Structural and stratigraphic trapping mechanisms in CO2 storage capacity and security

Abstract

Carbon capture and storage (CCS) has been identified as an important option that can be applied to stabilise CO2 concentrations in the atmosphere and limiting climate change. Structural or stratigraphic traps are the primary means by which injected CO2, as one component of the CCS system, is stored in geological formations until other trapping mechanisms influence the storage process. This thesis investigates this mode of trapping mechanism by constructing 3D static models based on different geological outcrops and then performing flow simulations. To reduce the reliance on a single seal, it seems desirable to utilise primary and secondary stratigraphic traps or small-scale structural features. In Chapter 3, three different outcrops are selected, each representing a shallow-marine system with varying heterogeneity provided by siliciclastic-carbonate mixing that may form a small or large stratigraphic trap and contribute to secure CO2 geological storage. It is demonstrated that facies interplay and associated sediment heterogeneity have a varying effect on fluid flow, storage capacity and security. Exhumed bleached palaeo-reservoirs provide a means of understanding fluid flow processes in geological media because the former movement of fluids is preserved as visible geochemical changes. In Chapter 4, a bleached palaeo-reservoir outcrop is used to test the importance of geological heterogeneity on fluid flow and identify possible pathways for fluids using flow modelling. Despite the permeability contrasts, the bleaching shows a remarkably uniform distribution within the palaeo-reservoir that crosses lithofacies boundaries that could be replicated by flow modelling, validating the Flora’s rule. In Chapters 5 and 6, small-scale deformation bands are used for CO2 flow simulation, to assess the extent to which these features act as effective mini-traps and contribute to long-term, secure CO2 geological storage. A comprehensive set of simulation scenarios is applied to a single set of conjugate bands and also on clusters of deformation bands to evaluate the effects of the: i) deformation band density; ii) contrast in host rock/deformation band permeability; and iii) deformation band geometry, orientation and distribution on fluid movement. The findings of this study show the significance of the geometrical architecture of the bands, permeability contrast and the permeability of the host rock. Furthermore, it is shown that the highest number of bands observed and modelled for Penrith Sandstone outcrop, with three orders of magnitude permeability contrast, is a configuration that can contribute to the secure storage of CO2 without causing an injectivity issue.

Date of Award	Mar 2023
Original language	English
Awarding Institution	Coventry University
Supervisor	Seyed Shariatipour (Supervisor)