# Fluid flow behaviour in vesicular basalt samples from the Skoll High, Vøring Margin

## TL;DR

This study examines how fluids flow through basalt samples from the Skoll High, finding that swelling clays and low permeability may hinder carbon sequestration potential.

## Contribution

The study provides new empirical data on fluid flow in altered basalts under subsurface conditions, relevant for carbon sequestration.

## Key findings

- Brine permeability is four orders of magnitude lower than gas permeability in the tested basalts.
- Swelling clays significantly reduce fluid accessibility in the pore space of altered basalts.
- Low matrix permeability and clay prevalence may limit injectivity into basaltic lava flows.

## Abstract

This study presents the fluid flow testing results of 32 lava flow samples recovered from IODP Sites U1571/U1572 (145–315 mbsf) on the Skoll High, Vøring Margin. Few past studies have investigated the mid-Norwegian margin’s basalt reservoir and flow properties. Even fewer implement subsurface-like conditions to explore in-situ fluid flow and the possible response to changing pore fluids during injection. These aspects are critical for large-scale carbon sequestration. In this study, hydraulic properties including porosity and permeability were measured at ambient conditions for all samples along with multi-stress, multi-fluid core flooding experiments on a representative sample enclosed in an X-ray µCT scanner. Petrographic observations reveal varying degrees of alteration with secondary clays, including smectite, commonly lining pores and vesicles. He-porosities (4.2–45.6%) fall mostly below the theoretical percolation threshold of ~ 30% for randomly distributed spherical pores. Klinkenberg-corrected nitrogen-gas permeability (0.0038–361.9 mD) shows weak correlation to porosity and no apparent depth dependence. Further, brine permeability is four orders of magnitude lower than gas permeability, with no notable flow reduction during injection of CO2. Rather than being stress-dependent, we argue that brine-induced swelling significantly reduced the accessibility of microstructural elements to fluids. The findings urge caution when using literature-reported, ambient gas measurements for basalts with similar levels of alteration as they may not accurately reflect in-situ fluid flow properties. Low matrix permeability of the moderately to highly altered vesicular basalts and prevalence of swelling clays may, without major contributions from fractures, limit the injectivity potential into the basaltic lava flows on the Skoll High, Vøring Margin.

Core flooding experiments indicate brine permeabilities roughly 4 orders of magnitude lower than to nitrogen gas.Fines and clay interactions narrow microstructural elements and render the pore space inaccessible to fluids.
Low matrix permeability and prevalence of swelling clays limits injection potential in the tested basalts.

Core flooding experiments indicate brine permeabilities roughly 4 orders of magnitude lower than to nitrogen gas.

Fines and clay interactions narrow microstructural elements and render the pore space inaccessible to fluids.

Low matrix permeability and prevalence of swelling clays limits injection potential in the tested basalts.