Abstract:

With sandstone as the object of this article, taking into account the main factors influencing the fracture deformation, including the stage of diagenesis，porosity, temperature and confining pressure, we analyse systematiclly the fracture deformation mechanism of the different nature of sandstone, the micro-structural characteristics and the formation of internal structure of fault zone.It is of great significance on the study of fault sealing in the sandstone. Studies have shown that fracture of pure sandstone occurs in non-consolidated to semi-consolidated of diagenetic stage. Deformation mechanism of grain boundary frictional sliding, called ‘particulate flow’, results in particle rotating and rolling. And the formed micro-structure is Disaggregation band, without significant decrease in porosity and permeability comparing with parent rock.Though fault zone being consist of fault nuclear and damage zone, it is the fluid channel for vertical migration with higher permeability than parent rock. The fracture develops in the consolidation of diagenesis stage (porosity is greater than 15%) which deformation mechanism is cataclasis.The cataclasis flow involves particle rotating and cataclasis between grains. And the formed micro-structure is cataclastic band, with 1 to 3 orders of magnitude decrease in porosity and permeability comparing with parent rock. And formed fault zone is lateral sealing and vertical penetration. The fracture developed in consolidation stage (porosity less than 15%), due to rupturing in the early stage, forms fault breccia, then forms cataclastic rock, accompanying with the occurrence of cataclastic flow. Thus, fault zone is high permeability in the early stage and then fault gradually closed. The deformation mechanisms of consolidation sandstone is cataclasis during the uplift process. It forms incoherent breccia and fault zone of a highly permeability. In different diagenetic stages, it formed overlay of multiple type deformation structures. For a section advanced formed of fault, the differences of deformation mechanism and the micro-constructed type in different depth result in selective filled of the oil and gas. Cataclastic band and solution and cementation band block oil and gas filling in the highly porosity of sandstone. Disaggregation band will became the channel of oil and gas and crack conducive to oil and gas priority filling. Thus, in the high porosity sandstone，due to not development fractured zone， relatively low porosity reservoir often contain the best oil, while in the low porosity sandstone, contain oil and gas well，due to cracking.

Key words: sandstone, deformation mechanism, granular flow, cataclastic flow, disaggregation band, cataclastic band, fault zone structure