Materials Performance

SEP 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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29 MATERIALS PERFORMANCE: VOL. 57, NO. 9 SEPTEMBER 2018 greater t han protective currents, and no break is observed as the cur- rent is increased further. For Well D, reduction of current below the protective value shows that a break still exists in the region of the origi- nal protective cur rent. Therefore, it is concluded that current require- ments indicated by the polarization curve method do not de crease after extended current appli cation, re- gardless of the potential shifts ob- served at lower currents. Although no change in current re quirements was obser ved, t he change in the shape of the curves is of inter est. The breaks are some- what more distinct, and the slopes of the straight line segments are more uniform for t he East Texas wells. The double break observed in some preliminary runs on the West Texas wells is retained in the curves for Wells D and F. Conclusions The major conclusions reached i n t h i s st udy may be l i sted a s follows: 1. Cathodic protection is feasible for wells to a depth of at least 13,300 feet. 2. For the types of polarization curves observed, the protective c u r re n t i s a t t h e b a s e o f t h e upper straight line segment or at the inflec tion point. Addi- tional studies on in terpretation of polarization curves would be desirable. 3. The average protective current per square foot of uncemented casing is in good agreement for wells in the same field with the s a m e c o m p l e t i o n s b u t v a r i e s from field to field and with com- pletion procedures. 4. A surface reference electrode gives an accurate representation of the entire casing for the pur- pose of conducting polarization curve surveys. 5. Increasing the current by 0.4 a m p a t f i v e - m i n u t e i n t e r v a l s gave interpret able curves and reproducible current require- ments. However, time inter val- c u r r e n t i n c r e m e n t r e l a t i o n should be determined for each new area surveyed. 6. Current requirements, as deter - mined from a polarization curve sur vey, do not change with ex- tended current application. 7. The absolute value of the casing- t o - s o i l p o t e n t i a l o r p o t e n t i a l shift has little significance in de- termining when protection is at- tained. Acknowledgment The authors thank the manage- ment of Socony Mobil Field Re- search Lab oratory for permission to publish this article. The cooperation and assistance of many operating personnel were necessary to complete this study. The efforts of C. H. Samples, R. F. Weeter, J. J. Bresenham, Jr. and J. B. Wells of Mobil Oil Company and A. V. Metler, R. J. Chandler, B. C. Arn- wine and B. G. Holmes of Socony Mobil Field Research Laboratory are gratefully acknowledged. References 1. S. P. Ewing and J. F. Bayhi. Cathodic Protection of Casings in London Pool. Corrosion, 4, 264 (1948) July. 2. K. Doig and A. Wachter. Bacterial Cas ing Corro- sion in the Ventura Field. Corrosion, 7, 212 (1951) July. 3. J. P. Barrett and E. D. Gould. World Oil, 142, 149 (1956) March. 4. E. W. Haycock. Current Requirement for Ca- thodic Protection of Oil Well Casing. Corrosion, 13, 767t (1957) November. Bibliography M. Estavoyer. Engineering and Design Problems Affecting Cathodic Protection of Lacq Field Well Casings. Corrosion, 16, 14 (1960) August. J. K. Ballou and F. W. Schremp. Cathodic Protection of Oil Well Casings at Ket tleman Hills, Califor- nia. Corrosion, 13, 507t (1957) August. G.L. Doremus, W. W. Mach and J. J. Lawnick. Ap- plication of Cathodic Pro tection to 48 Well Cas- ings and Associ ated Production Facilities at Waskom Field. Corrosion, 12, 4-15t (1956) Au gust. Discussion Question by T. J,. Lennox, Jr., Amer ican Smelting & Refining Co., South Planfield, New Jersey: Could you describe briefly the Ag/Ag 2 S reference electrode? Reply by P. W. Bohner: The Ag/Ag 2 S (silver-silver sul- fide) electrode was considered by sealing a length of silver wire (99.5 to 99.8 percent) through a glass tube with epoxy resin. The potential of this electrode is dependent on pH and the partial pressure of hydro- gen sulfide, but it was sufficiently stable in a given solution to mea- sure shifts in the working electrode potential. Feasibility Studies on Cathodic Protection of Deep Well External Casing Surfaces Next Month in MP Special Issue: The Future of Corrosion Control Corrosion of Bridges and Highways Roundtable Article: Corrosion Experts Look Ahead Leadership a Priority for Future of Corrosion Control Are You Ready to be a Disruptive Leader? NACE Standards for the Railcar Industry CORROSION 2019 Advance Program

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