The pore texture and origin of the Carboniferous-Permian reservoirs in the south slope of wulangar rise in the north part of Ordos Basin is studied by casting thin section

injecting mercury

SEM

etc..The result indicates that pore texture is not so good and the pores are mainly very small intra-interstitial materials and dissolved intragranular ones.The capillary pressure curves show dominatly type-4 and -5

especially type-5.Thepore texture therefore should be defined as grade 4 or grade 5.The reason caused the poorpore texture is related to the complicated and intensive diagenesis.Within 4 diagenesis stages

the compaction

filling and replacement in the first two stages greatly decreased the pore spaces

though there was dissolution in the third stage

they did not develop well and were filled again in the last stage.According to the fact that well No.Y17 has producedgas

the pores of the intra-interstitial kaolinite may still be available reserving spaces.