Sequential vertical gas charge into multilayered sequences controlled by central conduits

Four sets of stacked amplitude anomalies are described from a 3D seismic surveyacquired in Block A of the Dutch North Sea. The amplitude anomalies have a subcircularplanform and within each set they are stacked vertically, in that they have ahigh degree of spatial overlap in the vertical succession. These sets of amplitudeanomalies are interpreted as vertical anomaly clusters composed of 5‐7 majoramplitude anomalies each. Seismic interpretation of the vertical anomaly clusters andquantitative analysis of the reservoir intervals reveal that the vertical anomaly clustersare gas‐bearing silt‐rich reservoirs hosted in the upper section of the Upper North SeaGroup, a mixed clastic succession of Pliocene to Pleistocene age. Novel analysisbased on the geometry of the individual anomalies reveals that these are likely to bethe result of a gas migration process characterised by sequential upward gas chargeinto reservoir units and that the flow across the seals separating these reservoirs iscontrolled by central regions of focussed fluid flow. These regions function as seal‐bypass systems and are most likely formed by hydraulic fracturing