Genetic types of Daxing conglomerate bodies and their controls on hydrocarbons in the Langgu Sag, Bohai Bay Basin, East China

The genetic types, porosity and permeability characteristics, as well as oil-gas production capacity of the Daxing conglomerate bodies in the lower and middle sections of Paleogene Sha 3 Member, in the Langgu Sag of the Bohai Bay Basin are studied by combining various data such as seismic, logging, core analysis and formation testing. Three genetic models of conglomerate bodies including faulted-trough gravity flow, grain flow dominated nearshore subaqueous fans, and debris flow dominated nearshore subaqueous fans are built based on core, seismic and logging phases figured out by analyzing the sedimentary settings. The conglomerate bodies generated in faulted-trough flow are composed of matrix supported conglomerates and grain supported conglomerates, in which various kinds of secondary pores are developed; the conglomerate bodies generated in grain flow dominated nearshore subaqueous fans primarily consist of grain supported conglomerates, of which the reservoir space is mainly dissolved pores within gravels, intercrystal pores and fractures; the conglomerate bodies generated in debris flow dominated nearshore subaqueous fans are mainly composed of matrix supported conglomerates and are dominated by dissolved pores within gravels. The conglomerate bodies with different genesis have different reservoir characteristics and oil/gas production capacities. Among them, the conglomerate bodies generated in grain flow dominated nearshore subaqueous fans have the best porosity, permeability and the highest oil/gas production, thus are the key targets for petroleum exploration.