Abstract:

Industrial petroleum was discovered from Palaeozoic deep horizons in the Nanpu Depression, Bohai Bay Basin, which suggests significant deep petroleum potential in the area. One of the issues in exploration is forecasting favorable place for prospecting in the area. Hydrocarbons expulsion downward from the source rocks immediately overlapped buried hill should be useful in this aspect. Acoustic logging combined with geochemical approaches was utilized in this study to identify hydrocarbons expulsion and evaluate hydrocarbon potential. After a detailed correlative acoustic logging and geochemical study, a combined hydrocarbons expulsion model of the source rocks in the Nanpu Depression was established, which was used to investigate hydrocarbons expulsion of the source rocks from 33 wells in the Nanpu Depression. The results suggest that the average depths of the source rocks with the hydrocarbons expelled downward into the burial hill in the No.2 and 3Tectonic Belts are about 248 m and 358 m, respectively, and only 35 m for the No.1 Tectonic Belt. No obvious hydrocarbons expulsion into burial hill was observed in the No.4 and 5 Tectonic Belts in the depression. This result coincides with the hydrocarbons discovered up to now in the burial hills. We suggest that these factors including contact style between the source rock and the burial hill, the position of the hydrocarbon kitchen, the thermal maturity of the source rocks, the volcanic rock acting as barrier bed and faults developed, have a controlling of the amounts and characteristics of the hydrocarbons expelled by the source rocks and charged into the burial hill in the Nanpu Depression. A comprehensive study of hydrocarbons expulsion, migration and accumulation indicate that the No.2 and 3 Tectonic Belts and next the No.1 Tectonic Belt are prospective areas with burial hill hydrocarbons reservoir developed. This study also indicated that acoustic logging could be an important tool identifying hydrocarbons expulsion and would be useful in petroleum exploration.

Key words: acoustic logging, hydrocarbons expulsion, buried hill, source rock-controlling hydrocarbon