Life cycle impacts of offshore drilling and carbon storage operations

This PhD thesis assesses the environmental life cycle impacts of upstream oil and gas development, namely offshore drilling operations, and carbon capture and storage (CCS) value chains respectively. The PhD is carried out as an industrial research project in collaboration with the companies Maersk Drilling and INEOS Energy DK. The main objective of the PhD project is to evaluate the environmental consequences through the application of attributional life cycle assessment (LCA). 

The thesis is a synthesis of four peer-reviewed, and one submitted, scientific articles and is structured in two main parts, each supported by one or several articles. The first part deals with the LCA of offshore drilling operations and carbon capture and storage value chains. Firstly, it covers the work related to the mapping of operational activities related to offshore drilling, including an analysis of the supply chain and equipment maintenance, and on this basis quantification of the environmental impacts based on a case study of a well drilling campaign in the North Sea. Secondly, it covers a life cycle impact assessment of CCS projects in the Northern European region. This is based on the conceptualisation and planned deployment of the Greensand pilot-scale project and the permanent storage of carbon dioxide in the Danish part of the North Sea. It also considers three scaled-up scenarios that envisage an increase in the storage capacity and infrastructural expansion. The second part evaluates the results of the previous chapter from a broader perspective: partly by focusing on the application practice of reporting scope 3 emissions within the drilling industry, and partly by summarizing a set of best practices for LCA practitioners of CCS systems. In addition to the two main parts, an introductory and methodology chapter is presented describing the research approach for data collection and scenario building within the two companies, along with a conclusion chapter in the end. 

The thesis presents relevant results within different areas. The LCA of drilling operations showed that well drilling activities accounted for the largest overall contribution to environmental impact. The LCA of CCS scenarios showed a positive contribution to climate change mitigation in all cases.

The LCA case study of drilling operations in the North Sea identified maintenance of the mud system having the largest contribution to climate change, mainly related to the supply and disposal of glycol used for preservation, and the production and disposal of inorganic chemicals used in oil-based drilling mud. Furthermore, a smaller yet significant contribution is shown from downhole well materials and the production of non-alloy steel for casing and tubing, as well as the logistics and disposal of drill cutings. Overall, the production and distribution of maintenance parts for the drilling equipment and well materials are identified as the largest contributors to climate impact. Furthermore, a significant contribution is shown from the production of fuel for the drilling rig, as well as direct emissions from offshore supply vessels. Reporting of life cycle emissions in accordance with the GHG Protocol Scope 3 Standard reveal category 1 ‘Purchased goods and services’ as showing the largest magnitude of greenhouse gas emissions (GHG). 

The LCA of the Greensand pilot-scale project quantified the climate change impacts of capturing, transporting and storing carbon dioxide in the Danish part of the North Sea, concluding an overall positive contribution to climate change from capturing CO₂ at Danish biogas production facilities. Likewise, the LCA of the three scaled-up scenarios revealed a positive contribution with relatively little trade-off from expanding the infrastructural network across the Northern European region. It emphasizes the potential effect of scaling up the storage capacity in terms of positive climate change mitigation. The use of fossil energy sources for the capture process has significant influence on the results due to the high energy consumption for steam generation.

This thesis also emphasizes several challenges associated with the current accounting practices for scope 3 emissions based on the upstream oil and gas industry case study, as well as the use of LCA as method for assessing the climate change impact of CCS project. Furthermore, it identifies general lack in current reporting of processes related to the preparation of wells for receiving carbon dioxide, the injection and pumping of CO₂ into the reservoir, and leakage monitoring of the reservoir.

For each part of the thesis, a strategy is proposed with the goal of strengthening oil and gas companies' ability to evaluate and reduce climate change impacts: 1) Accounting of GHG emissions based on process-based LCA with the aim of improving the ability to identify and prioritise value chain activities. 2) Proposing best practices for LCA of CCS systems that increases comparability, alignment and conformity across reported studies.

Finally, a research outlook is outlined, pointing out new needs within the quantification of GHG emissions from CO₂ transport and storage activities, and a general need for LCA application within upstream oil and gas operations. This to further strengthen the companies’ decision-making process around climate change mitigation.