Low-porosity and low-permeability hydrocarbon reservoirs and their controlling factors in the Chang-6 and Chang-8 members of the Yanchang Formation in the Fuxian region,Ordos Basin

In the light of thin section examination,SEM,X-ray diffraction analysis and mercury injection analysis, the porosity and permeability and their controlling factors are explored for the hydrocarbon reservoirs in the Chang-6 and Chang-8 members of the Yanchang Formation in the Fuxian region,Ordos Basin. The hydrocarbon reservoirs in the Chang-6 and Chang-8 members of the Yanchang Formation consist dominantly of lithic feldspar sandstone and subordinately of feldspathic litharenite,which are moderately to well sorted,subangular to subrounded,and in contact cementation. The porosity types include residual intergranular pores,interstitial micropores,intergranular solution openings,intragranular solution openings and microfissures. Influenced by lithology and diagenesis,the hydrocarbon reservoirs in the Fuxian region are assigned to the low-porosity and low-permeability hydrocarbon reservoirs.