Study On Sequence Stratigraphy And Sedimentary Facies Of The Xujiahe Formation Of The Upper Triassic Series In Sichuan Basin

Sichuan basin is one of the most important oil-gas-bearing basin in China and the Xujiahe Formation of the Upper Triassic Series in Sichuan Basin is an important exploration target layer. Formed in the sea land transition-continental environment, Xujiahe Formation has the characteristics of frequently alternate of sandstone and mudstone and dramatic variation in thickness and sedimentary facies In the transverse direction. Therefore, based on outcrop data, well data and seismic data, this thesis systematically study in sequence stratigraphy and sedimentary facies of Xujiahe Formation in Sichuan Basin. It will not only provide new ideas and new momentum for further exploration for the oil field, but also can enrich and development the theory of terrestrial lacustrine sedimentary theory.Based on the sequence stratigraphy and sedimentology, Various types of sequence boundary in different levels are recognized on the Outcrops data, well log data and seismic data. According to those boundaries,Xujiahe Formation is divided into 3 Second-order secquence, 6 Third-order sequence, 21 Fourth-order sequence and hundreds of Fifth-order sequence.The Fifth-order sequence is closely related to sedimentary facies. One is Controlled by the fluvial depositional system and formed by the spin echo of lateral migration of the river, and the another is Controlled by wave-dominated depositional systems and formed by the progradation. The third-order secquence is divide into 5 types by the Rise hemicycle and Fall hemicycle, which can reflect the different tectonic background. Based on the sequence stratigraphy of single well, we made well connection contrasts and established The third-order sequence stratigraphic framework and also deeply investigates the characteristics of each third-order sequence in the transverse direction. After then we contrast the fourth-order sequence in the The third-order sequence stratigraphic framework and make the Time-sequence stratigraphy cross-section to investigates the characteristics of sequence In the vertical. On the basis of those study that the sequence development of Sichuan Xujiahe Formation is mainly controlled by the structural factors, followed by the ancient climate factors.Based on the outcrop observation, core observation, and combined with the investigating of well log, tidal flat facies, alluvial fan facies, braided river facies, braided river delta facies, lakes facies are recognized in Xujiahe Formation of Sichuan basin. By contrasting and analyzing the sedimentary facies in the third-order sequence stratigraphic framework, we conside that the island chain at the Longmen Mountain area in the early Late Triassic made the Sichuan basin be in gulf environment and widely developed tidal flat depositional system in the period of SQ1. Due to the continuing uplift of the Longmen mountain, it become a inland lake and widely developed alluvial fan-braided river-braided river delta-lakes depositional system in the period of SQ2-SQ6. On this basis, we established two kinds of sedimentary sedimentary facies models of the Xujiahe foemation..