Review on Fault Internal Structure and the Influence on Fault Sealing Ability

Recent studies have transformed the old polarized view of faults as either leaks or seals into realistic notions of more complex fault-fluid flow behavior.Only the sealing fault in inactive period could barrier oil and gas migration.Fault structure and the stage of fault growth control the mechanics and fluid flow properties in the crust.Usually,the internal structure of a fault can be divided into host rock,induced fracture zone with main slip plane and fault damage zone which include fault rocks and associated crack.Fault rocks filling in crack space include breccia,fault gouge and part of calaclastic rocks.The development of fault architecture in a layered sandstone and shale sequence is distributed in a consistent pattern determined by three factors: ① the relative contributions of different faulting mechanisms to faults growth and slip;② the intensities of fault activity;③ the distribution of rock types.Considering the physical process responsible for fault development,fault throw increases during activity,accompanying with fracture formation and rock clastation and mixture.The stages of faults growth can be measured by ratio between shale source rock thickness and fault throw.In an active period,faults become the main channels for vertical hydrocarbon migration.In a static period,faults show variability and dynamic characteristics of sealing,which could be measured by permeability and displacement pressure.Fault rock permeability in a layered sandstone and shale sequence has a favorable correlation with fault throw,shale content and the burial depth.Two methods are used to predict displacement pressure in faulted belt: ① evaluating the diagenesis of fault rocks that has an equivalent effect as buried depth of sedimentary rocks;② using the actual measured displacement pressure to match with key geological factors.Through the simplified fault model,we establish relationship between key geological factors and permeability and displacement pressure of fault rocks.Fluid migration in fault zone follows porosity seepage characteristics as it does in reservoir.Cross-fault pressure and petroleum column height can not be converted to seal capacities simply because charge history and sealing type influence sealing.