Research And Application Of Annular Packer Fluid For Offshore High Temperature And High Pressure Gas Wells

With the large-scale development of high temperature,high pressure and high acid gas fields,the safety problems of gas wells caused by annulus corrosion have been paid more and more attention.DF gas field is located in Yinggehai Basin of South China Sea.The highest formation temperature is 200℃ and the formation pressure coefficient is over 2.0.It is one of the three high temperature and high pressure areas in the world.The geological conditions are extremely complicated.The development of high temperature,high pressure and high acidity gas field is a world-class problem,and this gas field is the first developed "three high" gas field in the western South China Sea.Considering the characteristics of gas well development and the requirements of wellbore integrity management,a packer fluid with good high temperature resistance,strong CO2 corrosion resistance,good reservoir protection effect,wide density range and long-term stability in downhole casing annulus should be selected to ensure the smooth implementation of the project.In this paper,the annulus corrosion mechanism of high temperature and high pressure offshore gas wells and the anti-corrosion measures of packer fluid are studied in depth,and the CO2 corrosion evaluation method under high temperature and high pressure is established.Through a large number of laboratory tests,the corrosion of casing after contact between packer fluid and formation fluid and CO2 gas in annulus of casing was evaluated comprehensively.In order to solve the corrosion problem of formate packer after contacting CO2 gas,the formula of packer was optimized to meet the anticorrosion requirement and ensure the long-term safety of wellbore.Through the evaluation of corrosion degree of oil casing under various working conditions and the study of anti-corrosion measures,it provides quantitative reference and guidance for the development of wells with different reservoirs and different CO2 content in the later period.The research results in this paper can reduce the corrosion of oil casing,ensure the long-term safety of wellbore,prolong the workover cycle,reduce production costs,improve the economic benefits of oilfield development,and also have great reference value in the development of similar offshore oil and gas fields.