Seismic attenuation attribute and its implication to physical property analyses in less-reflective areas

As one of the interpretation tools of subsurface structures, we are developing a seismic attribute using attenuation, which provides spatial variation of relative attenuation. Recent laboratory measurements have indicated clear relationships between seismic attenuation and physical properties of rocks, for example, porosity and frictional strength of fault contact. The attenuation can be estimated from change in not only amplitude but also frequency contents, therefore obvious reflections having high amplitudes are not necessarily required in the attenuation attribute analysis. So this analysis can be applied to less reflective areas, such as volcanic areas and highly faulted zones, where the conventional seismic reflection methods that basically depends on amplitudes rarely provides useful information on structures and physical properties. In this paper, we would like to demonstrate two application examples of the seismic attenuation attribute. The first example is to map earthquake swarm activity in a volcanic area. Resulting attenuation profiles clearly figured out earthquake swarm activity caused by magma intrusions. The swarm activity in volcanic areas can be understood as open-crack development by hydrofracturing in reservoir rocks. In the second example, which is a trial to fault seal evaluation in an oil field, resulting spatialvariation in Q appears to be proportional to strength of fault seal. Higher Q values are observed along a fault that works as a lateral seal of hydrocarbon, whereas lower Q values are seen along faults that don’t form hydrocarbon traps.