Thrust fault evolution and hydrocarbon sealing behaviour, Qaidam Basin, China

In the past, fault seal analysis has been focused on extensional systems. How-ever, fault behaviour in terms of fault sealing is also critical within compressional thrust systems. The results of an evaluation of thrust fault evolution and hydro-carbon sealing behaviour in the Lenghu5 thrust belt of the Qaidam basin of NW China are reported. A multi-scale methodology, ranging from regional- to micro-scale, is utilized in this work to identify the detailed thrust fault architecture and its effect on hydrocarbon sealing properties.
Regional-scale sections and 3D modelling are used to evaluate the evolution of faults within this thrust system and as a platform for detailed seal analysis. The results allow assessment of the timing of deformation, shortening and shorten-ing strain rate. Trishear models are used to assess deformation in the Lenghu5 thrust belt. Based on trishear propagation geometric models, the Lenghu5 de-formation history is simulated using forward trishear modelling. A range of trishear modelling parameters is used to interpret the various structural styles presented. This provides new insights to the potential application of trishear mechanism in complex natural structures developed in different environments.
Meso-scale detailed structural maps of exceptionally well-exposed outcrops are used to extract information on local fault geometry. Main thrust faults, minor thrust faults and accommodation normal faults are all mapped in detail, making it possible to evaluate the differences of fault architectures between different types of faults. Models are proposed to define the elements of fault zones. Fault zone evolution models are constructed in order to understand the dynamic pro-cess of the fault development.
Micro-structural analysis (e.g., SEM) of rock samples is used for assessment of the deformation mechanisms associated with fault zone development. The vital influence of micro-scale deformation mechanisms on hydrocarbon sealing properties has been evaluated, in order to reveal the relationship between the deformation mechanism and hydrocarbon sealing behaviour.
This work illustrates the value of a regional- to micro-approach on thrust fault evolution and hydrocarbon sealing behaviour, and aims to identify the critical parameters that contribute to improving fault seal analysis in thrust systems.