Diagenesis of continental tight sandstone and its control on reservoir quality: A case study of the Quan 3 member of the cretaceous Quantou Formation, Fuxin uplift, Songliao Basin

Research on the diagenesis of continental sandstone reservoirs can provide scientific guidance for the prediction of reservoir sweet spots. The low permeable-interbedded thin and thick sandstone reservoirs of the Cretaceous Quantou Formation's Quan 3 Member in the Fuxin Uplift, Songliao Basin, were used as an example in this work to investigate the diagenesis of continental tight sandstone and its influence on reservoir quality. A large number of thin section, scanning electron microscopy, granularity, X-ray diffraction, and petrophysical property measurements were used to study the petrological characteristics and diagenesis. The reservoir space evolution mode of continental sandstones in this area was constructed by combining diagenesis sequences and the evolution of petrophysical properties of the Quan 3 Member. The results show that the compositional maturity of the sandstone reservoirs of the Quan 3 Member is relatively low and their lithologies are mainly lithic feldspar sandstone and feldspar lithic sandstone, followed by lithic arkose sandstone, feldspathic litharenite and a small amount of lithic sandstone. The average particle size of the target sandstones is 0.11 mm, and the fine sandstone to coarse siltstone are favorable reservoirs. The studied sandstone reservoirs have undergone intense diagenetic transformations, including compaction (pressure solution), cementation, dissolution, and metasomatism. Moreover, the complex diagenetic environment changes in the Quan 3 Member include early alkaline-acidic→mid-alkaline→late acidic. The shallow sandstones are in the meso-diagenetic A₁ stage; when the burial depth exceeds 800 m, they enter the meso-diagenetic A₂ stage; and when the burial depth exceeds 1600 m, they enter the meso-diagenetic B stage. It was found that diagenesis has significant control over the quality of continental sandstone reservoirs. Compaction is the primary factor controlling the quality of the target reservoir. It controls the differences in the petrophysical properties of the reservoirs in the eastern and western regions; that is, the physical properties of the Quan 3 Member in the east are higher than those in the west. Cementation and dissolution are secondary controlling factors of reservoir quality that control the differences in reservoir petrophysical properties in the northern and southern regions; that is, the physical properties of the Quan 3 Member in the north are better than those in the south. The most favorable reservoirs of the Quan 3 Member are developed in the Fuyu Oilfield, which is distributed in the southeast region and develops fine sandstones of branch channels and meandering river point sand bars of delta plains that suffer the least compaction and the strongest dissolution. This study may provide crucial clues for predicting the sweet spot reservoirs of the Quan 3 Member in the study area. Furthermore, the study provides a reference for the different diagenesis controls on the pore space evolution of continental tight sandstone reservoirs.