Accumulation mechanism of the Yingdong I field in the Qaidam Basin, NW China

The Yingdong I field is a large oil and gas field of shallow burial depth, high yield and high abundance. Its accumulation model is established by the analysis of the fault opening and sealing mechanisms. Faults in the field have the characteristics of sealing in shallow formations and opening in deep formations. Shallow faults are sealed because shallow formations were still in the stage of weak diagenesis, and under the influence of diagenesis, shale smear was formed in mudstones which were elongated and uninterrupted, and cataclasis happened in sandstones. On the other hand, deep faults are open because it was difficult for shale smear to form as mudstones in the fault zone had experienced so intense diagenesis that brittle fractures were produced and considerable cracks were formed. The accumulation model can be summarized as follows: deep faults transporting, shallow faults sealing, lower-generation and upper storage and late accumulation, that is to say, when oil and gas migrated along the deep opening faults upward from the source rock, the reservoirs were formed in the shallow layers because of faults sealing. The Shizigou-Youshasha, Kaitemilike, Yanshan and Youdunzi structures have a shallow structure style and accumulation model similar to that of the Yingdong I and are the favorable zones for exploration.