Exploring the micro-scale controls on fracturing in a Carboniferous limestone, and their implications for carbon capture and storage

Ellen, Rachael; Zihms, Stephanie; Garcia, Susana; Farooqui, Nazia M; Mercedes, Maroto-Valer; Lewis, Helen; Leslie, Graham. 2017 Exploring the micro-scale controls on fracturing in a Carboniferous limestone, and their implications for carbon capture and storage. [Poster] In: Tectonic Studies Group, Liverpool, UK, Liverpool, UK, 4-6 Jan 2017. British Geological Survey. (Unpublished)

Before downloading, please read NORA policies.

Preview

Text
TSGPoster.pdf
Download (8MB) | Preview

Official URL: https://www.liverpool.ac.uk/tsg-vmsg-bga/

Abstract/Summary

Characterising subsurface fracture properties is important for understanding their structure, distribution, and effect on fluid flow. Fractures often act to compartmentalise fluids in the crust, which has implications across a number of subsurface applications, including carbon-dioxide (CO2) storage. Within the U.K., limestone-rich Carboniferous strata are becoming increasingly economically important and as such it is vital to gain a better understanding of their mechanical properties in the subsurface. To help achieve this, core plugs (Ø 38mm) from one naturally fractured sample and one protolith (undisturbed) sample of the Namurian McDonald Limestone, exposed in the Spireslack Surface Coal Mine in East Ayrshire, were taken. To understand controls on newly formed fractures, i.e. those that may form as a result of CO2 injection, the protolith sample was deformed in axi-symmetric compression at 25 MPa confining pressures. The sample was deformed and then unloaded in order to replicate early stage deformation features. Early results indicate that fossil fragments in part control fracture propagation pathways. Carbonation (i.e. CO2-brine-limestone) experiments on the samples were conducted for 7.2 weeks in a batch high temperature/high pressure experimental system, in order to investigate their reactivity when in contact with supercritical CO2 under conditions representative of a CO2 storage reservoir in the North Sea region. XRT was performed on original and reacted samples to characterise fractures and deformation features occurring within the plugs. Early results indicate that, due to rock-fluid interactions, fracture surfaces have been partially dissolved and as a result are smoother and wider. Debris recovered in the batch cylinder after the experiment suggests that the induced fracture network (in the protolith sample) allowed for a higher interaction rate compared to the naturally fractured and un-fractured samples.