Division and identification of vertical reservoir units in Archaeozoic metamorphic buried hill of Bozhong Sag, Bohai Bay Basin, East China

Abstract

Based on the data associated with cores, sidewall cores, casting thin sections, reservoir physical properties, conventional logging and imaging logging, the classification schemes of vertical reservoir units are proposed for the two types of Archaeozoic buried hills (exposed and covered ones) in the Bozhong Sag, Bohai Bay Basin. The geological characteristics and storage spaces of these reservoir units are described, and their identification markers in conventional and imaging log curves are established. The Archaeozoic metamorphic buried hills can be vertically classified into two primary reservoir units: weathering crust and inner buried hill. The weathering crust contains four secondary units, i.e., the clay zone, weathered glutenite zone, leached zone, disaggregation zone; and the interiors contain two secondary units, i.e., interior fracture zone and tight zone. In particular, the inner fracture zone was further divided into cataclasite belts and dense-fracture belts. It is proposed that the favorable reservoirs of exposed Archaeozoic metamorphic buried hills are mainly developed in four parts including weathered glutenite zone, leached zone, disintegration zone superposed with the cataclasite belt and the cataclasite belt of inner fracture zone, and are controlled by both weathering and tectonic actions. Favorable reservoirs in covered Archaeozoic metamorphic buried hills are mainly developed in the weathering crust superposed with the cataclasite belts and the cataclasite belts of inner fracture zone, and are mainly controlled by tectonic actions.