Failure Analysis Of High Temperature Geothermal Well Casing

Geothermal energy is one of the cleanest and most abundant sources of energy in direct development and power generation.However,due to the high temperature characteristics of geothermal energy,the casing is subjected to a large thermal stress,which affects the strength and service life of the casing.Casing failure is a major problem in geothermal development.The failure modes of geothermal well casings mainly include deformation,misfiring,and corrosion.Many kinds of casing failure problems pose great difficulties for geothermal safety production.Therefore,this paper studies the problem of geothermal well casing failure,and provides a theoretical basis for prevention and control of geothermal well casing failure.In this paper,through the investigation of domestic and foreign literatures,the mechanical problems of geothermal well casing pipe string were studied from two aspects of theory and numerical simulation.By analyzing the stress of the casing during the production of geothermal wells,a physical model of the thermal stress of the casing during the geothermal production process was established.Then the physical model was analyzed to find the influence factors of thermal stress and provide the theory for the subsequent simulation.in accordance with.A casing-cement ring-stratum finite element model was established.The main research work and related conclusions are as follows:(1)Firstly,conduct research on domestic and foreign documents and domestically available data.At the same time,study the casing damage wells in domestic oilfields and find the influencing factors of casing failure,including failure type,failure time,failure horizon,etc.Analyze the cause of failure.(2)According to the high temperature characteristics of geothermal well casing,the definition of thermal stress is explained.Then,the heat transfer method of casing is studied.The expression of heat conduction stress is formulated and pushed,and the wellbore heat transfer law is physically modeled and analyzed.The wellbore heat transfer physics field was analyzed in many aspects such as casing material,cement ring,stratum and so on,which provided a good theoretical guidance for the establishment and simulation analysis of the finite element model.(3)Constrain the casing-cement-formation coupling model,add the boundary and load,so that the model can effectively reflect the stress state of the casing in the formation,and then use the large-scale finite element analysis software to simulate and analyze.The temperature change shows that the magnitude of the thermal stress on the casing is linear with the temperature.After the thermal stress caused by the high temperature receives the restraining effect of the cement ring in the radial direction,the axial stress is superimposed,and finally the casing fails.(4)It can be seen from the finite element analysis software that the thermal stress superimposed along the casing axial direction will cause the axial deformation of the casing,and the axial deformation will eventually cause the wellhead to rise,which will affect the construction and production of the project.