Depositional Facies And Seismic Reservior Prediction Of Bachu Formation-Silurian In Southwest Tahe Field

The stratum from the Lower Sand-mud Member of Lower Carboniferous Bachu Formation to Silurian is researched to predict thin reservoirs. Based on previous research, the object is redivided by means of the comprehensive technique of log and seismic. In this research, many principles are used, such as petrology, stratigraphy, sedimentology and petroleum geology. Then, depositional microfacies are analyzed, with integrated datas of logging, seismic, coring, and so on. The correlation betweem log parameters and microfacies change is researched for attempting. Furthermore, the types of sandstone reservoirs are found out, and the controlling factors of different reservoirs are resarched. Finally, the favorable reservoirs and traps are predicted.According to the conclusion, in Lower Silurian, Kepingtage Formation are divided into three members, such as the upper, the intermediate and the lower, which respectively develop sedimentary facies of fan delta - shallow shelf, deep shelf and three cycles deposition of "strand-shelf-strand". In Upper Kepingtage Formation, sandstone reservoirs are developed well, and well S112-2 is representational as an unconformity trap. In Tataaiertage Formation, tidal flat develop at the southwest area, with less reservoir. To Upper Devonian Donghetang Formation, the top surface of "Donghe Sandstone" is not considered as an isochronous surface, but inclining to the top of the Lower Sand-mud Member of Lower Carboniferous Bachu Formation. "Donghe Sandstone" is divided into two members, such as the upper and the lower. The deposition of strand and fan delta is evident, and three types of reservoirs are the ancient reservior, the low-extent structural reservoir and the bedded lithologic reservoir. The Lower Sand-mud Member of Lower Carboniferous Bachu Formation developed fan delat and lagoon, and the reservoirs are considered undeveloped after the stratum correlation.