Dictionary:Gas chimney, gas cloud
A region of low-concentration gas escaping and migrating upward from a gas accumulation. Generally shows as a region of severely deteriorated seismic data quality associated with low velocity and with velocity sags (push down) underneath the chimney. The effects are probably caused by incoherent scattering, absorption, and poor stacking because of nonhyperbolic NMO. S-waves appear to be little affected by gas chimneys.