Impedance inversion of the karst reservoir using diffraction

In unconventional exploration, karst or paleokarst reservoir in petroleum geology is usually recognized as a potential target. The investigation of karst is considered to be prime importance in exploration geophysics since nearly 50% of the world's hydrocarbon reservoirs are hosted in porous karst systems. Generally, diffraction is presented in seismic wavefield registered above the paleokarst reservoir. It is connected to sharp geometrical or lithological properties and the presence of cavities in the subsurface. Many techniques of diffraction detection and imaging have been proposed. However, the use of diffraction for the impedance inversion is limited. Here we present a method to estimate the impedance using the diffracted component of the total wavefield with the goal to improve the impedance model of karsts and its vicinity. The algorithm combines the diffractors position in the migrated depth domain and seismic amplitudes in the unmigrated domain to invert for impedance based on ray theory plus geometrical theory of diffraction. Using a karst model for illustration, our methods have the validation to estimate the impedance of the karst system in different scales, as well as utilizing preserved amplitude information without distortion.