渤中凹陷东二下亚段湖底扇分布特征及富砂性预测

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

湖底扇是渤海海域岩性油气藏勘探的主要沉积类型。针对渤中凹陷湖底扇发育特征不明、富砂性不清的问题,基于已钻井、三维地震资料,运用层序地层学、类比法等研究方法,通过层序划分、地震相识别,结合辽东湾地区已钻富砂湖底扇统计类比,建立湖底扇富砂综合评价指数,明确渤中凹陷东二下亚段湖底扇特征及富砂性。研究结果表明,渤中凹陷湖底扇主要发育在东二下亚段高位域及低位域,呈环带状分布。湖平面变化决定湖底扇发育类型及数量,古坡折控制湖底扇发育位置,可容纳空间决定湖底扇发育形态及规模。统计分析表明,物源区相对距离、地震反射构型、平面宽长比及最大厚度与面积比等参数与湖底扇富砂性呈明显线性关系。依据上述参数建立湖底扇富砂综合评价指数,预测渤中18-A构造区(1)、(2)号湖底扇为下一步最有利的岩性勘探目标。创新建立的湖底扇富砂综合评价指数,对渤海海域湖底扇岩性勘探具有重要的指导意义。

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 3 D 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.