Sea Water Injection System

Sea irrigate Injection SystemIn fiat to improve the oil recovery in an oil field the injection of sea water is used to increase the pressure inside the reservoir and kick upstairs the oil production. The graph given in Figure 1 is a typical seawater injection administration, before the injection process, water must chief(prenominal)tain a treatment to decrease the corrosion point caused by seawater in pipe lines, surface and downhole injection equipments. The treatment is based in a mechanical de-aeration process and chemical scavenger injection to decrease the concentration of oxygen in seawater.Figure 1. Seawater Injection SystemIn a normal operation of the seawater injection system the conditions of the process are 150,000 barrel per day, pipe diameter of 8 inches at 25 C, however in terms of corrosion parameters the data is provided in table 1, this table shows that the mechanical deaeration process reduce the most quantity of type O concentration in seawater. plank 1. Con centration of Oxygen in normal operationConcentration of O2 in different UnitsPPBmg/lmole/m3Feed Seawater7,00070.22 afterward mechanical de-aeration process1000.10.003After scavenger dosage100.010.0003With the data provided, the corrosion govern in normal operation condition is 0.0454mm/ course of study (the calculation step by step including unit conversion are shown in the appendix) hence the corrosion arrange is far less than the company pleasing value which is 0.1 mm/year, and it means that the system is working properly.It has been found that the mechanical de-aeration equipment requires repair, and it leave alone be out of operation for between one and three months.Water system Injection without a mechanical de-aeration processCalculating the limit current dumbness with the following equationConcentration of Oxygen only with the summing up of Scavenger dosing = 6.910 ppmK is the mass transfer coefficient and it calculations and unit conversions are shown in the appendi x.Calculating the corroding RateAssuming the main component of the pipe contract therefore n= 2M= 55.84 g/molDensity 7.87 g/cm3Now we drop compare the corrosion enumerate of each courtship and determine the implications of operating the system without the mechanical de-aeration.Hence the corrosion rate will increase 502 times without the mechanical de-aeration. Based on this result it is patent that the most important process for oxygen removal is the mechanical deareation.The company request the assessment in a technically and economically point of captivate three operational solutions during the repair of the mechanical de-aeration equipment.For the given delicious corrosion rate less than 0.1 mm/year, a corrosion rate value of 0.09 mm/year was used to calculate the implications of the possible solutions.a. Decreasing the Flow RateAssuming an acceptable corrosion Rate of 0.09 mm/year,From the equation above we net reach the Current minginessWith current density we roll in the hay reach mass transfer coefficient kNow we can reach the new Sh itemiseWith Sh bod we can puzzle Re numberThis value of Reynolds number means that we are in the transition regime between laminar coalesce and turbulent flow.Now we can reach the flow rateFrom the technical point of view and based on the concepts of fluids mechanics, diminish the flow volume to 260 barrels per day will generate a laminar flow (Re less than 3000) on the pipe, in other words it means that the velocity will non be in the required optimum range of 1.5 m/s to 2.5 m/s, according to Streeter. Doing the calculations the velocity will reach a very impenetrable value of 0.014 m/s in the pipe, which is by far lower than the minimum value of 1 m/s. Therefore technically, the reduction of flow rate to reach an acceptable corrosion rate is not a possible solution.In addition, this kind of diminution of the flow rate (577 times lower than the original) would arrive trespasss on the oil well. Specific ally, it would not be able to maintain the pressure at the desired level and therefore would have a big impact on oil production leading to money loss.b. Increasing the amount of scavengerAssuming an acceptable corrosion Rate of 0.09 mm/yearFrom the equation below we can reach the concentration of Oxygen that we need to contain in the water in commit to have an acceptable corrosion rateUsing Sodium sulfate as scavenger the following reaction will proceedHence counterfeit the stoichiometry of the reaction the relation between the compounds will be 2 moles of Scavenger and 1 mole of Oxygen.Therefore the amount of scavenger Sodium sulfate demand is = In an injection flow rate of 150,000 bbl/dayBased on scavengers calculations we need to provide the system with a high amount of scavenger to reduce the oxygen concentration that gives an acceptable corrosion rate, it is up to 1.3 net ton per day, it is nearly 80 times more than amount of scavenger used in normal operation, which is a bout 17 kg per day.On the economically point of view, if the scavenger will substitute mechanical de-aeration for a month, the need of scavenger will be approximately 40 ton per month. By using the commercial price of scavenger 0.64 USD/kg (https//www.icis.com), it will address around 832 USD/day and scaling it to a month it will cost nearly 24,960 USD/month.c. Corrosion InhibitorCorrosion inhibitor compound will reduce the corrosion rate by preventing both anodic and cathodic reactions. Anodic inhibitor will be adsorbed onto metal surface to form protective film and prevent metal dissolution while cathodic inhibitor will minimize O2 reduction reaction by forming non-conducting film on metal surface. And in technical terms it could be the solution of the problem. However, from the calculations, we know that corrosion rate without the mechanical deareation is 22.5 mm/year and the get down is to decrease the corrosion rate below 0.1 mm/year. Based on the corrosion inhibitor risk cat egory that is proposed by Hedges (2000), if the expected uninhibited corrosion rate is graeter than 6 mm/year inhibition is unlikely to provide integrity for the full field life. Therefore corrosion control of the system could not be efficient with a only corrosion inhibitor because of the high requirement of availability.Based on the results of the three possible options, on the economically point of view decreasing the injection flow rate will impact in the production of oil, and decreasing the main product (oil) of the industry it will have terrible effects in the oil company. Therefore in the corrosion engineering point of view the most accurately solution is to increase the amount of scavenger (Na2SO3) in order to reach a corrosion rate of 6 mm/year and then with the addition of corrosion inhibitors the corrosion rate can be reduce to an acceptable value of less than 0.1 mm/year.The dosage of O2 scavenger has to be interrupted for 8 hours per week for the injection of the bioc ide. During this time if there was not the corrosion inhibitor, the Corrosion rate would be 22.5 mm/yr. but if the Corrosion inhibitor inhibition rate is 98.5% (as from 6mm/yr to 0.09mm/yr), the corrosion rate would beTherefore the Corrosion rate would be The Corrosion rate is slightly above the required norm (0.002 mm/yr), but in the worst object lesson scenario, 3 months with no deaerator, due to the fact the Corrosion rate with the mechanical deaerator is 0.0454 mm/yr which is 0.0546 mm/year less than the required standard. So, in a year office the slightly more amount of Corrosion will be not significant and the system will work properly.Also, the amount of Na2SO3 needed to reach a CR of 6 mm/year is 905 Kg/day and it will cost around 580 USD/day.Finally, in order to choose the ideal corrosion inhibitor science laboratory tests must be performed in the same seawater that will be used. In situ tests would help to assure the quality of the results.Streeter, Victor L. Handbook o f fluid mechanics. McGraw-Hill, ed 1 (1961).Hedges, B. (2000) The Corrosion Inhibitor availability Model, NACE International, Paper 00034.Water system Injection with a mechanical de-aeration process and Oxygen scavenger additionConsidering the water system injection above and the following data we can reach a corrosion rate value in the next steps.Data providedPipe diameter = 8 inch, therefore the Area A = 50.26 in2 = 0.032429 m2Volume Flow Rate = 150000 bbl/dInitial Oxygen Concentration = 7 ppmConcentration of Oxygen After Mechanical De-aeretion = 100 ppbConcentration of Oxygen After Scavenger dosing = 10 ppbKinematic Viscosity 1.05 X 10-6 m2/sSchmidt number = 505Calculation of Re numberCalculation of Sh NumberIn turbulent Flow calculation of Diffusion coefficientFrom Sh number we can reach the mass transfer coefficient kNow compute the limit current density with the following equationConcentration of Oxygen after mechanical de-aeration and Scavenger dosing = 0.01 ppmCalcula ting the Corrosion RateAssuming the main component of the pipe straighten out thereforen= 2MFe 55.84 g/mol 7.87 g/cm3For 8 hours per week, the O2 scavenger dosing is interrupted for biocide to be injected. So, there is an Availability of = The Corrosion rate at a concentration of 0.1ppm of O2 isWater system Injection without a mechanical de-aeration processCalculating the limit current density with the following equationConcentration of Oxygen only with the addition of Scavenger dosing = 6.910 ppmCalculating the Corrosion RateAssuming the main component of the pipe Iron therefore n= 2M= 55.84 g/molDensity 7.87 g/cm3Now we can compare the corrosion rate of each case and determine the implications of operating the system without the mechanical de-aeration.Hence the corrosion rate will increase 502 times without the mechanical de-aeration.Evaluation of the following operational solutions diminish the flow rate of waterAssuming an acceptable corrosion Rate of 0.09 mm/yearFrom the equ ation above we can reach the Current densityWith current density we can reach mass transfer coefficient kNow we can reach the new Sh numberWith Sh number we can obtain Re numberThis value of Reynolds number means that we are in the transition regime between laminar flow and turbulent flow.Now we can reach the flow rateIncreasing the amount of scavengerAssuming an acceptable corrosion Rate of 0.09 mm/yearFrom the equation above we can reach the Current densityFrom the equation below we can reach the concentration of Oxygen that we need to contain in the water in order to have an acceptable corrosion rateUsing Sodium sulfate as scavenger the following reaction will proceedHence form the stoichiometry of the reaction the relation between the compounds will be 2 moles of Scavenger and 1 mole of Oxygen.Therefore the amount of scavenger Sodium sulfate needed isHence we need In an injection flow rate of 150000 barrels per day