INFLUENCE OF BOTTOM CURRENT ON SANDSTONE RESERVOIR OF HUANGLIU FORMATION IN THE DONGFANG AREA (YINGGEHAI BASIN), NORTH WESTERN SOUTH CHINA SEA

Large scale gravity flow sandstone is developed in the first member of the upper Miocene Huangliu Formation in the Dongfang Area of Yinggehai Basin. The permeability of the upper part of the sandstone reservoir is significantly better than that of the lower part. As one of the potential controlling factors, underflow reconstruction is worth further exploration.

This study identifies the phenomenon of bottom current in the study area based on cores, thin sections, logging data, seismic data etc. It discusses the reworking process of bottom current on gravity flow sandstone and the influence mechanism on reservoirs. The evidence for the reworking of gravity flow sandstone by bottom current in the study area is mainly as follows: (1) perpendicular to the source direction of gravity flow, the erosional effect of bottom current on sandstone is more obvious on the seismic profile; (2) In terms of cores, sedimentary structures such as ripple bedding, flaser bedding and hummocky politic strips are developed, which have obvious traction-current sedimentary structures; (3) In terms of rock components, the suspended mud in gravity flow sandstone is transformed into a muddy strip by the bottom current, and the sorting characteristics of thick sandstone become better, and the trend of directional arrangement of rock particles is observed in the thin section, and the biological cavity of foraminifera is mostly destroyed by underflow; (4) In terms of physical properties, the average porosity of sandstone reworked by bottom current is 18.6%, and the permeability is 105.2mD, which is significantly better than that of gravity flow sandstone.

Based on the permeability difference between the top and bottom of the sandstone reservoir in the Huangliu Formation in the Dongfang Area, we tried to explain that gravity flow sandstone reworked by bottom current can form high quality reservoir, which has guiding significance for the later favorable reservoir development.