Improving Drilling Geohazards Assessments of the Overburden Section by Performing Seismic Multi-Attribute Analysis

Abstract

We propose a more robust procedure than the traditional 3D seismic maximum negative amplitude volume extraction analysis to improve shallow gas assessments for sites on the North Slope, Alaska. 3D seismic maximum negative amplitude volume extractions have proven unreliable for prediction of shallow gas accumulations for sites on the North Slope (e.g. Qugruk-2 and Cirque-1 wells uncontrolled fluid release to the environment, and Kookpuk #1 gas influx to the wellbore). The incorporation of seismic multi-attributes to the traditional maximum negative amplitude analysis has improved the geohazards assessment within the overburden section for more than 40 wells in the North Slope of Alaska. This study uses a publicly available 3D seismic data set to reproduce and share the procedures applied over proprietary data for identification of gas-related amplitude anomalies with a focus on an evaluation of seismic amplitudes, relative acoustic impedance, sweetness and automatic gain control. The results reveal that when multiple seismic attributes are correlated and show a consistent response, they appear to be significantly better predictors than maximum negative amplitude analysis alone or other individual attributes as revealed by reported drilling results. This study contributes an improved 3D seismic method for predicting gas accumulations within the reservoir overburden section at proposed drilling sites on the North Slope.