Multiscale characterisation of chimneys/pipes: Fluid escape structures within sedimentary basins

•The STEMM-CCS & CHIMNEY projects conducted a novel field experiment in the North Sea.•Subsurface fluid flow below active pockmarks in shallow sediment overburden assessed.•Seismic chimneys/pipes characterised using a new multi-scale, multi-method approach.•Method capabilities, co-dependencies and required future developments explained.•New method approach integrates into risk-based frameworks for CO2 storage operations.