The Impact of Amplitude Variation with Offset (AVO) Analysis from 10 Years of Successful Exploration in Block 14 Angola

Peter Mitchell
Chevron, Luanda, Angola

Over the last 10 years, a greater than 80% exploration success rate has been achieved in Block 14, Angola for Miocene prospects. A critical factor to the success has been the careful application of AVO.
The application of AVO must consider both information provided by well control and seismic data. A sufficient well data base with the appropriate logs and conditioning must be developed. A data base of 35 wells has been developed including wells from both Block 14 and the Congo. Each well has full suite of logs that have been consistently processed. These logs have been used to forward model the AVO response for each of the Block 14 reservoirs. AVO response has been found to be depth dependent. Shallow reservoirs are dominated by Class III anomalies with deeper dominated by Class II.

Seismic data must be properly acquired and processed to capture and preserve amplitude changes. Over the past few years over 80% of Block 14 has been re-acquired with higher fold and smaller bin size seismic. In addition, this new data and legacy data have been reprocessed through Pre-Stack Depth Migration. The focus of the processing has been preservation of true amplitudes, improvement in signal to noise, and accommodation of anisotropy. The goal is “flat” events on final gathers with high signal to noise. Good agreement between the forward models and seismic has been verified.

The seismic data when integrated with the forward modeling can then be used to generate attributes that can identify hydrocarbons. Several examples from Block 14 are used to illustrate how simple attributes can be generated from the seismic data and used as powerful fluid indicators.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery