Experimental Study On The Mechanical Properties Of Fine Sandstone Under Internal And External Pressure

As a conventional non-renewable energy source,the development and utilization of petroleum has always been the focus of people's attention.The exploitation of oil usually involves a series of technical means such as drilling engineering.In the process of oil exploitation,the mechanical properties and characteristics of the surrounding rock of the well wall are closely related to the stability of the well wall,and it is also the key to the successful exploitation of oil and gas resources.During the drilling process,the occurrence and development of local shear cracks in the surrounding rock caused by the instability of the borehole wall under the action of different internal and external pressures is a hot and difficult point of current research.This paper takes the fine sandstone in the surrounding rock of the shaft wall as the research object.Through basic mechanical performance tests,the basic mechanical parameters of the fine sandstone are measured and the microstructure morphology of the fine sandstone is analyzed.On this basis,the structure of the high temperature and high pressure creep meter was developed and modified at the same time,and the triaxial compression experiment of fine sandstone under internal and external pressure was realized,and the relationship between the related mechanical property parameters and the confining pressure was explored.The fractured fine sandstone was observed by industrial CT slices,and the development and propagation of microscopic fractures were analyzed.The results obtained are as follows:(1)The basic mechanical performance parameters of fine sandstone were obtained,and the main mineral and chemical components were analyzed.The microscopic initial fracture structure morphology of fine sandstone was analyzed by scanning the electron microscope.(2)Obtained and analyzed the deviator stress-strain curve of the progressive failure process of the triaxial confining pressure experiment of the fine sandstone.It also summarizes the relationship between its confining pressure peak strength,residual strength,axial peak strain,elastic modulus and other mechanical parameters and their increasing range,and the confining pressure.The cohesion and internal friction angle are calculated by the linear equation after the regression of the maximum axial stress and the confining pressure.(3)Part of the structure of the high-temperature and high-pressure creep instrument is improved.The water pressure in the injection hole simulates the internal pressure,and the triaxial experiment under different internal and external pressures is realized.The influence of confining pressure and water pressure in the hole on the mechanical parameters of fine sandstone is analyzed.At the same time,it is found that the effect of water pressure in the hole delays the stress failure process of the fine sandstone during the compression and yield stage,and increases the ductile fracture degree of the fine sandstone.The cohesive force has little relationship with the change of the water pressure in the hole,and the internal friction angle shows an increasing trend with the increase of the water pressure in the hole.(4)With the increase of confining pressure,the rupture form of the rock gradually tends to transform into a single shear rupture form;at the same time,the main and secondary cracks are inverted "V" and "X" shapes,respectively.Under the action of only confining pressure,the cracks of the fine sandstone with holes are mainly single shear cracks,and there is a tendency to extend and develop in an "S"-shaped distribution around the central hole,and the intersection of the crack and the central hole wall is accompanied There is a phenomenon of rock collapse.(5)Under a certain confining pressure,the angle between the main shear fracture surface of the porous fine sandstone and the axial direction shows a law that decreases with the increase of water pressure in the bore,and the shear crack trajectory is determined by the rock The outside of the sample gradually deflects towards the central hole wall;at the same time,the rock block collapse mode in the hole wall changes from concentrated collapse to scattered collapse;the area and degree of rock block collapse in the hole wall become smaller.