Seismic attenuation for the investigation of gas-hydrates

Gas-hydrates have received global attention as a feasible major unconventional hydrocarbon energy resources. Hence, delineation is very imperative for evaluating the resource potential. Gas-hydrates are found out in shallow sediments of outer continental margins and permafrost regions, and have been recognized mainly by seismic experiment based on an anomalous reflector, known as the bottom simulating reflector or BSR. This is a physical boundary between gas hydrate-bearing sediments above and free-gas saturated sediments below, and mimics the shape of seafloor, has opposite polarity with respect to sea floor and crosscuts underlying dipping sedimentary strata. Since gas-hydrates have been recovered without a BSR and even have not been traced with a BSR, seismic attributes such as high velocity and amplitude blanking have played an important role in characterizing the gas-hydrates reservoir. Sediments below the BSR exhibit high reflection strength and frequency shadow. Here we show that the seismic attenuation (frictional energy loss per cycle) is another important attribute that can be used as a diagnostic tool for identification of gas-hydrates and characterizing the reservoir.