The Study Of Ordovician System Sequence Stratigraphy And Sedimentation Feature In The Southeastern Of Katake Uplift

The study area of this paper is located in the middle of the central uplift in Tarim basin,which is distributed along the southern fracture zone of Tazhong Area.It is composed of the southern of Shuntuoguole low Uplift,the western of Guchengxu Uplift and the southern of Katake Uplift,it has an area of 12978.94 sq km,and the target layer is Ordovician Formation.According to the present exploration situation of the southeastern of Katake Uplift and the main existing problems,integrating the present data of rock strata,biology strata,sequence strata and sedimentary facies,rely on theoretical direction of architectonic geology,sedimentary petrography,logging Geology,sequence stratigraphy and so on to make comprehensive research.On the basis of regional tectonic background,comparing each single well's sequence to divide and set up the region's sequence stratigraphic framework,and make sequence as a unit to compile sedimentary facies figure,then we can study sedimentary evolution and the distribution of the sedimentary facies within the sequence.Based on this,use reservoir sedimentology theory and hydrocarbon accumulation law,uniting the result of rock core observation and thin section identification to forecast beneficial reservoir facies belts on the basis of reservior space and reservoir physical property analysis.The forming of the Ordovician formation of the southeastern of Katake Uplift is deeply affected by the early Caledonian movement,the middle Caledonian movement,the late Caledonian movement and the early Hercynian movement.During the Ordovician,the southeastern of Katake Uplift experiences from stretching stress to crushing stress.The second stage of the early Caledonian movement isn't intensitive,and the first stage of the middle Caledonian movement make the southeastern of Katake Uplift endures crushing stress from the south side.Then the research area begin to lift,an different region has different uplift degree,we can see that the southernmost of Katake Uplift is overtopped than Guchengxu Uplift.Under the conjunct impact of the late Caledonian movement and the early Hercynian movement,the palaeostructure high part of the research area suffers different denudation degree.During the lower Ordovician,the ancient climate was arid,the research area is mainly in restricted platform facies,then the climate begin to be humid,the research area is mainly in open platform facies.During the later Ordovician,the sea levels starts to massively rising,and the southeastern of Katake Uplift is mainly in mixed product shelf facies.Take up sequence stratigraphy as a theoretical foundation,with the analysis of depositional systems and tectonic geology background,make comprehensive study of the rock strata,biostratigraphy,chronostratigraphy and seismic stratigraphy.The Ordovician sequence boundary is identified by 9,including Uplift unconformity and erosion unconformity,and then the sequence will be divided into 2 supersequence(SSQ1 ? SSQ2),eight sequences(SQ1 ? SQ8).On the basis of analysising of main sections,the author studies the sedimentary facies distribution and the major dominate factors within the sequence stratigraphic framework to establish the evolution of the sequence and deposition in the southeastern of Katake Uplift.Finally,the most important thing is to compile the sedimentary facies plan and disclose the sedimentary facies distribution regulation.The controlling factors of Ordovician sequence are: tectonic movement,sea-level varichange and ancient climate condition.The display of tectonic movement has two aspects,one is the control to sequence boundary,the other is the influence to the formation of the ancient deposition landscape.Base-level change caused by the double impact of the control to sequence boundary and the succession of the system tract.The erosion unconformity boundary is the result of the lowering of sea level.Different climate form different deposition condition,the change of paleoclimate effect the transition of carbonate rocks' type and site.Comprehensively analyze of the sedimentary,sequence stratigraphy and reservoir characteristics in the southeastern of Katake Uplift,the author deems that there are two potential reservoir facies belt.The reservoir body in Guchengxu Uplift and Shunnan wellblock is existing in SQ1-SQ4(lower-middle Ordovician),it can be divided into two section.The bottom side is around Gulong1 well in plane,it is existing in SQ1-SQ2(from Penglaiba formation to the bottom of Yingshan formation),the sedimentary facies is bank,the reservoir space is intergranular hole.The top side is around Shunnan1 well in plane,it is existing in SQ3-SQ4(from the top of Yingshan formation to Yijianfang formation),the sedimentary facies is bank,the reservoir space is crevice.The reservoir body in the southernmost of Katake Uplift is existing in SQ6(Lianglitage formation),it is around open platform deposit zone in plane,the sedimentary facies is platform edge shallow facies,the reservoir space is intergranular dissolved pore and interparticle dissolved pore.