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1 A D ti S T I< I A L A S 1)
li S ti I N 15 E H I N G C €1E bZ I Y T I< Y
Vol. 2 5 , No. 9
rl1 an effort to nieasure the effect of pII 011 tlie rate of is evideiit that they differ greatly fruiri those presented in settling of barytes, the aut,liors made experiments u-ith [lis- this paper, obtained by the same method. This discrepancy i)ersions of barytes intended for use as a paint filler and con- may he explained by a difference in the quality of the samples tnining no bentonite; but the rate of settling was so rapid used, particularly a difference in the gelling cbaracteristics that no measurements m r e possible. To secure the data of the bentonite. desired, it was necessary to use a sample of pure precipit.ated CONCLWSIONS barium sulfate of extreme fineness of size. The results are I t has been sliuwn that the stability of Baroid drilliiig illustrated in Figure 2, v;ith no niaxinia in either the acid or the alkaline range and showing very little irnprovement fluids are greatly iiifluenced by the p l I of the suspension. i n stability of suspension. Addition of 2 per cent bentonite Similar measurements by Parsons, using the height of sludge (by weight of water of the suspension) to this material re- method, are in error, for this method is not even roughly acciiratc when applied to a suspension of particles of nonstilted in a curve identical with that in Figure 1 . Tlis two minima shovrn in uniform size. .4ccordiue to I'arsnns' m e a s u r e m eri t s it Vigure 1 may he explained by would be necessary to make the presence of some ainphothe suspensionacid (pH = 5.7) teric m a t e r i a l that r e a c t s in order to have maximum stacheinically u+th both the liybility (98 per cent in suspenilrogen and hydroxyl ions besion). The authors' measurefore the latter are a d s o r b e d ments reveal that less t.han 60 with increased st.ability of the per cent of the solids are in suspension due to the charge suspension at the end of 12 imparted to the colloid. At the uiaxirnuin of the curve on hours under such conditions. The drilling fluid would alsir the alkaline side-the point of have u n d e s i r a b l e corrosive g.r e a t e s t s t a b i l i t y of the suspension---nraxim?~m adF~~~~~~ 5, s ~ A 25 ~ pEncENT ~ wATEn ~ D~ ~ ~ ..propertiesifstabilized ~ ~ by addsorption of the h y d r o x y l ion ~ s n s r o ~ o a B hwin% ~ o ~Vmnm ~, ~ € 1AVI'ER , Sm-risNG ing acid to a pH of 5.7. has taken place, followed by 12 Houns The authors' measuremerits by the height of sludge method decrease in stability as a result of the discharging effect of the catioii--in this case, sodium showed a niaxinium (100 per cent in stability) a t n pH of ion. Similar relations hold on the acid side. nhout 9; but using an accurate method for the case a t hand, Tlie viscosity (measured witli the Stormer viscometer a t 10 it was demonstrated that only about 25 per cent remained in revolutions per second) increases on both sides of the iso- suspension at the eiid of 12 hours at this value of the pH. electric point from a value of 3 centipises a t a pII of 9 to A water dispersion of IIaroid (10.2 pounds per gallon) a t 41 a t a plI of 11.2, approximately the point of maximum a plI of 10.5 to 11.5 is practically 100 per cent in suspension stability; this increase would be expected with increased a t the end of 12 hours. A suspension of the same weight gel formation of the bentonite in the dispersion. The latter using water, without adding the small amount of caustic to figure is not too high for use in actual drilling practice. make it slightly alkaline, has a pH of 8.7, and only 26 per Curve 1 of Figure 3 gives the rate of settling for the Baroid cent is in suspension at the end of 12 hours. The slight desuspension in wat.er alone, corresponding to a pII of 8.7 in gree of alkalinity is also desirable to niinimize corrosioii and Figure 1. Curve 2 gives similar data when the suspension to improve the lubrieating properties of the drilling fluid. lias been completcly flocculated with caustic, corresponding The viscosity increases from 3 centipoises a t the isoelectric to a pFI of 12.5 in Figure 1. A third curvc, corresponding point (water dispersion of Baroid) to 41 centipoises a t tlie point of maxiinurn stability, hut the latter figure is not too to a pEI of 10.5 to 11, would lie along the abscissa axis. Figure 4 shows the results obtained by the height. of sludge high for use in actual drilling practice. method, as used by Parsons. Curve 1 gives t.he percentage ACKNOWLEDGXENT in suspension after 12 hours as a function of the pH, takiirg the height of the sludge as the percentage of the total height ~ 1 authors , ~ wish to tile assistallce of 1 ~ 'r. . of the columil for the ordinate. Pilotographs Of the settling Schelling, a former nlember of this laborabry, in niakirrg the material, such as are shom~nin Figure 5, provide the data for meas,lreineiltsgiven in this paper. the construction of the curves. This illustration shows T.VTE~AT~TRI+ olainlv that a relativelv large amount of the suswension has .-..- Cirrn -..-Bet.t.le2 to the hottom i; the-bottles showing no free water a t (I) Ada,ns and Glasson, Thesis, Mass, Inst, Tech,, 1925 the ton. This fact demonstrates that the heivht of sludve m , ... ,.",.~-Phr.irr ~ ~ 1_,vm ~ I~-"~.,. I O R~ T~ i ~ j_, ~ ~ 1 ~.. ~~ -"" ..~"~-", inethod leads to gross errors when the settling particles (3) Lawton, Amhrose, and Loomi.. 1bid.. 2, 365; 3, IS5 (IWU. ~ Alexander's "Colloid Chemihtru." p. Sol. Chemical are not of uniform size. It is obvious that a larue anlount (1) O d h in I
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other words, the height of sfudge method can &e tlie rate of settling of the fine particles only in a suspension with a distj,ercfore, tiiat tile must,he triijution of sizes, results of Parsons are seriously in error. I n order t.o examiire the effect of time on B a r d suspensions, a sami,le 3 m e k s old vas used to obtain the data gireii in curve, 2 of Figure 4. It is ohservable that appreciable chauge lias occurred on tlie acid hut not 011 the alkaline side. This change is not nearly large enough, however, to account for the difference in Parsons' data and those of the authors. Parsons' data are represented by curve 3 of Figure 4. It
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~. .- . . . . (6) lloliauun. Ism E m . C:am., 18. 869 (1U2ij) R a c ~ w s oMarch 17, 1933. Presented beiore the Divizion of Petroleum Chemistry st t h e 85th Meeting of t i l e American Choinienl Society, Washington, D. C.. Marc11 26 to 31. 1933. ~
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CORRECTION. In the srt,icle "Empirienl bhlecular Ileut Cq~rat,ions from Spectroscopic Data" by W. M. D. Bryant [Im. Exn. emu., ZS, 820 (1933)], the second term of Equation 3 should read
($)*instead
of
hu
kT -.
