Climate impacts of oil extraction increase significantly with oilfield age

Abstract

The footprint of oil typically considers combustion emissions, neglecting extraction emissions. This study shows that production declines with depletion for 25 significant oil fields, whilst emissions increase through greater energy expenditure. Record-breaking temperatures1 have induced governments to implement targets for reducing future greenhouse gas (GHG) emissions2,3. Use of oil products contributes ∼35% of global GHG emissions4, and the oil industry itself consumes 3–4% of global primary energy. Because oil resources are becoming increasingly heterogeneous, requiring different extraction and processing methods, GHG studies should evaluate oil sources using detailed project-specific data5. Unfortunately, prior oil-sector GHG analysis has largely neglected the fact that the energy intensity of producing oil can change significantly over the life of a particular oil project. Here we use decades-long time-series data from twenty-five globally significant oil fields (>1 billion barrels ultimate recovery) to model GHG emissions from oil production as a function of time. 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. Depletion requires increased energy expenditures in drilling, oil recovery, and oil processing. Using probabilistic simulation, we derive a relationship for estimating GHG increases over time, showing an expected doubling in average emissions over 25 years. These trends have implications for long-term emissions and climate modelling, as well as for climate policy.