Deep reservoir quality prediction using diagenesis: a case study from Zhanjiaduo Oilfield of Subei Basin, China

Diagenesis study is used to predict deep reservoir quality in Zhanjiaduo Oilfield of Subei Basin. Based on the thin section, scanning electron microscopy, X-ray diffraction, and burial history analysis, it is found that with a significant burial depth, the third Member of Funing Formation shows good reservoir potential, which is believed to be the result of weak compaction. Abnormally high pressures caused by undercompaction lead to the development of intergranular pores in sandstones. Quartz overgrowth and ferroan calcite cementation are inhibited due to relatively high contents of clay, the premature sealing of the diagenesis system, and a short high-temperature experience. Therefore, the reservoir quality is dominated by clay cementation, and compaction is the most important factor to control reservoir physical properties. Under the same conditions of abnormally high pressures, the compaction loss rate of bar sandstones is lower than that of beach sandstones, so the bar sandstones in a high-pressure area are likely to become reservoirs with good quality. Studies over abnormally high pressure, sedimentary facies, and diagenesis reveal that the high-quality bar sandstones exist in the deep sag area. This finding has been validated by recent exploration wells which obtained high industrial oil flow.