Study On Characteristics And Main Controlling Factors Of Ordovician Carbonate Karst Reservoirs On The West Slope Of Shulu

In recent years,the Ordovician carbonate reservoirs on the west slope of Shulu have gradually become a major difficulty for oil and gas exploration and development of deep buried hills in the Jizhong Depression.Since carbonate reservoirs have the characteristics of strong heterogeneity in both horizontal and vertical directions,and the reservoirs have complex genesis,it is more difficult to explore and predict oil and gas in the Shulu West slope area.In this paper,based on the data of cores,thin slices,logging and oil and gas testing,the characteristics of Ordovician carbonate karst reservoirs in the west slope of Shulu were investigated by means of scanning electron microscopy,cathodoluminescence,inclusion temperature measurement and geochemical analysis.The main controlling factors,the petrological characteristics and the various types of diagenesis of the Shulu West slope reservoir were analyzed and summarized,and the corresponding diagenetic evolution sequences and pore increase and decrease characteristics are established as the basis for studying the genesis of the reservoir.In the Shulu area,limestone,dolomite,karst breccia and its transitional lithology are developed,and secondary pores,holes and fractures related to dissolution are the main storage space.The results of porosity and permeability test show that the porosity of matrix dolomite is higher than that of limestone,while the permeability of limestone is higher than that of dolomite.Due to the late tectonic action and karstification,there is a pore-increasing effect in limestone,and the reservoir property of limestone is better than dolomite.The Ordovician strata in the Shulu area have experienced destructive diagenesis and constructive diagenesis,the final porosity of the formation is close to 5%.Destructive diagenesis includes cementation,compaction-compression and filling,and constructive diagenesis includes quasi-identical dissolution,burial dissolution,surface dissolution,rupture.Karstification is a key factor for reservoir formation in Shulu area,the karst on the west slope of Shulu can be divided into quasi-syngenetic karstification,supergene karstification and buried karstification,and vertical seepage zone,horizontal subsurface flow zone and deep slow flow zone are developed in order from top to bottom.Ancient landform shows that near the Jin 2 well in the west of Shulu area is a karst highland,the Jin Gu 2 and Jin Gu 13 areas are karst depressions,and the rest are karst slope areas.The karst reservoir on the west slope of Shulu is controlled by diagenesis,tectonic activity,ancient landform and lithology.The lithology is influenced by the combination of the original sedimentary facies belt and lithology type,which is the material basis and prerequisite for affecting the reservoir differences.The effect of ancient landforms on karst reservoirs is mainly reflected in the direction of ancient water flow and fall of the diving surface.And tectonic process and its associated karstification are the key to the formation of the reservoir,not only can it produce cracks,but also provides channels for infiltration and upwelling of atmospheric fresh water and magma hydrothermal fluids,which promotes the diagenetic transformation in later reservoirs.