The Relationship Between Salty Characteristics And Source Rock Formation In Qianjiang Sag,Jianghan Basin

The Jianghan basin is the largest basin in the Paleogene salinization area in China.The Qianjiang Formation is the most developed layer for source rocks and salt rocks in Qianjiang sag.It is closely related to the salinization environment,characteristics,mechanism,and salinization and source rock formation in Qianjiang sag.The study of Qianjiang sag mainly focuses on unilateral studies,such as tectonics,sedimentary environment and source rocks.However,there are few comprehensive studies on the relationship between salty characteristics and source rocks formation.This paper conducts a thorough research on sedimentary environment,distribution,coupling relationship of gypsum-salt rock and source rock.It is great significance to reveal the symbiotic relationship between the gypsum-salt rock and source rock in the Qianjiang sag.Study on the common characteristics of the petroliferous basins by comparison of salty petroliferous basins in the world.Through core observation,logging and drilling data,seismic data,thin section authentication,tested for major and trace and rare earth elements,total rock X-ray diffraction,TOC and pyrolysis test,this paper conducts a thorough research on sedimentary environment,distribution,coupling relationship of gypsum-salt rock and source rock.It discusses the relationship between the salinization environment and source rock formation.Study on the common characteristics of the petroliferous basins by comparison of sedimentary environment,mechanism,influence of the source rock in salty petroliferous basins in the world.The distribution of source rocks and salt rocks are controlled by tectonic evolution in Qianjiang sag.The depositional center of gypsum-salt rocks also move along with it.The best quality hydrocarbon source rock in the Qianjiang Formation with the largest fault intensity is the early-middle stage of Structure IV.The analysis of geochemical show the high-salinity conditions and low oxygen contents when organic-rich mudstones were deposited in Qianjiang sag.As a whole,it is in subtropical semi-arid humid climate.Vertical stratigraphic deposition and tectonic activity show the vertical distribution of gypsum-salt rocks and source rocks mainly a mixture of salt rock and mudstone(salt rhythms)and halite-mudstone section.Through core observation,I found three types of rocks,which are a pure rock salt,gypsum mudstone interbeds and salt rock filling cracks,and salt rock in the fracture filling due to iron showed red brown.The redox indexes of Ni,Cr,Ga,Rb and rare earth elements was significantly higher than the normal grey halite deposition.There are three main sources of salt in Qianjiang sag: surface runoff,deep brine floods and reserve basins(heavy brines).It reveals that the composition of sedimentary minerals is complex by tested for total rock X-ray diffraction.It is found that the hydrocarbon generation potential of dark mudstones near salt rocks is much better than that of dark mudstones far from salt rocks by TOC and pyrolysis test.In addition,the hydrocarbon generation potential of the source rocks in the rhythm of single salt has gradually become better.The dark mudstones on the salt are darker than the dark mudstones in the inter-salt section,and in the upper part of the salt,the dark mudstones near the salt layer have better hydrocarbon generation potential and gradually become worse.In the Qianjiang sag,the deep-water salt lake area is the most favorable oil production area.It is great significance to study shale oil and gas in the inter-salt source rocks.It is found that many similarities between the Qianjiang depression and the other salty petroliferous basins.Qianjiang sag belongs to the type of saline lacustrine.Its salts gather in deep fracture.Most salty petroliferous basins in Paleogene.The salty source rocks are mainly rich in carbonaceous dark layered mudstone / shale,rich algae dark gray layered dolomitic mudstone / shale.