Corrosion Analysis Of Pipeline And Evaluation Of Corrosion Inhibitor In Tuha Oilfield

As for the serious corrosion of gathering and transportation pipelines in Tuha oilfield, the research of corrosion and protection was conducted by oilfield investigation and laboratory simulation. Weight loss test and polarization curves were adopted to analyze the influencing factors of corrosion of produced water to pipeline steel as samples in the laboratory. The appearance and composition of the corrosion product from different regions in Tuha oilfield were observed and analyzed. The main reasons for corrosion of oil pipelines in Tuha oilfield have been studied by simulation of flow type in the pipe. The corrosion inhibitor available for oilfield was selected by the weight loss test, AC impedance and polarization curves. The function mechanism and composition of corrosion inhibitor were studied. The filling equipment and process of corrosion inhibitors were analyzed to make inhibitor be more fully applied in oilfield, this study functions as the basis of corrosion and protection work in the production of oilfield, and the results of this study are as follows:1. The results of the dynamic weight loss test to the influencing factors of corrosion of pipeline in the oilfield show that the corrosion rate of coupons grows with the increase of flow velocity. When the flow rate of the medium is more than2m/s, the corrosion rate of coupons is stable. The corrosion rate of coupons grows rapidly with the increase of the temperature when the test temperature is below60℃, but drops obviously when the temperature is more than60℃. When the test lasts less than30days, the corrosion rate of coupons drops slowly with the increase of test time, and drops gradually with the increase of oil water ratio of produced water, the crude oil helps to reduce corrosion.2. The results of the static electrochemical test to the influencing factors of corrosion of pipeline in the oilfield show that the corrosion rate decreases after the first increase as the temperature rises, and the maximum corrosion rate is at65℃. The corrosion rate increases with the extension of time after the first decrease, with an overall trend of decrease. When the test time is36hours, the corrosion rate is minimal. When the concentration of Cl" is more than44000mg/L, with the increase of concentration of Cl-, the corrosion rate grows alternately in two stages of the rapid increase and stable trend. When the pH of solution is less than6.5, the corrosion rate is increases with the decrease of the pH of solution, but there is an unapparent change in the whole process. Under normal pressure, the corrosion rate decreases with the increase of the velocity of CO2, and the corrosion rate increases before the decrease with the increase of O2flow, with an overall trend of accelerated corrosion. When the CO2and O2in a ratio of1:1, flow into the medium with high flow velocity, the corrosion rate is between the separate rate of O2and CO2, and it is closer to the corrosion rate of O2.3. The results of the weight loss test in oilfield pipeline are as follows:The corrosion of coupons are uniform corrosion in sewage pipe and produced water pipe, but pitting corrosion in oil and water pipeline, extremely severe corrosion in produced water pipe and severe corrosion in sewage pipe and oil and water pipeline. The corrosion products from different gathering and transportation system were tested. The surfaces of corrosion products in produced water pipe, sewage pipe, crude oil pipe are fluffy and bumpy. And the surface of corrosion product is compact eddy shape. The composition of corrosion products and of corrosion are different. The simulations of flow pattern in pipe by FLUENT soft vare shows the flow in the straight pipe is homogeneous, and the pressure and flow vel city increase rapidly in the bend of pipe.4. The corrosion inhibitors on market were evaluated through dynamic weight loss test. Corrosion inhibitors of type LQ ZK682and YC560are relatively with efficient inhibition. The ZK682corrosion inhibition is the best one,with a rate of up to80.258%.The threekinds of corrosion inhibitors were tested by electrochemical method at dosage40,120,240m g/L When the concentration of corrosion inhibitor is120mg/L, the three kinds of corrosion inhibitors show the best inhibition effect. The corrosion inhibition rate of ZK682is up to83.75%,which is the best one. And it has a stable inhibition effect with the increase of dosage Analysis on the change of anode and cathode polarization curves slope of ZK682corrosion inhibitor shows that ZK682is a combined inhibitor with anode and cathode. Analysis on the molecular structure of the ZK682corrosion inhibitor shows that ZK682is a kind of amine compounds containing nitrogen and oxygen. The polar group with nitrogen and molecules can make inhibitor molecules solidly adsorb on the surface of carbon steel. Hydrophobic protection membrane forms in Long chain as non-polar groups, which can prevent corrosive medium molecules getting close to the surface of carbon steel. The circuit simulation of ZK682fits for electric double layer structure and its simulation parameters show that the effect is best.5. The filling process and the filling equipment of the corrosion inhibitor were studied. The filling equipment and the filling process for use in Tuna oilfield was put forward under different conditions.