The Geological Conditions And Sealing Mechanism Of Clay Smear

The deformation mechanism of faulting is different at different depth and different diagenetic stages,and then the internal fault zone structure and sealing ability is different.This paper has studied the formation condition and the sealing mechanism of smearing faults based on the combination of outcrop,numerical modeling and physical modeling.The competence contrast of the mechanical layered rocks is the essential foundation of fault growth and propagation.And the competence contrast can be qualitative and quantitative evaluated.From the qualitative prospect we can determine relatively competent layer based on the macro and micro deformation feature.And from the quantitative prospect we can evaluate the rock competence based on the rock physical parameter,rebound value and the percent strain before fracture or faulting of triaxial compression experiment.There are three geometric arrangement of fault propagation,extensional overlap,contractional bend and netural overlap.Large number of outcrop and physical modeling have conformed the extensional overlap contribute to the formation of smearing fault and maintaining its continuity.Based on outcrop and physical modeling and combined with a wide range of domestic and overseas literature research,we have focused on the internal fault zone structure of smearing fault in different diagenetic stages.The sand bed forms a continuous smear while the clay deformed as clay patches along the fault surface.We attribute this behavior as competency inversion.With the increase of burial depth and the diagenetic stage the relative competence of clay decrease gradually,and the fault zone will gradually evolved into clay smearing fault zone.While in the uplifting process,the ductile mudstone will gradually retransform to brittle and form the throughgoing faults and then the oil and gas will migrate vertically through the caprock.With the outcrop and oil field anatomy,and based on the analysis of fault deformation mechanism of mudstone in brittle,ductile and uplifting stages,a quantitative evaluation method for fault sealing and leaking is put forward,which will be an effective guidance for the determination of primary reservoir boundary and the exploration of secondary reservoir.