Sedimentary And Reservoir Characteristics Of Sand-Conglomerate Bodies In The Es3 Members Of Downthrown Block In Yidong Fault Zone

Sand-conglomerate oil and gas reservoirs in the rift lacustrine basin is the focus of the current exploration and development.Sand-conglomerate has the characteristics of fast deposition,great thickness,unstable in transverse distribution.Sand-conglomerate reservoirs have problems in complex internal structure,large sedimentary facies change,strong heterogeneity,and those seriously restricted the process of exploration and development.This paper takes sand-conglomerate bodies in the Es3 Members of downthrown block in Yidong fault zone,Zhanhua depression,as the study object.Internal structure,genetic types and its distribution rules,reservoir characteristics and its distribution rules of sand-conglomerate were studied by the analysis of seismic data,logging data,drilling data,logging data,core,ordinary flake analysis,casting sheet analysis,SEM analysis,cathodoluminescence analysis.By studying the relationship between sand-conglomerate and lake level changing in the Es3 Members of downthrown block in Yidong fault zone,the internal structure division process of sand-conglomerate under sequence stratigraphic framework constraints was established:(1)Determine the scope by integrating earthquake date with drilling date;(2)Determine the period by seismic profile in parallel source direction;(3)Determine the lobe by seismic profile in vertical source direction.The sand-conglomerate bodies' genetic types in Es3 member of Yidong fault zone thrown side has the dual structure.The development of retreated nearshore subaqueous fan was controlled by early episodic fault activity and water level gradually deepening.The development of prograded fan delta was controlled by late stable tectonic and water level gradually shoaling.Main deposition of nearshore subaqueous fan which on the bottom,is gravity flow.Massive bedding can be found in the core.Sediment grain size probability cumulative curve shape mainly was uphill arched arc pattern.Main deposition of fan delta which on the top,is traction current.Graded bedding,current bedding,whorl fossils and bioclast can be found in the core.Sediment grain size probability cumulative curve shape mainly were bisegment pattern,one bouncing “population-one suspension population-transitional zone” pattern,high slope multi-bouncing population-one suspension population.Controlled by the enrichment carbonate parent rock sedimentary setting,the main controlling factors of sand-conglomerate reservoirs are carbonate cementation,followed by compaction,and organic acid dissolution had improved the physical properties of reservoirs.Fan delta reservoirs were formed in a state of layer.The relatively high quality reservoirs are mainly developed in the middle of the underwater distributary channel.The reservoir space is mainly composed of feldspar dissolved pores and Lithic dissolved pore.The mouth bar and distal bar are characterized by the interbedding of the oil layer and the gray layer,and the dissolution pores formed on the top in which thick sandstone is supported by grain.Melange accumulation is the typical characteristic of nearshore subaqueous fan.And it has a poor resevior physical property,which only developed less feldspar and debris dissolution pores applying to organic acid.