Features and influencing factors of Chang 7 reservoir of Yanchang Formation in Hujianshan area, Ordos Basin

The Chang 7 strata in the Ordos Basin were regarded as source rocks in the past. Plenty of industrial oil wells have been found in the Chang 7 strata of the Yanchang Formation in Hujianshan area of the Ordos Basin in recent years; however, the reservoirs are unevenly distributed and have different industrial productivities. Based on rock thin section, cast thin section, mercury penetration and physical property analyses, the features of the Chang 7 reservoir were studied, and the influencing factors were discussed. Arkose and lithic arkose sandstones are most common in the Chang7 strata. The main interstitial materials are ferroan calcite and hydromica. Residual intergranular pore and dissolved pore are the dominant reservoir spaces. The Chang 7 reservoir is a low porosity and ultra-low permeability reservoir with micro-throat and poor physical property. The main affecting factors include quartz content, size of detrital grain, depositional micro-facies and diagenesis, etc.