Characteristics Of Sedimentary Facies And Reservoirs In The Suhongtu Formation Of The Lower Cretaceous In Hule-barun Fault Zone Of Chagan Sag

The reservoir of Lower Cretaceous in Hule-Barun fault zone of the Chagan sag of YingenEjinaqi Basin at Inner Mongolia has good prospects for oil and gas exploration and development,However,the study on the sedimentary and reservoir characteristics of the main target layer of Suhongtu formation is relatively weak,especially in the evolution of sedimentary system,reservoir distribution,the main controlling factor of physical property and favorable reservoirs distribution are unclear,which restricts the efficient exploration and development of oilfields.In this paper,the reservoirs which in the Suhongtu Formation of the Lower Cretaceous in Hule-Barun fault zone of Chagan Sag is taken as the research object,based on drilling,logging and interpretation of seismic data,Conducted research on reservoir sedimentology and diagenesis,Established evolution model of the sedimentary facies and diagenesis facies,Clarifying the main controlling factors of reservoir quality,Predicted the favorable reservoirs distribution.The paper has achieved the following main results:(1)The Suhongtu Formation in the study area mainly developed fan delta of shallow-water.During the sedimentary period of the first section of the Suhongtu Formation,the climate is warm and humid,the source of the northern part of the Hule fault is sourced,the fan delta plain is narrow,the front edge has a wide bandwidth,and the distributary channel develops,showing the “small plain,large front” deposition characteristics.During the sedimentary period of the second section of the Suhongtu Formation,the climate is arid and hot,the lake basin is relatively contracted,the fan delta plain is widely distributed,the front marginal zone is narrow,and the subaqueous distributary channel is relatively stable,showing “large plains,small fronts”deposition characteristics.The subaqueous distributary channel in the fan delta front is the skeleton sand body of reservoir,and the gravel sandstone,glutenite and fine sandstone reservoirs have the best physical properties.(2)The clastic reservoir of the Suhongtu Formation in the Research area is mainly in the the middle stage of diagenesis,The effect of compaction and cementation on reducing porosity is obvious,dissolved by the tectonic uplift with leaching and the organic acid effectively improve the reservoir physical properties.The diagenetic facies can be subdivided into early weak compaction phase,early weak dissolution and strong cementation phase,medium-term weak compaction and strong dissolution phase,medium-term weak dissolution phase and late strong cementation phase;medium-term weak compaction and strong dissolution phase is the most favorable diagenetic facies.(3)The favorable reservoir of the Suhongtu Formation in the Hulu-Barun fault zone is mainly distributed in the fan delta front facies belt.Among them,the sand body of subaqueous distributary channel which dissolved is the favorable target of exploration and development in the next step.