Uncertainty in Life Cycle Assessments of Well-to-Wheel Greenhouse Gas Emissions of Transportation Fuels Derived from Various Crude Oils

Abstract

Growing concern over climate change has created pressure on the oil and gas industry to reduce their greenhouse gas (GHG) emissions. Several life cycle assessment (LCA) studies have examined various crude oils in an attempt to determine which have the lowest and highest well-to-wheel (WTW) GHG emissions. The majority of these studies published deterministic point estimates with a limited sensitivity analysis. Due to the variation in results between studies and the lack of an uncertainty analysis, the usefulness of the results for policy makers and industry representatives is limited. The goal of this study is to expand on the previous research by identifying a realistic range of WTW emissions for various crude oils. This research builds on the previously published FUNdamental ENgineering PrinciplEs-based ModeL for Estimation of GreenHouse Gases in Conventional Crude Oils (FUNNEL-GHG-CCO). The FUNNEL-GHG-CCO model produced point estimates of the WTW emissions for five North American crude oils. This work makes improvements to the model, adds a Monte Carlo simulation to calculate uncertainty, analyzes additional scenarios to examine the effect of field age on WTW emissions, and expands the model to include three crudes from outside North America. A sensitivity analysis is used to identify sensitive inputs. Then distributions for the sensitive inputs are determined from the literature and used to run the Monte Carlo simulations. The resulting WTW emission ranges for gasoline are 95.3-99.9 (Saudi Arabia), 99.9-105.5 (Maya), 96.4-104.0 (Mars), 101.6-109.9 (Venezuela Low Steam), 101.1-109.2 (Sirri), 102.5-114.2 (Bow River), 104.6-114.5 (Alaska North Slope (ANS) historical), 105.5-113.2 (Kern historical), 113.6-138.5 (Venezuela High Steam), 133.2-163.2 (ANS current), and 131.5-155.0 gCO2eq/MJ (Kern current). For ANS and Kern, the current scenarios use lifelong average iii | P a g e production data and the historical scenarios use recent production data to illustrate how the WTW emissions change as the fields age. For the Venezuela crude, two scenarios are used as a wide range of steam-to-oil ratios appear in the literature. The results of this study will be beneficial to both policy makers and industry representatives. The results identify which pieces of information policy makers would require from industry in order to get accurate WTW emissions estimates. The uncertainty ranges provide a better understanding of how WTW GHG emissions vary between crude oils. This will help policy makers understand the limitations of such models.