Wellhead Uplifting Prediction In Offshore High-temperature High-pressure Gas Wells

Due to the high temperature of offshore high-temperature high-pressure gas wells during production,the resulting thermal stress on the wellhead and the annulus thermal expansion pressure cause axial deformation of the casing string,resulting in wellhead uplift,which poses a serious threat to the safety of offshore platform equipment and staff.Carrying out research on the temperature field and casing stress changes of offshore high-temperature and high-pressure gas wells,predicting the wellhead uplift height,identifying wellhead uplift risks,and formulating reasonable preventive measures to further reduce the risk of casing damage are of great significance on the safe and efficient production of offshore oil and gas.Based on the temperature field model and the calculation model of annulus thermal expansion pressure,calculation model of wellhead uplift is studied with comprehensively considering the influence of factors such as wellbore structure,cement return to height,thermal conductivity of each layer of casing,borehole trajectory,production string type and parameters,etc.In this paper,the main reason and key influencing factors of wellhead uplift are studied by analyzing the wellbore structure and stress situation of offshore high temperature and high pressure gas wells.This paper first uses heat conduction theory to consider the wellbore temperature conduction in the casing,deduces the wellbore temperature field model of offshore high-temperature and high-pressure gas wells,and studies the distribution law of casing temperature at different levels in the wellbore with the well depth.Based on the annulus pressure theory,the calculation model of the annular thermal expansion pressure is studied with the influence of the free section of casing.The theoretical value calculated by the example is compared with the software calculation value and the measured data,and the error is only 1.74% and 2.12%,which meets the prediction accuracy requirements.Therefore,the model can be well used for the prediction analysis of the lifting height of the offshore wellhead.It can provide a theoretical basis for research and analysis of offshore wellhead lifting mechanism and optimization of wellhead equipment.