Fluid conducting chimneys: Mechanism of formation and implications for fluid injection operations Viktoriya Yarushina (1) Ludovic Räss (2), Nina Simon (1), Yuri Podladchikov (2) (1) Institute for Energy Technology, Kjeller, Norway (2) University of Lausanne, Switzerland

Seismic chimneys: flow localization Plaza-Faverola et al., EPSL, 2011 Chimney features from the Nyegga area on the mid-Norwegian margin (pockmarks & seismic). Seismic chimneys represent preferrential flow pathways

In some cases chimneys are linked to nearly circular sea- floor craters (pockmarks) at the top and overpressured reservoir regions at the bottom Løseth et al, Marine and Petroleum Geology, 2011 Seismic chimneys: flow localization

Occurence of seismic chimneys Norway Seismic chimney are quite common features observed at sub-seabed sediments on continental margins. They were found offshore Norway, Nigeria, Namibia, in the Adriatic Sea, Gulf of Mexico

Occurence of seismic chimneys Norway Seismic chimney are quite common features observed at sub-seabed sediments on continental margins. They were found offshore Norway, Nigeria, Namibia, in the Adriatic Sea, Gulf of Mexico

Chadwick & Noy, 2013 Seismic chimneys: (1) when did they form? (2) potential leakage pathways? CO 2 plum profile at Sleipner

Man-made chimneys Seafloor crater (40m wide and 7m deep) at the Tordis Field in the Norwegian North-Sea. Accidental escape of waste water during a 5,5 months injection experiment. Løseth et al, Marine and Petroleum Geology, 2011

Force balance Mass balance Rheology: Darcy’s law Modeling of flow localization in porous rocks poroelastoplastic viscous Yarushina & Podladchikov, JGR, 2015

Räss et al., Energy Procedia, 2014 Chimney formation due to flow instability

Formation and evolution of high-permeability regions traveling upwards in unconsolidated sandstone (upper panel) and shale (lower panel) Räss et al., Energy Procedia, 2014 Characteristic scales of chimney formation 120 m/year 0.8 m/year

Effective pressure, porosity and equivalent shear stress during fluid focusing

Flow localization under combined pressure and shear loading 1D crossection of 3D channel p f ≈0.7p tot

Conclusions There is evidence for fast and focused fluid transport associated with human activities New model provides a mechanism of the formation of self-propagating high porosity channels High porosity channels is a natural outcome of coupled porous flow and visco(-elastoplastic) deformation of the rock Fast CO 2 migration at Sleipner can be explained by the formation of high porosity and permeability channels due to porosity waves