Wellbore Corrosion Life Prediction Based On Temperature And Pressure Coupling

The proportion of abundant oil and gas energies in ocean accounts for about one third of the world's total amount.With the development of petroleum technology,it has been the current trend to develop and research on offshore oil and gas fields.However,compared with the development environment of terrestrial oil and gas fields,it possesses special geographical environment,which means that there are more difficulties and challenges in the marine oil and gas exploration.Especially,the casing corrosion damage is a very serious problem for its shortening the service life of the shaft.Such conditions as high temperature,high-pressure and high CO2 during the exploitation in the domestic offshore oil and gas fields will greatly accelerate the corrosion rate of the casing,so it is of great significance to predict the life span of the selected pipe in advance on the basis of specific development environment in order to reduce the security risks caused by casing damage and huge economic losses.To solve the problem of serious corrosion casing damage existing in the development of offshore oil and gas fields,theoretical analysis and combined methods of experimental research and practical application are adopted in this paper.The extensive research and study from mechanism research views on the current types of oil and gas casing damage have been conducted.Contrastive analysis in the simulation experiment of corrosion has been carried out,which has established a new model of corrosion prediction based on the existing model of corrosion prediction to predict the corrosion rate and determine the corrosion amount.According to the calculation model of casing residual strength,the strength calculation model of uniform corrosion casing has been chosen and applied.Based on the law of conservation of momentum and the fourth-tier calculation method proposed by Runge-Kutta,the coupling model of temperature and pressure in wellbore has been established to predict the life span of corrosive wellbore.Meanwhile,computer language and iterative mathematical methods are used for the software compilation to predicting the corrosion life.The research of this subject can help oilfield users to make a better assessment of casing system in offshore oil and gas well based on a wider collected information,and help to rationally select materials in order to prolong the life of oil casing,ensure the safe production of oil casing,reduce the maintenance cost,and meet the requirements.The main achievements and understandings are as follows:?1?Combining the corrosion parameters and experimental data such as oil and gas field temperature,CO₂ partial pressure,CL^-,etc.at sea,determined the feasibility of the regression model through experimental comparison,and the average relative error was less than 10%.?2?Through the study of the temperature and pressure in the wellbore,a coupling calculation model of wellbore temperature and CO₂ partial pressure under the conditions of CO₂ corrosion was established,and the temperature field and CO₂ partial pressure profiles in the wellbore were formed,providing parameters for the accurate calculation of corrosion quantities in the later period.?3?In the calculation process,the fourth-order Longerkuta method was used to compile a software for predicting the corrosion life of wellbore under temperature and pressure coupling.By comparing with actual material selection,the results are consistent and the software is applicable.?4?In the design of the JZ25-1 oilfield,the casings of 1Cr,N80,47#were selected.However,the calculation results of the prediction software for the corrosion life of the wellbore under the coupled temperature and pressure in this paper show that in the expected production life of 20 years,It is suggested that 1Cr and 47#pipes should be selected for the oil casing in JZ25-1 oilfield.