PALEOGENE VALLEY SYSTEM AND ITS CONTROL ON PROXIMAL CLASTIC DEPOSITS IN THE SOUTHERN SUB-SAG OF MIAOXI SAG, BOHAI BAY BASIN

In order to seek for subtle reservoirs and favorable sand bodies in low exploration blocks, this paper is devoted to the study of valley system and its controls over the proximal clastic deposits based on logging, drilling, seismic data, taking the Paleogene southern sub-sag of the Miaoxi Sag, Bohai Bay Basin as a case. It is observed that the basement faults roughly in east-west direction perpendicular to the Tan-Lu fault are characterized by long-term tensile subsidence in Paleogene. These faults always form regional valleys and control the secondary subsidence in the period. However, the northwestern or north-northwestern faults, which intersect the Tan-Lu fault at an acute angle, are general under extrusion stress. Mostly, they form small compressive faulting valleys. According to the geometry of the small valleys, they can be divided into subvalleys in various shapes, such as V-type, U-type, W-type subvalleys. The performance of these small valleys on the gentle slope are rather different to those on the steep slope. On the side of steep slope, small valleys control the development of compact fan delta. On the side of gentle slope, however, small valleys control the development of large-scale braided delta. It is useful and profitable to identify and determine the distribution of terrigenous clastic deposits at different layers using seismic reflection, seismic facies, attribute analysis, drilling data and so on as tools. The northeastern or near east-west regional valleys tend to form the macroscopic progradational direction of terrigenous clastic deposits. The smaller of the regional valleys, the more can control the direction of the main terrigenous clastic material into the basin. The small northwestern valleys, belonging to the compressive broken trench, can only control partial progradation of terrigenous clastic materials. Along the direction of these small valleys into the basin, it is often able to accurately find the location for proximal clastic deposition. To clarify the location of these small valleys is conducive to the following exploration and deployment.