反射法地震探査データの減衰特性を利用した断層シール能力評価の試み

抄録

A new seismic attribute method using seismic attenuation is present. Contrary to conventional seismic attributes providing reflection strength and phase properties, the attenuation attribute method maps relative Q spatially. Although the method has disadvantage in resolution, it potentially bears big advantage in applicability to analyses of physical properties of rocks in less reflective areas such as volcanic and highly-faulted areas where continuous reflections are rarely observed. The present paper reports on its applicability to evaluate fault seal ability, through a case study using 3D seismic data over two oil fields. As the result of the case study, a fault that traps oil is characterized by lower attenuation, whereas a fault that doesn't trap oil is marked by higher attenuation. According to recent laboratory measurements, seismic waves highly attenuate when they pass through a fault with lower coupling, reversely they don't attenuate very much within a fault with higher coupling. Assuming that the strength of fault coupling is proportional to the ability of fault seal based on existing microscopic observations on fault contact surface, we can form a hypothesis that the higher the fault seal is the lower the attenuation becomes. The hypothesis is supported by the present case study.