Discovered in recent years, Chang 4+5 reservoir group of Yanchang Formation in Jiyuan area is ultra-low permeability reservoir. The evaluation and prediction of the reservoir is the most critical technology in reservoir development. Comprehensive analysis with multiple research approaches shows that the storage potential of the ultra-low permeability reservoir is jointly controlled by sedimentation and diagenesis. Sedimentary factor includes lithology and sedimentary facies, two basic factors affecting the storage potential. The reservoir lithology is of fine-grained debris-arkose and miliary arkose. Pore types are mainly intergranular pores and dissolved pores. The sandstone microfacies in the delta front underwater distributary channel has the best storage potential. Diagenetic factors, including diagenesis types, evolution, intensity, combination etc., have direct influence on the reservoir storage potential. Compaction and calcite cementation are the main factors that weaken the storage potential, whereas carbonate dissolution, especially the dissolution of feldspar plays an important role in the improvement of the storage potential.
The Factors of Threshold Pressure Gradient for CO²Miscible Flooding in Low Permeability Reservoir
