Characteristics and main controlling factors of the sweet spot reservoir in the first member of Lower Shihezi Formation of well J58 in Hangjinqi area, Ordos Basin

For a long time, the characteristics and main controlling factors of the sweet spot reservoir of tight sandstone gas in the first member of the Shihezi Formation in Hangjinqi area of Ordos Basin are not clear, which restricts the natural gas productivity in this area.Core observations, rock slice image, mercury intrusion experiments and logging data, etc.are used comprehensively to determine the petrological characteristics, reservoir physical properties, sedimentary facies and diagenesis of the tight and high-yield reservoir in the first member of the Lower Shihezi Formation in well J58 block of the Hangjinqi area, Ordos Basin.In-depth research was carried out to identify and classify the favorable sedimentary-diagenetic facies types of the first member of the Lower Shihezi Formation in the study area to establish the corresponding relationship between logging response characteristics and sedimentary diagenetic facies, and discuss the development law and main controlling factors of sedimentary microfacies controlled sweet spots in well J58 block.The results show that there are still many sweet spots in the reservoir of Hangjinqi area under the condition of compact rock formation.The lithology of high gas producing area is mainly litharenite and lithic quartzite, with large particles and good sorting.The original sedimentary environment is mainly braided stream delta with strong hydrodynamic force.Besides, dessert area is mainly controlled by sedimentary facies, and it is mainly developed in high-energy sedimentary facies and favorable diagenesis facies.The prediction and evaluation of dessert reservoir focus on the medium weak compaction debris dissolution diagenetic facies and high-energy beach sedimentary microfacies.