW non-attainment counties, the Barnett Shale attainment counties, and the East Texas area. More information about the Barnett Shale Special Inventory can be found at: .Pneumatic devices: TCEQ conducted two pneumatic device surveys in 2011 and 2012. The first survey covered the Barnett Shale area and corresponded with the Barnett Shale Phase II Special Inventory. The second survey covered the rest of Texas. Based on the data obtained, basin-specific pneumatic device emission factors (weighted-average bleed rates and VOC compositions) and activity data (number of devices per well) were developed. The bleed rates are based on information from the CenSARA study 2011 Oil and Gas Emission Inventory Enhancement Project for CenSARA States, prepared for CenSARA by ENVIRON and ERG, December 2012. Available at: . An update for the 2014 inventory is the use of updated numbers of devices per well for oil wells where a statewide average had previously been used due to a low survey response rate (areas other than the Eagle Ford Shale area and the Permian Basin). The updates were taken from the 2014 EPA oil and gas tool (which are based on 2014 EPA GHGRP data).Drilling rigs: ERG developed drilling rig emissions characterization profiles in the 2010 study Development of Texas Statewide Drilling Rigs Emission Inventories for the years 1990, 1993, 1996, and 1999 through 2040, available at: . The emission profiles and calculation methodologies were used by TCEQ to develop an Excel spreadsheet calculator similar to the Appendix D and Appendix E TCEQ oil and gas calculators. While the ERG study projected drilling activity from 2010 into the future, the TCEQ obtains actual annual drilling activity data from the RRC and re-calculates drilling rig emissions using the actual activity data combined with the year-specific engine emission factors taken from the ERG study. Updated drilling rig emissions characterization profiles were developed by ERG in the 2015 study 2014 Statewide Drilling Rig Emissions Inventory with Updated Trends Inventories, based on a new survey of Texas drilling companies. This study is available at: .Oil and gas well flaring: Data on the amount of oil and gas well venting and flaring is obtained annually from the RRC and used with EPA AP-42, Section 13.5 flare factors to estimate the amount of flaring emissions. The EPA AP-42 flare factors (most recently revised in April 2015) are available at: . An update made to the 2014 inventory involved splitting well flaring emissions between oil wells and gas wells. Previously, all of the well flaring emissions were reported under an oil well SCC code, due to the gas well flaring being substantially less than oil well flaring (gas wells accounted for only 7.8% of the gas being flared in 2014).EPA Oil and Gas Emissions Estimation tool: Review of this tool identified sources (drilling mud degassing, pneumatic pumps, and hydraulic fracturing pump engines) to include in the TCEQ oil and gas calculator. Using the emission factors and equipment profiles from the EPA tool, these sources were added to the Appendix E calculator. Review of this tool also identified updated emission factors for artificial lift engines and well completions (taken from the 2011 CenSARA study). The EPA oil and gas emissions estimation tool is available at: .Oil and gas well adjustments: Based on a review of an Alamo Area Council of Governments (AACOG) 2014 study Oil and Gas Emission Inventory, Eagle Ford Shale, the number of oil and gas wells was adjusted to reflect that new wells are active on average for half the year (instead of active for the entire year). The adjusted well count for a specific year was changed to equal the total number of active wells minus half the number of well completions for that year. The AACOG report is available at: .Mud degassing: ERG developed region-specific VOC mud degassing emission factors in the 2014 study Specified Oil and Gas Well Activities Emissions Inventory Update, available at: .Hydraulic fracturing pumps: ERG develop region-specific hydraulic fracturing pump engine activity data for eight geographic regions in Texas as well as year specific engine emission factors for 2012, 2013, and 2014 that take into account the effect of Tier 3 and Tier 4 engine emission standards in the 2014 study Specified Oil and Gas Well Activities Emissions Inventory Update, available at: .NSPS OOOO controls: ERG estimated the impact controls required by the New Source Performance Standards (NSPS) Subpart OOOO rules would have on the 2013 area source oil and gas emissions inventory, and developed a method to estimate the impacts using future years’ RRC activity data in the 2014 study Specified Oil and Gas Well Activities Emissions Inventory Update, available at: .Storage tank controls: ERG developed region-specific control factors for crude oil storage tanks and condensate storage tanks based on a survey of Texas oil and gas operators in the 2015 study Upstream Oil and Gas VOC controls. The study includes both VRU and flare control factors. The TCEQ combined the ERG survey results with 2014 EPA Greenhouse Gas Reporting Program (GHGRP) data, available through the EPA’s Envirofacts website at: in order to develop alternative control factors, as detailed in an Addendum to the ERG report. The ERG study and TCEQ Addendum are available at: [Note, not yet posted on TCEQ website] Loading loss controls: ERG developed region-specific control factors for crude oil and condensate loading losses based on a survey of Texas oil and gas operators in the 2015 study Upstream Oil and Gas VOC controls. The study includes both VRU and flare control factors, and is available at: [Note, not yet posted on TCEQ website]Oil well blowdowns: Emissions were previously estimated using the factors for gas well blowdowns taken from the 2010 ERG study. However, the EPA oil and gas tool does not estimate these emissions, and information on the internet indicated that oil wells are not routinely blown down. Therefore, these emissions have been zeroed out.Well completions: Emissions from well completions of hydraulically fractured gas wells are assumed to be 100% controlled by flares for the 2014 EI, due to NSPS OOOO control requirements (green completions are required starting in 2015, so future EI’s will reflect that). Emissions from well completions of hydraulically fractured oil wells are assumed to be 90% controlled by flares, based on a survey of oil and gas operators in the Permian Basin and Eagle Ford Shale area conducted by the TCEQ in the fall of 2015. Once NSPS OOOOa requires green completions for oil wells, future EI’s will reflect that.Piping component fugitives: The TCEQ calculator was updated to add light liquid components to gas well fugitives, and gas/vapor components to oil well fugitives, similar to the EPA tool. Instead of adding the same number of components of each type to both gas wells and oil wells, the components were split according to the type of well. For gas wells, the split in components was 75% gas/vapor and 25% light liquid; for oil wells, the split in components was 25% gas/vapor and 75% light liquid. ................
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