Basic characteristics of Yanchang Formation reservoir in Hejiaji area and their main control factors

Medium-fine arkose is mainly sandstone of the Chang 4+5-Chang 6 reservoir of Yanchang Formation in Hejiaji area.There have line and point-line contact forms which are overgrowth-pore and pore-thin film cementation between rock grains.The Chang4+5-6 reservoir is characterized by low component maturity and upper textural maturity.The main pore types are granular pore and secondary feldspar-dissolution pore which are composed of megalospore and axial canal mainly.The Chang 6 reservoir are super low permeability and accessed densified reservoir of which the majority permeability less than 10×10-3 μm2.The sedimentary facies,mineral composition and grain diameter of the sandstones are the key factors of influencing the reservoir formation and evolution.Furthermore,the strong compaction and cementation are the main factors which result in the low porosity and low permeability of the reservoir,while dissolution is the main factor for improving the physical property porosity of the reservoir.