Reservoir characteristics and controlling factors of physical properties of the Dongying Formation of the CFD6−4 Oilfield in the Bozhong Sag

CFD6−4 Oilfield is a high−quality, fully−loaded medium−sized oil field discovered in the west−central Bohai Sea. However, drilling results indicate that the reservoir properties of the Dongying Formation in this area are highly variable, the reservoir characteristics and controlling factors of physical property are still unclear. In order to solve the problem of predicting favorable reservoirs in the exploration process of CFD6−4 oil field, the petrology, diagenesis, physical properties and reservoir space characteristics are studied based on the test methods and data of ordinary and casting thin section, scanning electron microscopy, physical properties and grain size analysis.The results of the study revealed that:①The lithologic of the reservoir are mainly medium−fine grained debris−feldspathic sandstones with low composition maturity and medium−low textural maturity. The reserving space is mainly secondary dissolved pores. ②The controlling factors of physical properties include sedimentary microfacies, type of cuttings and diagenesis. Among them, distributary channel of the braided delta front and distributary channel of braided delta plain including distributary channel of fan delta front underwater are the sedimentary microfacies type of the main control favorable reservoir,which have larger grain size, good sorting and strong anti−compaction ability, is conducive to the preservation of primary pores. Rhyolite and andesite are the favorable debris type,which have more content of feldspar are more likely to dissolve and form secondary pores, improving the reservoir physical properties.The reservoir physical properties in the study area are obviously changed by diagenesis, the diagenetic facies types that mainly control the high quality reservoir are strong dissolution facies, medium compaction facies and weak cementation facies.③Two anomalously high porosity and permeability zones were found in this area. The first is controlled mainly by the sedimentary microfacies in the background of relatively weak compaction while the second is controlled by the type of parent rock and strong dissolution.