The Characteristics And Regularity Of Distribution Of Dolomite Reservoir From The Majiagou Formation,Ordovician,Ordos Basin

Ordos Basin is an important basin for marine oil—gas exploration in western China which is abundant in oil and gas resources.The Majiagou Formation,which belongs to Ordos Basin,is one of the important marine strata.The current researches mainly focus on weathering crust karst reservoirs on Jingbian Field at the top of the Ordovician.However,researches of reservoir which concentrate on intervals of M₆ and below M₆ are extremely basic.In order to deepen the understanding of basic characteristics,void origin and development rules of those intervals,this dissertation will attempt to show the petrology and reservoir geology researches about core observation,microscopic identification,logging interpretation and reservoir characteristics of dolomite reservoir in intervals from M₆ to M₁₀ in the Majiagou Formation which located in the east—central of Ordos Basin to confirm genesis of reservoir and regularity of distribution which could further benefit prediction of favorable exploration zone.This dissertation has systematically analyzed the carbonate sedimentary facies,diagenesis,diagenetic model and reservoir characteristics.This dissertation will first confirm the target sedimentary type.In the relative regression period of M₁₀,M₈ and M₆,the gupsum—lagoon has developed in Mizhi Depression in the east while the mudly dolomite and dolomite flat deposit have developed in Wushenqi—Dingbian Depression in the west.In the relative regression period of M₉ and M₇,the calcific dolomitic flat and dolomite flat have developed in the whole area.Secondly,this dissertation has ascertained the dolomite's genesis of reservoir in study area,which is seepage—reflux metasomatism of high—density brine in shallow burial stages and adjustment of recrystallization and burial diagenesis in the later stage.Thirdly,the most important reservoir rocks are residual grain dolostones and relatively fine—crystal dolostones which the grained texture has generally been completely preserved.Karst cave,inter—grain pores(dissolved inter—grain pores)and intercrystalline pore(dissolved intercrystalline pore)etc.are all major pore types.In addition,palaeogeomorphology in sedimentary and grain bank controlled by cyclic of sea level are benefit for the development of advantageous reservoir,and they also controlled the distribution of reservoir planar.Moreover,the dolomitization and karstification are critical factors of reservoir's formation.Consequently,according to three researches which are analysis of main control factors,the researches of diagenesis and diagenetic environment,it could be estimatied that there are three favorable exploration zones.