T-1946 the Effect of Sodium On

T-1946 THE EFFECT OF SODIUM ON CEMENTS FOR GEOTHERMAL AND DEEP OIL WELLS By Erik B - Nelson ARTHUR LAKES LIBRARY. COLORADO SCHOOL of MINES GOLDEN, COLORADO 80401 ProQuest Number: 10782112 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10782112 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 A Thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfill ment of the requirements for the degree of Master of Science in Chemistry, Signed: ^tuA. X?. -fli j&tn Golden, Colorado Date: (Jpjj t. // 1977 Golden, Colorado Date: CLpnjJ >0- , 1977 11 SCHOOL L.VJXV* — aOlDEN. T-1946 ABSTRACT The results of this study on the effects of sodium on potential calcium silicate hydrate binders showed the fol lowing. Pectolite, Na 2 0 -4CaO•6Si0 2 -fÔ, is a stable phase over a wide temperature range in the system. At higher Na20 concentrations pectolite appears to co-exist with a sodium silicate gel. It may possibly contain lattice Na+ in excess of that in the formula. The phase Na2 0 -2CaO• 2SiC>2 ‘IÔ, re ported previously, was synthesized unreproducibly; it appears to be a metastable phase. Tobermorite may accommodate a small amount of Na+ in its lattice, but xonotlite and foshagite do not. Sodium sulfate and sodium carbonate reacted to various extents, ^depending on concentration and temperature and time of exposure, with a 7% A ^ O ^ substituted tobermorite forming CaSO^ and CaCO^, respectively. The NaCl reaction with the to bermorite was minimal at 250°C; at 325°C the NaCI still ap peared in the product but the tobermorite transformed to xon otlite . iii TABLE OF CONTENTS, Acknowledgements ......... -....... vi Introduction .................. 1 Materials ............. ........... ......... ........ 9 Procedures . ....... ....................... ............ 10 Results and Discussion Pectolite .... .................... .......... 14 NC 2S2H .... ...................................... 21 Tobermorite, Xonotlite, and Foshagite ........... 26 Sodium Salts .............. ....................... 29 Dicalcium Silicates ............... 34 C o n c l u s i o n ........ 35 Reference^ ............. ......................... 35 ! IV T-19 4 6 LIST OF ILLUSTRATIONS AND FIGURES FIGURE 1 - Schematic Diagram of a Typical Well ...... 2 FIGURE 2 - Compressive Strength Curve for 7% AlÔ^ Substituted Tobermorite .............. 7 FIGURE 3 - Flow Diagram of Experimental Procedure ... 11 FIGURE 4 - Flow Diagram of Sodium Analysis .......... 13 FIGURE 5 - X-ray Diffraction Patterns Showing Sodium Substitution in Pectolite ........... 17 FIGURE 6 - Plot of Computed (N+C)/S Ratios vs. N/C Ratios in Mixes ......................... 20 FIGURE 7 - X-ray Diffraction Patterns Showing The Effect of NaOH Solutions on NC 2S 2H .... 25 v T-1946 ACKNOWLEDGEMENTS This research has benefitted from the assistance and advice of many people- X-ray diffraction work on the cement samples was performed by Dr. Maynard Slaughter and Ann Math ews. The advice from Drs. Ronald W. Klusman and Samuel B. Romberger is appreciated. Special thanks goes to my thesis advisor, Dr. George L. Kalousek, for his guidance in the ex perimentation and his patience in helping me become familiar with the highly complex and occasionally unpredictable chem istry of cements. vi T-1946 1 INTRODUCTION This paper reports the results of an investigation of the effect of sodium on the hydration products of calcium silicate cements. Improved modifications of such cements for use in geothermal and deep oil wells are currently being investigated at the Colorado School of Mines. The results in part have been published (Kalousek and Chaw, 1976) and in part are pending publication (Kalousek and Chaw, 1977) . The present research is a part of that investigation for develop ing fundamentals relating to the saline water corrosion of the cements. Some background information is as follows. Figure 1 is a simplified diagram of a typical deep well. i The well itself is depicted in the center. The o.uter shading represents the wall rock and the white area in the middle is the open well. The solid black zone between the wall rock and the open well is blown up at the top left. The wall rock is coated with residual drilling mud. The cement, represen ted here by the thin strip, binds the steel casing to the wallrock and drilling mud. Incidentally, the layer of resi dual drilling mud is not drawn to scale on this figure? it should be much thinner. Ideally there would be no residual drilling mud. As depth increases, the character of the waters that are T-1946 2 FIGURE 1 - Schematic Diagram of a Typical Well o I- CD, z CQ o ’ CD LU cc CD CD CO LU CO O c CQ <3> O H- Z I— LU CC i WATER co 2 w cC o o ■ 1 0 0 c CD CD cc SOLUTION LU cc m SO„, ETC CO o £ + h- 200 TURE,PERA°TEMC < o LU t -J $ CO 5^ o + Z CO o Cl x o 300 SALINE WATER T-1946 3 encountered changes. At shallow depths, the temperature is relatively low and the waters are generally fairly pure ex clusive of saline areas. As depth increases strata of both fresh and saline waters are encountered. At depths where the temperature is in the range of 200 to 400°C, the waters are generally highly saline and corrosive. These waters are es pecially evident in geothermal wells. The pressure encountered in wells also increases with i depth. In this study, the pressure was limited to that of saturated steam at the selected temperatures. The saturated steam pressures are much lower than those encountered under actual conditions. The most common cement used in wells today is portland * cement. The hydrated product is known as CSH II (calcium silicate hydrate II), cement gel, or simply set cement, toith increasing temperatures portland cement, generally with added silica, hydrates to different phases. As pictured on Figure 1, at a temperature of approximately 105°C, using a cement containing SiO^f tobermorite becomes the stable phase Tobermorite persists up to about 150°C when it transforms to xonotlite (C^S^H). Xonotlite is a denser phase and its for- t/c In cement chemistry, abbreviated formulas are used m which Si02=S, CaO=C, A 1 20 3=A, Na20=N, and H 20=H. T-1946 4 mation is accompanied by a volume decrease which may cause the fracture of the cement bonds with the casing and/or the wallrock or the formation of a network of pores. Either way, the pressure-tight seal is broken and the ultimate result may be well failure. Another problem with portland cement is that it hardens very quickly at higher temperatures resulting in a premature loss of pumpability of the slurry. Therefore portland cement may generally be unsuitable for geothermal and deep oil wells | at high temperatures. j The cements currently being developed for geothermal and deep oil wells are based on dicalcium silicates. In fact, one such cement, a mix of beta dicalcium silicate and silica, is now being used in the field. The dicalcium silicates (C2S) are more suitable because they harden at a slower rate than Portland cement at higher temperatures. Thus, premature loss of pumpability is prevented. Part of this study was devoted to determining the reaction kinetics of five dicalcium silicates: one alpha prime, one gamma, and three beta modifications of which one was in a proprietary cement, Unadeep (made by Univer sal Atlas). They are listed in Table 1. Alpha prime C 2S is an impure dicalcium silicate contain ing 4.3% Fe2C>3 , 5.2% A 1 20 2 , and 1.25% B 2C>2. Gamma C 2S is pre- pared from reagent grade CaCO^ and quartz; thus, it contains T-1946 5 T A B L E 1 DICALCIUM SILICATES o c t2s X C2S p c 2sB @ ^2ÂM Unadeep (^) T-1946 6 only trace amounts of impurities. Beta C-S is stabilized ^ B with 0.34% ênce t h e subscript "B." Beta C2SAM is sta- bilzed with 1.6% an<^ 0*7% MgO. The stabilizer is not known in the third beta dicalcium silicate, Unadeep. Although research on dicalcium silicates was an impor tant part of this study, the major emphasis was to study the reaction behavior of calcium silicate hydrate (CSH) binders with sodium. Among the principal binders at elevated tem peratures are tobermorite (C 5 SgH 5 )* xonotlite (C^S^H), and truscottite (C^ScjH) . Two other interesting binders under con sideration are pectolite (NC^S^H), and foshagite (C4S 3H). Substitution of A1 into the tobermorite lattice (up to 7% A1 2C>2 by weight) has two important effects; strength is in creased and the temperature stability is increased to about 250°C from 150°C. As Figure 2 shows, the compressive strength of tobermorite increases almost 50% when 7% Al^ ^ is substi tuted (Kalousek and Chaw, 1976) . This study was concerned with the substitution of Na+ into the potential CSH binders and in two NaÔ-bearing phases, pectolite and NC 2S 2H. To evaluate the behavior of CSH binders in the corrosive environment encountered in geothermal wells, the binders were subjected to high temperatures and pressures in the presence of solutions containing sodium.

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