Abstract: By adopting quantitative evaluation of pore throat parameters under different depositional and diagenetic conditions,and with reference to the test results of physical property,casting section,SEM,constant speed mercury injection,particle size and X diffraction,the pore throat types of Chang 8 reservoir of Heshui Region and Chang 6 reservoir of Xuecha Region in Ordos Basin were analyzed,contrasted and reasons for how they were formed were revealed.Results show that the pores are better developed in Chang 8 reservoir in Heshui Region,with a high quantity of intergranular,dissolved,intercrystalline and micro pores,as well as necking down throats with weak compaction,tube-shaped throats with dissolution and clay cementation; while pores are less developed in terms of both types and range in Chang 6 reservoir of Xuecha Region,with high quantity of lamellar and curved lamellar throats with compaction.For the two studied reservoirs,the differences in pore parameters are not as significant as those in throat parameters.Compared to Chang 6 reservoir,Chang 8 reservoir developed better and larger throats with apparent differences,bigger pore-throat ratio,and wider distribution of throats that are conducive to permeability.Under the condition of same permeability,the average throat radius,main flow throat radius and pore-throat ratio of Chang 8 reservoir are all bigger than those of Chang 6 reservoir.It can be concluded that the hydrodynamic conditions in sediments,particle size,detrital component,interstitials,diagenesis types and their respective influence degrees,are the main reasons for the differences in the development of pores,throat types and pore throat parameters.

Key words: quantitative evaluation, pore throat type, pore throat parameter, tight sandstone, Ordos Basin