Experimental Investigation On The Creep Behavior Of Mudstone Under High Temperature And High Pore Pressure

As a common rock medium in deep oil and gas field engineering,mudstone is very complicated in mechanical properties under high temperature and high permeability.It directly affects the stability and safety of engineering.The study of transient and creep mechanics under high depth is the frontier scientific problem which needs to be solved urgently.Mudstone oil and gas reservoirs are important positions in the oilfield's new reserves and the key targets of the next exploration.The casing damage is easy to occur in the deep buried blocks,mainly due to the rock creep of the strata.Therefore,it is very important to study the creep mechanics characteristics of mudstone under the effect of real environment,which is of great significance to evaluate the long-term stable and safe operation of the project.Based on the investigation of the site survey and its physical characteristics,this paper studies the creep mechanics of the mudstone under the action of high temperature and high pore pressure: firstly,based on the analysis of the physical properties of mudstone,the indentation hardness test and the conventional triaxial compression test were carried out.The mineral composition and transient mechanical properties of the mudstone were studied,and the strength parameters were obtained.Secondly,under low temperature stress,Stress and higher stress creep mechanics test,studied the creep mechanics characteristics of mudstone under high temperature,and obtained long-term strength.Finally,the creep mechanics test of mudstone under different atmospheric pressure is studied,and the creep deformation.And the pore stress threshold of mudstone porosity is obtained.This threshold is very important for studying the stability of casing.The results show that the mudstone minerals are mainly composed of anhydrite,stone salt and plagioclase.The hardness of the rock mass in the rock indentation hardness test is low to high,and the failure morphology is in the form of crack,The results show that the deformation and failurecharacteristics can be described by the linear yield surface,and the deformation and failure characteristics can be described by the linear buckling and the ductile deformation.The destruction is a typical shear damage;cohesion of 17.58 MPa ~25.71 MPa,the internal friction angle of 4.42 ° ~ 7.53 °.In addition,based on the series of creep mechanics tests,the mudstone has significant creep characteristics,creep curves are obvious attenuation creep,steady-state creep and accelerated creep of the three-stage characteristics;infiltration and confining pressure constant,The creep rate increases,the creep strain increases,the creep strain decreases,and the creep rate in the steady-state creep stage is exponentially related to the stress.When the stress and confining pressure are constant,the pore pressure increases,The creep rate is slowed down and the creep strain is reduced because the deep mudstone structure is dense and the permeability is poor.The increase of the pore pressure causes the effective stress to decrease.The long-term strength of the mudstone is 55 MPa and the pore stress threshold is 23 MPa.On the basis of the above,a series of useful conclusions are obtained,which provide technical support and basis for the stability and safety of rock engineering.