In this study, we bring together the two main categories of time-lapse seismic analysis — amplitude analysis and time-shift analysis — to estimate simultaneously the changes in thickness and velocity of a 4D seismic anomaly. The methodology is applied to time-lapse seismic monitoring of carbon dioxide [Formula: see text] storage at Sleipner field, Norway, that shows significant 4D effects. The 4D anomalies resulting from [Formula: see text] injection appear as a multilayer reflection pattern within the relatively shallow Utsira Sand. This multireflective appearance within the sand layer is interpreted as [Formula: see text] layers trapped below thin shale layers. Because most of the [Formula: see text] layers are believed to be thin [Formula: see text], the interference between top and base of these layers needs to be taken into account in 4D seismic analysis. By studying the reflected event from a horizon below the Utsira Sand, we estimate 4D traveltime shifts caused by the presence of the [Formula: see text] layer above thishorizon. We then combine these traveltime shifts with measured amplitude changes for the top and base of the [Formula: see text] layer to estimate velocity and thickness changes for the thin [Formula: see text] layer. In 1999, after three years of injection, the most likely velocity change was around [Formula: see text] and the thickness of the [Formula: see text] layer was around [Formula: see text]. In 2001, the corresponding velocity change and thickness estimates were [Formula: see text] and [Formula: see text], respectively. Finally, in 2002, the most likely velocity change was [Formula: see text] and the thickness of the [Formula: see text] layer was [Formula: see text]. It is not straightforward to apply this method to a stack of [Formula: see text] layers because 4D time shifts below the Utsira Sand only provide information about the average time shift for all layers. The amplitude information for each individual [Formula: see text] layer cannot be resolved without knowing the velocity change within each layer. However, our result from a single [Formula: see text] layer may be used to constrain the velocity changes for the multilayer [Formula: see text] case.

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Reliable quantification of carbon dioxide (CO 2 ) properties and saturation is crucial in the monitoring of CO 2 underground storage projects. We have focused on quantitative seismic characterization of CO 2 at the Sleipner storage pilot site. We evaluate a methodology combining high-resolution seismic waveform tomography, with uncertainty quantification and rock physics inversion. We use full-waveform inversion (FWI) to provide highresolution estimates of P-wave velocity V P and perform an evaluation of the reliability of the derived model based on posterior covariance matrix analysis. To get realistic estimates of CO 2 saturation, we implement advanced rock physics models taking into account effective fluid phase theory and patchy saturation. We determine through sensitivity tests that the estimation of CO 2 saturation is possible even when using only the P-wave velocity as input. After a characterization of rock frame properties based on log data prior to the CO 2 injection at Sleipner, we apply our two-step methodology. The FWI result provides clear indications of the injected CO 2 plume being observed as low-velocity zones corresponding to thin CO 2 filled layers. Several tests, varying the rock physics model and CO 2 properties, are then performed to estimate CO 2 saturation. The results suggest saturations reaching 30%-35% in the thin sand layers and up to 75% when patchy mixing is considered. We have carried out a joint estimation of saturation with distribution type and, even if the inversion is not wellconstrained due to limited input data, we conclude that the CO 2 has an intermediate pattern between uniform and patchy mixing, which leads to saturation levels of approximately 25% AE 15%. It is worth noting that the 2D section used in this work is located 533 m east of the injection point. We also conclude that the joint estimation of CO 2 properties with saturation is not crucial and consequently that knowing the pressure and temperature state of the reservoir does not prevent reliable estimation of CO 2 saturation.

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In this paper, the effectiveness of airfoil-shaped pier with and without a collar on local scour depth reduction is numerically investigated utilizing FLOW-3D model. The results show that on a constant T* = VT/D (V: velocity, T: time, D: pier width), increasing the width of the ballet of pier would result on the reduction of maximum scour depth and it would mitigate the scouring depth behind the piers. Also, because of lack of uplift vortices in using airfoil-shaped pier, there would be no scouring behind the piers. Utilizing collar on the airfoilshaped pier would result in a reduction of maximum scouring depth in front of the pier as well and the uplift vortices behind the pier would reduce. Investigation of orientation discipline of the airfoil-shaped pier on flow route shows that the pier which is reversely placed in the flow direction (the keen part in front), will cause the horseshoe vortex to weaken and make the scouring to start from downstream. However, scouring caused by horseshoe vortex in front of the airfoil-shaped pier is strongly more than scouring caused by wake vortex in the rear of the pier.