Oil Wells vs. Gas Wells – A Texas perspective Paige Sprague and Michael Ege Air Quality Division Texas Commission on Environmental Quality (TCEQ) National Oil and Gas Committee May 11, 2017

Overview Where does Texas oil and gas activity data come from? Railroad Commission of Texas (RRC) oil well versus gas well definitions Differences between EPA oil and gas tool and Texas’ oil and gas activity data Comparison of emissions per well (or per barrel of liquids production) for Texas Conclusions

Where does Texas oil and gas activity data come from? Oil and gas operators report production at the lease level to the RRC. Oil and gas production data can be queried from the RRC website at: http://webapps.rrc.state.tx.us/PDQ/generalReportAction.do County-level monthly and annual production data is available in a variety of ways: County-level totals Operator totals Lease-level totals

RRC oil well versus gas well definitions Statutory definition: Based on the gas/oil ratio (GOR) in thousands of cubic feet of gas per barrel of petroleum liquids (MCF/BBL) GOR > 100 MCF/BBL : gas well GOR < 100 MCF/BBL : oil well In practice, additional criteria are applied. For wells with a GOR between 12.5 – 100 MCF/BBL API gravity > 50 : gas well API gravity < 50 : oil well

Differences between EPA oil and gas tool and Texas’ data GOR (MCF/BBL) RRC well type EPA tool well type > 100 Gas 12.5 – 100, API gravity > 50 Oil API gravity < 50 < 12.5 For one subset of wells (GOR between 12.5 and 100 MCF/BBL, with an API gravity > 50), the wells would be classified differently. All other wells would be classified the same.

Differences between EPA oil and gas tool and Texas’ data (cont.) Some gas wells shifted to oil wells based on the GHGRP GOR definition used by ERG About 10% of gas wells were shifted to oil wells (impacts compressor engine emissions) About 95% of condensate was shifted to oil (impacts storage tank and loading loss emissions) HPDI data used for EPA tool double counts some of the oil well data for Texas RRC data is reported at the lease level, not the well level. Oil leases can have multiple wells, which leads to double counting in the HPDI data. Gas leases only have one well, so no double counting of gas well data.

Differences between EPA oil and gas tool and Texas’ data (cont.) Activity data EPA Tool HPDI data original HPDI data adjusted* Texas RRC Oil wells 479,144 246,760 189,706 Crude oil, Mbbls 2,109,061 1,124,263 954,954 Casinghead gas, MMcf 6,458,542 4,209,643 2,072,280 Gas wells 90,070 104,446 Condensate, Mbbls 5,424 144,890 Natural gas, MMcf 4,318,593 6,279,338 *HPDI activity data adjusted to remove effects of double counting of oil well data

Comparison of area source emissions by well type for Texas To compare emissions between well types, Texas statewide emissions by source type were divided by the number of wells (tons per well) or by the amount of production (tons per thousands of barrels). While there are differences in emissions per well (or per production) between different basins in Texas for many sources, statewide averages were used here to simplify the comparisons.

Comparison of VOC emissions by well type for Texas Tons of VOC emissions per thousands of barrels of product: Condensate storage tanks have about 3.55 times the emissions as crude oil storage tanks. Type of source Oil wells Gas wells Crude oil storage tanks 0.40 - Condensate storage tanks 1.42

Comparison of VOC emissions by well type for Texas (cont.) Tons of VOC emissions per well: For sources present at both types of wells, the total emissions are almost the same. However, gas wells have additional emissions: blowdowns and dehydrators (0.66 tons VOC per well total), so the well type is important. Type of source Oil wells Gas wells Pneumatic devices 0.74 0.35 Piping fugitives 0.34 0.48 Pneumatic pumps 0.04 0.31 Total: 1.12 1.14

Comparison of NOX emissions by well type for Texas Tons of NOX emissions per well: Gas wells have over 11 times the NOX emissions as oil wells for these sources. Well type is VERY important for NOX emissions. Type of Source Oil wells Gas wells Wellhead compressor engines - 1.47 Lateral/gathering compressor engines 0.31 Artificial lift engines 0.16 Total: 1.78

Conclusions For the 2014 National Emissions Inventory (NEI), Texas used the RRC activity data to estimate emissions. Texas relies on the RRC to make the determination between oil wells and gas wells (and crude oil versus condensate). Since condensate has higher emissions than crude oil, condensate should not be reclassified as crude oil in the EPA tool. Since the number of gas wells significantly impacts NOX emissions, gas wells should not be reclassified as oil wells in the EPA tool.

Questions?

Contact Information Paige Sprague (512) 239-6732 Paige.Sprague@tceq.texas.gov Michael Ege (512) 239-5706 Michael.Ege@tceq.texas.gov TCEQ area source Web page http://www.tceq.texas.gov/airquality/areasource