Research On The Carboniferous Sedimentary Facies And Reservoir Characteristics In The Eastern Margin Of The Pre-Caspian Basin

The Precaspian Basin is one of the largest prospecting oil and gas basins and it is a major oil and gas producing area in Kazakhstan.The main research object of this paper is the Carboniferous in the eastern of the Precaspian Basin.Based on drilling and logging data,Combining analytical assays,logging interpretations and previous research results.Applying theories of sedimentary petrology and petroleum geology,Comprehensive analysis of the characteristics of the Carboniferous strata,sedimentary facies,diagenesis and pore evolution.Finally,the distribution of reservoirs was determined.Carboniferous formations in the study area are development bottom-up Bashkir,Moscow,Kasimov and Gzhelian.And it is divided into lower carbonate(KT-?),regional mudstone(MKT)and upper carbonate(KT-?).Oil and gas are mainly in KT-? and KT-?.Through the study of the biomarkers,sedimentary structures and log marks.It is considered that the KT-? and KT-? oil layers in the study area are mainly open platform sediments,partially restricted platform and the edge of the platform.Micro-phase mainly for the platform shoal,gray matter shallow sea,muddy depression and so on.And the platform shoal(sand shoal,Oolitic shoal,biology debris shoal)is benifitde to the form and evolut the reservoirs.Through the thin slices and core observation,the lithology of the Carboniferous reservoir in the study area is mainly biolithic limestone,algal aggregate limestone,sandstone limestone and oolitic limestone.The main storage space is intragranular dissolved pores,interparticle dissolved pores and biological internal pores.Secondly grain cracks,structural joints and dissolution joints,cave visible.The average porosity of the samples in the KT-? reservoir group was 7.20%,The average permeability is2.00×10-3?m2.The average porosity of the samples in the KT-? reservoir group was 7.63%,The average permeability is1.26×10-3?m2.Reservoir types are divided into the type of pores-hoies and cracks-pores.The pores of the Carboniferous reservoirs in the study area have been substantially reduced through the compaction-autolysis,thid calcite cementation and filling.The current reservoir is formed by epigenetic karst and burial dissolution.These reservoirs are mainly distributed longitudinally in the ?6 section of KT-? and B3,B2,?2 sections of KT-? and mainly distributed in flat directions of the T well area,secondly the H well area.