Controls of multi-stage strike-slip faults on migration and accumulation of hydrocarbon: Ordovician reservoirs in the north slope of Tazhong, Tarim Basin, China

Abstract

The diversity of stress states in different regions along the principal displacement zone of strike-slip fault leads to the complexity of hydrocarbon migration in the fault zone, especially under multi-stage tectonic movements and hydrocarbon charge conditions. The pools with different fluid phases are distributed along strike-slip faults in the Tazhong area of the Tarim basin. However, the coupling and comparison of strike-slip faults, hydrocarbon migration, and distribution patterns remain poorly understood. In this research, we integrate structural analysis and geochemical methods to analyze the control mechanism of multiphase strike-slip motion on hydrocarbon migration pathways and their influence on hydrocarbon distribution. The strike-slip fault formed as a result of a three-stage evolution with different slip directions: the Middle to Late Ordovician (sinistral), Silurian to Devonian (sinistral), and Permian (dextral). The change in the occurrence of strike-slip faults and the combination of secondary and tertiary strike-slip faults lead to the formation of linking, bend, and tip damage zones. The regular changes in maturity and chromatographic geochemical parameters in the direction away from strike-slip faults indicate the overall pattern of hydrocarbon migration along strike-slip faults. However, it is not possible to explain the changes in the properties of adjacent regions. Therefore, we propose a model in which the characteristics of fault motion during the hydrocarbon migration period (crude oil: the Silurian-Devonian and Permian, gas: the Himalayan) and the combination of faults within the fault zone jointly control hydrocarbon migration and distribution. The reversal of the Late Caledonian and Late Hercynian faults from sinistral to dextral resulted in changes in the local tension area within the fault damage zone. Therefore, the migration pathways of the two phases of crude oil are different, and the maturity of crude oil around the fault is different. During the Himalayan period, the strike-slip fault and the intersection of the faults opened and controlled by NE-trending principal stress. The degree of tensioning of the fault has led to different natural gas charging intensities in the neighboring area. This research explains the mechanism of hydrocarbon distribution in the Tazhong area from the perspective of multi-stage strike-slip faults and provides a reference for hydrocarbon exploitation of complex strike-slip fault zones.