Research On Characteristics Of Ordovician Karst Reservoir Of The Ka 1 Block In Tazhong Region

Tarim basin is one of the most significant oil-bearing basin in China.Ka 1 block is located in the west part of the No.10 tectonic belt in Tazhong region.At present,the Ordovician carbonate become the key point of the exploration in Ka 1 block,and it has already maken a breakthrough in Yingshan formation of Zhong 1 well.However, the previous studies show that the reservoirs in Ka 1 block are of the characteristics of strong heterogeneities,multiple influencing factors and petroleum exploration is characterized by large difficulty. The main influence and control factors of karstic carbonate reservoirs is karstification.According to the structure characteristics of the study area, this paper deals with the diagenesis and also focus on the types ,the times and the control factors of the karstification.And all these studies are based on the theoretical guidance of sedimentary petrology,reservoir geology,reservoir gechemisty,et.Combining with the space types and physical property characteristics of the reservoir,the character of the Ordocician kast reservoir is determined.Through the studies of the cores and the thin section,limestones,dolomites and the transition rocks between them are supposed to be the main reservoir rocks of Ordovician in Ka 1 block. This paper has generalized petrology characteristic and diagenesis of Ordovician carbonate rock in research area.What's more,the corresponding diagenesis sequence is also established.Karstification is the crucial factor during the formation of Ordovician carbonate reservoir. The syndepositional karstification doesn't develop in Ordovician reservoir ,it is mainly controlled by epigenetic karstification and burial karstification. Different types of karstification can form different characteristics of solution pores, cave,and dissolve seam.This paper identified the signs of different types of karstification,including the signs of cores,thin section,well-logging, and FMI imaging logging.There are four times of epigenetic karstification which have great influence on the Ordovician reservoir.They are the first act of the karst in middle Caledonian,the second act of the karst in middle Caledonian,the third act of the karst in middle Caledonian,and the karst in early Hercynian. The burial karstification here maily means to the hydrothermal karst,and the formation of the hydrothermal karst may be related with the magma movement at late Caledonian or Hercynian period.The hydrothermal karst is controlled by the fault system,the closer ,the more possible to development.The reservoir space formed by hydrothermal karst are mostly small dissolved pore and cracks.With the analysis of diagenesis,reservoir space and physical property of Ordovician reservoir in interesting area,it is considered that the reservoir space of Lianglitage are nonselective solution pores,cracks and caves,while the reservoir space of Yingshan are intercrystal pores,intercrystal solution pores,cracks ,solution pores and caves.The porosity and permeability of the Lianglitage and Yingshan Formations are really low,and there is not a relation between the porosity and permeability.The porosity and permeability of Yingshan is better than that of Lianglitage,it is because the permeability of dolomite reservoir is better.There are several factors controlling the carbonate reservoir of Ka 1 block,such as karstification,dolomitization and structural fracture.Comprehensive study shows that the favourable reservoir mainly lacated in the region of Zhong1 well-Zhong17 well-Zhong18 well.The epigenetic karstification of Lianglitage Formation doesn't develop very well,this may be related with the low energy of the platform.Controlled by the karstification ,the Lianglitage reservoir doesn't develop very well.The favourable reservoir often develops in the upper and middle of Lianglitage formation,and the maximum thickness is more than 10 meters.The Yingshan reservoir develops quite well,and the thickness of the reservoir changes from 5.4metres to 69.4 meters,most of them are distributed in 20~30 metres. The favourable reservoir mainly lacated in the regions of Tazhong18 well-Tazhong46 well and Zhong 1 well-Zhong 11 well-Zhong17 well-Zhong18 well-Zhong19 well. Controlled by the karstification,the reservoir usually develops in the upper Yingshan formation,but reservoir also develops in the middle and under part of Yingshan formation in some wells.