Quantitative Analysis And Simulation Of Structural Deformation In The Fold And Thrust Belt Based On Discrete Element Method

As a new method to study the deformation of the tectonic,DEM(Discrete Element Method)can observe and analyze the evolution process of internal stress and strain in a quantitative way.It can help to reveal the deformation characteristics and mechanism of fold and thrust belts,and analyze the influence of stress and strain distribution on physical properties of oil and gas reservoir,which has important theoretical significance and practical value.On the basis of literature research,field geological survey,the structural interpretation of seismic profiles and analogue experiments,a comprehensive analysis was conducted on the characteristics of compressive tectonic and their deformation mechanism and controlling factors based on DEM.Some important research results were achieved as following:(1)The structure array was used to construct the basic data structures of DEM.By improving the neighbor search algorithm based on grid,increasing the speed of the neighbor search and contact judgement,and restructuring the neighbor search and contact judgement and contact force update module,the lock-free parallel computing of discrete element method named VBOX was achieved.The linear elastic contact model and Hertz-Mindlin contact model were embedded into VBOX.It is suitable for the structure simulation.And the discrete element program testing process is given.(2)The concept of equivalent parameters and the equivalent model was put forward.Through the angle of repose and biaxial test,the microscopic parameters of quartz sand was calibrated.A typical physical simulation(AM)and discrete element numerical simulation experiment(DEM)was constructed and a wedge quantitative method based on grid was put forward.The similarities and differences between two methods were compared In a quantitative way,such as the angle of slope,the dip angle of the fault.(3)By a series of biaxil test,the corresponding tables of micro and macro parameters of rock are given.The effect of the cohesive and internal friction angle of rock and the thickness and strength of the detachment on the formation and evolution of fold thrust structure were investigated.It can provide basis of the theory of complex fold-thrust structure geology by analyzing the deformation characteristics and the deformation mechanism of fold thrust tectonic in a quantitative way.When the cohesion is low,the internal strain is dispersed and the fracture distribution is dispersed.When the cohesion of rock strata is strong,the strain is concentrated,the fault fault spacing is large,the displacement of a single fault is large,and there may be obvious back-thrusts inside the wedge.That is to say,rock layers with weak cohesion have no obvious stress concentration,and cracks in the extruded wedge are loose and uniform,with connected pores,which are conducive to oil and gas storage and filtration.The fractures in the rocks with strong cohesion are concentrated and formed into bands,which can be used as an advantageous oil and gas migration channel.The strength of the detachment has a great influence on the structural morphology of the fold thrust zone.In the low friction detachment model,the thrust structure is formed by the occurrence of forward and back thrust fault intervals.The strength of overburden rock in fold thrust zone has little influence on fold thrust.Moreover,the thickness of the detachment layer has little influence on the deformation pattern of the structure.(4)The Cenozoic fold and thrust belt of Kuqa depression was taken as the entry point,the microscopic parameters of salt rocks were calibrated.Through numerical simulation,it is proved that syntectonic sedimentation plays an important role in controlling deformation of the structure in Qiulitage.Because of salt rocks,the structures of the western Kuqa depression has the characteristics of "vertical stratification".The structure under salt is dominated by closely packed thrust faults,while the structure above salt is dominated by wide and gentle folds.It is revealed that the initial salt-basin width may be the main controlling factor affecting the structural evolution of the western Kuqa depression along the strike.The structural deformation of Kuqa depression is characterized by "transverse segmentation" due to the difference of initial salt-basin width and salt-layer thickness.The stress in the stratum has obvious stratification because of the salt rock.The stratum is divided into thress layers:upper salt layer,salt layer and lower salt layer.The stress in the salt layer is the minimum and the stress in the lower salt layer is the maximum.The flow of salt rock has certain diectivity.The syntectonic sedimentation makes the salt rock show obvious characteristics of bedding flow,and the general flow trend is the same as the direction of compression.