Study On The Mechanical Properties Os Layered Rock Body Interface

With the continuous deepening of oil and gas exploration and the increasing demand for oil and gas resources,the transformation object of hydraulic fracturing has developed from sandstone reservoir to complex reservoir,shale reservoir and coal seam.This kind of reservoir has a distinct formation interface,in which the sand mudstone reservoir shows the formation level of the vertical sand mudstone,and the shale reservoir and coal seam are bedding development.Stratum rock is the carrier of fracturing construction.The mechanical properties of rock will have a great impact on fracturing construction.It is closely related to the in-situ stress existing in rock mass,and has great influence on the initiation pressure of cracks,and controls the value of fracture width and static pressure.The different elastic properties also affect the geometry of cracks.Formation mechanics parameters are indispensable data for fracturing initiation pressure prediction and fracture geometry prediction in fracturing design.It is necessary to define the rock mechanics parameters such as Yang's modulus,Poisson's ratio,compressive strength,shear strength,internal friction angle and so on,and the size of elastic modulus and Poisson's ratio reflect the difficulty of elastic deformation under certain stress conditions,and the more elastic modulus is,the more elastic modulus is,the more elastic modulus is,the more elastic modulus is,the more elastic modulus The harder the formation is,the harder the stratum is,and the Poisson's ratio is small.On the contrary,the smaller the elastic modulus is,the weaker the stratum is,and the stratum will be easily deformed and Poisson's ratio is large.For the fractured layer,it is always hoped that the elastic modulus of the oil layer is small and the elastic modulus of the barrier layer is large,thus the larger stress difference can be formed,and the vertical expansion of the hydraulic fracture can be prevented effectively.At the same time,a wider crack can be formed in the production layer,and the sand plugging can be prevented effectively and the success rate of the fracturing operation can be increased.It can be seen that the accuracy of the mechanical parameters is of great significance to the engineering problem of hydraulic fracturing at the interface.If the correct rock mechanics parameters can not be obtained,the fracturing design will lose its significance.Taking stratified sandstone in Xujiahe formation as the research object,this paper takes microcosmic and macro mechanical tests as the main means and combines fractal theory to analyze.Firstly,the mineral composition of the sandstone of the Xujiahe formation,the degree of the interface,the size of the particles at the interface,the close contact and whether the occlusion is embedded.At the micro level,the characteristics of the cementation type and the arrangement state of the sandstone are experimentally analyzed.On the basis of understanding the microscopic morphology of the rocks,the three axis mechanical test and the indoor direct shear test of two types of sedimentary interfaces are established.The Poisson's ratio,modulus of elasticity,cohesive force,internal friction angle,and shear strength at the interface are analyzed,and the accuracy of the mechanical parameters is obtained by observing the failure mode of rock samples.Finally,a set of methods to estimate the interfacial shear strength through the surface roughness of rock samples is established and verified.