Identification and Complex Non-structural Hydrocarbon Traps Using AVO-Analysis in the Hapchagai Megaval

One successful solution for gas prospecting is to combine Bayesian classification and AVO. The calculation of a probability cube based on a “benchmark” (“AVO anomaly”) in an interval with established gas inflows allows the identification of complexly built hydrocarbon traps throughout the study area. The technology was tested in a field located within the Northern Vault of Western Siberia with test results from more than 130 wells. The calculated probability in the tested intervals was P > 0.8. After successful testing, the technology was applied in the Hapchagai megavalley of the Vilyui syneclise to identify complex traps in Lower Triassic sediments. Formation of a “benchmark” was performed on the basis of AVO cross-plot in the interval with identified gas inflows, which was stored in the database in the values of probability density function involved in the algorithm of seismic cube transformation into probability cube. Based on the predicted probability maps, well 22 was recommended. In the current season, drilling of this well revealed gas saturated interlayers based on logging data. Thus, the new drilling data confirmed the prediction based on a combination of AVO analysis and Bayes classification.