Use of AVO Processing Techniques for Shallow Gas Assessment

The paper describes the interest of using AVO (amplitude versus offset) processing techniques in offshore drilling site surveys for shallow gas assessment. Presently, shallow gas evaluation is mostly based on the aspects of the amplitude anomalies of seismic reflectors. This practice is undoubtedly conservative as amplitude anomalies may not correspond to gas charged horizons; hence, the need to qualify seismic amplitude anomalies, in particular in environments where such anomalies are numerous. With this objective, AVO processing techniques enable discrimination of events which are gas charged or not. The paper presents results of HR surveys with map and seismic sections for which AVO techniques were used. Examples from Thailand, Tonking Gulf and Indonesia are presented, showing practical consequences for drilling site selection and drilling programs.