Active deformation over multiple earthquake cycles in the southern Junggar fold and-thrust belt, NW China and fractured reservoir characterization using 3D geomechanical restorations

Abstract

This dissertation investigates natural deformation processes over multiple earthquake cycles in the seismically active, southern Junggar basin, NW China and additionally explores the capabilities of 3D geomechanical restoration as an effective tool for fractured reservoir characterization. Chapter 1 presents a detailed 3D fault model of the active Southern Junggar Thrust (SJT) – constrained by seismic reflection data – in the southern Junggar basin. This work demonstrates the significance of mid-crustal detachments as a physical mechanism to accommodate destructive, multi-segment earthquakes in active thrust sheets. Moreover, it highlights the efficacy of surface folds to delineate fault geometries at depth in the absence of subsurface data constraints. Chapter 2 describes active thrust sheet deformation across the Tugulu anticline, which sits in the hanging wall of the SJT, from Late Quaternary to present. Holocene terrace deformation records of surface faulting and folding yield consistent fault slip rates. We develop a quantitative method for extracting fault slip rates from terrace fold geometries using a mechanical modeling approach, yielding a 250 kyr history of SJT slip. This study provides new insights into natural fold growth associated with fault slip. Moreover, it addresses several shortcomings of traditional seismic hazards assessment methodologies. Chapter 3 characterizes the styles, timing, and sequence of deformation across southern Junggar. Southern Junggar underwent extension followed by tectonic inversion and shortening, forming a series of imbricate structural wedges. A kinematic model for the evolution of shear fault-bend fold wedges is presented. We discuss the implications of structural style, fold growth and thrusting sequence on the ~175 Myr evolution of this fold-and-thrust belt and its petroleum system. Chapter 4 investigates the impact of natural fold strains on fractured reservoir properties in the Permian Basin, West Texas. This study details the ability of 3D geomechanical restorations to accurately model natural strain distributions associated with fold growth. Modeled strains from geomechanical restorations are integrated with proxies for natural deformation and production data to describe how tectonic strain impacted observed gas production, water cuts and reservoir temperatures. When used in conjunction with additional datasets, geomechanical restoration shows promise for predictive abilities in characterizing conventional and unconventional fractured reservoir properties.