Tectonic analysis and petroleum significance of Cenozoic faults in Dongping-Niuzhong area in Altyn slope

Abstract

The evolution process and petroleum significance of two groups of fault structures, the NW-SE trending and near EW trending ones in the Cenozoic of Dongping-Niuzhong area of the Altyn slope, Qaidam Basin, were investigated using high precision 3-D seismic data. The NW-SE faults were generated in Oligocene, causing the formation of a series of folds related to transpression faults in the Niuzhong and Dongping area. After the Miocene, with the continuous extension of the Altyn Tagh strike-slip fault zone, the EW trending faults began to develop massively in Altyn slope. The activity of near EW trending faults and large-scale uplift of the bedrock in the northern Niuzhong area shared most of the compression torsion in Niuzhong and Dongping area, consequently, the activity of NW-SE trending faults weakened significantly after the Miocene. Then good hydrocarbon source rocks developed in the inherited Jurassic sags. The faults were effective pathways for oil and gas migration in Dongping and Niuzhong areas, and the oil and gas charging time matched well with the formation period of the NW-SE trending faults and their related structures, making the fault-related anticlines favorable targets for oil and gas accumulation. The Niuzhong area has been less affected by the Cenozoic movement after the Miocene, and thus has better conditions for gas reservoir preservation. Key words: Qaidam Basin, Altyn slope, Cenozoic, tectonic analysis, strike-slip fault, petroleum significance, Dongping-Niuzhong area