Coal And Rock Mechanics Test Under Different Temperature Conditions Around Wells And Numerical Simulation Of Borehole Deformation

In the process of coal-bed methane mining,because of the heat exchange between the drilling fluid and the stratum at the high speed,the formation temperature changes rapidly in a short time,and the ground stress changes,which makes the wellbore suffers from uneven formation pressure and prone to wall collapse.At present the study on the mechanism of the mechanical deformation of coal and rock by the tenperature field is not clear,this paper studies the mechanism of the mechanical deformation of coal rock under different temperature by the triaxial high temperature test,through calculation and analysis,optimizing the experimental design,taking the temperature field as the core,comprehensive mechanical experiment results,A mechanical model considering the influence of clay content on the mechanical properties of coal and rock is established.Through the establishment of wellbore mechanical model and combined with numerical simulation software(Comsol Multiphysics),the stress analysis,borehole deformation analysis and borehole flow analysis under different temperature conditions are analyzed.The research contents are as follows:(1)Under different temperature conditions,a triaxial high temperature test is carried out to analyze the mechanism of mechanical deformation of coal and rock,the strength characteristics and deformation characteristics under different temperature conditions,and the conventional triaxial mechanical tests of coal and rock are carried out to test the compressive strength,internal friction angle and Poisson ratio and elastic modulus of basic mechanical parameters.(2)Based on the clay content,the porosity and permeability equation of coal and rock is established,and combined with the effective stress principle,the wellbore seepage control equation,temperature field control equation and deformation field control equation under different temperature conditions are established.And combined with finite element software Comsol multiphysics determines the accuracy of the established wellbore mechanical model(3)In this paper,combined with the actual area of many seams in yanan formation of Honghe oilfield,the mathematic model is imported into Comsol Multiphysics software,and the wellbore stress,deformation,porosity and The numerical analysis of permeability and the size of the Darcy velocity in the well is given,which is of guiding significance to the solution of the problem of caving.Because of the particularity of the physical and mechanical properties of coal and rock and the strong stress sensitivity of coal and rock,compared with the traditional shale,sandstone and mudstone,the thermal expansion effect is more obvious in the process of drilling during drilling in oil and gas well.The research results of this paper deepen the understanding of the mechanism of wellbore stability of coalbed methane wells affected by temperature change.