VOC Task Force – Development of the Bakken Emission Factors

In 2010, numerous Oil and Gas operators were tasked with attempting to develop an emission factor (EF) representative of the relatively volati le oil/condensate being produced from the Bakken formation in North Dakota. For the purpose of this study, the Bakken Pool was defined as the accumulation of oil and gas found in the interval 5 0 feet above the top of the Bakken formation to 50 feet below the top of the Three Forks Formation. This was a collaborative effort that utilized an extensive array of sampling and modeling data fr om producing wells from this reservoir. The goal was to provide a conservative, yet reasonable EF associated with flashing, working and breathing VOC emissions from any crude oil produced from any reservoir where the Bakken Formation is the source rock. Ultimately, this study yielded an EF that has been used to drive permitting and control requirements for all production facilities in the B akken and Three Forks. The control requirements and timelines have been established by the North Da kota Department of Health and have been posted in various regulatory guideline documents re leased in 2011. The overall result has been a well-documented, rigid control program that has dra matically lowered actual emissions from production facilities in these areas and establishe d clear timelines for installing tank vapor control s both existing and new wells. It has also establish ed definitive timelines for registering wells producing from the Bakken and Three Forks reservoir s. Emission Factor Development Process Numerous data were compiled from seven companies wi th wells producing from the Bakken formation, primarily in Mountrail and McKenzie Coun ty where the higher producing wells were initially clustered. A few different testing metho ds were utilized to estimate potential VOC emissions from oil tanks, all of which are used to assess tank emissions for a wide range of permitting applications. These methods include: 1. Direct Measurements (Fox Flow Meter, etc.) 2. E&P Tanks 2.0 in conjunction with pressured liquids samples upstream of tanks 3. Flash gas analysis of liquids samples flashed in la b setting Companies Providing Emission Data: • Whiting Petroleum • EOG • Hess Corporation • Fidelity E&P • ConocoPhillips • Marathon Oil • Zenergy Sample Data Population Attributes : • All wells assessed in study are Bakken formation we lls; • Vast majority from new Bakken wells (< 4 yrs old); • Sample data collected in warmer months of May-Octob er when tank vapors are most volatile; • Primarily Mountrail County wells (others from Dunn, McKenzie and Williams Cty); • Separator pressure varied from 16 psig-60 psig; • API gravity of oil ranged from 42-48 for all wellsInitial Tank Emissions Data:

• Total of 112 data points were initially amassed as part of the EF development study • 103 were direct measurement using Fox Flow Meter or equivalent; • Remaining points were from liquids sampling data an d subsequent E&P Tanks 2.0 modeled data using the liquids analysis as input; • For all data points, tank vent vapor flow was eithe r measured or estimated (E&P Tanks 2.0) Final Tank Emissions Data: • Final EF based on 87 direct measurement (DM) data points; • 15 of 103 direct measurement points were deemed out liers and not used in final EF development; • Data points amassed from 5 of 7 companies listed ab ove; • No E&P Tanks 2.0 data was used as these were consid ered outliers and yielded much higher estimated VOCs than all of the direct measur ement points; • Direct measurement data points all from 2009-2010

 82 data points from Mountrail County

 2 from McKenzie County

 2 from Williams County

 1 from Dunn County • Direct measurements sampled actual vapor flow rates (scf/bbl) • Direct measurements also provided vent gas composit ion by weight Final Emission Factor (EF) Development (see attache d calculations): • Average flow rate from tank vent of 55.26 scf/bbl f rom 87 DM points; • 90 th percentile of 97.91 scf/bbl ; • Average VOC weight percent 69.57%; • 90 th percentile of 79.83% ; • Average HAP weight percent 1.26%; • 90 th percentile of 2.26% ; • Average tank vapor molecular weight 40.66 lb/lb-mol ; • 90 th percentile of 45.19 lb/lb-mol ; • Using the average data yields average EF :  4.12 lbs/bbl VOC

 0.07 lb/bbl HAP • Using the 90 th percentile data yields 90 th percentile EF :  9.31 lbs/bbl VOC

 0.26 lb/bbl HAP Why did VOC Task Force decide on using 90 th percentile for EF? • Intended as a “screening” tool to trigger tank vapo r control requirements; • Using this EF in conjunction with NDDH Guidance Document (May 2, 2011), any Bakken/Three Forks well that produces >=12 bopd wou ld require controls with 98% DRE; • ALL Bakken/Three Forks wells produce well above thi s even after years of active production; • As such, using a more stringent percentile (>90 th ) is inconsequential and ineffective in terms of control requirements in the Bakken/Three F orks.