From Angle Stack To Fluid And Lithology Stacks – A Case Study From Norwegian Sea.

Abstract

Landmark Graphics Seismic amplitudes contains some additional information about lithology and pore-fluid in the reservoir. By combining AVO intercept and gradient attributes along an angle of rotation, an optimal seismic stack can be designed to provide maximum discrimination between either fluids or lithologies. The fluid stack is an optimal stack for enhancing fluid effects in the seismic data. This stack is used to highlight hydrocarbon reservoirs. A lithology stack is an optimal stack for enhancing lithology variations where fluid effects are removed or reduced. This stack is used for mapping instances of sand. In this case study, AVO intercept and gradient attributes were computed from a combination of nearmid-far angles stacks. Then crossplot intercept and gradient data at the reservoir to define background/shale trend and classify how lithologic and/or pore fluid changes are separated from the background trend. After computed intercept and gradient was properly calibrated to the modelled synthetic data, crossplot analysis can be performed with much greater confident. Rotation angle is typically defined as the angle between background trend and the vertical axis in crossplot. With this angle, fluid and lithology stacks were generated to verify successfully the fluid contact and lithology/facies changes in the reservoir across the entire 3D seismic survey.