Analogue modelling of leakage processes in unconsolidated sediments

Abstract

Cenozoic sedimentary basins typically contain young, unconsolidated sediments, potentially suitable for CO2 storage, e.g. the Utsira sand in the Norwegian North Sea Basin. During burial and compaction, formation fluids are squeezed out of the sedimentary deposits. These fluids can mobilize and transport sediments to overlying strata, forming seismic-scale clastic intrusions and shallow gas accumulations, to the Earth’s surface, or to the sea floor, where they are expelled through pockmarks or mud volcanoes, respectively. These deformation processes are described as subsurface sediment remobilization (SSR). Little attention has been paid to the formation mechanisms of SSR in the search for CO2 storage formations, though they may be relevant for storage safety, either occurring naturally, triggered by CO2 injection, or being fossil features providing pathways for fluid migration in the subsurface. Structural characteristics of SSR features are well known, but formation processes and dynamics are poorly understood. We have developed a scaled analogue experimental approach and performed systematic laboratory experiments in order to comprehend and quantify the conditions controlling and triggering SSR, the critical rheological properties of sediments, and storage structures (layer thickness, anticlines, faults). Experimental results are presented and potential implications for the selection of storage sites and storage safety are discussed in this article.