Imaging fluids in rocks (oil and gas)

Amplitudes of seismic reflections are related to small changes in acoustic velocity and density. These changes are caused by variations in rock composition and porosity. Sharp changes in acoustic velocity and density can occur depending on whether the pore spaces in the rock are filled with water, oil, or gas. The measured amplitude of a reflection can be used, with adequate calibration, to determine the composition of pore fluids. This picture on the right is a seismic amplitude map from a 3D survey of a producing oil field in the United States. Reservoir areas containing oil are in red and gas in yellow. Blue (water), are areas from which the oil has already been extracted. Note the patches of oil left behind by encroaching waters. The entire field is dissected by large and small faults.