| The corrosion problem of gas wells containing CO2 has influenced the development of Daqing deep gas field and greatly reduced the operation benefit. With the development of the deep gas field, the CO2 corrosion problem is becoming more and more serious. It is an urgent issue to find the measures to solve the problem to ensure the normal production of the existing CO2-containing gas wells and also to provide technology reserves for further development of the gas field.Based on the present field surface gathering process, through investigation, we've done the researches on down hole string anti-corrosion and CO2 removal technology in order to provide a robust technical support for follow-up gathering system management.This paper, through laboratory test, analyzed the influencing factors and the characteristics of corrosion under the conditions of gas wells, evaluated and selected the optimum CO2 removal technique and studied the feasibility of the removal process.Four kinds of corrosion inhibitors commonly used in gas fields, five different anti-corrosion coatings and nine different steel materials were evaluated in laboratory, and the best forms suitable for down-hole CO2 environment were selected. The field test of corrosion was carried out. Three groups of testing materials were put into down-hole during the period of down-hole operation, the down-hole string materials were evaluated and selected through the test.Adopting corrosion inhibitor for anti-corrosion in CO2 and H2S corrosion environment of oil and gas fields has a lot of unique advantages over other methods.According to the investigation and gas well status on site, four kinds of two-phase inhibitors commonly used in gas wells were selected, including CT2-15, CT2-17, HT-6A,HT-6B. The test data indicates that epoxy coatings can be used for corrosion protection in gas wells and surface gathering pipeline system with temperatures relatively low and velocities not very high, but coating is not an ideal kind of corrosion protection method for gas wells with high temperature.By comparing several CO2 removal techniques, the chemical absorption method adopting DEA solvent was selected, based on the natural gas characteristics of fangshen-7 gas wells.Through Research on corrosion protection technology for gas field gathering system with high CO2 content, this paper concludes a set of anti-corrosion techniques suitable in Daqing Oilfield. The main conclusions are summarized as follows:1) For anti-CO2 corrosion of down-hole strings,1Cr13 stainless steel may be used as the material. For the gas wells with high CO2 content, high temperature and high Cl-content,00Cr22Ni5Mo3N may be used as the material of down-hole strings.2) For field surface gas gathering system, the protection measure of carbon steel material with corrosion inhibitor injection may be used. For important equipments, special shaped fittings, bends, standpipes, valves and so on, corrosion-resisting materials or carbon steel lined with stainless steel may be used so as to insure the overall protection effect.3) Using corrosion inhibitor can solve the problem of CO2 corrosion. 4)For gas wells with temperatures relatively low and velocities not very high, Epoxy coatings can be used for corrosion protection. But for gas wells with high temperature, Epoxy coatings are not recommended.5)For natural gas CO2 removal of remote wells and stations, small-scale skid-mounted equipments shall be preferred in order to reduce investment cost. DEA absorption process is suitable for the removal. Removal under high pressure will have a better effect and may reduce operating cost.
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