## 2 Materials and Methods
### Identification of Levers for Reducing GHG Emissions
#### 2.4.1 GHG Emissions Reduction from Upstream Activities  
For what concern upstream emissions, they can be summarized as follows:  
* Upstream energy efficiency improvements and use of renewable energy: IEA suggests that energy consumption represents approximately 27% of GHG of upstream emissions. These emissions could be reduced by:
* Implementing energy efficiency improvements, e.g., by using better/newer equipment and energy management;
* Replacing fossil energy with renewable power from the grid or generated locally or using renewable heat.  
There is limited data on the subject of use of renewable heat and power in upstream crude oil operations; therefore, this study assumes the technical limit of 100% replacement of energy-related emissions with biogenic or renewable emissions, and thus a GHG reduction of 27% is assumed.  
* Flaring reduction: Approximately 14% of upstream emissions arise from flaring operations. Factors for reducing flaring include [30]: better operational management, particularly during start-ups, shutdowns and upsets; flare gas recovery for re-injection as fuel or gas export; flare gas recovery for local conversion to syncrudes (e.g., a modular Fischer-Tropsch process). A complete ban on flaring is technically achievable, therefore the technical potential for GHG emissions reduction is 14%. There is a \"Zero Routing Flaring by 2030\" aspiration supported by the European Commission, oil majors and national governments, but specific targets and regulations vary between countries.
* Methane emissions reduction: Methane emissions are the main source of GHG emissions in upstream crude extraction and production. A weighted average of 59% of total emissions could be considered. Reducing methane emissions can be achieved by several actions: eliminating \"economic\" venting and replacing it with flaring; eliminating fugitive emissions, e.g., from seals and purges; improving operational practices to avoid gas release, e.g., during well completion. A complete reduction in these emissions is technically feasible; therefore, the maximum GHG reduction accounts for the 59% of upstream emissions.  
Another option sometimes proposed for lowering crude upstream emissions is the use of CO\({}_{2}\) for enhanced oil recovery (EOR): CO\({}_{2}\)-EOR involves the injection of liquid  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Energy Source (EU Aggregate)** & **\% of CO\({}_{2}\) Emissions** & **\%** \\ \hline Manufactured H\({}_{2}\) & 19 & 19 \\ \hline Purchased natural gas & 14 & \\ \hline Purchased steam & 4 & 29 \\ \hline Purchased power & 11 & \\ \hline Self-produced fuel gas & 32 & \\ \hline Self-produced liquid fuels & 5 & 50 \\ \hline FCC coke & 13 & \\ \hline Other & 2 & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Distribution of EU aggregate CO\({}_{2}\) emissions from Downstream Oil Refining.  
CO\({}_{2}\) into the reservoir where it mixes with the crude oil, making it more mobile--typically primary and secondary production recover only 40% of the oil. CO\({}_{2}\)-EOR is an energy-intensive operation but its own emissions can be captured and used. On the other hand, it also involves recirculation of huge amounts of CO\({}_{2}\) and poses the risk of substantial fugitive CO\({}_{2}\) emissions. Whilst CO\({}_{2}\)-enhanced oil recovery (EOR) can be applied in crude production, there is significant uncertainty as to whether the potential can be achieved and if all identified CO\({}_{2}\) storage sites are feasible. This is less of an issue when the focus is purely on oil-recovery than it would be if the main aim of CO\({}_{2}\)-EOR was refocused from oil recovery to CO\({}_{2}\) mitigation. There is uncertainty about the number of suitable sites (geology, well design), the ability to store enough CO\({}_{2}\) and the fugitive CO\({}_{2}\) emissions from storage sites [31; 32; 33]. As a result, CO\({}_{2}\)-EOR was not considered further for the purposes of this paper.