The Research Of CO₂ Injection-Production Well's Corrosion Mechanism And Servive Life

Carbon dioxide-Enhanced Oil Recovery(CO2-EOR)is an oil displacement technology which has attracted much attention at home and abroad in recent years.Its technical advantages lie in two aspects:one is that CO2 has a good displacement effect on crude oil,the other is that CO2 injection-production technology is conducive to the geological storage of greenhouse gases.This technology has become a commonly used stimulation technology abroad,and its oil increment is second only to thermal recovery.A lot of preliminary research and application have been carried out in Jidong and Shengli oilfields in China.However,the development of CO2-EOR technology is restricted by the problems of CO2 corrosion,wellbore failure caused by CO2 corrosion and the decrease of service life of string.Through investigating a large number of domestic and foreign literatures and deeply analyzing the technical data of CO2EOR in oil field,this paper studies the corrosion mechanism of CO2 injection-production wells,puts forward the technical idea of using CO2 solubility instead of partial pressure design corrosion experiment,and establishes the prediction method of service life of CO2 injectionproduction wells string,which provides theoretical basis and technical support for the improvement of economic benefits of CO2 injection-production wells and the development of CO2-EOR technology.Aiming at the most prominent corrosion problem of CO2 huff and puff technology in CO2 flooding injection and production wells,this paper chooses CO2 huff and puff wells as the research object,divides huff and puff cycle into four stages(gas injection,baking,pressure relief and production).It deeply analyses the technological characteristics of the four stages and the flow state of fluid in wellbore,clarifies the main factors affecting the corrosion of CO2 injection and production wellbore string,and discusses the solution with CO2.Feasibility of solution instead of partial pressure to design corrosion experiment scheme;Combining with the characteristic parameters of CO2 injection and production wells,using the solubility prediction model of DUAN,a software for predicting the solubility of CO2 was developed,and the variation law of CO2 solubility along well depth in four stages of typical well huff and puff cycle was analyzed;the corrosion mechanism of CO2 injection and production wells was studied by simulated corrosion experiment with high temperature and high pressure autoclave;The prediction model of CO2 corrosion rate was selected and optimized.According to API TR 5C3 and other standards,the strength of CO2 injection and production wells after corrosion is analyzed,and the calculation method of residual strength of oil casing after CO2 corrosion is put forward;the variation law of safety factor of string in multicycle huff and puff cycle is studied,and the service life prediction method of injection and production wells considering CO2 corrosion is put forward;the typical wells are analyzed and the typical wells are obtained(gas injection,baking,pressure relief and production).The corrosion rate of four stages,namely,soaking well,pressure relief and production,obtained the variation law of safety factor of tubing string after corrosion in typical wells.The results show that the sensitive area of tubing failure in typical wells is in the middle and upper section,and the sensitive area of casing failure is in the middle and lower section.