1 Land Use Greenhouse Gas Emissions from Conventional and Unconventional Oil ProductionYeh et al. (2010)
Land Use Greenhouse Gas Emissions from Conventional and Unconventional Oil Production
Sonia Yeh[1], Institute of Transportation Studies, University of California, Davis, Email:
Sarah M Jordaan, Energy and Environmental Systems Group, Institute for Sustainable Energy, Environment and Economy, University of Calgary, Email:
Adam R. Brandt, Department of Energy Resources Engineering, Stanford University,
Merritt Turetsky, Department of Integrative Biology, University of Guelph, Email:
Sabrina Spatari, Civil, Architectural, and Environmental Engineering Department, Drexel University , Email:
David Keith, Energy and Environmental Systems Group, Institute for Sustainable Energy, Environment and Economy, University of Calgary, Email:
Overview
Debates surrounding the carbon emissions from land use of biofuels production have created a need to quantify the relative land carbon intensity of petroleum-based fuels. Compared with biofuels, we found the energy yields of conventional and oil sands production are at least 2-4 orders higher per disturbed area. Land use greenhouse gas (GHG) emissions range from 0.1 to 4 g CO2 equivalent per MJ of refined fuel produced, a very small portion of total fuel cycle emissions. An exception is mining-based oil sands cases, in which land use conversions occurring in high carbon stock areas such as peatlands and methane (CH4) emissions from unmanaged tailings ponds, can lead to high GHG emissions (up to 10 g CO2 eq.). Our findings emphasize the importance of restoration activities to reclaim ecological landscapes to recover CO2 loss, sustain high biodiversity, hydrologic cycles, and forest ecosystems after oil sands production has been completed. Our study estimates are based on assumptions aggregated over large spatial and temporal scales. Values on finer spatial and temporal scales that are relevant to policy targets need to account for site-specific information, the baseline natural and anthropogenic disturbance, and the annual variations in carbon storage due to climate and natural disturbance such as fires or pest outbreaks.
Methods
The land disturbance intensity I for conventional oil production and in situ bitumen production can be calculated as:
(Equation 1)
where A is the total disturbed area by the fuel production, AW is the area of land disturbed for each production well. W is the total number of wells and E is the total energy of fuel produced in MJ. For the case of surface mining of petroleum resources, the land disturbance intensity is calculated by the disturbed area divided by the energy in the petroleum produced in that area.
The inverse of Eq 1 can be interpreted as the energy yield per unit disturbed area (e.g., in PJ/ha). The greenhouse gas emission intensity associated with land disturbance (CILU) in grams of CO2 equivalent per MJ of energy in fuel can be expressed as follows:
(Equation 2)
CLU is the GHG emissions associated with land disturbance in grams or tons of CO2e per unit area. Carbon stock and emission changes before and after the disturbance were estimated.
Carbon stocks in boreal ecosystems depend on climate, hydrogeology, and natural disturbance regimes such as wildfire and disease (Kurz et al. 2009). Some boreal regions store large carbon stocks below ground in the form of peat (Turetsky et al. 2005; Turetsky et al. 2002; Vitt 2006). When subject to either natural or anthropogenic disturbances, these ecosystems may release large amounts of carbon into the atmosphere as CO2 or CH4(Turetsky et al. 2002). The evolution of carbon stocks over time was modeled for a reference scenario with no land disturbance for fossil fuel production and a land disturbance scenario over 150 years. Once disturbed, soil and biomass carbon are released to the atmosphere, but the reclaimed land can slowly re-accumulate carbon in reclaimed ecosystems.
Results
The results in energy production per disturbed area are summarized in the Table below. Compared with biofuels, of which the net energy yields range from 14 – 28 GJ/ha/yr (or 7.2×10-4 – 1.4×10-3 PJ/ha over 50 years of continuous cultivation)(Tilman, Hill, and Lehman 2006), the energy yields of conventional oil and oil sands production are at least 2-4 orders higher.
Table. Energy yield (PJ/ha disturbed) of conventional oil production in California and Alberta and oil sands production.
California oil / Alberta oil / Oil sands - surface mining / Oil sands – in situHistorical impacts / 0.79 (0.48−2.6) / 0.33 (0.16−0.69)
Marginal impacts / 0.55 (0.33−1.8) / 0.20 (0.092−0.40) / 0.89 (0.59−1.1) / 3.2 (2.1−5.0)
The figure below is an illustration of carbon dynamics over time after land disturbance and reclamation for the case of surface mining (tailings emissions are ignored in this illustrative example). Reclaimed peatlands will have a much lower soil carbon after it is reclaimed to upland.
Figure. Illustration of land carbon stocks under disturbance and regrowth over time for the case of surface mining.
Conclusions
As Canadian oil sands production may reach 1.5 billion barrels per year in 2030, GHG emissions resulting from land use and tailings emissions may result in additional carbon emissions, and a net of 3.4 – 44 million tonnes GHG may still remain in the atmosphere 150 years after its initial release (assuming 44% is surface mining and the rest is in situ recovery (EIA 2004)), compare with 635 – 769 million tonnes GHG emissions from bitumen production (including upstream emissions) and use. Our results highlight the importance of the GHG emissions associated with soil carbon emissions from peatland conversion and tailings ponds methane emissions, both can potentially cover large tracts of land. It is, however, important to note that CO2 emission derived from the use of oil is orders of magnitude higher compared to land use emissions. Our findings emphasize the importance of restoration activities for land-related CO2 emissions from oil sands, which more importantly aim to recover ecological landscapes from heavily mined areas after oil sands production has been completed. Post-mining reclamation such as the restoration of habitat that can sustain high biodiversity, hydrologic cycles, and forest ecosystems will be important.
References
EIA. 2008. Natural Gas Consumption in Canadian Oil Sands Production Energy Information Administration, Department of Energy, [accessed July 29, 2008].
Kurz, W. A., C. C. Dymond, T. M. White, G. Stinson, C. H. Shaw, G. J. Rampley, C. Smyth, B. N. Simpson, E. T. Neilson, J. A. Trofymow, J. Metsaranta, and M. J. Apps. 2009. CBM-CFS3: A model of carbon-dynamics in forestry and land-use change implementing IPCC standards. Ecological Modelling 220 (4):480-504.
Tilman, David, Jason Hill, and Clarence Lehman. 2006. Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass. Science 314 (5805):1598-1600.10.1126/science.1133306.
Turetsky, Merritt R., Michelle C. Mack, Jennifer W. Harden, and Ktisten L. Manies. 2005. Spatial Patterns of Soil Carbon Storage Across Boreal Landscapes. In Ecosystem Function in Heterogeneous Landscapes: Springer New York.
Turetsky, Merritt, Kelman Wieder, Linda Halsey, and Dale Vitt. 2002. Current disturbance and the diminishing peatland carbon sink. Geophys. Res. Lett. 29 (11):1526, doi:10.1029/2001GL014000.
Vitt, D. H. 2006. Functional Characteristics and Indicators of Boreal Peatlands. In Ecolological Studies, edited by K. Wieder and D. H. Vitt. Verlag Berlin Heidelberg: Springer.
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