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## Oil and Gas Production Emissions and NSPS Baseline Estimates

Background: Methane Emission from the 2 009 U

. S

. Greenhouse Gas Inventory

This section provides background information on methane e missions from the oil and gas sector
from the 1990

- 2009 U.S. Gr eenhouse Gas Inventory (published in 2011) with a focus on oil and gas production. As shown in Figure 1, t he 1990

- 2009 U.S. GHG Inventory estimates 2009
methane emissions from oil and n atural gas systems (not including petroleum refineries) to be
624 Bcf ( 251.55 MMtCO2e). Of that total, oil and gas production is estimated to be 64% 1

.
Figure 1: 2 009 U.S. Oil and Gas Industry Methane Emissions

Figure 2 shows the breakdown of production related methane emissions by source

. For onshore oil and gas produ ction, well venting and flaring (detailed below) is the largest source followed by pneumatic devices, dehydrators and pumps, compressor emissions sources , and storage tanks.

1 EPA. (2011) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2009 , U.S. EPA. April, 2011.
Available online at <http://epa.gov/climatechange/emissions/usinventoryreport.html>Internal draft deliberative: do not cite, quote or distribute

Figure 2

. U.S. Inventory Emissions by Source Categories

The following table s h ows a detailed breakdown of the specific emission sources related to well venting and flaring

. As shown below, well clean ups by liquids unloading is the largest source of well related emissions followed by hydraulically fractured completions and workover s. H owever liquid lo ading is not typically an issue for new wells and only becomes a serious problem when the well has reached a mature age ( which will vary by well but may be 10 years or greater ).

Well Venting and Flaring 2009 M ethane E missions (Bcf ) 2 Well Clean Ups (LP Gas Wells) 187.3 Unconventional Gas Wells Workovers 14.6 Unconventional Gas Well Completions 12.1 Power River CBM Venting 2.4 Black Warrior CBM Venting 0.48 Well Drilling 0.05 Conventional Gas Wells Workovers 0.04
Oil Well Completions 0.007 Oil Well Flaring 0.004 Oil Well Workovers 0.003 Conventional Gas Well Completions 0.0004
Total 217

2 The estimates already account for existing controls first in the form of existing regulations and then in the form of voluntary reductions via Natural Gas STAR. The U.S. Inventory subtracts Natural Gas STAR reductions at the sector (e.g. Production or Natural Gas Processing) level. For the purpose of this analysis , EPA apportioned reductions to each source category

. The se emissions pie charts are posted on the Gas STAR Program web site

annu ally

- http://www.epa.gov/gasstar/basic

- information/index.htmlInternal draft deliberative: do not cite, quote or distribute

Baseline Well Emission Factors used in NSPS Impacts Analysis :

In the development of this proposed r ule, for emissions f rom well completions and workovers, EPA analyzed emissions from conventional gas well completions, unconventional gas well completions (e.g., “tight” formations such as shale , tight sands, and CBM), and oil well completions from the 2009 U.S. Inventory an d the Mandatory Reporting Rule, Subpart W Technical Support Document (TSD)

. Since hydraulic fracturing is most common in and closely associated with unconventional formations, this analysis assumes unconventional wells are hydraulically fractured and conve ntional wells are not. The 2009 U.S. Inventory and the Subpart

W T SD estim ate that on average 9,175 thousand cubic feet of natural gas (or 158.3 and 44 short tons of methane and VOC respectively) is emitted per gas well completion with hydraulic
fracturin g

. 3 As illustrated below, the largest methane and VOC emissions are from hydraulically fractured wells. Conventional wells and oil wells are relatively small source of methane and
VOC emissions.

For the purposes of the NSPS estimates, EPA used 0.0208 sho rt tons per Mcf of methane density from EPA Method 18 to convert volume of methane emissions. Volatile organic compound (VOC) emissions are estimated assuming a 0.278 to 1 VOC to methane (by mass) ratio. Hazardous air pollutant (HAP) emissions are estima ted assuming a 0.0105 to 1 to HAP to methane (by mass) ratio. The resulting methane, VOC, and HAP emission factors for gas well completions with hydraulic fracturing, without hydraulic fracturing, and for oil well completions
are summarized in the table b elow.

3 EPA (2010). Greenhouse Gas Emission Reporting from the Petroleum and Natural Gas Industry: Background Technical Support Document. Appendix B page 87. Available Online at: http://www.epa.gov/climatechange/emissions/downloads10/Subpart

- W_TSD.pdf (note: the Subpart W TSD published the whole gas factor and the inventory publishes the methane portion, determin ed by NEMS region). Emissions from Tight Sands: It is important to note that the emissions estimates for well completions and recompletions (workovers) in the 1990

– 2009 GHG I nventory exclude a significant number of wells completed in tight sand plays due to limited data availability when the 2009 Inventory was developed. The estimate in the NSPS proposal includes an adjustment for tight sand plays when estimating new sources ( which is being considered as a planned improvem ent in development of next year’s Inventory for not just new sources but
all sources ). This adjustment is estimated to increase the 2009 Inventory estimate by approximately 7 6.7 MMtCO2e (or at 0.02082 tons m ethane/1000 scf, about 1 7 5 Bcf)

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NSPS Baseline Emission Factors by Species in Short Tons per Completion Emission Species Unconventional Gas Well Completions with Hydraulic Fracturing (short tons/completion) Conventional Gas Well Completions without Hydraulic Fracturing (short

tons /completion) Oil Well Completions (short tons/completion)

Methane 158.3 0.76 0.02

VOC 44.0 0.21 0.004

HAP 1.662 0.008 0.0002