Carbon capture and storage (CCS) is a necessary technology to enable the global economy to achieve internationally agreed Net Zero climate targets. The economic advantages of storing CO2 close to industrial emitters and existing infrastructure means that, very often, non-ideal, compositionally complex sandstone reservoirs will need to be utilised. Around the Asian Pacific margin, as well as other volcanically affected basins, the impact of highly reactive volcaniclastic rocks on CO2 storage is poorly understood. It is imperative, therefore, that their complex diagenetic histories are fully characterised to better understand the factors that may affect injectivity, and reservoir and sealing capacity, as well as establish their potential to enhance CO2 sequestration via mineral trapping. By studying rocks with volcanic rock fragments that range in composition (e.g. mafic v felsic, subalkaline v alkaline), texture (crystalline, glassy) and abundance, the potential and roles of volcaniclastic rocks in CO2 storage complexes can be fully assessed.

Photomicrograph of a mafic volcaniclastic sandstone dominated by devitrified volcanic glass. The pore space has been filled by analcime. Field of view is approximately 1250 µm wide

The Impact of Volcaniclastic Rocks on CO2 Storage theme aims to develop a database-driven set of rules to quantify the risk for CCS projects encountering volcaniclastic rocks. The first phase of research will constrain the reservoir and sealing properties of volcaniclastic rocks with a wide range of geochemical compositions, burial depths and environmental settings, via a number of complementary analytical techniques. Whole-rock and mineral chemistry in conjunction with estimated reactive surface areas will also be used to evaluate the potential of mineral carbonation in relation to the mineralogy, porosity and permeability.

The first phase of research within the Impact of Volcaniclastic Rocks on CO2 Storage theme comprises two projects:

• Project 1: Petrophysical database for volcaniclastic rocks (CASP.IVR.1)
• Project 2: Pore connectivity analysis of volcaniclastic rocks (CASP.IVR.2)

The insights gained from this work will not only be extremely useful for assessing the capability of volcanic sequences in sequestering and storing CO2 and H2, but will also have implications for modelling fluid flow in sediment-hosted geothermal systems and for hydrocarbon exploration in volcanically affected basins. It is envisaged that the database will continue to expand into the future, particularly with the incorporation of site specific case studies.

This research theme will begin to address the paucity of information on the potential of volcaniclastic rocks to store CO2. The global distribution of volcaniclastic rocks, particularly where they coincide with industrial hubs such as East and Southeast Asia, means these rocks could be hugely important in the mitigation of CO2 emissions into the atmosphere. The consistent use of a variety of different analytical techniques for the studied volcaniclastic samples will provide an unparalleled resource that can be expanded and data extracted for future petrophysical modelling to ultimately de-risk uncertainties in volcaniclastic CO2 plays.

KeyFacts Energy Industry Directory: CASP