Study On The Corrosion Mechanism Of Packer Rubber In CO₂ Environment

As a green technology,CO2 flooding can not only solve the problem of CO2 gas treatment,but also improve oil recovery.However the rubber material is easy to be corroded in CO2 environment,which leads to the decline of mechanical properties of rubber,then damages the sealing performance of the packer rubbers.Therefore,the research of the corrosion damage and applicability of rubber material in a CO2 gas injection wellbore conditions is great significance.First,simulate a carbon dioxide gas injection wellbore conditions with pressure of 5 MPa,10 MPa and 15 MPa,temperature of 90?,and 100vol%CO2,the corrosion tests on nitrile rubber,hydrogenated nitrile rubber,fluorocarbon rubber,and AFLAS dumbbell type samples were performed and the applicability of the four kinds of rubber materials were evaluated.In addition,combined with SEM,EDS,TGA,V.,and FT-IR,the corrosion damage mechanism of rubber material in wellbore environment was explained.Finally,a set of load-bearing rubber material corrosion experiment which simulating the situation under the CO2 injection wells has been designed to conduct.Then,with pressure of 15 MPa,temperature of 90?,the corrosion tests on hydrogenated nitrile rubber under different loads were performed and the applicability of the rubber materials was evaluated.The results obtained were as follows:(1)Under the condition of gas phase corrosion,with the increase of the pressure of CO2,the tensile strength of nitrile rubber,hydrogenated nitrile rubber,fluorocarbon rubber,and AFLAS decreased by 4%?38%,2%?18%,37%?68%and 45%?52%,respectively.The elongation at break decreased by 13%?23%,1%?8%,44%?56%,and 26%?38%,respectively.The reduction rate of elastic modulus is 4%?61%,28%?30%,11%?29%and 37%?50%.Under the condition of liquid phase corrosion,with the increase of the pressure of CO2,the tensile strength decreases by 8%?35%,7%?18%,32%?65%and 38%?51%respectively.The elongation at break decreased by 12%?21%,1%?5%,29%?51%and 28%?34%,respectively.The reduction rates of elastic modulus were 5%-42%,23%?32%,5%?35%and 32%?42%,respectively.After corrosion,tensile strength,elongation at break and elastic modulus all decreased significantly,and the decline rate increased with the increase of CO2 pressure.Of the four materials,hydrogenated nitrile butadiene rubber has the best corrosion resistance to CO2.(2)The high temperature,high pressure and high carbon dioxide would cause the rubber molecular chain fracture,crosslinking and recombination.Meanwhile,some of the particles and their surface active groups will also decompose,which leads to reduce the bonding effect between the particles and the matrix,causeing the performance of the rubber material degradation.Among them,the Vr of hydrogenated nitrile rubber decreased at a low rate of 5.6%,and the binding between the particles and the rubber matrix was stable.Therefore,the hydrogenated nitrile rubber could still maintain better mechanical properties after corrosion.(3)Under the condition of non-corrosion,when the load is 0,3,6 and 8kN,the compression permanent set of hydrogenated nitrile rubber(a)is 6.22%,7.82%,9.23%and 12.52%,respectively.The compression performance retention is 98.50%,98.10%,97.70%and 96.86%,respectively.Under the condition of no corrosion,when the load is 0,3,6 and 8kN,the compression permanent set of hydrogenated nitrile rubber(b)is 5%,8.58%,10.7%and 9.61%,respectively.The compression performance retention is 98.75%,97.86%,97.32%and 97.60%,respectively.Under the condition of gas phase corrosion,when the load is 0,3,6 and 8kN,the compressive permanent set of hydrogenated nitrile rubber(a)is 10.24%,12.34%,13.32%and 15.53%,respectively.The compression performance retention is 97.24%,96.88%,96.64%and 96.18%,respectively.Under the condition of gas phase corrosion,when the load is 0,3,6 and 8kN,the compressive permanent set of hydrogenated nitrile rubber(b)is 10.51%,13.95%,14.32%and 15.77%,respectively.The compression performance retention is 97.37%,96.51%,96.39%and 96.06%,respectively.Under the condition of liquid corrosion,when the load is 0,3,6 and 8kN,the compressive permanent set of hydrogenated nitrile rubber(a)is 15.64%,15.34%,19.25%and 21.44%,respectively.the compression performance retention is 96.10%,96.11%,95,16%and 94.63%,respectively.Under the condition of liquid phase corrosion,when the load is 0,3,6 and BkN,the compressive permanent set of hydrogenated nitrile rubber(b)is 15.58%,15.54%,21.3%and 21.9%,respectively.The compression performance retention is 96.11%,96.11%,94.68%and 94.52%,respectively.The compression performance retention reduced and the compressive permanent set increased after corrosion.The damage to rubber after corrosion in liquid phase was larger than that in gaseous phase.Hydrogenated nitrile rubber(a)has better CO2 corrosion resistance.