Factors influencing fault-propagation folding in the Kuqa Depression: Insights from geomechanical models

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Understanding the rock mass deformation and strain state is critical to a range of endeavors. Geomechanical modeling is an excellent approach simulating the formation processes of faulting and folding, which can reproduce the geometry of fold structures and track strain and stress through the whole deformation process. In this study, five series of two-dimensional (2D) elastic-plastic finite element models were built to investigate the influences of shortening distance, ramp cutoff angle, interlayer slip, fault friction, fault number and fault slice width on structural styles and strain distribution patterns during fault-propagation folding in the Kuqa Depression of Tarim Basin. The results indicate that, i) All above mentioned factors can influence the structural style and strain distribution of fault-propagation fold (FPF) to varying degrees. Fault friction, interlayer slip and fault slice width are the most important parameters influencing the deformation geometry and strain patterns of FPF; ii) There are critical values for fault friction coefficient and shortening distance to create a secondary fold besides the FPF; iii) A “step pattern” occurs both in the forelimb and backlimb of the FPF when fault slice width reaches a certain high value; iv) Structural position in the FPF controls volumetric changes. The evolution of FPF can be divided into two stages: layer parallel shortening and volume loss, and folding; v) The steep forelimb region of FPF develops more natural fractures, which may serve as a favorable location for potential reservoirs in the Kuqa Depression. The results are also expected to provide clues for the exploration and development of oil and gas in regions with similar geological conditions.