Study On Corrosion And Scale Mechanism Of Three - Element Composite Flooding And Its Influencing Factors

At present, most of the oil fields of China have been stepping into the middle-late stage of exploitation.The produced fluid from those fields has a growing percentage of water. As the development of alkaline-surfactant-polymer (ASP) flooding technology, the constituents of the produced fluid have got more complex and changeable with high salinity, a lot of corrosive Inorganic ions, scale ion and some dissolved gas that may cause corrosion. Which broughts a serious problem of corroding and scaling to Gathering System during gathering and transferring process. Trough a large scale of corroding and scaling experiment on gathering steel pipelines by simulating field quality of produced fluid, the thesis has studied corroding and scaling mechanism of produced fluid and various factors impacting on corroding and scaling rules.At first, the dynamic and static corrosion rates of X65are tested by using Dynamic and Static Weight-lose Method under the influence of different factors, which indicates that as the temperature rises from30℃to70℃, the dynamic corrosion rate is higher than static corrosion rate.The dynamic corrosion rate reaches a maximum at50℃and the static corrosion rate reaches a maximum at60℃. As the salinity rises from6170mg/L to30850mg/L, the trend of dynamic corrosion rate is from sharp decrease to slow increase while the trend of static corrosion rate is from increase to decrease. The dynamic corrosion rate reaches a minimum at24680mg/L, and the static corrosion rate reaches a maximum18510mg/L. The test also shows that as the HPAM density rises, the trend of static corrosion rate is on the decreases while dynamic corrosion rate experiences the fluctuation of increase, decrease and increase. When the concentration of HPAM stands at1000mg/L, it has the maximal inhibitory effect on the dynamic corrosion. As the pH rises, the trend of static corrosion rate is on the decrease. As the flow velocity rises, the trend of dynamic corrosion rate is on continuous increase.Next, different factors’ effects on scaling rules of the produced fluid are tested by using EDTA titration method under the dynamic situation which indicates that as the temperature rises, the concentration tendency of Ca2+is on the decrease while the concentration tendency of Mg2+changes in a waving way. As the flow velocity rises, the concentration tendency of Ca2+experiences the fluctuation of decrease,increase and being flat while the concentration of Mg2+presents a downward trend. As the pH value grows, the concentration tendency of both calcium and magnesium ions is on the increase. As the concentration of HPAM grows, the concentration tendency of Ca2+is from increase to decrease while the Mg2+shows little change. Combining EDTA titration method and method of hard and soft scale, different factors’effects on scaling rules of the produced fluid are tested under the static situation which shows that as the value and the temperature rise, the concentration of calcium and magnesium ions decreases while the number of scale increases. The amount of scale containing polymer solution with higher concentration of HPAM is less than that containing polymer solution without HPAM. HPAM has the maximal inhibiting effect in the scaling process when its concentration stands at1500mg/L. As time passes, the amount of scale containing polymer solution experiences the fluctuation of increase, decrease and increase.In the end, SEM and XRD analysis is made on the products’ membrane of X65samples reactting in different length of time. The analysis results are listed below. After two hours’ reaction, the product on the sample’s surface looks like a needle with tentacles on the tip. After four hours’ reaction, the tentacles become bigger. In addition, the number of tentacles increases, and they gradually spread towards the middle of the needle. After eight hours’ reaction, the number of tentacles increases significantly, and they grow in groups covering on the needles gradually. In this experiment, corrosion electrochemical reaction is the main reaction in the reaction system in the first two hours. During this period, the product of corroding and scaling are Fe3O4, Fe(OH)2and trace amount of CaCO3. Four hours later, Fe2O3comes out. Further more, the number of calcium carbonate scale increases. Eight hours later, the quantity of CaCO3, Fe2O3and Fe(OH)2gradually increases. The energy spectrum analysis on the membrane layer of X65sample reactting eight hours shows that the membrane of sample has3layers, oxide layer, interlayer and scaling layer. Meanwhile, the forming process analysis on the membrane layer of X65sample shows that the forming process can be roughly divided into3stages. The First stage is the generation of oxide layer on the surface of metallic material. The second one is the growth of the product layer on the surface of metallic material. The third one is the stationary phase of corroding and scaling layer.