Thermo-mechanical Analysis Of Geothermal Well Pipe System

Nowadays,one of the renewable energy sources,geothermal energy,is getting attention worldwide as a reliable,clean and consistent energy resource used for electricity production.However,in extracting the heat resource from natural reservoirs,the steam fluid with high temperature passes through geothermal well pipe system.It is uncertain and challenging within this underground buried pipe system structure,because there can be different modes of failure of the pipe system in the construction stage and in the operation.In this study,five types of geothermal well sections are picked from the pipe system of geothermal well for the thermo-mechanical analysis.These are unjointed casing,jointed casing,and jointed casing with weak cement sheath band positioned at three different locations of cement sheath.The thermo-mechanical analysis is carried out in a staggered way(sequentially coupled)using numerical software ABAQUS.The thesis reviews and checks the thermal and mechanical load response of five well section models by carrying out parametric thermo-mechanical analysis and comparing results between the five models.The boundary conditions specify that the models are restraint along longitudinal and radial directions fixed to these ends with no displacements.High temperature load 300-550? from steam fluid acting on the internal surface of steel casing considered.Far field pressure or external pressure from fonnation acts on the external surface of cement sheath.Well pressure from the steam fluid applied to the inside surface of the steel casing.Ranges of well material parameters are taken from literatures.The air voided cement sheath band is modeled with low mechanical and thermal parametric values.FE analysis is carried out by varying each parametric values of thermal and mechanical properties.The results indicate that the materials properties of the well system,such as thermal conductivity,specific heat,and Young's modulus effect the magnitudes of stresses in the thermo-mechanical analysis.In addition,the temperature gradient induced thermal stress plays a dominant role in well materials integrity.It is found from the numerical analysis that the magnitude of the temperature and stress around the coupler/collar of the joint of the steel casing is higher than at normal well sections.These high stress and temperature magnitudes are derived from high coefficients of thermal conductivity of well materials.When the air void-weakened cement sheath band located at the off side of coupler,the maximum principal stresses are higher in magnitude for fonnation and cement sheath materials.