(521a) Greenhouse Gas Intensities and Energetic Productivity Dynamics of Giant Global Oilfields: A Life Cycle Approach 

The steady increase in world energy consumption, coupled with record-breaking earth surface temperatures have induced governments to implement targets for reducing future greenhouse gas (GHG) emissions. Use of oil products contributes ~35% of global GHG emissions, and the oil industry itself consumes 3-4% of global primary energy. Most GHG analysis of the oil sector has focused on comparing the impacts of oil-derived transport fuels to other transport fuel options. This is a reasonable focus as the largest source of emissions from oil use is mostly the combustion of finished fuels (e.g., gasoline burned in an automobile). However, emissions from oil and gas extraction and processing are sometimes significant, particularly for unconventional resources or when energy-intensive enhanced oil recovery (EOR) strategies are used. Also from a national viewpoint, oil and gas extraction can cause a significant fraction of domestic emissions in fossil fuel exporting countries like Canada (~20% of national emissions), Russia (~20%), and Norway (~28%). Since oil resources are becoming increasingly heterogeneous -- requiring different extraction and processing methods -- GHG and energy studies should evaluate oil sources using detailed project-specific data.

Unfortunately, prior oil-sector GHG and energetic productivity analyses rely on “snapshot” data of varying quality and vintage, and have largely neglected the fact that the energy intensity of producing oil can change significantly over the life of a particular oil project. These changes result from age-related changes in engineering practice (e.g. water/gas/steam injection) and processing requirements (e.g., fluid separation). Neglecting temporal trends in oil-sector emissions is problematic for long-term climate and integrated assessment modeling, where emissions trends over decades are of interest.

Here, via a detail engineering-based life cycle approach, we use decades-long historical data from twenty-five globally significant oil fields (> 1 billion barrels ultimate recovery) to model GHG intensities and energy return on investment (EROI) from oil production as a function of time. The net energy ratio (NER) and external energy ratio (EER) are used as two measures to estimate oil fields EROI. We find that volumetric oil production declines with depletion, but this depletion is accompanied by significant growth – in some cases over tenfold – in per-MJ GHG emissions. At the same time while energetic productivity decline significantly, with some fields seeing declines in excess of 90%. Depletion and reservoir exhaustion requires increased energy expenditures in drilling, oil recovery, and oil processing.

Probabilistic Monte Carlo simulation is used to draw generalized historical trends from the aggregated data of onshore/offshore, and light/medium/heavy oil fields: over 25 years, this model predicts about two-fold increase in GHG intensities, and ~ 30% and ~ 20% declines in NER and EER, respectively. We also derive a general relationship for projecting evolving dynamics of GHG emissions, NER, and EER trends over time.

In summary, the per-MJ GHG emissions and EROI from oil fields change from “oil-to-oil”, but also differ significantly “time-to-time” over a field’s productive life. These trends have implications for long-term climate and energy system modeling, as well as for climate policy, due to potential large increases in carbon intensity and extraction energy as global oilfields age. These effects may result in significant underestimation of future energy demand in the global oil sector in long-run models like integrated assessment models.