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Texture Inversion From Seismic Amplitude: Application to Facies Characterization, Offshore Angola, West Africa

Abstract

In reflection seismology, amplitude has been commonly used to invert impedance based on 1D reflectivity convolution at a point of reflection; however, a seismic response actually comes from a zone of reflection known as Fresnel zone. Unlike a point of reflection, a zone of reflection can be better characterized by textural character that is defined by the internal configuration of micro-reflectors. Based on this concept, here we develop a texture inversion method to evaluate textural roughness from seismic amplitude. Unlike conventional impedance inversion, texture inversion is performed based on 3D texture convolution in Fresnel zone. At each sampling location, a texture model is built and convolved with an extracted wavelet. After comparing the synthetic waveform to real seismic waveform within an analysis window, the algorithm updates the texture model until the synthetic waveform best matches real seismic waveform. Application to a 3D seismic survey in offshore Angola (West Africa) demonstrates that a high textural roughness is associated with channels and fans, whereas a low textural roughness is associated with marine shale. We interpret that channels and fans have a rough texture because they formed in a higher-energy depositional environment, whereas marine shale has a smooth texture because it formed in a lower-energy depositional environment. Remaining to be tested by future drilling in the frontier basin, our results demonstrate that Fresnel zone based texture inversion provides a potentially useful tool for facies exploration in the deep-marine depositional setting.