Shiyou shiyan dizhi (Jul 2021)
Fault systems and their relationships to oil and gas in Dabancheng subsag, Chaiwopu Sag, Junggar Basin
Abstract
The Chaiwopu Sag of Junggar Basin experienced a major breakthrough in oil and gas exploration for the first time in the late 1980s, however, the exploration effect in this area is still restricted by the complexity of faults and the uneven distribution of oil and gas. As the main body of the sag, the Dabancheng subsag has been strongly extruded by the Bogda Mountain thrust belt to the south, the Yilian Habirga Mountain (abbreviated as Yishan) thrust belt to the northeast, and the Heishan Mountain to the northwest since Permian. A compressive and narrow ramp structural system superimposed by multiple stress fields was developed, which led to the complexity and particularity of fault characteristics and evolution in the Dabancheng subsag. Approaches including logging, seismic and field geological survey data were applied to study the fault systems in the subsag, including the Southern Bogda Mountain fault system, the Yishan fault system and the Heishan fault system. The Southern Bogda Mountain fault system has a shallow detachment surface, which belongs to an orogenic wedge structure with plastic detachment layers. The Yishan fault system is a basement-involved structure. The Late Hercynian, Indosinian, Yanshanian and Himalayan tectonic movements have geological records in this area, forming different scales of faults. The late Hercynian period is a breakup stage, the Indosinian-Yanshanian period is a fault-shaping period, and the Himalayan period is a fault adjustment period. The distribution of detachment belt in the Southern Bogda Mountain fault system is consistent with that of the Middle-Lower Permian source rocks. Combined with the analyses of tectonic movement period, stratigraphic characteristics and fault systems, the Southern Bogda Mountain fault system is a potential oil and gas accumulation area.
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