Gas Chimneys -A Key to Risking Prospects

Gas chimneys can indicate fluid migration pathways between a source rock and the seabed, as well as indicate hydrocarbon charged reservoirs, leaky faults and dry reservoirs. To be able to map gas chimneys in a consistent manner, a method was developed for detecting chimneys in 3D seismic data. The method makes use of multi-attributes, which are fed into a neural network. The networks trained on these attributes to recognize chimneys. The output is a seismic cube which exhibits the shape and spatial distribution of the chimneys. Application of this recently developed method shows consistency in the way chimneys appear above hydrocarbon charged reservoirs, and above dry reservoirs. Alternatively, or in combination with chimneys, mud volcanoes can give similar indications. Examples from the Nigerian Continental Slope, as well as the Norwegian Shelf, the Gulf of Mexico and the Caspian Sea show how the mapping of gas chimneys (and mud volcanoes) can be used to high-grade or down- it. grade prospects. The presence of chimneys in seismic data are in numerous cases observed to coincide with faults, suggesting these faults are acting, or have data between source rocks and reservoirs and between reservoirs and the seabed. Chimneys may also take the shape of widely extended clouds, in which case they do not seem to be related to faults. Different scenarios of chimney appearance can be related to dry or hydrocarbon charged reservoirs