Abstract:

Based on the seismic profile interpretation，the tectonic feature of Saihantala Sag in Erlian Basin and its control on reservoir-forming were researched. It was concluded that there were different levels of faults which constituted the fault system in Saihantala Sag. The faults can be classified into four classes:the first-class faults controlled the tectonic pattern;the second-class faults controlled the secondary structural belt;the third-class faults controlled the local structure;the fourth-class faults complicated the local structure. The fault active stages can be divided into five stages as follows，the fault-depression period in Jurassic，the initial fault-depression period in Aershan Formation，the strong fault-depression period in Tengger Formation，the fault-depressed diversionary period in Tengger Formation and the ending of fault-depression period in Saihantala Formation. The Saihantala Sag exhibited a east-west belted and south-north partitioned pattern，and developed five first-order tectonic units，four secondary structural belts and various types of local structures. The fault activity controlled the source-reservoir-cap assemblage and its  development，and the fault provided oil and  gas  accumulation space. The long-term active faults were major transporting hydrocarbon fault types in Saihantala Sag. Controlled by structural belts，the oil of Saihantala Sag has accumulated mainly in the central fault zone and the eastern depression zone.

Key words: fault, tectonic pattern, reservoir-forming control, Saihantala Sag, Erlian Basin