Thrust Fault Evolution and Hydrocarbon Sealing Behaviour, Qaidam Basin, China

Pei, Yangwen; Knipe, Rob J.; Paton, Douglas A.; Lickorish, Henry; Li, Anren

In the past, fault seal analysis has been focused on extensional systems. However, fault behaviour in terms of fault sealing is also critical within compressional thrust systems. The results of an evaluation of thrust fault evolution and hydrocarbon sealing behaviour in the Lenghu5 thrust belt of the Qaidam basin of NW China are reported. A multi-scale methodology, ranging from macro-, meso- to micro-scale, is utilized in this work to identify the detailed thrust fault architecture and its effect on hydrocarbon sealing property.

Macro-scale section analysis, balance restoration and 3-D 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, shortening strain and shortening strain rate. Trishear models are used to assess deformation in the Lenghu5 thrust belt. The Lenghu5 deformation history is simulated using forward trishear modelling. A range of trishear parameters is used to interpret the various structural styles present. This provides examples on the potential application of trishear models for understanding the evolution of 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. The main thrust faults, minor thrust faults and accommodation normal faults are all mapped in detail and used to interpret the differences in fault architectures between different types of faults. Models are proposed to define the elements of fault zones. Fault zone evolution is constructed in order to understand the dynamic process of the fault development.

Micro-structural analysis (e.g. SEM) of rock samples is used for an assessment of the deformation mechanisms associated with fault zone development. These micro-scale deformation mechanisms have a vital influence on hydrocarbon sealing properties. Petro-physical measurements of typical rock samples are also used to assess the fluid sealing properties, in order to reveal the relationship between the deformation mechanism and hydrocarbon sealing behaviour.

The work illustrates the value of a macro- to micro-approach on thrust fault evolution and hydrocarbon sealing behaviour, and identifies the critical parameters that contribute to improving fault seal analysis in thrust systems.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013