| The Rongshengpu Sag is considered as one of the oil-rich sags in the southern part of the Damintun Depression,Bohai Bay Basin.With the discovery of deep natural gas from the Well Rongtan 1 located in the center of the sag,explorers need to re-evaluate the gas resource potential of the Rongshengpu Sag.However,few exploratory wells have been drilled to encounter the deep strata,resulting in unclear understanding of the quality and distribution of deep source rocks and consequently unware of the gas migration and accumulation patterns,which restrict further natural gas exploration.In this paper,we combine seismic data,logging data and geochemical results with basin modeling techniques to clarify the geochemical properties and gas contribution of source rocks,characterize the hydrocarbon generation history,and establish the migration and accumulation model of nature gas.It provides scientific basis for further comprehensive gas evaluation and favorable targets location.The results show that:(1)The SQ1 sequence of Paleogene Shahejie Formation in the Rongshengpu Sag are dominated by coal-type gas source rocks and oil-type gas source rocks,which are located in the west and the south subsidence centers,with an average thickness exceeding 300 m and a TOC content ranging from 2%～3%.They are in the mature to high mature stage.The SQ2 sequence of Paleogene Shahejie Formation has a small amount of coal-type gas source rocks and biogenic gas source rocks,which reach the mature stage only adjacent to subsidence center.Immature coal gas source rocks and biogenic gas source rocks widely occur in the SQ3-SQ5 of Shahejie Formation..(2)Only one hydrocarbon generation stage occurred around the time of40-30 Ma for source rocks in the Rongshengpu Sag.(3)Biogenic gas originated from sapropelic organic matter is mainly present in the SQ4 and SQ5 stratum of the Qianjin structural zone.Oil degraded gas widely occurred in the entire sag.Thermogenic gas generated from humic organic matter is predominantly preserved in the SQ1 of the center of the Rongshengpu Sag;(4)Natural gas migrated along the carrier beds consisting of open faults and connected sand bodies with high permeability.It then encounters closed faults or dense mudstones and accumulates.The sandstone interbeds in the deep sag area are proven to be favorable exploration targets.The deep area of Rongshengpu Sag has good conditions about hydrocarbon generation and preservation,which is a favorable exploration direction. |
