SEDIMENTARY EVOLUTION AND NEOGENE RESERVOIR-SEAL ASSEMBLAGE ANALYSIS OF BOZHONG DEPRESSION

Bozhong Depression with vastly thick Tertiary System deposit underwent two evolution stages of structure-deposit: rifting stage and post-rifting depression stage. In the rifting stage three sets of hydrocarbon rocks of Sha-Ⅲ, Sha-Ⅰ,and Lower Dongying Formation were developed, being of very good hydrocarbongenerating potential developed. The depression contains very rich oil and gas resources. The deposit of fluvial plain facies,developing the braided stream to meandering stream and nearshore shallow lacustrine sedimentary system,characterizes the Neogene post-rifting down-warping stage of Bozhong Depression. There are two sets of reservoir-seal assemblages generated in the Neogene system:one is composed of the mudstones of fluvial-lacustrine-marsh to shallow lacustrine facies and the thick-layer sandstone of Guantao Formation,being a very favorable regional reservoir-seal assemblage;the other is a interbedding reservoir-seal assemblage consisting of overflooding plain mudstone and the sandstone of meandering stream. These two sets of assemblages provide a very favorable condition for the oil and gas accumulation in the middle to shallow layer of Bozhong Depression.