Reservoir Characteristics And Controlling Factors Of The Sub-member _1-4 Of The Ordovician In The Tao 7 Block Of The Sulige Gas Field

Tao 7 area is located in the central-southern middle part of Sulige gas field,which covers an area of 459km2.The carbonate reservoir in lower Paleozoic Ordovician Majiagou Formation is an important production layer.In this paper,the characteristics of the reservoirs and controlling-factors of Mawu1-4 are systematically analyzed.Using the methods of observing the rock core and describing the micro-section indoors,combing the mercury penetration and physical properties,the characteristics of stratigraphic reservoirs in the area are studied and analyzed in detail.The lithology of Mawu 1-4 is mainly dark-gray dissolved pore dolomite containing gold(mold),less grain dolomite.The type of reservoir is mainly induced by cavitation shell with dissolved seam-hole,and the pore structure types of the reservoir are mainly macropore-middle throat and macropore-fine grain throat,followed by pore type with visible smallpore-micro throat,which show that Mawu1-4 is a typical low porosity-low permeability reservoir,and has a strong heterogeneity.This paper divides and contrasts the strata of the Mawu 1-4in the Tao7 area by drilling data,logging data and other concerning data.The exposed strata in the top of the Ordovician has gradually become the trend of aging to the northwest(Mawu 1-3).Based on the reservoir characteristics and the distribution of the stratum,the four controlling factors of the reservoir concluding sedimentation,diagenesis,low-amplitude structure,paleogeomorphy are studied.Several conclusions can be drawn:the sedimentary facies of the Mawu1-4 are mainly dolomite flat with anhydrite concretion in supratidal zone and dolomite flat in intertidal zone;the pattern of the diagenesis is the diagenetic evolution model of gypsum-bearing mud-fine-grained dolomite;the inheritance of low-amplitude structure is good,which displays en echelon;The palaeogeography of Tao7 area belongs to the ancient highland and the ancient terraces of the karst highland,and mainly the ancient highland.It is found that the sedimentary microfacies favorable for the development of effective reservoirs are dolomite-bearing dolomite flat with anhydrite concretion;quasi-synchronic dolomitization and ointment play a material basis for the development of the reservoir's main reservoir space(dissolution pores,intergranular pores),and phenotypic karstification and burial dissolution play a constructive role in the development of reservoir space;the higher tectonic position of low-amplitude structure is conducive to the accumulation of natural gas;the paleomorphic unit transition zone adjacent to the eroded depressions develop good physical properties.Paleomorphology is the main controlling factor of effective reservoir development in Mawu1-4.Based on the influence of controlling factors on the physical properties of reservoirs,the assessment and filtering of advantage layers were carried out in combination with production and test-gas data.The conclusion is that the development zone covers an area of 18.5km2,the less-development zone covers an area of 57.47km2 and the low-development zone covers an area of 149.6km2.