Characteristics Of Storage-sealing Formation And Gas-controlling Study In The Ordovician Of West Ordos Basin

This article studies the sedimentary evolution,diagenetic evolution,pore types,physical properties,and oil-gas possibility of lower Palaeozoic reservoir on the basis of core observation,micro-observation,geochemical analysis,log interpretation,physical characteristic analysis,and discusse the lower palaeozoic potential reservoir of west margin of ordos basin.The carbonate reservoirs in the west margin of Ordos basin is characterized by multi-factors controls,comprehensive genesis of multi-phase,and various reservoir types.In the lower Paleozoic of west basin,the open platform,restricted platform,platform edge reef,platform margin slope and basin facies are developed,and the inner platform beach is developed inside the open platform.The dominant facies for reservoir are the platform edge reef faices and platform margin slope facies.The diagenesis,including dissolution,dolomitization,consolidation,pressure solution,cementation and so on,play an important role in the porosity development in the Lower Palaeozoic of west margin of Ordos basin,and pressure solution and dolomitization play a constructive role.The limestone strata in Kelimoli formation and Zhuozishan formation in the Ordovician of western basin is mainly composed of karst caves and structural fractures,while the dolomite strata is composed of intergranular pores and dissolved pores.In terms of petrologic characters,pores composition and comprehensive studies of carbonate reservoirs,the pore structure can be divided into 5 categories,intergranular pore,solution-intergranualar pore,dissolved-microfracture,microfracture-sulture,and tight microfracture,and intergranular pore,solution-intergranualar pore,dissolved-microfracture are the main types in the study area.The Ordovician reservoirs in western Ordos basin are of remarkable division,which is the dolomite dissolved pores distribution range in the west,the powder-fine grain of dolomite in the middle and the dissolved breccia in the east.The favorabl area of reservoir in the lower Palaeozoic of Ordos basin is the grain limestone reservoir of Kelimoli formation and dolomite reservoir of Zhuozis han formation,type ??? of reservoir being developed,so the next petroleum exploration direction will be around Tianchi.