Fracture types and distribution of Archaean rocks in west Shandong, China

Key words:  fracture  Archaean  west Shandong  Jiyang Depression

Abstract:

Based on outcrop observations and image logging data, the origin and types of Archaean rocks fracture were revealed in west Shandong.Integrating a large amount of measurements for fracture properties, this research focuses on the genetic type, the formation date and the characteristics of Archaean fracture systems in the region. Formation period and distribution of structural fracture were studied by drawing connection between the regional tectonic setting and the fracture occurrence inferred from observations of screened section from the typical faults and the associated fractures. The results show that the Archaean fracture system in west Shandong consists of two genetic types. One is the regional tectonic joint, which was formed in the Meso-Cenozoic era. The formation of low and high angle joint was in the Indo-Chinese epoch and the Yanshan-Himalayan period, respectively. The other type is local structure fracture, which is not typical but of great significance in improving the Archaean reservoir quality in some areas. Faults with similar length scale but different mechanical properties have different influences on reservoir properties:the tenso-shear faults seem to have minimal effects, the compressive faults have the maximum effects, and the compresso-shear faults are in the middle. The increase of the fracture areal density within the influenced fault mainly causes more infill of regional tectonic joints or new structure fractures, which are generally parallel to or at a small angle oblique to the fractures.