SAND DISTRIBUTION PATTERN AND CONTENT PREDICTION FOR SUBLACUSTRINE FAN SYSTEMS IN THE LOWER ED2 FORMATION, BOZHONG DEPRESSION

The sublacustrine fan is the major exploration target for lithologic reservoirs in the Bohai Sea. However, the distribution pattern and sand content of the fans still remain unclear in the Bozhong Depression. In this paper, using well and 3D seismic data acquired, taking sequence stratigraphy, analogy analysis and other research methods as means, we established for the first time an integrated index of sand content for reservoir evaluation. Based on depositional sequences and seismic facies, combined them with the statistical analogy result of the sand-rich sublacustrine fans in the Liaodong Bay depression, the Lower Ed₂ Formation of the Bozhong Depression is carefully studied. The results show that the sublacustrine fans are mainly formed in a ring-like shape in the highstand and lowstand system tracts of the Lower Ed₂ Formation. The changes in lake level determined the type and quantity of the sublacustrine fans, the ancient slope break controlled their position, and the accommodation space determined their development patterns and scales. Statistical analysis shows that the sand content of the sublacustrine fan has a linear relationship with the distance to the source area, seismic configuration, aspect ratio, and the ratio of maximum thickness versus area. The integrated evaluation index of the sublacustrine fan is established on these parameters, It is predicted that the No. 1 sublacustrine fan and the No. 2 sublacustrine fan in the Bozhong 18-A tectonic area are the most favorable lithological exploration targets. The integrated evaluation index established in this paper is of guiding significance to the exploration of sublacustrine fans in the Bohai Sea.