The Study Of Sequence Stratigraphy And Sedimentary Characteristics Of Ordovician Period In Katake Uplift Of Tarim Basin

The study area of this paper is located in the middle of the central uplift in Tarim Basin.The target layer is Ordovician Period.Based on the present exploration situation of the study area,the bottlenecks of exploration and development,theoretical direction of architectonic geology,sedimentary petrography,logging geology,sequence stratigraphy and the like are applied to make comprehensive research.On the basis of regional geological background,making an analysis of the drilling,logging and seismic data,massive results of thin section identification and rock core observation are utilized to study the petrological and sedimentological features of this area deeply.The author of this thesis combines drilling with seismic data to recognize the sequence boundary,and then compares each single well's sequence to divide and set up the region's sequence stratigraphic framework.From point and line to plane,we make a research in the distribution and evolution of the sedimentary facies within the sequence,and then summarize the sedimentary model.The characteristics of reservior spaces in the stratigraphic framework are studied.Then the relations of sequence boundaries to karst are analyzed so as to predict the favorable reservoir facies belts finally.Katake Uplift,which is controlled by the basement structures,is developed from Sinian basement of Tarim Basin.It has experienced prototype stage of early Caledonian Episode?,formation stage of middle Caledonian(divided into?and?episode),and reformation and shape-finalized stage of late Caledonian-early Hercynian.During the Ordovician,it experienced the process from stretching to compression.Episode? of early Caledonian caused a gentle uplift in this area,so a prototype of Katake uplift was formed.During episode? of middle Caledonian,Katake uplift was affected by the squeezing from the south.The fracture of Tazhong No.1 was active again and caused formation of most factures controlling the secondary tectonic belt.And Katake uplift was under disintegration,becoming a fault uplifted in northwest direction(slope break).During episode?of middle Caledonian,the compressional stress continued,and eastern Katake uplift was lifted and denuded,becoming a “broom” prototype that spread westward.During late Caledonian movement,Katake uplift was lifted further,causing Silurian-middle to upper Ordovician to be under severe denudation and middle to upper Silurian to be lost.Early Hercynian movement made the early faults revive.The whole Katake uplift was lifted.After the early Hercynian,the activity of main faults ceased,and Tazhong No.1 fault belt no longer revive.Due to the tensile background of Carboniferous-Permian,there were rifting and subsidence instead of orogeny in Tazhong fault fold,making Katake uplift preserved in the water.During the Ordovician,Khattak Uplift is stable sedimentary of carbonate platform among the craton.Through a combination of lithology,logging response and seismic facies identification,5 sedimentary facies exist in the area:the development platform,open platform,platform margin,marginal slope and continental shelf(mixed continental shelf).What's more,the lower Penglaiba formation develops restricted platform.The lower to middle Yingshan formation develops restricted platform-open platform,and the shoal can be seen partially.The middle Yijianfang formation develops open platform.The upper Qiaerbake formation develops deepwater platform subfacies within open platform.Lianglitage formation develops open platform.Sangtamu formation develops shallow continental shelf facies.Taking up sequence stratigraphy as a theoretical foundation,with the analysis of tectonic and sedimentary background in the area,making comprehensive study of the sequence boundary,3 supersequence boundaries(SSB1,SSB2,SSB3),whose type is uplift unconformity,and 6 sequence boundaries(SB2,SB3,SB4,SB6,SB7,SB8),whose type is erosion unconformity,are identified.And then it is divided into 2 supersequences(SSQ1~SSQ2)and eight sequences(SQ1~SQ8).Through drilling and seismic studies,the stratigraphic framework is established.On the basis of analyzing point(single well,thin section,rock core)-line(well section)-plane(seismic),the sedimentary facies distribution and the major dominate factors are studied within the sequence stratigraphic framework to set up the evolution model of the sedimentary sequence.The factors controlling Ordovician sequence are: tectonic movement,sea-level change and paleoclimate condition.Tectonic movements mainly control sequence boundaries and ancient depositional landscapes.Sea-level changes lead to the formation of sequence boundaries and the succession of system tracts.Changes of the paleoclimate affect the types of carbonate platforms and their location.The carbonate reservoirs in Katake uplift develop mostly in the carbonate platform and the platform margin.Limestone,dolomite and the transitional ones between them of Yingshan formation and particle limestone of Lianglitage formation are included.The reservoir spaces are mainly pores,holes or seams formed by the exposure and erosion.Katake uplift has experienced multi-stage tectonic movements and sea-level changes,leading to different levels of sequence boundaries and different periods of interrupted interfaces,where syngenetic dissolution-supergene weathering crust karst(carstification)develops.Levels of dissolution can be divided into syngenetic dissolution in late highstand(fourth-order sequence boundary),syngenetic dissolution in erosion unconformity(third-order sequence boundary),supergene weathering crust karst in upift unconformity(second-order sequence boundary),and supergene weathering crust karst that's enduring in orogenic unconformity(first-order sequence boundary).Dissolutions in high-level sequence boundary can superpose lower ones.The development of carbonate reservoir in Katake uplift is controlled by the sedimentary facies and sequence boundaries.The favorable reservoir facies belts are upift unconformity(supersequence bundaries)where the weathering crust karst develops and the rimmed platform margin zone.