Deep geological storage of CO2, offshore UK – Supplementary note D: Well leakage results

This document provides additional technical information that underpins our assessment of the containment certainty of deep geological storage of CO2 in offshore sites on the UK continental shelf (UKCS). The aim of this document is to present a thorough explanation and justification of the key findings and conclusions of the main report, and is aimed at a technically experienced engineering audience.

Large scale geological storage of CO2 is yet to be undertaken on the UK continental shelf (UKCS) and so estimating the risk of leakage from CO2 wells relies on failure data from relevant analogous sites globally. The topic of potential leaks from CCS wells has been the subject of considerable study over several decades, and CO2 injection has been undertaken worldwide for more than 40 years for Enhanced Oil Recovery (Duncan, 2009) and 25 years for CO2 storage (Furre, 2017). There is therefore a significant body of research that can be used to estimate the probability of different sizes of leak from a well penetrating the cap rock of a CO2 geological store. However, relatively few studies have estimated leak rates linked to probabilities and durations as this study has attempted and often, they only contain part of the picture.

In estimating the probability of leakage from CO2 wells, two approaches have been taken:

1. A review of literature. Relevant data for active and inactive wells on CO2 stores on the UKCS has been extracted and normalised into common units to allow comparison and analysis between data sources. This is addressed by this Supplementary Note.
2. Access to the WellMaster database provided by Peloton has allowed a review of real well failure data and the creation of a representative well model with overall failure rates built up from individual component failure rates. This is addressed in Supplementary Note C.