The Study Of Depositional Facies And Sequence Stratigraphy Of Ordovician In E Block Of Southern Tahe

In this paper, the study area is located in the southern of Tahe oil field which is part of the northernTarim Basin, the purpose of layer is Ordovician. Based on the theory of sequence stratigraphy, combinedthe research status of sequence stratigraphy, biological strata, sedimentary facies and reservoir at home andabroad, we divided the sequence of single well by the method of Logging, drilling and well combined withseismic, and compared, finally established the framework of sequence stratigraphy and the distributionmap of sedimentary facies. Based on the above analysis results, combined with the analysis of reservoircharacteristics, we discussed the relationship between reservoir characteristics and sequence in the studyarea.The Tarim plate was between10oof northern latitude and18oof southern latitude, the south is theNorth Kunlun ocean, the north is the South Tianshan ocean, the southeast is the small Alpen Gold oceanicbasin, the northeast is Kuluketage deep sea basin. There are2sedimentary units in the Tarim plate, that isthe carbonate platform of the west and the Shelf basin of the east, there was a narrow slope belt betweenthem (roughly in the area of Kunan1-Mancan1). The range of carbonate platform in west roughly equal tothe area that from the Shaya uplift in north Tarim to the Central uplift of Tazhong, it experienced threestages of development, including mesa growth, uplift and depression alternate, submerged, it was the resultof Caledonian movement, there was a close relationship with the interaction that between Tarim plate andother plates around.This paper divides the Ordovician strata into5rock stratigraphic units from below, includingYingshan formation (O1-2y), Yijianfang formation (O2yj), Qarbeg formation (O3q), Lianglitage Formation(O3l), Sangtamu formation (O3s). After the finishing analysis of a lot of core date and thin slice date, wesummarized the petrological characteristics of each stratigraphic unit of Ordovician in E block of southernTahe.According to the macro description of drilling core of12wells and the microscopic identification ofmore than800piece of thin slice, based on the detailed analysis of the sedimentary facies and sequencestratigraphic research, combined with the research results of6seismic cross sections, we made outcarbonate platform, platform edge, slope, shelf, inter platform basin etc five sedimentary system.Based on the detailed analysis of the sedimentary facies and the research about key sequence interface,fully absorbs and utilizes the research findings of Chronostratigraphy and biostratigraphy, we divides thesequence of Ordovician in E block of southern Tahe into14third-order sequences, the average time of thethird-order sequence is about4.21Ma. In which Penglaiba formation includes SQ1, SQ2(no hit), Yingshanformation includes SQ3, SQ4, SQ5, SQ6SQ3, SQ4(not hit), Yijianfang formation includes SQ7, Qarbeg formation includes SQ8, SQ9, Lianglitage formation includes SQ10, SQ11, Sangtamu formation includesSQ12, SQ13, SQ14. Based on the research about main profile, to study the evolution of sequencelithofacies paleogeography, we use the sequence or sequence system as the mapping unit to draw thesedimentary facies map of sequence lithofacies palaeogeography, and then reveals the sequencedepositional model.Combined with the previous research results of reservoir characteristics and the research results ofsequence in this paper obtained that the Ordovician carbonate rock matrix of E block in southern Tahe iswith heterogeneity, the space of reservoir and permeability is including:①dissolution pore;②dissolution hole;③dissolution cave;④crack. Dissolution, rupture and dolomitization are conducive tothe improvement of the carbonate rock’s reservoir and permeability. Base on the vertical sequence ofreservoir and the characteristics of reservoir rock, the Ordovician reservoir of E block in southern Tahe canbe divided into two types:①the Lianglitage Formation’s limestone crack-hole reservoir;②theYijianfang Formation’s limestone pore-crack-hole reservoir, they are both the main Ordovicianproducing formation of E block in southern Tahe. There are two regional caps in Ordovician:①themudstone of Sangtamu Formation;②the nodular limestone of Qarbeg formation.