Seismic Attribute Assisted Analysis of the Interpretational Variations in the Time and Depth Migrated Datasets: an Example From Taranaki Basin, New Zealand

Abstract

In the regions with complex geology together with the apparent stratigraphic and seismic sequence events, time migration algorithms do not provide high-quality imaging for seismic interpretation due to strong lateral velocity contrasts, usage of average velocities in the vertical and horizontal directions, and without defining the ray -bending at interfaces. Therefore, the depth migration method using interval velocities and bended ray-traces at interfaces, provides more accurate results. There are also interpretational differences between the time and depth-migrated seismic data. The objective of this research is to compare these differences using several seismic attributes. In this context, we used the Toro 3-D pre-stack time and pre-stack depth migrated datasets from the Taranaki Basin, offshore New Zealand, because the Giant Foresets Formation presents suitable examples for the different types of channels like distributary, sinuous and meandering channels. Comparisons indicate that dip angles of the faults increased, channel walls become steeper and indicate more curvature, and structures get narrower in the depth-migrated data. There are also amplitude and phase variations in and around the channels. Most of the seismic data in the world are in the time domain and there is no sufficient borehole and velocity data. This situation may affect the attribute calculations in both migration data sets. The main goal of this investigation is to provide an understanding about the possible seismic differences in the time and depth migrations, the reasons behind them and, relationship between the lithology and probable seismic responses by using geomet-rical and physical attributes used in the seismic industry. These steps allow an accurate interpretation and more reliable evaluation of the subsurface structures. This study will also provide a toolkit and guidance for the in-terpreters in the time and depth migrations.