SEISMIC INVERSION OF TARANAKI BASIN

Abstract

Seismic inversion, pre-stack or post-stack, is regularly performed in order to derive seismic impedance. This impedance is then used to derive other petrophysical properties such as porosity. In this thesis, I have performed post-stack seismic inversion of the Ngatoro region in the Taranaki Basin of New Zealand. After scanning more than 20 seismic volumes and over 600 wells I narrowed down to Ngatoro region owing to the availability of post-stack seismic data and a vertical well in the region, which I have used to carry out the post-stack inversion. Using the well, I identified the target zone of inversion to be between the depths of 1000 m to 1250 m. This zone is mostly fresh water saturated and can be approximated to contain sand as the major matrix component owing to the very less percentage of clay minerals in the zone, found using the mudlog data. After receiving good correlation of seismic to well tie, I have upscaled the log to derive the P-impedance which comes with good agreement with the impedance derived from seismic data. After deriving the density porosity using the upscaled log, I have correlated the P-impedance and porosity to derive a linear relation between the two parameters. The porosity in the zone varies from 13 to 19%. The best fit line gives a good estimate of the porosity trend in the water saturated zone as evident from the high value of coefficient of determination