The Mechanisms And The Influence On Fluid Flow Of Deformation Bands

The response of deformation in high porous rock and low-no porous rock are different.In low-non porous rock,sharp discontimuties structure developed by fracturing,such as fracture,joints and so on.In high porous rock,the dominant deformation mechanisms are granular flow,cataclasis and phyllosilicate smearing.The subseismic structure is deformation bands.Deformation bands are tabular structures that result from strain localization processes in highly porous sandstones.They are characterized by grain reorganization due to grain sliding,rotation and/or fracturing associated with dilation,shear and/or compaction mechanisms.The mainly characteristics are low porosity and permeability.In different stress states,types,characteristics and mechanisms are different.In order to clarify the mechanisms and influence on fluid flow of deformation bands,this thesis focus on deformation bands which developed in bore hole core in Xicaogu structural belt of Jizhong depression and and outcrops in YouShashan structural belt of Qaidam Basin.By analyzing macro,micro and petrophysical properties,the types of deformation bands have been determined.Applying stress states and q-p diagram,analysis mechanism of deformation bands.The influence of on fluid flow of deformation bands was studied by numerical model.The studies show that high porous rock applied stresses yield distinct deformation processes facilitated by availability of pore space.These include:(1)rigid grain reorganization(granular flow)resulting in compaction,dilation or isochoric strain;(2)grain fracturing/crushing(cataclasis)related to high stress concentrations at grain contact points,promote shear.Based on kinematics-based classification,deformation bands can be classified compaction bands,shear-enhanced compaction bands,compactional shear bands,shear bands,dilation shear bands and dilation bands.Dilatant bands are formed by tensional stress in low mean stress.Compactional bands are formed by compressional stress in high mean stress.If there is differential stress,shear bands developed by shear.The combinations of lower differential stress and higher mean stress develop shear-enhanced compaction bands,compactional shear bands and dilation shear bands.Cataclastic bands which are formed in contraction developed by low differential stress and high mean stress in Youshashan structural belt.They are distributed compactional shear bands which are characterized by reduction of porosity and decrease in permeability of one to two orders of magnitude with respect to the host rock.They have no significant influence on fluid flow.The deformation bands are also cataclastic bands which developed in Xicaogu structural belt,but they are developed by higher differential stress and lower mean stress in the extension.They are localized shear bands which are characterized by reduction of porosity and decrease in permeability of two to three orders of magnitude with respect to the host rock.They have significant influence on fluid flow.