AGGREGATION AND ALLOCATION OF GREENHOUSE GAS EMISSIONS IN OIL AND GAS PRODUCTION: IMPLICATIONS FOR LIFE-CYCLE GREENHOUSE GAS BURDENS

Qining Chen (McKetta Department of Chemical Engineering, The University of Texas at Austin, Center for Energy and Environmental Resources, http://orcid.org/0000-0003-1690-8091, More by Qining Chen), Jennifer B. Dunn, David T. Allen*

Abstract:  Methods used for emission aggregation and allocation have significant impacts on life-cycle greenhouse gas (GHG) emission estimates for oil and gas products; however, because of limited data availability for upstream and mid-stream oil and gas operations, the influence of the allocation technique has not been extensively explored in previous studies. GHG emissions associated with oil and gas production and processing in the Eagle Ford Shale (with 34 gas processing plants and classified into 12 production regions) are estimated, using data from 2013, at three different scales of spatial aggregation (production region, gas plant and basin levels), to characterize the spatial variabilities in GHG emissions within the Eagle Ford Shale. GHG emissions per energy content of oil and gas products vary from 3.4 to 14 g CO2e/MJ among the regions within the Eagle Ford Shale, and from 3.5 to 23 g CO2e/MJ when assigned at the individual gas processing plant level, with a basin average of 6.8 g CO2e/MJ. GHG emissions are also disaggregated at the equipment and operations level and allocated to gas and/or oil products. Using this disaggregated allocation method, a basin-wide average of 9.5 g CO2e/MJ GHG emissions are allocated to gas products and 3.5 g CO2e/MJ are allocated to the oil product. These emission estimates are compared to benchmark emission estimates from other datasets. This study provides insights into how choices of aggregation and allocation level influence GHG emission estimates for oil and gas products.

Consistent metrics needed for quantifying methane emissions from upstream oil and gas operations

David T. Allen* (Department of Chemical Engineering, The University of Texas at Austin, http://orcid.org/0000-0001-6646-8755, More by David T. Allen), Qining Chen, Jennifer B. Dunn

Environmental Science & Technology Letters 8 (4), 345-349

Abstract: Methane emissions from oil and natural gas sources are often characterized as a methane emissions intensity, which is typically defined as methane emissions divided by natural gas production. Reporting methane emission intensities implicitly assigns all methane emissions from production activities to natural gas, but many of the regions that supply large amounts of natural gas to world markets simultaneously produce natural gas, natural gas liquids, and oil. The importance of whether methane and other greenhouse gas emissions from production activities are allocated to natural gas alone or to multiple products was examined using data from the Eagle Ford Shale production region in south central Texas. In the Eagle Ford, differences in emission allocation methods can produce differences in estimated emissions of 50–110 g CO2e/MJ of natural gas. This is comparable to the difference in combustion emissions between coal and natural gas.