Estimating emission rates of volatile organic compounds from oil and natural gas operations in the Piceance Basin
Date
2015
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Abstract
Oil and natural gas production has been steadily increasing in Colorado for the past 10 years. Garfield County is partially located above the natural gas rich Piceance Basin. Horizontal drilling techniques provide increased access to subsurface gas deposits while hydraulic fracturing is employed to increase the permeability of the tight gas formations by pumping pressurized fluids into the ground to allow more cost-effective oil and gas extraction. Once fractured, the fluid is allowed to flow back to the surface to be captured before the well is considered producing. Our team conducted field measurements from 2013 to 2015 in Garfield County to determine emission rates of methane, hazardous air pollutants, and ozone precursors at 18 oil and gas operations. Drilling and well completion operations were targeted because they are understudied relative to production. We estimate the emission rates of methane and 58 additional VOCs (focusing on benzene, toluene, and ethane) for three common operations. We found benzene had mean emission rates of 0.72, 0.23, and 0.055 g/s for drilling, hydraulic fracturing, and flowback operations respectively. We calculated mean methane emission rates of 6.2, 29, and 64 g/s for drilling, hydraulic fracturing, and flowback operations respectively. We use the estimated methane emission rates from drilling and well completion operations to compare to typical well lifetime emissions during a 30 year production phase and find that drilling and well completion operations may be contributing from 0.1 to 10% of total well pad emissions. These results are based on a limited sampling size (18 sites) and limited overall measurement time (4.25 hours of total measurement time included in results). It is possible we did not perform measurements for long enough periods of time at enough sites. This study is beginning to fill the information gap by focusing on drilling and well completion operations. AERMOD is an atmospheric dispersion model used for new source apportionment. We compared our measured concentration fields to AERMOD predicted concentration fields by replicating fieldwork locations and conditions. Meteorological conditions were taken from an on-site meteorological station for use in the dispersion model. Comparing to the measurements, we found there was a low log-mean bias (-0.007) with a large amount of scatter (r = 0.0007). Additionally, we use AERMOD and data from the NCEP North American Regional Reanalysis database to predict the distribution of concentrations experienced throughout for various meteorological conditions in Garfield County at various distances surrounding oil and gas wells. We normalized these predicted concentration fields by emission rate and created cumulative distribution functions.
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Subject
Colorado
emission rates
Garfield County
methane
natural gas
oil