Abstract:

The Kuqa fold-thrust belt is a typical complex salt-bearing fold-thrust system with multiple detachment layers. Based

on the analysis of high-quality continuous 3D seismic data, it has been discovered that there are multiple detachment layers beneath the salt in the eastern segment of the Kelasu structural belt. Both the Jurassic coal-bearing strata and the Triassic detachment layers serve as the primary subsalt detachment layers. Using the discrete element numerical simulation method, two sets of numerical simulation experiments were designed to investigate the impacts of the distribution of subsalt detachment layers on the structural geometry and evolution of the salt-bearing fold-thrust belt. This helped to analyze the structural deformation characteristics and mechanisms of the eastern segment of the Kelasu structural belt and implications for oil and gas exploration. The simulation results indicate that the presence of multiple subsalt detachment layers promotes the formation of multiple rampflat-
ramp fold structures, with complex subsalt deformation. The presence of coal detachment layer leads to a weakly decoupled deformation at the deformation front, characterized by small fault spacings and displacements, with faults not directly penetrating through the sub-salt layers. In the single subsalt detachment model, the subsalt structural deformation is relatively consistent, with faults directly connecting upwards to the salt layer. In this model, the fault spacing is larger, fault displacement is greater, and there are fewer fault-separated blocks. By comparing the simulation results with the structural characteristics of the eastern segment of the Kelasu structural belt in the Kuqa depression, it was found that the deformation in the eastern segment of the Kelasu structural belt is complex due to the influence of multiple subsalt detachment layers. The coal bed primarily serves as a detachment layer, with stronger deformation above the coal layer than below. Deep faults do not propagate through the sub-salt layer. The presence of multiple subsalt detachment layers may result in the formation of two independent reservoir systems in the Triassic and Jurassic strata. Hydrocarbon migration and accumulation in the Jurassic and Triassic strata occur separately, and there may be multiple small traps. The Triassic source rocks generate abundant hydrocarbons, and the faults below the coal layer have small displacements and consist of relatively simple structures, indicating considerable potential for hydrocarbon exploration. 

Key words: Kuqa depression, Kelasu structural belt, multiple detachment layer, discrete element, stress-strain, tectonic
deformation