Abstract:

A parameter system for exploration risk assessment and a spatial attribute property set of oil & gas wells and dry holes was created based on study of oil accumulation patterns as well as their main controlling factors in the third member of Shahejie Formation in Shenxian sag of Bohai Bay Basin.In combination with the drilling data,templates for exploration risk assessment were established by using data integration methods,such as Mahalannobis distance method and Fuzzy mathematics method,and Bayes probability model.They were used to predict and visualize the risk probability of exploration for every point in the whole sag.The results revealed several low risk targets: Shenxian low amplitude structure,Shenxi,Hengshui and Shennan fault terrace.This work offered important information for further exploration in this area.However,disparity exists in the prediction results because of the limitations of these methods.The accuracy of the above former two methods is 73.7% and 79% respectively,and that of the integrated method is 86%.Since the Fuzzy assessment method employs all the information that represents favorable geological conditions,the low risk areas predicted with it is relatively large,hence increasing the exploration risk.On the contrary,Mahalannobis distance method only selects effective geological factors that can distinguish the oil & gas wells from dry holes,the favorable exploration area it predict is relatively small and the targets are more accurate.However,it may miss some potential exploration areas.

Key words: exploration target, risk visualization, exploration risk, Shenxian Sag, Jizhong Depression