Geological characteristics of the low-permeability reservoir in the Chang82 reservoir subgroup in the Upper Triassic Yanchang Formation in the well Z19 area, Qingcheng, Gansu, China

The Chang82 reservoir subgroup is a horizon containing relatively abundant reservoir sandstone in the Upper Triassic Yanchang Formaiton in the well Z19 area in Qingcheng, Gansu. However, as the sandstone has a pronounced low-permeability feature, it is the main geological factor which affects the growth of oil reserves in the area. According to the well core observation, log analysis and reservoir rock test, combined with previous work, the authors have analyzed in detail the geological characteristics of the low-permeability reservoir of the Chang82 reservoir subgroup in the well Z19 area and think that the sedimentary microfacies, compaction and cementation are the main geological factors for controlling the development and distribution of low-permeability reservoir sandstone. To look for sandstone of the favorable reservoir facies belt represented by subaqueous distributary channel microfacies is an important direction for petroleum exploration.