DHIs: Amplitude Anomalies Anomalous amplitudes Change in amplitude along the reflector Low High Amplitude Slide 19 These images are from some modeled seismic data with noise included The left image shows two regions with anomalous amplitudes – dark blacks and big excursions in the troughs (whites) In the upper region, the basal strong reflection also appears rather flat – another clue In the right image, the modeled reservoir is thicker There are several clues to note: the reflection at the top (yellow line) changes from low to high amplitude as it goes from a water sand to a HC sand the strong basal reflection on the right indicates the bottom of the HC-filled sand towards the center, the strong black becomes nearly flat this flat to dipping geometry at the base of the HC-bearing zone is called a “hockey stick” the central (flat) portion is a reflection off the fluid contact – HC-filled sand above with water-filled sand below although the sand properties are the same, having different fluids results in different velocities and densities for the formation So on the right we have two lines of evidence an amplitude anomaly at the top and base of the HC-bearing rock, and a fluid contact reflection Courtesy of ExxonMobil L12 – Data Analysis