Swelling of Clay Under Pressure

7/27/2019 Swelling of Clay Under Pressure

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S W E L L I N G O F C L A Y U N D E R P R E S S U R EP A U L G . N A I - I I N

U n i o n O i l C o m p a n y o f C a l i f o r n i aA B S T R A C T

A n e x p e r i m e n t a l t e c h n i q ue f o r s t u d y i n g t h e s w e l l i n g o f c l ay u n d e r c o n s t r a i n t a n ds o m e p r e l i m i n a r y r e s u l t s f o r t h e s w e l l i n g o f W y o m i n g b e n t o n i t e i n s e v e r a l m e d i a a r ep r e s e n t e d a n d d i sc u s se d . F r a c t i o n a t e d , p o w d e r e d c l a y i s m ix e d w i th a n e q u a l we ig h to f n o n - s w e l l i n g m i c r o p o r o u s p o r c e l a i n , w h i c h s e r v e s t o d i s t r i b u t e t h e s w e l l i n g a g e n tr a p id ly a n d u n i f o r m ly . T h e m ix i s c o m p a c t e d i n a c el l a t h ig h p r e s s u r e a n d p e r m i t t e dto im b ib e f l u id t h r o u g h a p o r o u s p o r c e l a in p l a t e u n d e r s im u l t a n e o u s ly a p p l i e d a lm o s te q u a l p r e s s u r e s f r o m 0 t o 1 0 ,00 0 p s ig o n b o th s id e s o f t h e f l u id - g e l i n t e r f a c e . T h eu n i d i r e c t io n a l l y c o n s t r a in e d v o l u m e c h a n g e o f t h e s a m p l e is m e a s u r e d b y d i s p l ac e m e n to f m e r c u r y i n a st e e l b u r e t . De g r e e o f s w e l l i n g is t a k e n a s t h e v o lu m e r a t i o o f g e l t o105 ~ C d ry c lay .I n t h e r a n g e o f p r e s s u r e f r o m 0 t o 1 0 ,0 0 0 p s ig , t h e c o l l o id a l m a g n e s iu m s o d iu mm o n tm o r i l l o n i t e s we l l s f r o m a b o u t 9 3 t o 2 31 p e r c e n t ( v o lu m e r a t i o 1 .9 3 t o 3 .31 ) d e -p e n d in g o n t h e c o m p o s i t i o n o f im b ib e d f l u id . Aq u e o u s 0 .1 7 1 N s o d iu m c h lo r id e a n dm a g n e s iu m c h lo r id e s o lu t i o n s p r o d u c e 1 4 a n d 1 1 p e r c e n t , r e s p e c t i v e ly , m o r e s we l l i n ga t 1 , 5 0 0 t h a n a t 0 p s ig . S w e l l i n g i n c a l c iu m c h lo r id e s o lu t i o n i s i n s e n s i t i v e t o t h i sp r e s s u r e c h a n g e . A t 1 0 ,00 0 p s ig t h e s e s o lu t i o n s , a nd h y d r o c h lo r i c a c id, p r o d u c e l e s ss we l l i n g t h a n a t 1 ,5 00 p s ig a n d, i n f a c t, p r o d u c e a lm o s t e q u a l s we l l i n g s o f 1 3 0 - - 4 p e r -c e n t . I t i s i n f e r r e d t h a t s we l l i n g i n c h lo r id e s o lu t i o n s a t t h i s p r e s s u r e m a y b e e s s e n -t i a l l y c a t i o n - in d e p e n d e n t . W i th in t h e c o n c e n t r a t i o n r a n g e o f 0 t o 1 .71 N th e r e a p p e a r sto b e l i t t l e p r a c t i c a l d i f f e r e n c e i n t h e d e g r e e o f s we l l i n g o f t h e c l a y b y s o d iu m c h lo r id ea n d c a l c i u m c h l o r i d e s o l u t i o n s ; t h e s w e l l i n g i s a l i n e a r f u n c t i o n o f t h e l o g a r i t h m o fth e s a l t c o n c e n t r a t i o n .C o m p a r i s o n o f d ( 0 0 1 ) s p a c in g s c a l c u l a te d f r o m s w e l l in g r a ti o s w i t h t h o s e o b t a in e db y X - r a y d i f f r a c t i o n l e a d t o t h e c o n c l u s i o n t h a t t h e m e t h o d m e a s u r e s c r y s t a l l i n es we l l i n g i n c o n t r a d i s t i n c t i o n t o o s m o t i c s we l l i n g .

I N T R O D U C T I O NThe p roduc t ion b ranch o f the pe t ro leum indus t ry i s in te res ted in theswel l ing p rop er t i e s o f c l ays because these m inera ls occur w ide ly in o il p ro -duc ing rocks (N ah in , M er r il l , G rena l l and Crog , 1951) . W i th the i r r e l a -t ive ly l a rge su r f ac e a reas the c lays a re capab le o f a f f ec t ing s ign i fi can tly thef low o f o i l to p rodu c ing we lls . In p r im ary p roduc t ion i t i s imp or tan t tomain ta in the g rea tes t o i l pe rmeab i l i ty in the max imum dra inage vo lumeimm edia te ly su r rou nd ing the bo reho le ; in ~secondary r ecov ery , the a im i sto ob ta in op t im um in jec t iv i ty o f f lood w a te r th roug h the in jec t ion we ll s.I n b o t h o p e r a t io n s t h e d e g r e e o f h y d r a t i o n o f t h e c l a y s i n th e v i c in i ty o f

the bo rehole af fects the ef ficiency of th e process , t t i s im por ta nt t he refo reto know how, and to wha t ex ten t , the va r ious f lu ids in t roduced in to we l l sdu r ing th ei r dr il ling , m aintenance, o r use as secon dary in jec tors af fec t thephys ica l vo lume o f the c lays .174


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PAUL G. NAH IN 175

A s i s w e l l k n o w n , t h e r e i s c o n s i d e r a b l e l i t e r a t u r e d e v o t e d t o t h e c l a y -w a t e r r e l a t i on and sw e l l i ng (B r ind l ey , 1951 ; Card we l l , 1954 ; F o s t e r , 1953 ;G r i m , 1 9 5 3 ; H e r m a n s , 1 9 49 ; H e n d r i c k s , N e l s o n a n d A l e x a n d e r , 1 9 4 0 ;K a t z , 1933 ; K i s t e r , 1947 ; Marsh a l l , 1949 ; M er in g , 1946 ; Ov erbee k , 1952 ;T r a n s . F a r a d a y S o c., 1 9 4 6 ). H o w e v e r , n e a r ly all o f t h is w o r k c o n c e r n ss y s t e m s a t a t m o s p h e r i c p r e s s u r e a n d u n d e r c o n d i t i o n s f a r r e m o v e d f r o mt h o s e t h o u g h t t o e x i s t in a p e t r o l e u m r e s e r v o i r . T h e c l o s e s t p u b l i s h e d a p -p r o a c h t o t h e t y p e o f s w e l l i n g s t u d y d e s c r i b e d i n t h i s p a p e r w a s t h a t b yP o w e r , T o w l e a n d P l a z a ( 1 9 4 2 ) . T h e y m e a s u r e d t h e p r e s s u r e d ev e l op e db y a c o n fi n ed p l u g o f W y o m i n g b e n to n i te a s a f u n c t i o n o f t h e a m o u n t o ff lu i d , a t a t m o s p h e r i c p r e s s u r e , i m b i b e d t h r o u g h a p a p e r b l o t te r . T h i s i s t h ec l a s s i c a l s w e l l i n g e x p e r i m e n t o f P o s n j a k ( 1 9 1 2 ) i n w h i c h t h e g e l v o l u m ei s h e l d c o n s t a n t . I n t h e p r e s e n t s t u d y o f c l a y s w e l l in g a s r e la t e d t o o i lr e s e r v o i r s i t a p p e a r e d n e c e s s a r y t o r e c o g n i z e t h a t i n t h e r e s e r v o i r b o t h c l a ya n d f l u id s e x i s t in a h i g h p r e s s u r e i s o b a ri c e n v i r o n m e n t . F u r t h e r m o r e ,b e c a u s e t h e v o l u m e o f a g e l i s l e s s t h a n t h e v o l u m e s u m o f t h e s e p a r a t ep h a s e s ( K a t z , 1 9 3 3 ) a n d , s ec o n d l y , b e c a u s e p r e s s u r e f a v o r s d i m i n u t i o n o fv o l u m e , a c c o r d i n g to t h e l a w o f v a n ' t H o f f a n d L e C h a t e l i e r, s im u l t a n e o u sp r e s s u r e o n b o t h l i q u i d a n d g e l s h o u l d i n c r e a s e sw e l l in g . T h e s w e l l in gs y s t e m d e s c r i b e d h e r e i n w a s d e s i g n e d t o r e a l iz e t h i s p r o c e ss .T h e m a i n p u r p o s e o f t h i s p a p e r i s t o r e p o r t t h e d e v e l o p m e n t o f a n a p p a -r a t u s f o r s t u d y i n g c l a y s w e l l i n g a t c o n s t a n t p r e s s u r e i n th e r a n g e o f p r e s -s u r e f r o m a t m o s p h e r i c t o 1 0,0 00 p si g . T h e r e s u l t s o b t a i n e d o n a W y o m i n gb e n t o n i t e w i t h t h i s i n s t r u m e n t a r e c o n s i d e r e d a s p r e l i m i n a r y i n n a t u r e a n df o r m o n l y p a r t o f a r e c o n n a is s a n c e s t u d y o f c l a y s w e l li n g u n d e r a v a r i e t yo f c o n d i t io n s , s o m e o f w h i c h m a y b e e n c o u n t e r e d i n r e s e r v o i r o p e r a t i o n s .

M A T E R I A L S , A P P A R A T U S A N D P R O C E D U R ET h e " W y o m i n g " b e n to n it e f r o m B e ll e F o u r c h e , S o u t h D a k o t a , u s e d i na l l o f t h e t e s t s a s a " t y p i c a l m o n t m o r i l l o n i t e " w a s o b t a i n e d f r o m t h e B a r o i d

D i v i si o n o f N a t i o n a l L e a d C o m p a n y . A l e ss - th a n 0 .2 - m i c ro n f r a c t io n w a sp r e p a r e d f r o m a 2 p e r c e n t s u s p e n s i o n o f t h e c l a y i n d i s t i l l e d w a t e r b yc e n t r i f u g a t i o n i n a S h a r p l e s s u p e r c e n t r i f u g e . A n a l y s i s o f t h is f r a c t i o n i n d i -c a t e d a m a g n e s i u m - s o d i u m - c a l c i u m io n e x c h a n g e c l ay w i t h 3 9 , 3 8 a n d 1 7m i l l ie q u i v a l e n ts p e r 1 00 g m . , re s p e c ti v e ly . T h i s e x c h a n g e c o m p o s i ti o n m i g h tb e e x p e c t e d t o t y p i f y t h e c l a y s u r f a c e i n a n o il r e s e r v o i r c o n t a i n i n g am e d i u m - h a r d c o n n a t e w a t e r. T o t a l c a ti o n e x c h a n g e c a p a c it y o f t h e c la y b yt h e a m m o n i u m a c e t a te m e t h o d i s 9 4 m e q . / 1 0 0 g i n.T h e s a m p l e s u s e d in t h e s w e l l i n g t e s t s c o n s i s t o f a m i x t u r e o f 4 . 5 0 g m .e a c h o f 1 05 ~ C d r i e d p o w d e r e d c l a y a n d s m a l l e r - t h a n 5 0 m e s h b a l l- m i ll e dS e l a s 0 6 m i c r o p o r o u s p o r c e l a in . T h e l a t te r , o f m a x i m u m p o r e r a d i u s 0 .3 0 -m i c r o n , s e r v e s a s f l u i d d i s t r i b u t i o n m e d i u m a n d i s o b t a i n e d b y c r u s h i n g3 - in c h d i a m e t e r x ~ g - i n c h th i c k d i sc s s u p p l ie d b y B o d e r S c i e n ti fi c C o m p a n y ,P i t t s b u r g h , P e n n s y l v a n i a . T h e w e i g h e d , t h o r o u g h l y m i x e d s a m p l e is c o m -p a c t e d i n t h e s w e l li n g c e ll ( F i g . 2 ) a t 1 ,8 20 p s i b y m e a n s o f a c a l i b r a te d


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176 SWELLING OF CLAY UNDER FRESSUREh e a v y d u t y s p r in g c o m p r e s se d b y a m a n u a l l y o p e r a t e d h y d r a u li c j a c k . T h ef il led-cell i s then de pth-g aug ed f or ca lcula t ion of sam ple volum e. T heporos i ty i s de te rmined by he l ium d i sp lacemen t fo l lowing which the ce l l i sconnec ted to the swe l ling un i t (F ig . 1 ) . A th in su rg ica l rubber o r neopren ed iaphragm separa tes the m ercu ry -c lay in te r f ace . Th e s ampIe i s evacua tedto 0 .001 r am. m ercu ry p res su re and , a s is ind ica ted in F igu re 1 , n i t rogen i sin t roduced to p res su re the sys tem to 1 ,500 ps ig , the swe l l ing agen t i s ad -mi t t ed to the s ample th rough the po rous Se las 06 d i s c (Par t D , F ig . 2 ) , andthe he igh t o f the mercu ry co lumn in the ca l ib ra ted s t a in les s s t ee l bu re t i sr eco rded a t the beg inn ing o f the run and usua l ly da i ly the rea f t e r un t i l anappa ren t equ i l ib r ium i s r eached . In opera t ion a t 10 ,000 ps ig the metho di s s imi la r excep t the s to rage cy l inder o f a p res su re in tens i f i e r i s cha rgedwi th abou t 11 ,500 ps i o f n i t rogen which , ov er a pe r iod o f l e s s than a m inu te ,i s l eaked to the swe l l ing un i t p rev ious ly p res su red to 1 ,500 ps ig f rom as tandard n i t rogen bo t t l e .

Upon admis s ion o f the swe l l ing f lu id the c lay beg ins to swe l l , apparen t lyimmedia te ly . P ro gre s s o f the swe l l ing i s m an i f es ted by the d i sp lacemen t o fa x ta - inch d iamete r so f t i ron ba l l ly ing a top the co lumn o f mercu ry in theburet . T he pos i t ion of the bal l i s located b y a m agn et ic indu ct ion coi l s l id-ing on the s t ee l bu re t . Th e fg - inc h th ick 1 89 d iam ete r co il o f No . 34mag ne t w i re w oun d on a luc it e spoo l fo rm s one a rm o f an 11 ,000 cyc les pe rsecond impedance b r idge . Ba lance i s shown by nu l l ind ica t ion on a He w le t t -P a c k a r d M o d e l 4 0 0 C v a c u u m t u b e v o l tm e t e r . T h e b a ll c a n b e l o ca t e d towi th in 4 - I mm. ; ca l ib ra t ion va lues fo r the e igh t bu re t s u sed va r i ed in therange 20 -23 cm . /cc . ; d i sp lacemen ts r an ged f rom abo u t 2 -70 cm.

C A L C U L A T I O N O F S W E L L I N GThe quan t i t a t ive expres s ion o f swe l l ing i s de f ined he re as the Swel l ingRat io , SR , g iven by the equ i l ib r ium vo lume ra t io o f ge l to d ry c lay .Symbolically,

S R = v .~ V e + p + A V o v e 1 p~-- - +lwe_p+/kVo_,w~-(w h e r e

V t = v o lu m e o f c la y g e l a t e n d o f r u nV ~= vo lume o f c l ay so l id ph ase a t 105 ~ Cp= poros i ty , o r vo id vo lume o f c l ay -Se las mix tu re , ava i l ab le to c l aygel/ S V o = v o l u m e c ha n g e o f c l a y -S e l a s m i x t u r e u p o n s w e l li n g a s o b s e r v e do n b u r e tp~= so lid phase dens i ty o f c l ay by he l imn d i sp lacemen tM e = w e i g h t o f 1 05 ~ C d r ie d c l a y i n s a m p l e .

The po ros i ty ava i lab le to c l ay ge l is ob ta ined f rom the r e la tion ,p =:Vb-V c-V a-VI = Vb-V,~e-Vl = Vb-VH~-0.2685Ma,


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NITROGEN_~., 0"0 84 1'D '~/4"0 'P R E S S U R E

M E R C U R YS U P P L Y3 W A YV A L V E . L

S A M P L E

S W E L L I N G [ "A G E N T I -R E S E R V O I R E

P AUL G. NAt t lN 177~ T U B I N G

B U R E T

~ V A C U U M I1] - I I R O N B A L L - ~

D E T E C T O Rc o ,J

I IO 0 0 N |) ' M L g E S C A L EFIGUP.E 1 . - Schem atic diagram of high pressure clay swelling unit.

w h e r eV u = b u l k v o l u m e o f c l a y - S e l a s m i x t u r eV d = v o l u m e o f S e l as s o li d p h a s eV i = v o l u m e o f i n t e r n a l p o r e s o f S e l a s n o t a v a i la b l e t o c la y g e l

V ~ e = h e l i u m d i s p la c e m e n t o f d r y s a m p l e b e f o r e s w e l li n g ( s u m o f s o l i dp h a s e v o l u m e s o f c l a y a n d S e l a s )M d = w e i g h t c r u sh e d S e la s.

T h e f a c t o r , 0 . 2 6 8 ~ M d , i s V t a n d w a s d e t e r m i n e d i n a s e p a r a t e h e l i u m -m e r c u r y d is p l ac e m e n t e x p e r i m e n t o n c r u s h e d S e la s 0 6. F r o m m e a s u r e m e n to f t h e m e r c u r y d i s p l a c e m e n t a t a s e r i e s o f p r e s s u r e s i n t h e r a n g e 5 0 0 t o1 , 300 ram. t he i n t e rna l po ros i t y o f t he S e l as no t ava i l ab l e t o c l ay ge l a t7 6 0 m m . w a s c o m p u t e d t o b e 0 . 26 8 2 c c . / g m . T h i s a m o u n t s to t h e t a c i ta s s u m p t i o n t h a t t h e s p a c e n o t a v a i l a b l e t o m e r c u r y a t o n e a t m o s p h e r e p r e s -su re i s t he s am e as t ha t unav a i l ab l e to c l ay ge l .

E x p e r i m e n t a l l y , t h e h e l i u m d i s p l a c e m e n t V a , o f t h e c r u s h e d S e l a s w a sf o u n d t o be 0. 36 7 c c . / g m . H e n c e , t h e d e n s i t y o f t h e c l a y i sM c _ M c M c

P c = V c V ~ e - V a - - VHo-O.367MaF r o m t h e f o r e g o i n g , i t i s e v i d e n t t h a t t h e p e r c e n t s w e l l i n g m a y b ee x p r e s s e d a s

% S w = (~---~-'g 1 ) 1 0 0 = ( S R -1 ) 100.


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178 S W E L L I N G O F C L A Y U N D E R P R E SS U R E

SWELLING AGENT INLE T

B U R E TA - S A M P L E H O L D E R , B - LO C K I NG N U T

C - M E R C U R Y R E S E R V O I R , D - S E L A S 0 6 P O R O U S D IS CE - S T A I N L E S S S T 'L OIS C H O LD E R

F - E L A S T O M E R D IA PH R AG M , G - N O . 2 3 " O " R I N G

FIGUr,E 2 .- -H ig h pressure swelling cell .

I n u s i n g t h e s e f o r m u l a s i t i s a s s u m e d t h a t t h e S e l a s m i c r o p o r o u s p o r c e -l ai n , f u s e d d u r i n g m a n u f a c t u r e a t t e m p e r a t u r e s u p t o 2 ,6 5 0 ~ F , d o e s n o ts w e ll . E x p e r i m e n t a l e v i d e n c e t h a t t h e p r e s e n c e o f S e l a s d o e s n o t s e n s i b l ya f f e c t t h e e v a l u a t i o n o f t h e e f f ec t i v e p o r o s i t y o f t h e s a m p l e i s a d d u c e d f r o mt h e r e s u l t s o f p o r o s i t y d e t e r m i n a t i o n s o n W y o m i n g b e n t o n i t e c o m p a c t e dw i t h a n d w i t h o u t a n e q u al p a r t o f S e l as 06 . W i t h S e l a s a b s e n t th e d e n s i t yw a s c a l c u l a t e d t o b e 2 . 62 5 g m . / c c . I n d e t e r m i n a t i o n s o n f iv e d i f f e r e n t s a m -p l e s w i t h 1 : 1 c l a y - S e l a s t h e d e n s i t i e s w e r e 2 . 6 4 , 2 . 6 8 , 2 . 5 6 , 2 . 6 7 , 2 . 6 5 ;a v e r a g e 2 . 6 4 g m . / c c .

R E S U L T S A N D D I S C U S S I O NT h e d a t a o n s w e ll in g o f f r a c t i o n a t e d W y o m i n g b e n t o n i t e in v a r io u s m e d i aa r e s u m m a r i z e d i n T a b l e I .I n t h e r a n g e o f p r e s s u r e f r o m 0 t o 1 0 , 0 0 0 p s i g , t h e c o l l o i d a l m a g n e s i u m -s o d i u m m o n t m o r i l l o n i te sw e ll s f r o m 9 3 t o 23 1 p e r c e n t ( v o l u m e r a t io 1 .9 3t o 3 . 3 1 ) d e p e n d i n g o n t h e s w e l li n g a g e n t c o m p o s i t i o n . I n n o c a s e w a s t h em i n i m u m o b s e rv a b l e s w e ll in g o f 3 2 p e r c e n t ( A V o = O , p = 0 . 5 5 c c., p c =


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P A U L G . N A H I ~ rTABLE I.--SW ELL ING OF WYOMI NG BENTONITE AT 25 ~ C

1 7 9

SwellingSwell ing age nt Press ure,agen t concen t ra tion ps ig S R. 10 aH O H 100% 1,500 331-----51(3)~'l "H O 'H 100% 10,000 272---+1 2 )(NaPO~)a 0.171N 1,500 326-----7(3)'I 'CA~H~20~I 10 % aq ua 1,500 316---+7 8 ) 1'N a O H 0.171N 1,500 309---+12(3) ~'N H ,O H 15N 1,500 199---+I 3)CH 3O H 100% 1,500 201 --+6 4)H O CH 2C H ~O H 100% 1,500 193-----3(3)t'HC1 0.171N 1,500 265-+5 (3)HC1 0.171N 10,000 228_+4(4) 4'CaC h 0 .171N 0 256-+6(4)C aC h 0.171 N 1,500 255-----5 4 )CaCI2 0.171N 10,000 23 6-+4 (4)Ca Ch 0.171N 1,500 291 (4)C aC h 1.71N 1,500 226-+7 (3 )Na CI 0.171N 0 237-+10(4)Na CI 0.171N 1,500 251-+ 9(7)NaC1 0.171N 10,000 224-+3 (5 )NaC1 0.0171N 1,500 310-+12(4)NaC 1 1.71N 1,500 214---+7 4 )MgCI2 0 .1 7 1 N 0 2 31 + 6 ( 4 )M gC h 0.171N 1,500 242-+ 2(4)MgC12 0.171N 10,000 23 1-+3 (3)LiCI 0.171N 1,500 24 1-+4 (4)N H , CI 0 .171N 1,500 232-+2 (4)

1 Ar i thm et ic averag e deviation f rom the a verageNumber of samples tested.s A rro w up denotes equil ibrium no t reached, SRS R .still increasing at end of run.

2 . 6 4 g m . / c c . , M e = 4 . 5 0 g m . ) n o t e d . T h u s , th i s c l a y s w e ll s m e a s u r a b l y i na l l s w e l l i n g a g e n t s t e s t e d , v i z . , a l l v a l u e s o f S R e x c e e d 1 . 3 2 .I n a ll e x p e r i m e n t s t h e i n it ia l r a t e o f s w e l l i n g w a s v e r y g r e a t . I t w a s n o tu n u s u a l f o r f r o m 7 0 to 9 0 p e r c e n t o f t h e s w e l li n g to o c c u r w i t h i n a r e l a -t iv e l y f e w m i n u t e s a f t e r j o i n i n g t h e t w o p h a s e s . T h e r e m a i n d e r o f t h es w e l l i n g to a n a p p a r e n t e q u i l ib r i u m t o o k f r o m t h r e e t o s i x d a y s f o r t h ec h l o r id e s o lu t io n s t o o v e r s e v e n w e e k s f o r d e io n i z e d w a t e r . ( C o n s t a n tb u r e t r e a d i n g f o r t w o d a y s w a s ta k e n a s i n d i ca t iv e o f s w e l l in g e q u i l i b r i u m ) .A p p a r e n t l y , t h e r a t e o f s w e l l i n g d e p e n d s m a i n l y o n t h e r a t e o f a c c e s s i b i l i t yo f c l a y s u r f a c e .

M e c h a n i s mT h e s l o w i n g d o w n o f t h e r a t e o f s w e ll in g m a y b e c o n s i s t e n t w i t h a t w o -s t e p m e c h a n i s m : f ir st , th e m a j o r i t y o f th e p la t e le t s a r e in d ir e c t s u r f a c ec o n t a c t w i t h a t l e a s t o n e m i c r o p o r e o f t h e p o r c e l a i n t h u s e n s u r i n g a l m o s ti n s t a n t c o n t a c t b e t w e e n f lu i d a n d t h e s u r f a c e i o n s o r l a tt ic e c h a r g e s b e -


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180 S W E L L IN G O F C L A Y U N D E R P R E SS U R E

l ie v e d t o b e r e s p o n s ib l e f o r s w e l l i n g ; a n d s e c o n d l y , t h e m i n o r i t y o f p l a t e le t sh a v i n g c o n t a c t o n l y w i t h o t h e r p t a t e l e ts a r e h y d r a t e d b y t h e r e l a t i v e l y s lo wp r o c e s s o f d i f f u s io n o f f lu i d t h r o u g h t h e s u r r o u n d i n g g e l f o r m e d i n th e f i r sts t e p . T h e s e r e l a t i o n s , w h i c h m a y e x i s t b e t w e e n t h e c l a y a n d t h e m i c r o -p o r o u s p o r c e l a i n b e f o r e a n d a f t e r s w e l l i n g , a r e s h o w n i n t h e i d e a l i z e ds k e t c h , F i g u r e 3 .Ef fec t o f Pressure

T h e e f fe c t o f h y d r o s t a t ic p r e s su r e o n s w e l li n g o f W y o m i n g b e n t o n i te i n0 . 1 7 1 N s o l u t i o n s o f h y d r o c h l o r i c a c i d a n d t h r e e c o m m o n s a l t s i s s h o w n i nF i g u r e 4 . C o n c e n t r a t i o n o f 0 . 1 7 1 N w a s c h o se n b e c a u s e t h i s c o r r e s p o n d sa p p r o x i m a t e l y to t h e io n i c s t r e n g t h o f a 1 0,0 00 p p m s o d i u m c h l o r i d e b r in e ,c h a r a c t e ri s ti c o f c e r ta i n C a l i f o r n i a r e s e r v o i r w a t e rs . H o w e v e r , i t m u s t b en o t e d t h a t w i t h t h e r e c o r d e d a v e r a g e f l u id i m b i b i d o n o f 3 t o 4 c c ., t h i s

B E F O R E S W E L L I N G

A F T E R S W E L L I N GFIGURE 3. -- Po ro sit y relation in clay-microporous porc elain syste m (idealized).


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PAUL G. NAI-IIN 181SW ELLING vs . HYDROSTATIC PRESSURE270 ( ~ ' ~ Clay : WYOMING BENTONITE

,Z ~ ~ / f ~ ~ C l Size :


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182 S W E L L I N G O F C L A Y U N D E R P R E S S UR E

m o n t m o r i l l o n i t e a n d n e g l e c t s s w e l l i n g a t t h e p l a t e l e t e d g e s , a s w e l l i n g r a t i oo f 2 . 30 ( 1 3 0 p e r c e n t s w e l li n g ) a m o u n t s t o a c - a x is e x p a n s i o n t o o n l y 2 2 A .( F o r a 1 , 0 0 0 A l o n g b y 2 0 0 A w i d e d r y p l a t e l e t t h e e d g e a r e a is l es s t h a n5 p e r c e n t o f t h e b a sa l a r e a . ) T h e m a x i m m n o b s e r v e d s w e l li n g r a t io ( n o n -e q u i l i b r i u m , t o b e s u r e ) o f 3 .3 1 w o u l d i n d i c a t e a c - a x i s e x p a n s i o n t o a b o u t3 2 ) ~ ; t h e m i n i m u m o b s e r v a b l e sw e l l i n g r a t io o f 1 .3 2 , a n e x p a n s i o n t o12.7 A. O n t h i s b a s i s p e r h a p s n o t a l l o f t h e c r y s t a l l i n e s w e l l i n g m e n t i o n e db y N o r r i s h w a s c o m p l e t e d u n d e r t h e c o n d i t i o n s o f t h e s e e x p e r i m e n t s .I t i s i m p o r t a n t t o n o t e h e r e t h e e n o r m o u s v o l u m e t r i c d if f er e n ce s b e tw e e nf r e e " s w e l l i n g " i n a n o p e n s y s t e m , w i t h t h e a t t e n d a n t m a x i m u m o p p o r -t u n i t y f o r o s m o t i c d il u ti o n o f t h e g e l m i c e tl e s t o o v e r a t h o u s a n d p e r c e n t i ns o m e c a s e s , a n d t h e c o n s t r a i n e d s w e l l i n g s o f t h e p r e s e n t e x p e r i m e n t s t o am a x i m u m o f le s s t h a n 2 5 0 p e r c e n t . C o m p a r i s o n o f d ( 0 0 1 ) s p a ci n g s c a lc u -l a t e d f r o m s w e l l i n g r a t i o s w i t h t h o s e o b t a i n e d b y X - r a y d i f f r a c t i o n ( T a b l eI I ) l ea d t o t h e c o n cl u s io n th a t t h e m e t h o d m e a s u r e s c r y s t a l li n e s w e ll in gi n c o n t r a d i s t i n c t i o n t o o s m o t i c s w e l l i n g .

T h e e f f ec t o f p r e s s u r e o n s w e ll in g i n w a t e r ( T a b l e I ) m a y b e a p p r e c ia b l ea n d i n d i c a t e s , p e r h a p s , t h a t t h e s w e l l i n g p r e s s u r e i s I e s s t h a n 1 0 , 0 0 0 p s i g .I f , i n f a c t , e q u i l i b r i u m w a s r e a c h e d a t 1 0 , 0 0 0 p s i g i t m i g h t b e i n f e r r e d t h a ts w e l li n g p r e s s u r e s c o u l d b e r e a d il y d e t e r m i n e d w i t h t h i s a p p a r a t u s f r o m t h em a x i m a o f p l o t s o f s w e l l i n g r a t i o s v e r s u s a p p l i e d h y d r o s t a t i c p r e s s u r e s .Effect of Concentration

T h e e f f e c t o f v a r y i n g c o n c e n t r a t i o n u p o n s w e l l in g a t 1 , 5 00 p s i g w a s s t u d -i e d w i t h s o d i u m a n d c a lc i um c h l o r id e s o l ut io n s ( F i g . 5 ) . W i t h i n t h e r a n g eo f 0 t o 1 . 7 1 N t h e r e a p p e a r s t o b e l it t l e d i f f e re n c e i n t h e d e g r e e o f s w e l l i n gi n t h e s e s o l u t io n s . T h i s f i n d in g s e e m s t o c o n f l ic t w i t h t h e a s s e r t i o n t h a te x c h a n g e o f m o n o v a l e n t i o n s a g a i n s t d i v a l e n t i o n s d e c r e a s e s s w e l l i n g( O v e r b e e k , 1 9 5 2 ) . P e r h a p s , t h e p r e s e n t r e s u l t i s a r e f le c ti o n m e r e l y o f t h eTABLE II.--COM PAR ISON O F c - A x i s E X P AN S IO N S O F W Y O M I N G BE N T ON IT E

FROM SWELLING RATIOS AN D X -R AY DIFFRACTION

SR at d(001) by d(001) byFluid 1,500 psig SR, A XRD, AH O H 3.31 1~ >32 35-osmotic fHC1 0.171N 2.65 25.4 22.5 (


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P A U L G . N A I I I N 18334_~n~- S W E L L I N G v s . A Q U E O U S S A L TC O N C E N T R A T I O Ni ~ & S O D IU M C H L O R ID Eo C A L C I U M C H L O R I D E

C la y : W Y O M I N G B E N T O N I T E~ ) " - " ~ S i ze : < 0 . 2 - M IC R O N~ P r e s s u r e : 1 5 0 0 P S I G

0 2 8 0 t " ~ T em p : 2 5 ~I ~ B oo k : B 6 5 4 6 - 4 8

I^ ^ ^ I I i9 u u ~ ! N O R M A L I T Y.~i.-, j7! 1.71FmuRE 5 . - Swelling vs aqueous salt concentration.

l a r g e a m o u n t s o f b o t h c a l c i u m a n d s o d i u m i o n s i n t h e c l a y s u r f a c e r e l a t i v eto t he so lu ti on . P lo t t ed s em i - l ogar i t hmica l l y , t he da t a fo r NaC1 f rom 1 ,000to 100,000 p pm f i t t he s t r a i g h t - l i ne e qua t i on :S R = 4 .54-0 .481 loglo (N aC 1) ,

w h e r e ( N a C 1 ) i s c o n c e n t r a t i o n i n p a r t s p e r m i l li o n o f N a C1 . T h i s e q u a t i o nind i ca t es t ha t shou ld t he r e l a t i on ho ld down to , s ay , abou t 1 pp rn , t he swe l l -i n g r a t i o i n e s se n t i a ll y p u r e w a t e r , m i g h t b e in t h e n e i g h b o r h o o d o f 4 - 4 . 5 ;: e x p e r i m e n t a l l y , t h e o b s e r v e d n o n - e q u i l i b r i u m v a l u e w a s 3 . 3 1 .

Effect of HydroxylT h e r e s u lt s f o r s o d i u m h y d r o x i d e , a m m o n i u m h y d r o x i d e , a n d s o d i u mh e x a m e t a p h o s p h a t e i n d i c a t e t h a t a l k a l i n i ty m a y b e a p ro - s w e l l i n g f a c t o r .T h e t e n p e r c e n t s u c r o s e s o l u t i o n w a s r u n t o d e t e r m i n e w h e t h e r s u c h ah y d r o x y l a t e d b u t u n c h a r g e d m o l e c ul e i n h i g h c o n c e n t ra t i o n m i g h t l o w e r t h ea c t i v i t y o f t h e w a t e r s u f fi c ie n t ly t o d e p r e s s t h e d e g r e e o f s w e l l i n g ; t h e o b -s e r v e d s w e l l i n g r a t i o a p p e a r s t o b e a b o u t t h e s a m e a s f o r d e i o n i z e d w a t e r .A b s o l u t e m e t h y l a lc o h o l a n d a n h y d r o u s e t h y l e n e g ly c o l g a v e s w e l l in g r a t io so f 2 .0 1 a n d 1 .9 3, r e s p e c t iv e l y . T h e s e a m o u n t t o e s ti m a t e d c - a x i s e x p a n s i o n sto 19 . 3 A and 18 . 5 A wh ich app rox imate , rough ly , t he 17 A spac ings fo re t h y l e n e g l y co l a n d e t h a n o l o b se r v e d w i t h X - r a y s ( B r a d l e y , 1 9 4 5 ).


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184 SWEL LING OF CL AY UNDER PRESSUREL i m i t a t io n s o f t he M e t h o d a n d R e s u l t s

E m p h a s i z i n g a g a i n t h e p r e l i m i n a r y n a t u r e o f t h e se r e s u lt s i t is c le a r th a tt h e m e t h o d h a s c e r t a i n l i m i t a t i o n s a n d t h a t , w i t h i n t h e s e l i m i t a t i o n s , s o m ei m p r o v e m e n t s a r e po s si bl e. T h e l im i t a t io n s o n m e a s u r e m e n t o f d e g r e e s o fs w e l l in g b e l o w a b o u t 3 2 p e r c e n t i s a s e v e r e o n e . I m p r o v e m e n t in t h i s r e g a r df o r t e st s a t 2 5 ~ C d o e s n o t a p p e a r p r o m i s i n g ; e x p e r i m e n t s w i t h S e l a s 0 6 :c l a y r a t i o s o f l e s s t h a n u n i t y r e s u l t e d i n u n d e s i r a b l e i n c r e a s e s i n ti m e r e -q u i r e d t o r e a c h s w e ll in g e q ui li b ri u m . T h i s d e f e a t s t h e p u r p o s e o f t h e m i c r o -p o r o u s p o r c e l a in o f f a c il i ta t in g r ap i d , u n i f o r m s a t u r a t i o n o f t h e c l a y b yf lu i d . R a i s i n g t h e t e s t t e m p e r a t u r e t o 1 0 0 ~ C a n d h i g h e r w i l l in c r e a s e t h er a t e o f s w e l l i n g a n d t h e r e b y e n a b l e l o w e r i n g t h e a m o u n t o f S e l a s r e q u i r e df o r c o m p l e t i o n o f r u n s w i t h i n s p ec i fi e d t i m e i n t e rv a l s . T h u s , a t t h e h i g h e rt e m p e r a t u r e s i t s h o u l d b e p o s s i b l e t o d e t e r m i n e t h e s m a l l e r d e g r e e s o f s w e l l -i n g . T h e v a r i a t i o n o f t h e s w e ll in g w i t h t e m p e r a t u r e w i ll , o f c o u r s e , d e p e n do n w h e t h e r t h e p r o c e s s i s e x o t h e r m i c o r e n d o t h e r m i c . V a r i a t i o n s i n t h ed e g r e e o f i n h o m o g e n e i t y o f t h e S e l a s - c l a y m i x t u r e i s b e l i e v e d r e s p o n s i b l ef o r t h e d i f fe r e n t a v e r a g e d e v ia t io n s r e c o rd e d . B e t t e r m e a n s f o r m i x i n g t h et w o s o l i d s s h o u l d r e d u c e t h i s s o u r c e o f e r r o r a n d , t h e r e b y , p e r m i t g r e a t e rp r e c i s i o n i n d e t e r m i n a t i o n o f s w e l l i n g r a t i o w i t h f e w e r r u n s p e r s a m p l e .

I t i s l ik e l y t h a t s o m e o f t h e r e l a t i v e l y s m a l l s p r e a d o f t h e e x p l o r a t o r y d a t ap r e s e n t e d h e r e m a y b e a c o n s e q u e n ce o f t h e u n f a v o r a b l e i o n ic c o n c e n t r a ti o nr a t i o o f c l a y : s o l u t i o n ; g r e a t e r d i f f e r e n c e s a m o n g t h e v a r i o u s s o l u t i o n s m a yb e c o m e e v id e n t a t ra t io s o f u n i t y a n d h i g h e r . I n t h e p r e s e n t e x p e r i m e n t s ,b e c a u s e o f e x c h a n g e , t h e o r i g i n a l - c a t i o n c o n c e n t r a t i o n i n t h e l i q u i d p h a s ea t e q u i l ib r i u m w a s c e r t a i n ly b e lo w 0 . 1 7 1 N i n t h a t c a t io n . M o r e r e a d i lyi n t e r p r e t a b l e r e s u l t s w o u l d b e o b t a i n e d b y t h e s w e l l i n g o f s u r f a c e - h o m o -i o n i z e d c l a y s in s o l u t io n s o f l i k e c a t io n a n d a t a c l a y : s o l u t i o n i o n s y m m e t r yo f n e a r u n i t y .

A C K N O W L E D G M E N TT h e a u t h o r is e s p ec ia l ly g r a t e f u l t o W . E . S h o w a l t e r a n d R o b e r t P a v l o -v i c h f o r v a lu a b l e as s is t an c e a n d t o U n i o n O i l C o m p a n y o f C a l i f o r n i a f o r

p e r m i s s i o n t o p u b l i s h .R E F E R E N C E S

Brindley, G. W. (Ed itor) (195 1) X -ra y identif ication and crysta l s truc tures of c layminera ls : M ineralogical Society, British M useum , Lond on.Bradley, W. F. (1945) Molecular asso.c iations between montmoril lonite and some poly-fu~*ctional organic liquids: J. Am . Ch em . Soc., vol. 67, pp. 975-981.Cardwell, W. T. Jr., (California Research Corporation, La Habra, California) S w e l l -ing clay identification: 1954 Pacific Coast R egional Co nference on C lay s and ClayTechno logy, University of California, Berkeley, California.Foster, M. D. (1953) Geochemical s tudie s of c lay min erals: H . Rela tion betwee n ionicsubs t i tu t ion and swe l l ing in montmar i l lon i te : Am . M ineral., v o l. 38, pp. 994-1006.Grim, R. E. (1953) Clay minera logy: M cGraw-Hill Book Com pany, Inc., New York,pp. 161-189.


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Swelling of Clay Under Pressure

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