Constraining the physical properties of chimney/pipe structures within sedimentary basins

Evaluation of seismic reflection data has revealed structures cross-cutting the overburden within many sedimentary basins worldwide, including those in the North Sea and Norwegian Sea. These seismically-imaged pipes and chimneys are considered to be possible pathways for fluid flow. Natural fluids from deeper strata have migrated through these structures at some point in geological time. We test the hypothesis that many chimney and pipe structures imaged on seismic reflection profiles worldwide are the consequence of (1) a fracture network that has been reactivated by pore fluid pressure which facilitates the migration of fluids upwards; and (2) shallow sub-seafloor lateral migration of fluids along stratigraphic interfaces and near-surface fractures. An experimental approach to determine the physical properties of these structures beneath the sub-seafloor is described, with particular reference to an investigation of the Scanner Pockmark complex in the North Sea. The study is relevant to storage operators, policy-makers and those keen to demonstrate that it is possible to constrain and fully understand the physical properties and possible fluid flow pathways in the sedimentary overburden above sub-seafloor CO₂ storage reservoirs.