Water-In-crude Oil Emulsions From the Norwegian Continental Shelf Part I. Formation,

7/23/2019 Water-In-crude Oil Emulsions From the Norwegian Continental Shelf Part I. Formation,

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Colloids an d Surfaces,

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E l s e v i e r S c i e n ce P u b l i s h e r s B .V . , A m s t e r d a m - - P r i n t e d i n T h e N e t h e r l a n d s

W a t e r - in - C r u d e O i l E m u l s i o n s f r o m t h e N o r w e g i a n

C o n t i n e n t a l S h e l f

P a r t I . F o r m a t i o n C h a r a c t e r i z a t i o n a n d S t a b i l i t y

C o r r e l a t i o n s

E I N A R J . J O H A N S E N 1, I . M A G N A R S K J ~,R V 0 1'* , T O R G E I R L U N D I,

J O H A N S J O B L O M TMH E L E N A S ~ )D E R L U N D 2 a n d G U N B O S T R ( ) M 3

IStatoil A /S , Prolab, Bo x 300, N-4001 Stavanger Norway)

2Institute for Surface C hemistry, Box 5607, S-114 86 Stoc kho lm Sw eden )

3Department of Physical Chemistry, .4bo Aka dem i, SF-20500.4bo Finland)

( R e c e i v e d 6 A p r i l 1 98 8; a c c e p t e d i n f i n a l f o r m 2 2 A u g u s t 1 9 88 )

A B S T R A C T

P r o p e r t i e s o f d i f f e r e n t c r u d e o i l s f r o m t h e N o r w e g i a n c o n t i n e n t a l s h e l f , t o g e t h e r w i t h t h e i r

e m u l s i o n s ( w i t h s y n t h e t i c f o r m a t i o n w a t e r ) , a r e r e p o r t e d . T h e c r u d e o i ls , i n m o s t c a s e s, a r e c h a r -

a c t e r i z e d b y a h i g h a m o u n t o f s a t u r a t e d h y d r o c a r b o n s , a v a r y i n g a m o u n t o f w a x e s ( 2 - 1 5 % ) a n d

a l o w c o n t e n t o f a s p h a l t e n e s ( 0 - 1 . 5 % b y w e i g h t ) . T h e c r u d e o i l s ( f r o m 3 2 d i f f e r e n t w e l l s ) h a v e

b e e n c h a r a c t e r i z e d b y m e a n s o f d e n s i t y , v is c o s i ty , s u r fa c e a n d i n t e r r a c ia l t e n s i o n m e a s u r e m e n t s .

T h e a b i l i t y t o f o r m s t a b le e m u l s i o n s v a r ie s v e r y m u c h , d e p e n d i n g o n t h e c r u d e o i l. E m u l s i o n

s t a b i l i t y h a s b e e n e v a l u a t e d b y m e a n s o f v i s u a l i n s p e c t i o n a t n o r m a l g r a v i t a t i o n a n d b y m e a n s o f

u l t r a c e n t r i f u g a t i o n a t 6 5 0 - 3 0 00 0g . T h e r e p r o d u c i b i l i t y i n t h e s t a b i l i t y s e q u e n c e b y t h e s e t w o

i n d e p e n d e n t m e t h o d s i s s a ti s f a c to r y . M e a n d r o p l e t s i ze s in t h e i n t e r v a l 1 0 - 1 0 0 / n n w e r e c o n s i d-

e r e d t o r e p r e s e n t r e a l i s t ic l a b o r a t o r y p r e p a r a t i o n c o n d i t i o n s . I t w a s f o u n d t h a t h i g h e r m i x i n g r a t e s

r e d u c e d t h e d r o p l e t s i z e , w h i l e a p r o l o n g a t i o n o f t h e e m u l s i f i c a t i o n t i m e g a v e a n a r r o w e r d i s t r i -

b u t i o n o f d r o p l e t si z es . I n c r e a s e d t e m p e r a t u r e w a s f o u n d t o c a u se i n s t a b i l i ty , w h i l e e x t re m e p H

v a l u es g a ve r e s t o r e d o r e v e n e n h a n c e d s t a b i l it y . T h i s l a s t o b s e r v a t io n w a s t a k e n a s a n i n d i c a t i o n

o f a l o w s u r fa c e c h a r ge d e n s i t y , a s t r e n g t h e n i n g o f t h e i n t e r f a c ia l fi l m b y t h e b i n d i n g o f h y d r a t i o n

w a t e r a n d a l a c k o f s t a b i l i z in g p a r t i c le s .

A c o r r e l a t i o n b e t w e e n e m u l s i o n s t a b i l i t y a n d m e a s u r e d p h y s i c o c h e m i c a l p a r a m e t e r s s h o w e d

t h a t t h e e m u l s i o n v i sc o s i ty , t h e c r u d e o i l v i s c o s it y a n d t h e c o n t e n t o f w a xe s w e r e t h e m o s t s i g n i f-

i c a n t p a r a m e t e r s ( R 2 = 0 . 7 1 , w h e n c o m p a r i n g o b s e r v e d a n d c a l c u l a t e d s t a b i l i t y ) .

I N T R O D U C T I O N

I n t h e o f f s h o r e p r o d u c t i o n o f c r u d e o i l , t h e p r o b l e m o f c r u d e o i l e m u l s i o n s i s

e n c o u n t e r e d a t a n e a r l y s t a g e . I n t h e p l a n n i n g a n d c o n s t r u c t i o n o f t h e p l a t f o r m

* P r e s e n t a d d r e s s : J o t u n A / S , B o x 40 0, N - 3 2 0 1 S a n d e f j o r d , N o r w a y .

* *T o w h o m c o r r e s p o n d e n c e s h o u ld b e a d d r e s s e d . P r e s e n t a d d r e s s : I n s t i t u t e f o r C h e m i s t ry , D e -

p a r t m e n t o f P h y s i c a l C h e m i s t r y , U n i v e r s i t y o f B e r ge n , N - 5 0 14 B e r g e n -U , N o r w a y .

0 1 6 6 - 6 6 2 2 /8 9 / 0 3 . 5 0 © 1 98 9 E l s e v i e r S c i e n c e P u b l i s h e r s B . V .

e n o u g h s p ac e m u s t b e r e s e r v e d f o r e m u l s i o n d e s ta b i l i z a ti o n e q u i p m e n t , s u c h

a s s e p a r a t o r s a n d c o a l es c e r s. W i t h r e li a b le i n f o r m a t i o n a b o u t c r u d e o il a n d i ts

t e n d e n c y t o f o r m e m u l s io n s , th i s s p a c e c o u l d b e r e s e r v e d f o r o t h e r m o r e u s e f u l

p u r p o s e s . T h e c r u c ia l s t e p w i ll h e n c e b e t o p r e d i c t e m u l s i o n s ta b i li ty f r o m

m e a s u r e d a n a l y t i c a l o r p h y s i c o c h e m i c a l p r o p e r t i e s o f c r u d e o i l s a m p l e s o r p r e -

p a r e d s y n t h e t i c c r u d e o il e m u l s io n s .

C r u d e o il e m u l s i o n s ta b i li ty h a s b e e n t h e s u b j e ct o f i n t e n s e d e b a t e a n d r e-

s e a r c h d u r i n g t h e l a s t e i g h t y y e a r s [ 1 - 1 0 ] . T h e r e is a la c k o f a f u n d a m e n t a l

u n d e r s t a n d i n g o f t h e m e c h a n i s m s g o v e r n i n g t h e s ta b i l it y o f o i l - c o n ti n u o u s

e m u l s i o n s . T h e r e a s o n f o r t h i s is t h a t t h e m o s t i m p o r t a n t s ta b i li z in g m e c h a -

n i s m s a r e d i f fe r e n t f ro m t h o s e o f w a t e r - c o n t i n u o u s e m u l s i o n s , s o t h a t d i r e c t

p a r a ll e ls c a n n o t b e d r a w n . T h e d i r e c t a p p l ic a t i o n o f a n e l e c tr o s t a ti c m o d e l fo r

s t a b i li z a ti o n , i n o r d e r t o p r e v e n t f l o c c u l a t i o n o f t h e w a t e r d r o p l e t s d i s p e r s e d

i n t h e o il , d o e s n o t s e e m t o b e ju s t i fi e d . F o r c r u d e o i l e m u l s i o n s , t h e i m p o r t a n c e

o f a r ig id a n d p r o t e c t i v e f il m s u r r o u n d i n g t h e w a t e r d r o p l e t s is u s u a l ly p o i n t e d

o u t [ 1 1 - 1 4 ] . T h e d e t a i le d p r o p e r t i e s o f t h i s f il m , t o g e t h e r w i t h a f u n d a m e n t a l

k n o w l e d g e o f t h e c h e m i s t r y o f t h e i n te r f a c ia l ly a c t iv e c o m p o n e n t s in t h e c r u d e

o i l , a r e f a r f r o m u n d e r s t o o d . H o w e v e r , e m p i r i c a l s t u d i e s h a v e s h o w n t h e i m -

p o r t a n c e o f c o m p o n e n t s lik e a s p h a l t e n e s , p o r p h y r i n e s a n d w a x e s fo r t h e s ta -

b i l iz a t i o n [ 1 5 - 2 2 ] . T h e f i r s t t w o c o m p o n e n t s a r e b e l i e v e d t o p o s s e s s s u r f ac e -

a c t i v e p r o p e r t ie s a n d h e n c e t o a c c u m u l a t e a t t h e i n t e rf a c e o f w a t e r a n d o il.

W a x e s c a n a c t e i t h e r o n a m o l e c u l a r l ev e l a s li p id s , o r as p a r t ic l e s o f t e n to -

g e t h e r w i t h c l a y s ) i n t h e i n t e r f a c ia l f i lm , o r a l t e r n a t i v e l y a s v i s c o s if ie r s in t h e

c o n t i n u o u s o i l p h a s e . F o r m a t i o n o f a n i n te r f a c ia l f i lm p o s s e s s i n g c e r ta i n s u r -

f a c e - r h e o lo g i c a l p r o p e r t i e s , i n c o m b i n a t i o n w i t h a p a r t i c le a n d / o r s t e r ic s t a -

b i li z a ti o n , i s o b v i o u s l y o f f u n d a m e n t a l i m p o r t a n c e f o r t h e s t a b i li ty o f c r u d e o il

e m u l s i o n s . I n a d d i t i o n , t h e h y d r o d y n a m i c b e h a v i o u r o f e m u l s i o n s w h e n s t i r r e d

o r p u m p e d a ls o a f f e c ts t h e s t a b il it y . T h i s a s p e c t w i ll n o t b e c o v e r e d i n t h i s

i n v e s t i g a t i o n .

I n t h e f i r s t p a r t o f o u r s t u d y w e r e p o r t o n t h e f o r m a t i o n , c h a r a c t e r iz a t i o n

a n d s t a b il it y c o r r e l a t i o n s o f w a t e r / o i l w / o ) e m u l s i o n s b a s e d o n N o r t h S e a

c r u d e o i ls . I n s u b s e q u e n t p a r t s w e w il l r e p o r t o n c h e m i c a l d e s t a b i l i z a t io n

m e c h a n i s m s P a r t 2 ) , a n d s y n t h e t ic w / o e m u l s io n m o d e l s y s te m s p o s s e ss i n g

s i m i la r p r o p e r t ie s t o n a t u r a l c r u d e o i l e m u l s i o n s b a s e d o n N o r t h S e a c r u d e o i l s

P a r t 3 ) .

EXPERIMENTAL

naly tical and physicochemical properties of the crude o ils investigated

O f a to t a l e x p e r i m e n t a l m a t r i x o f 3 2 c ru d e o i l sa m p l e s f r o m t h e c o n t i n e n t a l

s h e lf , w e p r e s e n t i n t h i s r e p o r t d a t a o f s el e c te d s a m p l es . T h e o il s a m p l e s c o v e r

a l a rg e g e o g r a p h ic ar e a, e x t e n d i n g f r o m t h e E d d a f ie l d i n t h e s o u t h to t h e S n S h -

v i t fi e ld i n t h e n o r t h . T h e c r u d e o i ls h a v e b e e n s e l e c t e d i n s u c h a w a y t h a t a

l a rg e v a r i e t y o f e m u l s i o n s t a b i l it ie s w e r e o b t a i n e d .

T h e a n a l y ti c a l p r o c e d u re i n v o lv e s d e t e r m i n a t i o n o f t h e c o n t e n t o f a r o m a t i c

c o m p o u n d s , s a tu r a t e d h y d r o c a r b o n s , p o la r c o m p o u n d s , w a xe s a n d a s p h al -

t e n e s . T h e f o ll o w in g e x p e r i m e n t a l p r o c e d u r e h a s b e e n a d o p t e d :

( i) A s p h a l t e n e s w e r e p r e c i p i t a t e d b y d i lu t i n g t h e c r u d e o il w i t h n - p e n t a n e

( 1 : 4 0, v / v ) a t r o o m t e m p e r a t u r e . T h e s u s p e n s i o n w a s f i lt e r e d t h r o u g h a 0 .4 5 -

/ l m fi lt er . ( M o d i f i e d I P m e t h o d 1 4 3 .)

( ii ) W a x c o m p o n e n t s w e r e p r e c i p i t a te d in a c e to n e a t - 2 0 ° C a n d i s o la te d

b y f i l te r i n g t h e s u s p e n s i o n t h r o u g h a g la s s - fi b r e f il te r . T h e w a x f r a c t i o n w a s

f u r t h e r p u r i fi e d o n a s i lic a a d s o r b e n t i n h e x a n e s o l u t io n . T h e p r o c e d u r e w a s a

s l ig h t m o d i f i c a t i o n o f a m e t h o d d e s c r i b e d b y B u r g e r e t a l. [ 2 3 ] .

( ii i) S a t u r a t e d , a r o m a t i c a n d p o l a r c o m p o n e n t s w e r e is o l a te d a n d q u a n t i fi e d

b y p r e p a r a t i v e h i g h - p r e s s u re li qu id c h r o m a t o g r a p h y ( H P L C ) . B o t h s il ic a- a n d

c y a n o - c o l u m n s w e re i n c lu d e d in t h e c h r o m a t o g r a p h i c sy s te m . T h e s e p a r a t i o n s

w e r e o b t a i n e d b y b a c k f l u s h i n g t e c h n i q u e s , in v o l v i n g b o t h h e x a n e a n d t e tr a -

h y d r o f u r a n a s m o b i l e p h a s e s .

( iv ) M o l e c u l a r w e i g h t s w e r e d e t e r m i n e d o n a C r y e t t e A ( P r e c i s i o n S y s t e m s

I n c. ) t h r o u g h m e a s u r i n g t h e f r ee z in g p o i n t d e p r e s s i o n o f b e n z e n e .

T h e p h y s i c o c h e m i c a l p r o c e d u r e i n v o lv e s a d e t e r m i n a t i o n o f th e p o u r p o i n t ,

w a x a p p e a r a n c e p o i n t , d e n s i t y , v i s c o s i t y ( a t 1 0 0 s - 1 ), s u r f a c e (Y o/a ) a n d i n t e r -

f a c ia l t e n s i o n (Y o/w ). T h e s e q u a n t i t i e s w e r e d e t e r m i n e d a s f o ll ow s :

( i) W a x a p p e a r a n c e p o i n t s w e re d e t e r m i n e d b y t r a n s m i s s i o n m i c r o sc o p y

u s i n g p o l a r i z e d l ig h t .

( ii ) P o u r p o i n t s w e r e m e a s u r e d a c c o r d i n g t o s t a n d a r d p r o c e d u r e s [ I P m e t h o d

1 5 / 6 7 ( 7 5 ) ] .

( ii i ) M e a s u r e m e n t s o f c r u d e o i l d e n s i t ie s w e r e p e r f o r m e d a t 4 0 ° C w i th a n

A n t o n P a a r D M A 6 0 2 H i n s t r u m e n t , u s in g a ir a n d d i st il le d w a t e r a s r e f er e n ce

m a t e r i a l s .

( iv ) S u r f a c e a n d i n te r f a c ia l t e n s i o n s w e r e m e a s u r e d a t 2 0 a n d 4 0 ° C w i t h a

M G M L a u d a R i n g T e n s i o m e t e r c o n n e c t e d t o a H P - 1 7 3 2 A R e c o r d er . S a m p l e

t h e r m a l i z a t i o n t i m e w a s l o n g e n o u g h t o e n s u r e i n t e r f ac i a l e q u i li b r iu m b e f o r e

m e a s u r e m e n t .

( v ) V i sc o si ty m e a s u r e m e n t s w e re p e r fo r m e d a t 4 0 ° C o n a C o n t r a v e s L o w

S h e a r 3 0 R o t a t i o n a l V i s c o m e t e r . A t i m e o f 1 0 m i n w a s a l l o w e d f o r t h e r m a l

s t a b il iz a t io n b e f o r e i n i t ia t i n g t h e m e a s u r i n g p r o g r a m m e . R e a d o u t s w e r e ta k e n

a t a s h e a r r a t e o f 1 00 s - 1.

Physicochemical properties of the water in crude oil emulsions investigated

I n a l l e m u l s i f i c a ti o n s w e u s e d a n a q u e o u s p h a s e w i t h t h e c o m p o s i t io n :

Ion Concent ration (mg 1-1)

Na + 13 844

K + 193

Ca 2+ 1275

Mg2+ 335

Ba 2+ 50

CI- 24 775

The densi ty of the aqueous phase was 1.0264 g cm -~ and its surface tension

73.3 mN m -1 at 20°C.

The emulsions investigated were prepared under different conditions. Either

100 ml emulsion {with 50 synthe tic formation water) was emulsified with a

standard propellar rotor for 2 h at 650 rpm (A), or 12 ml emulsion was prepared

with an Ultra-Turrax equipment at 20,000 rpm for 5 min (B). In the legends

to the figures, emulsification procedures A or B are specified.

When checking the influence of pH on the crude oil emulsions, a buffer

solut ion was used, 1 litre of which contained 6.008 g citric acid, 3.893 g potas-

sium sulphate, 1.796 g boric acid, 5.266 g diethyl barbituric acid and 58.440 g

sodium chloride. The final pH was adjusted with HCI or NaOH.

Viscosities of the emulsions were determined in an analogous way to the

crude oil samples. Ultracentrifugations were carried out with a Beckman

ultracentrifuge.

RESULTS

This study contains an analytical and physicochemical characterization of

crude oils from the Norwegian continenta l shelf and their water-in-oil emul-

TABLE1

Analytical chemical properties of appropriate representatives of crude oils from the Norwegian

continental shelf

Crude Aromatics Saturates Polar Waxes Asphaltenes M.W.

oils ( , w/w) ( , w/w) compounds ( , w/w) ( , w/w) (g tool -1)

( ,w/w)

A 11.2 84.7 4.0 3.9 0.2 190

B 17.4 78.2 4.4 4.3 0.7 200

C 36.4 50.7 12.9 4.5 0.6 240

D 28.5 66.3 5.2 10.1 0.4 260

E 36.0 59.1 4.9 14.5 0.4 210

F 29.2 68.2 2.6 2.9 0.0 150

G 36.1 58.2 6.0 8.6 1.5 260

H 47.7 46.0 6.2 3.6 0.8 240

I 32.9 61.0 6.1 4.6 0.2 200

J 40.6 53.0 6.4 2.4 0.4 240

X Crude off

® Crude oil

0 Crude oil C

o Crude oil

• Crude

• Crude oil I

No wate r Crude o i l

. . . . Crude oil E

. . . . l

0 20 40 60 80 100 120

Time min}

F ig. 1 . S e p a r a t i o n o f w a t e r f r o m e m u l s io n s b as ed o n d i f f e r e n t c r u d e o il s f r o m t h e N o r w e ~ a n

contin ental shelf. Emulsification conditions according to procedure A described in Experi mental.

Separation is at room temperature. The original conten t of synthet ic formation water was 50

(v/v).

C R U D E O I L

Ultracentrifugation, 50°C {A]

~ ] Ultracentrifugotion, 20°C {A)

Grovity seporo tion, 50°C S}

Fig. 2. A comparis on of stability numbe rs obtai ned by ultracentrifugat ions and gravity separation

at different temperatur es. Emulsi fication conditio ns as specified in t he figure, A or B. The aqueous

phase was 50 (v/ v).

s io n s . A l t o g e t h e r , o u r e x p e r i m e n t a l m a t r i x o f c r u d e o i ls i n c l u d e s 32 s a m p l e s .

O f th e s e , w e h a v e c h o s e n c a t e g o r i e s w i t h v a l u e s c o v e r i n g t h e b r o a d e s t p o s s i b l e

i n te r v a l e x p e r i m e n t a l ly . T a b l e 1 giv e s s o m e f u n d a m e n t a l a n a l y t i c a l c h e m i c a l

p r o p e r ti e s o f t h e c r u d e o ils . T h e a m o u n t o f a ro m a t i c c o m p o u n d s v a r ie s f r o m

10 t o 5 0 ( w / w ) , a n d s a t u r a t e d h y d r o c a r b o n s f r o m 5 0 t o 8 5 . T h e a m o u n t o f

non-specified polar components is between 4 and 13 . The content of waxes

precipitating in acetone varies from 2 to 15 . Finally, the amount of asphal-

tenes is strikingly low, ranging from 0 to 1.5 (w/w). Molecular weights de-

ter mined by means of freezing point depression are all in the interval 150-260

g mo l- 1.

Table 2 gives some physicochemical properties of the same crude oils at 20-

40°C. The densities vary from 0.79 to 0.89 g cm -~, viscosities (measured at

100 s -1 ) from 2 to 41 mPa s, surface tens ions are all in the narrow interval 24-

30 mN m -1, while the interfacial tensions (towards synthet ic formation water)

are between 23 and 36 mN m-1. The table reveals a clear correlation between

a high content of wax particles and a high viscosity. In two cases it can be seen

that the interfacial tension significantly exceeds the surface tension. This is

also the case for high amount s of waxes. The table also gives the pour points

and the wax appearance points, both expressed in degrees centigrade.

The ability of each category of crude oils to form stable w/o emulsions was

checked by visual inspection and is reported in Fig. 1. It is quite obvious that

the different crude oils have varying emulsion-stabilizing properties. In order

to obtain a stability sequence, we have compared two independent methods.

First, an ordinary visual evaluation was carried out to see how long it takes for

a fixed volume of water to separate from the emulsions. In this case we mea-

sured the time it takes for 20 (v/v) of the emulsified amount of water to

separate. The stability number has been calculated from In (t.g), where t is the

separation t ime and g is gravity. Under normal room conditions, normalized

g = 1. The stability numbers obta ined are summarized in Fig. 2. As an alter-

native and independent method, ultracentrifugation was used in order to speed

up the separation process. In this method, one determines the time at which

the separation of water levels out, as in Fig. 1. Since this t ime will be a function

of centrifugal force, we have performed ultracentri fugations at different g val-

ues. As previously, the stability number is calculated from In

( t g ) .

In order to

show the influence of increased temperature , the visual determinat ions were

performed at 50°C, while the ultracentrifugations were carried out at room

temperature. For the sake of comparison, one ultracentrifugation was per-

formed at 50 ° C. The stability number obtained from this exper iment gives

good agreement with visual inspection at the same tempera ture. The gravity

separation in Fig. 2 gives a stabi lity sequence of G > M > N > D, while the se-

quence obtained from ult racentr ifugations is G > N > M > D. Considering the

experimental conditions, this is considered to be a good reproducibility. A lower

stability of each crude oil emulsion at the higher temperatu re is to be expected,

especially for those crude oils which contain wax particles that melt at these

higher temperatures. Crude oil D seems to be especially sensitive to this.

In order to create realistic laboratory conditions for the emulsion tests, dif-

ferent emulsification conditions must be examined. An acceptable measure of

the approprite emulsification conditions is the size of the emulsion droplets.

F rom t h e l i t era t u re i t i s k n own t h a t n a t u ra l l y occu rr i n g wat er - i n - cru d e o i l

e m u l s i o n s ar e b u i lt u p b y d r o p l e ts w i t h a d i a m e t e r o f 1 0 - 1 0 0 m [ 1 5 , 2 4 ] . I n

F i g. 3 w e s u m m a r i ze t h e i n f l u e n c e o f d i ff e r e n t e m u l s i fi c a t io n c o n d i t io n s o n t h e

m e a n d r o p le t s iz e . T h e m i x i n g t im e r a n g e s fr o m 0 .5 t o 1 2 0 m i n , a n d t h e e m u l -

s i on s are b as ed on cru d e o i l G .

I n s u m m ary , h i gh er m i x i n g ra t e s w i l l r ed u ce t h e m ean d rop l e t s i ze wh i l e a

p ro l on gat i on o f t h e em u l s i f i ca t i on t i m e wi l l m a i n l y g i ve r i s e t o m ore eq u i d i -

m en s i on a l d rop l e t s . T h i s l a t t er t ren d i s m an i f e s t ed i n F i g . 4 , wh ere t h e s t an -

d a rd d e v i a ti o n ( S D ) o f t h e m e a n d r o p l e t s i ze i s p r e s e n t ed . A l o n g e r e m u l s if i -

ca t i on t i m e gen era l ly re s u l t s i n s m a l l er S D va l u es . How ever , a l l em u l s i on s are

ch arac t er i zed b y a h i gh l eve l o f p o l yd i s p ers i t y .

IO 30 80 90 120 5 I0 30 80 1 2 4 8 0.5 1 2 4

MIXING TIME

m i n )

F i g . 3 .

M e a n dr o p l e t s i z e o f w a t e r - i n - c rude o i l e m ul s i o ns ba s e d o n c r ude o i l G f or d i f f e r e nt

p r e p -

a r a t i o n

c o nd i t i o ns . F o r t he l o w e r m i x i ng r a te s pr oc e dur e A w a s us e d w h i l e pr o c e dur e B w a s us e d

f o r t h e t w o h i g h e s t r a te s. T h e a q u e o u s p h a s e w a s 5 0 ( v / v ) .

RUDE OIL G

I ~ ~ ~ ~ I ~ ~ ~ 8 rpm 2 rp m

10 30 80 90 120 5 10 30 80 1 2 4 8 0.5 1 2 4

MIXING TIME ra in )

F i g . 4 .

S t a n d a r d d e v i a t i o n fo r m e a n d r o p l et s i z e s i n

F i g . 3 .

[ ] [ ]

2 4 6 8 1 12

[ ] O IL E

a OIL G

Fig. 5. Separation of waterfromcrude oil em ulsions based on crude oils C, D, E and G as a fun ction

of pH in bufferedsystem s. Preparation according to procedure A. The aqueous phase was 50

(v/v) .

A w a t e r - i n -o i l e m u l s io n i s b u i lt u p b y w a t e r d r o p le t s s u r r o u n d e d b y a n i n -

t e r fa c i a l f il m w h e r e t h e p o l a r c o m p o u n d s a r e a c c u m u l a t ed . T h e p r o p e r t i e s o f

t h i s s t ab i l i z i n g f i l m wi l l b e h i gh l y d e c i s i ve f or t h e s t ab i l it y o f t h e w h o l e s y s t em .

I n ord er t o g i ve a q u a l i t a t i ve p i c t u re o f t h e ac i d - b a s e p rop er t i e s o f t h i s f i l m ,

w e r e p o r t o n e m u l s i o n s t a b il it y a s a f u n c t i o n o f p H . F i g u r e 5 s u m m a r i z e s t h e

r e s u lt s f r o m t h e p H a d j u s t m e n t s i n b u f fe r s o lu t i o n s o n t h e s t a b il it y o f d i f f e r e n t

cru d e o i l em u l s i on s b as ed on f ou r d i f f eren t cru d e o i l s . T h e i n f l u en ce i s n o t

u n i f o r m . O n l y o n e e m u l s i o n ( b a s e d o n c ru d e o il E ) s h o w s a c o m p l e t e s e p a ra -

t i o n i n t h e p H i n t e r v a l 5 - 7 . T w o o t h e r s , i . e . C a n d D , s h o w s o m e i n s t a b i l i t y

a r o u n d p H 6 a n d 9. T h e i n f l u e n c e o f p H o n e m u l s i o n s b a s e d o n c r u d e o i l G i s

ra t h er n eg l i g i b l e . S u m m ar i z i n g , on e can con c l u d e t h a t a t very h i gh an d very

l o w p H v a l u e s, t h e e m u l s i o n s s e e m t o b e s t a b le , w h i l e in t e r m e d i a t e p H v a l u e s

s eem t o cau s e i n s t ab i l i ty . T h e ran ge an d d egree o f i n s t ab i l it y , h o wev er , is very

d e p e n d e n t o n w h i c h c r u d e o i l t h e e m u l s i o n i s b a s e d o n .

I t i s c o m m o n l y k n o w n t h a t t e m p e r a t u r e c h a n g e s w i ll a f fe c t t h e s t a b i li ty o f

em u l s i on s . E s p ec i a l l y f or cru d e o i l em u l s i on s , a t em p era t u re i n creas e i s gen -

e r a ll y c o n s id e r e d t o d e s t a b i li z e t h e s y s t e m . T h i s i s m a i n l y d u e t o t h e f a c t t h a t

t h e v i s c o s i t y o f t h e c o n t i n u o u s p h a s e w i l l su b s t a n t i a l ly d e c r e a se , h e n c e f a c i l i-

t a t i n g a c o l l is i o n b e t w e e n a q u e o u s d r o p l e t s. I f t h i s e n h a n c e d c o l li s io n r a t e o f

d rop l e t s re s u l t s i n an i n creas ed coa l e s cen ce an d s ep ara t i on , a d es t ab i l i za t i on

o f t h e e m u l s i o n i s a c c o m p l i s h e d . F i g u r e 6 s u m m a r i z e s t h e s e p a r a t i o n p r o c e s s

a t th r e e d i f fe r e n t t e m p e r a t u r e s a s a f u n c t i o n o f t i m e . T h e s e p a r a t io n p r o c e s s

h as b e en ob s erved f or 24 h . A r i se i n t em p era t u re f rom 20 t o 70 ° C ca u s es a

s ep ara t i on o f wat er , w h i ch i s, h ow ever , n o t co m p l e t e a t 50 ° C . E v en a t 70 ° C ,

t h e e m u l s i o n s b a s e d o n c r u d e o i ls B , D a n d E s h o w a l o w te n d e n c y t o s e p a ra t e .

F o r t h e o t h e r e m u l s i o n s i n v e s t i g a t e d , t h e s e p a r a t i o n p r o c e s s i s a l m o s t c o m -

p l e t e f o r t h e h i g h e s t t e m p e r a t u r e .

A n i m p o r t a n t i n d i v id u a l p a r a m e t e r f o r t h e s t a b il it y o f t h e c r u d e o il e m u l -

I~ 8 0

e-~ 8O

e'~ 8O

v ~ v v •

4 8 1 2 1 6 2 0 2 4

( ho urs )

5 0 ~ C

_~ _ o o

, , , • , , • ,

1 2 1 6

2 0 2 4

[ h o u r s )

2 2 ~ C

o . ~ o

f . _ m

8 1 2 1 8 2 0 2 4 ( ho urs )

o Cru de o f f A

[ ] Cru de o f f B

V C r u d e o i l C

A C r u d e o i l D

• C r u d e o i l E

C r u d e o i l H

• C r u d e o i l I

× C r u d e o i l J

Fig. 6 .

S e p a r a t i o n o f w a t e r fr o m c r u d e oi l e m u l s i o n s b a s e d o n d i f f e r e n t c ru d e o i ls a s a f u n c t i o n o f

t i m e a n d a t d i f fe r e n t te m p e r a t u r e s . P r e p a r a t i o n t o o k p l a c e a c c o r d i n g t o p ro c e d u r e B . T h e a q u e o u s

p h a s e w a s 5 0

( v / v ) .

s i o n s s e e m s t o b e t h e e m u l s i o n v i s c o si t y . W e h a v e c h a r a c t e r i z e d t h e e m u l s i o n

v i s c o s i t y f or d i f fe r e n t c o n t e n t s o f w a t e r i n t h e e m u l s i o n . T h i s w a s p e r f o r m e d

a t l o w s h e a r r a t e s o f 10 0 s - 1 . A t t h e s e c o n d i t i o n s t h e e m u l s i o n w a s o b s e r v e d

t o f o l l o w a n e q u a t i o n o f R i c h a r d s o n t y p e [ 2 5 ] , i .e .

~_e = e n ~ + k

w h e r e ~e a n d 0 o a r e t h e v i s c o s i t y o f t h e e m u l s i o n a n d t h e c r u d e o i l, r e s p e c t iv e l y ,

i s t h e v o l u m e f r a c t io n o f w a t e r e m u l s i f i e d , a n d n a n d k a re c o n s t a n t s . T h e

d e v i a t i o n f r o m a n i d ea l R i c h a r d s o n e q u a t i o n i s t h e i n t r o d u c t i o n o f a n i n t e r c e p t

d i f f e r e n t f r o m z e ro k ¢ 0 ) i n a l o g a r i t h m i c p l o t . T a b l e 3 s u m m a r i z e s t h e v a l u e s

o f t h e c o n s t a n t n , t o g e th e r w i th R 2 v a l u e s a n d t h e m a x i m u m a m o u n t o f w a t e r

~ H20.m a~) t h a t c a n b e e m u l s i f i e d i n t o e a c h c r u d e , w i t h o u t i m m e d i a t e s e p a r a -

T A B L E 3

R i c h a r d s o n ' s c o n s t a n t ( n ) a s d e t e r m i n e d b y l i n e a r r e g r e s s i o n ( l e a s t s q u a r e s m e t h o d ) , a n d

~H._,o . . . ( , v / v ) , t h e m a x i m a l a m o u n t o f w a t e r t h a t c a n b e e m u l s i f i e d i n t o t h e c r u d e o i l w i t h o u t

s e p a r a t i o n o r i n v e r s i o n

C ru de oi l CH~O n R 2

( ,v/v)

A 8 0 3 7 0 9 7

C 7 0 4 7 1 0

D 7 0 2 4 0 9 8

E 7 0 2 5 0 9 4

G 8 0 4 7 0 9 9

H 6 0 3 1 0 9 9

I 8 0 3 9 0 9 7

J 7 0 3 6 0 9 9

t i o n o f w a t e r o r i n v e r s i o n o f e m u l s i o n . T h e l i n e a r i t y b e t w e e n l n( ~/e /t/o ) a n d @

is s h o w n i n F i g . 7. A t lo w s h e a r r a te s , m a n y o f t h e e m u l s i o n s in v e s t i g a t e d d o

n o t s h o w N e w t o n i a n b e h a v i o u r.

I n t h e f i n a l c o r r e l a t io n o f a n a l y ti c a l a n d p h y s i c o c h e m i c a l p r o p e r t i e s o f t h e

3 2 c r u d e o i ls a n d t h e i r e m u l s i o n s w i t h r e g a r d t o e m u l s i o n s t a b i l it y , t h e f o ll ow -

i n g p a r a m e t e r s w e r e s e le c te d : t h e c o n t e n t o f w a x , p o l a r c o m p o u n d s a n d a s -

p h a l t e n e s , t h e v i s co s i t ie s o f t h e c r u d e o i l a n d t h e p r e p a r e d e m u l s io n , a n d , f i-

n a ll y, t h e i n te r f a c ia l t e n s i o n ( c r u d e o i l / f o r m a t i o n w a t e r ) . T h e s e l e ct io n w a s

b a s e d o n a p r e l i m i n a r y d e t a i le d c h a r a c t e r i z a t i o n ( 14 p a r a m e t e r s ) o f e i g h t c r u d e

o ils a n d t h e i r c o r r e s p o n d i n g e m u l s i o n s .

E m u l s i o n s t a b il it ie s w e r e e x p r e s s e d a s t h e s e p a r a t i o n t im e ( in m i n u t e s ) a t

2 0 w a t e r b r e a k - o u t . T h e v e ry b r o a d r a n g e t o s e p a r a t i o n ti m e s w a s c o m -

p r e s s e d o n a l o g a r i t h m i c s c a le ( lo g r a i n ) f o r c o n v e n i e n c e .

T h e o b s e r v e d s i n g l e - p a r a m e t e r c o r r e l a t i o n s a r e p r e s e n t e d i n T a b l e 4 . A s

m e n t i o n e d p re v i o u s ly , t h e r e s e e m s to b e a s i g n i f ic a n t re l a t i o n s h i p

0 .59 )

b e t w e e n e m u l s i o n s t a b i l i t y a n d e m u l s i o n v i s c o s it y , a s i l l u s t r a t e d i n F i g . 8 . F o r

a ll o t h e r p a r a m e t e r s , l e s s s ig n i f i c a n t c o r r e l a t i o n s w e r e o b s e r v e d .

A g r e a t n u m b e r o f m u l t i p a r a m e t e r m o d e l s w e r e a l so i n v e s t i g a t e d b y r e g r e s-

s i o n a n a ly s is . T h e m o d e l ty p e s c a n b e d e s c r i b e d b y t h e f o ll o w in g t h r e e g e n e r -

a l i z e d e q u a t i o n s :

Y=ao +alX1

+ a 2 X 2

+ a 4 X 4

+asXs +a6X6

Y = l og ( e a°. X ~ I - X ~ 3 . X ~ 3 . X ~ - X ~ . X ~ )

H e r e

r e p r e s e n t s t h e e m u l s i o n s t a b i l i t y i t h e s i x c r u d e o i l p a r a m e t e r s a n d

a i t h e r e g r e s s i o n c o e f f i c i e n t s .

~ 2 . 0

4 . . 0

~ 2 . o

R U D E O I L D

i i J i f

0 . 2 0 . 3 0 . 4 0 . 5 0 . 6

VO LU ME FRACTION WATER ~b

0 . 7 0 . 8

C R U D E O I L J

L i i ~ i i

O , 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 7 0 . 8

V O L U M E F R A C T I O N W A T E R ~ b

Fig. 7. The viscosity of crude oil emulsions ( e) normalized to that of the pure crude oil ( o) as a

function of varying water contents (~). (a) Crude oil D, (b) crude oil J. Emulsificationaccording

to procedure A.

T A B L E 4

D efinition s of param eters, symbols, measuring con dition s an d th e significance o f each individual

param eter in the stabil i ty corre la t iona

Param ete r Symbol R 2

(condi t ions /uni t s )

Con tent of wax ( , w/w )

Co nten t of polar compounds ( , w /w )

Con tent of a spha l tenes ( , w/w )

Oil v i sc os ity ( T=4 0°C , D = 100 s - i ) ( mP a s )

Emuls ion v i sc os ity ( T=4 0°C , D = 106 s - 1 ) ( mP a s )

In te rfac ia l tens ion o i l /wa te r (T = 20 ° C ) ( raN m - 1

Em uls ion s tab i li ty (T= 50 °C , w a te r sep .) ( log m in)

X 0 . 1 3

x2 o.oo

X3 0.11

X4 0.06

X5 0.59

Xe 0.19

aThe con tent of synth etic form ation wa ter is 50 (v /v ) and the emulsions were prepared accord-

ing to procedure B ( see the Exp er imenta l ) .

. . . . . i - - - - - i . . . . . i - - - - - ~ . . . . . , - - - - , - - - - ' - - - - , - - . , - - - - , . . . . . i - - - - 4 - - - - - i . . . . .

i , , , , , , , , , , , ,

12 . . . . . - - - - ' : - - - - - ' - - - . : . . . . . ' - - - - ' - - - - ' - . - - ' - - - - ' - - " . . . . . L - - - - - - - - " . . . . .

i i ] i i i ~ i i i i i J

. . . . . , , - , - , , , - - , " , - - , , , , . . . . . [ - - T - - - i . . . . .

. ~ 1 0 . . . . . ~ - - - - ~ . . . . . , . - , - - - - - , - - - , ' - - - , - - - - - , - - - , - - - - , . . . . . " - - - - - - - . . . . .

, " - ' , . _ . ' . . ~ _ . . . , : . . . . _ _ _ ' , _ . . . " . . . . . ; . . _ . } . . . _ " . . . . .

. . . . . i T ~ I "

. . . . ~ - - - - 4 - - - - ~ - o - ' - - - - . ~ - - - - , - - - , - - - - , - - - - , - - - - , . . . . . " - - - - ' - - - - " . . . . .

S . . . . , - - - - , - ' ' ' - - - - ' ' ' . . . . . } - -- - -t -- -- ~ . . . . . I -- -- - ~- -- -~ . . . . .

. . . . . i . . . . 4 . . . . i . _ . . i _ . + . _ _ _ _ _ . i _ . . . . . ~ - _ _ _ b _ _ i - - - - - - - - - - - - - - . . . . .

4 . . . . ' - - - - ' - - - ' - - - - ' - - - - " - - - ' - - - - ' . . . . . " - - - - ' - - - - " . . . . . ~----:----~'. . . .

o : i o i O i i i i i i i

. . . . ~ - - - - J - - - i - - - -~ . . .. . ~ __ _ _ L - - .. ~ . . . .. ~ - - - . , . . . ~ . . . .. ~ - - -. , . . . .. . . .. .

2 - - - ' - - - ' - - - - ' - - - - ' - - - - - ' - - - - ' - - - - ' . . . . . ' - - - - ' - - - - ' - - - - - ' - - - - ' - - - - ' . . . . .

l e l i i i i i i i i i i

.- ,. - o - - = - - T - - - ~ i - - i . . . . . [ [ i . . . . . V T - - - i . . . . . [ T i . . . ..

o O i i i i i ~ , ~ , i , , ,

0 2 0 4 0 S 0 8 0 1 0 0 1 2 0 1 4 0

E M U L S I O N V I S C O S I T Y I m P s . s ]

Fig. 8 . Corre la t ion between stabil i ty num ber an d viscosi ty of emulsions based o n 32 crude oi ls

from the Norwegian con tinen tal shelf . Em ulsification according to proc edu re B.

T h e s t a t i s t ic a l a n a l y s i s r e v e a l e d a t h r e e p a r a m e t e r m o d e l c a p a b l e o f p r e -

d i c t i n g 7 1 o f t h e t o t a l v a r i a n c e in e m u l s i o n s t a b i l i t y :

Y = l o g ( e 9 .6 1. X } .9 1 oX 4 3 .63 . X5 5 .0 6 )

T h i s i s i l l u s t ra t e d i n F ig . 9 . T h e m o d e l i n p u t w a s l i m i t e d t o w a x c o n t e n t ( X 1 ) ,

c r u d e o il v i s c o s i ty ( X 4 ) a n d e m u l s i o n v i s c o s i t y ( X s ) . O n l y i n s i g n i f i c a n t i m -

p r o v e m e n t s o f p r e d i c t i v e a b i l i t y c o u l d b e o b t a i n e d b y i n c l u d in g m o r e

p a r a m e t e r s .

. .. .. i - i - i - - i - i - - i - ~ - i - - F - i o - i . . . ..

. . . . . i - - - t - - - i - - i - - - - " - - - i - - - . . . . . i - - - - f f f - - - i t i - . i . . . . .

. . . . . i - - 1 - t i - - T - - ~ i . . . . . ; ~ T ~ I . . . . . l t - - i . . . . .

. . . . . i - - i . . . . . i - - i - - - i - - - i - o i - - - - - ~ - - i - - - i * - i - - - - - - - i . . . . .

. . . . . , - - - - , - - - - - , - - - - , - - - - - , - - - - , - - - - , ,, , , , , . . . . . ~ - , . . . . . . 4 - - - - - I - - - - - ~ - - - - 4 , , , . . . .

. . . . . , _ _ _ _ , . . . _ _ , _ _ . . , _ _ _ _ . , . , _ , _ _ _ _ , . . . . . L _ _ A . . . . . . . . L _ _ _ _ L - - - . . . . .

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. . . . . i . . . _ i _ . . . T - y . - y . . T - - - i ~ . ~ - - i . . . - t - - - - y - T - - - i . . . . .

. . . . . t - - - - - ~ - - - - q - - - - - 4 . . . . . F - - - - I - - - - - 4 . . . . . , - - - - , - - - - ,- - - - - , - - - - , -- - - , . . . . .

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. . . . . I - T - ' ; - - - - I - - , ' - ' ' U - - - I . . . . . F - - - ' T - - - - I ' - - - F ' - T - ' ' ~ . . . . .

. . . . . i - i - - i - i . . . . . i . . . . .

. . . . ~ . t ~ _ _ _ __ P . _ _ . . . - -, ~ . . .- i - - -- ~ . . . . . ~ - - - - i - - - - - - - - - ~ - - - - i - - - - ~ . . . . .

. . . . . . . . . . . . . ~ . . . . . i . . . _ . i . . _ _ L . . . i . _ . . . i _ _ _ _ L _ _ i . . . _ _ L . . . L . - . . . . .

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2 4 6 S 1 12 14

CALCULATED STABILITY [log e

m i n u t e s

F i g . 9 . O b s e r v e d s t a b i l i t y n u m b e r v e r s u s c a l c u l a t e d s t a b i l i t y n u m b e r d e r i v e d f r o m a b a s e s e t o f

t h r e e s i n g l e p a r a m e t e r s , i .e . w a x c o n t e n t , c r u d e o i l v i s c o s i t y a n d e m u l s i o n v i s c o s i t y R2= .71 .

E x p e r i m e n t a l c o n d i t i o n s a s in F i g . 8 .

D I S C U S S I O N

T h e s t a b il it y o f w a t e r - c o n t i n u o u s e m u l s i o n s h a s b e e n t h e s u b j ec t o f f u n d a -

m e n t a l r e s e a r c h f o r a lo n g p e r i o d o f t i m e . I t is b y n o w w e l l r e c o g n iz e d t h a t t h e

s u r fa c e f o r c e s i n v o l v e d i n t h e s t a b i li t y o f t h e s e e m u l s i o n s a r e e le c t r o s t a ti c r e -

p u l s i o n b e t w e e n t h e o i l d r o p l e ts , s te r ic e f f e c t o r i g i n a t in g f r o m a d s o r b e d p o l y -

m e r l a ye r s , p a r t i cl e s a d s o r b e d a t t h e o i l / w a t e r i n t e r f a c e a n d t h e s p e c i f i c a s s o -

c i a t io n t e n d e n c y o f t h e s u r f a c t a n t s t o f o r m l iq u i d c r y s t a ls w i t h a la m e l la r

g e o m e t r y . T h e e l e c t ro s t a t ic r e p u l s i o n i n t h e a q u e o u s e n v i r o n m e n t i s g e n e r a l l y

c r e a t e d b y t h e s t a b i li z e r t h e s u r f a c t a n t ) . I n o r d e r t o s c r e e n t h i s s t a b i li z i n g

m e c h a n i s m , t h e e m u l s i o n s a r e n o r m a l l y d e s t a b il iz e d b y t h e a d d i ti o n o f m u l t i-

v a l e n t e l e c t r o ly t e s . F o r o i l - c o n t i n u o u s e m u l s i o n s , t h e i m p o r t a n c e o f a r ep u l -

s i o n o f e le c t r o s ta t i c o r i g in i s n o l o n g e r d i s c u s s e d i n a se r i o u s w a y . T h e b a s i c

r e a s o n f o r t h i s i s t h a t t h e l o w p e r m i t t iv i t y m e d i u m w i l l c a n c e l t h e e l e c tr o s t a t ic

r e p u l s i o n a n d a n y i m p o r t a n c e o f m u l t i v a l e n t c o u n t e r - i o n s a s d e s ta b i li z e r s.

W h e n d i s c u s s i n g t h e r o le o f p a r t i cl e s a s s t a b i li z e r s f or c r u d e - o i l - c o n t i n u o u s

e m u l s i o n s , o n e g e n e r a l l y r e st r ic t s t h e d i s c u s s i o n t o c l a y s a n d w a x e s . O f t h e s e ,

a t le a s t f o r t h e c o n d i t i o n s s t u d i e d h e r e , w a x e s s h o u l d b e c o n s i d e r e d t o b e m o r e

i m p o r t a n t . T h e s iz e o f w a x p a r t i c le s h a s b e e n c o r r e la t e d t o t h e s t a b i l it y o f

c r u d e o il e m u l s i o n s . I t w a s f o u n d t h a t t o o l a rg e p a r ti c le s d o n o t e n h a n c e t h e

s t a b i li t y o f t h e e m u l s i o n . H e n c e , th e m e l t i n g a n d c r y s t a l l i z a t io n a n d r ec r y s-

t a l l iz a t i o n ) s e q u e n c e o f t h e w a x e s i s o f i m p o r t a n c e f o r t h e s t a b i l iz i n g p r o p e r -

t i e s o f t h e s e c o m p o u n d s [ 2 2 ] . I f t h e m e l t in g p o i n t i s e x c e ed e d , t h e w a x e s w i ll

m a i n l y a c t a s a c o m p o n e n t i n t h e c r u d e o i l b u l k a n d t h e i r a c t i v it y a t t h e o i l /

w a t e r i n t e r f a c e is n o r m a l l y s u b s t a n t i a l l y r e d u c e d . T h i s is c l e a rl y o n e r e a s o n

w h y a n i n c r e a s e in t h e t e m p e r a t u r e n o r m a l l y d es t ab i li z e s a c r u d e o il e m u l s io n .

T h e e x i s t e n c e o f n a t u r a l p o l y m e r s i n th e s e c r u d e o i ls c a n b e q u e s t i o n e d a n d

h e n c e a ls o t h e i m p o r t a n c e o f a st e ri c s t a b i li z a t io n a s a m e c h a n i s m d e p e n d e n t

o n i n d i g e n o u s p o l y m e r s . H o w e v e r d u e t o t h e a d d i t i o n o f p o l y m e r - b a s e d p r o -

d u c t i o n c h e m i c a l s i n d i f f e r e n t s t ep s i n t h e r e c o v e r y o f t h e c r u d e o il a s t e r ic

s t a b i li z a t io n o f t h e c r u d e o il e m u l s i o n s c a n b e m a d e p o s si bl e.

T h e a s s o c i a t io n o f s u r f a c e -a c t iv e a g e n t s a n d t h e i m p o r t a n c e o f s t r u c t u r e s

f o r m e d s h o u l d b e c o n s i d e r e d to h a v e s i g n i f ic a n t im p o r t a n c e w h e n d i s c u s si n g

t h e s t a b i li t y o f o i l - c o n t in u o u s e m u l s i o n s [ 2 6 - 2 8 ] . O n e n o r m a l l y sp e a k s o f

r ig i d a n d p r o t e c t iv e f il m a s a r e s u l t o f t h e a c c u m u l a t i o n o f s u r f a c e -a c t iv e m a -

t e r i a l a t t h e o i l / w a t e r i n t e rf a c e . A m o r e d e t a i l e d k n o w l e d g e o f t h e p r o p e r t i e s

o f t h i s f i lm a n d o f t h e d e t a i l e d m e c h a n i s m s i n v o l v e d i n i t s e f fe c t o n s t a b i l it y

is h o w e v e r m o s t l y l a c k in g . I t is t h o u g h o b v i o us t h a t o n e c a te g o r y o f c h e m i c a l

c o m p o u n d s o f im p o r t a n c e f o r t h e f o r m a t i o n o f a n i n t e r fa c i a l fi lm i n c r u d e o i l

e m u l s i o n s is t h e a s p h a l t e n e s . I n a r e c e n t p u b l ic a t i o n s o m e e x p e r i m e n t a l e v i-

d e n c e w a s g i v e n o n t h e a s s o c i a t i o n o f a s p h a l t e n e s a t t h e w a t e r / o i l i n t e r f a c e

[2 9 ] . I t w a s p o i n t e d o u t t h a t a s p h a l t e n e p a r t i c l e s a p p e a r t o b e r e g u l a r l y s t a c k e d

i n l a m e l l a r s t r u c tu r e s r e s e m b l i n g t h e s t r u c t u r e o f t h e l a m e l l a r li q u id cr y s ta l -

l in e m e s o p h a s e D w h i c h o cc u r s i n s u r f a c t a n t s y s t e m s a n d e n h a n c e s si gn if i-

c a n t l y t h e e m u l s i o n s t a b il it y .

U s e f u l i n f o r m a t i o n c a n b e e x t r a c t e d f ro m t h e p H d e p e n d e n c e . F i g u r e 5 c l e a rl y

i n d i c a t e s t h a t v e r y h i g h a n d l o w p H v a l u e s g iv e a r e s to r e d o r e v e n e n h a n c e d

s t a b il it y a s c o m p a r e d t o i n t e r m e d i a t e p H v a l ue s . C o n s i d e r i n g t h e s t a b il iz i n g

m e c h a n i s m s e a r li e r p r e s e n t e d t h e o b s e r v a t i o n i n F ig . 5 r e v e a ls so m e e x t r a

d e t a il s n o t a c c o u n t e d f o r e ar li e r. T h e p o l a r g r o u p s o r i g i n a ll y p r e s e n t i n t h e

i n t e r f a c ia l f i lm w i ll m o s t l ik e l y b e i o n i z e d a t t h e s e e x t r e m e p H v a l ue s . D e s p i t e

t h i s fa c t t h e e m u l s i o n s m a i n t a i n o r e v e n i n c r e a se t h e i r st a b il it y . N o c o n v e r -

s i o n t o w a t e r - c o n t i n u o u s e m u l s i o n s w il l t a k e p l a c e . T h i s s h o u l d b e t a k e n a s a n

i n d i c a t i o n o f a lo w n u m b e r o f i o n iz a b l e g r o u ps . H e n c e e x t r e m e p H v a l u e s a re

n o t c a p a b l e o f c r e a t i n g h i g h s u r f a c e c h a r g e d e n s i t ie s t h a t w o u l d d r a s t i c a ll y

c h a n g e t h e f il m p r o p e r ti e s b y i n t r o d u c i n g a n i n t e r n a l r e p u l s i o n i n t h e f il m

d e s t r o y i n g th e m e c h a n i c a l p r o p e r t ie s t h a t g iv e r is e to p r o t e c t i o n a g a i n s t c o a -

l e sc e n c e . A p o ss i b le m e c h a n i s m f o r e n h a n c e d s t a b i l it y i s t h e w e a k h y d r a t i o n

o f t h e d i s s o c ia t e d p o l a r i n t e r fa c i a l g r o u p s a t t h e v e r y h i g h a n d l o w p H v a l u e s.

T h i s h y d r a t i o n o f t h e f ew a v a il a bl e c h a r g e d e n d g r o u p s w i ll f u r t h e r e n h a n c e

t h e r i g i d it y o f t h e i n t e r f a c i a l f il m . F u r t h e r m o r e t h e s t a b i l i ty a t e x t r e m e p H

v a l u e s r e v e a ls t h e a b s e n c e o f p a r t i c l e s s t a b i li z in g t h e e m u l s i o n s b a s e d o n t h e s e

c r u d e oil s. M i n e r a l p a r t ic l e s w o u l d a t t h e s e e x t r e m e p H v a l u es h a v e d i f fe r e n t

w e t t i n g p r o p e r t i e s w h i c h w o u l d b e r e f l e c t e d i n a d i s lo c a t i o n a t t h e i n t e r f a c e

a n d a s a c o n s e q u e n c e e m u l s i o n i n s ta b i li ty . T h i s h a s b e e n o b s e r v e d f o r e m u l -

s i o n s b a s e d o n c r u d e o il s a n d s t a b i l i z e d b y S i 0 2 p a r t i c l e s [ 3 0 ] .

I n c r e a s e d t e m p e r a t u r e is k n o w n t o d e s t a b i li z e c ru d e o i l e m u l s i o n s . T h i s e f-

f e c t is a s u m o f t h e c h a n g e s in m a n y p a r a m e t e r s . T r iv i a ll y , i t h o ld s t h a t t h e

b u l k v i s c o si ty o f t h e c r u d e o il w il l d e c re a s e w i t h i n c r e a s i n g t e m p e r a t u r e , h e n c e

f a c i li ta t in g a n i n c r e a s e d c o l li si o n b e t w e e n t h e w a t e r d r o p l et s . A h i g h e r t h e r m a l

e n e r g y w i ll o f c o u r s e e n h a n c e t h e c o l li si o n f re q u e n c y o f d ro p l e ts . T h i s t r e n d is

n o t s u f f i c ie n t t o e x p l a i n t h e s e p a r a t i o n o f w a t e r ( t h e c o a l e s c en c e o f d r o p l e t s ) ,

s i n c e t h e s y s t e m c o u l d r e m a i n i n a f l o c c u l a t e d s t a te . E s s e n t i a l f o r t h e c o a l e s-

c e n c e w il l b e t h e c h a n g e s t a k i n g p l a c e i n t h e i n te r f a c ia l f i lm a s t h e t e m p e r a t u r e

i n c re a s e s. T h e i n te r f a c ia l v i sc o s i ty is k n o w n t o b e t e m p e r a t u r e s e n s it iv e . B u t

c o n t r a r y t o b u l k c r u d e v i sc o s it y , w h i c h f a ll s w i t h i n c r e a s i n g t e m p e r a t u r e , t h e

i n te r f a ci a l v is c o s it y m a y d e c r ea s e , i n cr e a s e o r r e m a i n u n c h a n g e d , d e p e n d i n g

o n t h e t y p e o f in t e r f a c e [1 4 ]. A n o t h e r p a r a m e t e r o f si g n if ic a n c e is t h e c o m -

p r e s s i b i l it y o f t h e i n t e r f a c i a l fi lm . I t h a s b e e n r e p o r t e d t h a t a c o a l e s c e n c e o f

w a t e r d r o p l e t s i n a w a t e r - i n - c r u d e o i l e m u l s i o n is a c c o m p a n i e d b y a r e d u c t i o n

i n s u r f a ce a r e a a n d , h e n c e , a c o m p r e s s i o n o f t h e a d s o r b e d i n d i g e n o u s c r u d e o i l

s u r f a c t a n t s [ 14 ]. F o r m a t i o n o f a n i n c o m p r e s s i b l e a n d n o n - r e l a x i n g i n t e rf a c ia l

f i l m a t h i g h t e m p e r a t u r e s i s i n d ic a t iv e o f a h i g h e m u l s i o n s ta b il it y . T h e c o m -

p r e s s i b i li t y o f t h e f i lm s h o u l d b e r e g a r d e d a s t h e r e s u l t o f a l t e r e d s o l u b i li ty

p r o p e r t i e s o f t h e c r u d e o i l s u r f a c t a n t s o r t h e r e s u l t o f a d e g a s s i n g p r o c e s s i n

t h e f i lm [ 1 4 ]. I n a d d i t i o n to t h e s e m e c h a n i s m s , o n e s h o u l d a l so b e a w a r e o f

t h e c h a n g e s o c c u r r i n g i n t h e a s s o c i a t i o n p a t t e r n o f t h e c r u d e o il s u r f a c t a n t s a s

a r e s u l t o f in c r e a s i n g t e m p e r a t u r e [3 1 ]. E s s e n t ia l ly , t h e p a c k i n g c o n d i t i o n s o f

t h e m o l e c u l e s w i ll b e d i f f e r e n t, a n d h e n c e a d e s t a b i l i z a t io n o f t h e e m u l s i o n w i ll

O u r p r e s e n t s t u d y s h o w s t h a t t h e c o r r e l a t io n b e t w e e n o b s e r v e d a n d c a lc u -

l a t e d s t a b il it y i s d e s c r ib e d a c c e p t a b l y b y a n e q u a t i o n c o n t a i n i n g th r e e c r u d e

o il p a r a m e t e r s . T h e s e p a r a m e t e r s a r e t h e c o n t e n t o f w a xe s , t h e c r u d e o il v is -

c o s i t y a n d t h e e m u l s i o n v is c o s i ty , i n o r d e r o f in c r e a s i n g s i g n i fi c a n c e .

T h a t u s e fu l i n f o r m a t i o n c a n n o t b e e x t r a c t e d o n p a r a m e t e r s l i ke th e c o n t e n t

o f p o l a r c o m p o u n d s a n d a s p h a l t e n e s d o e s n o t i m p l y t h a t t h e s e a r e i n s i g n if ic a n t

f o r e m u l s i o n s t a b il it y . I t c a n , h o w e v e r , b e c o n c l u d e d t h a t t h e p r o p e r t i e s o f

a c t i v e c o n s t i t u e n t s , w h e t h e r t h e y a r e s u r f a c e a c ti v e a n d / o r a g g r e g a t e- f o r m i n g ,

is n o t r e f le c t e d b y t h e g r o ss w e i g h t o f t h e s e o p e r a t i o n a l ly d e f i n e d p e t r o l e u m

f r a c t i o n s .

T o s o m e e x t e n t , t h e s a m e a r g u m e n t a l s o a p p l i e s t o t h e w a x f r a c t i o n , a l -

t h o u g h w a x a m o u n t s in e x c es s o f a b o u t 6 c a n be s h o w n e m p i r i c a ll y t o c o n -

t r i b u t e t o e m u l s i o n s ta b il it y . H o w e v e r , t h e m o s t i m p o r t a n t s t a b il iz i n g c o n tr i -

b u t i o n f r o m w a x c o m p o n e n t s i s a s s o c i a t e d w i t h w a x p a r t i c l e n u m b e r a n d

m o r p h o l o g y a n d , h e n c e , c lo s e ly r e l a t e d to w a x m o l e c u l a r s t r u c t u r e a n d t h e

t e m p e r a t u r e h i s t o r y o f t h e c r u d e o i l.

A l t h o u g h t h e i n te r ra c ia l t e n s i o n m e a s u r e d b y t h e r in g m e t h o d o n l y w e a k l y

c o r r e la t e s w i t h e m u l s i o n s t a b il it y , t h e i m p o r t a n c e o f in t e rr a c ia l f i l m p r o p e r t i e s

s h o u l d n o t be u n d e r e s t i m a t e d . I n fa c t, a t 50 w a t e r c u t, i m p l y i n g a sm a l l m e a n

d r o p l e t d i s t a n c e , c o a le s c e n c e m u s t r e a ll y b e t h e r a t e l i m i t i n g s te p i n t h e s e pa -

r a t i o n p r o c e ss . A c t u a l ly , t h e c o r r e l a t i o n s t u d y h a s b e e n p e r f o r m e d u n d e r c o n -

d i t io n s f o c u s i n g o n f i l m p r o p e r t i e s , w i t h a m i n i m a l c o n t r i b u t i o n f r o m S t o k e s

s e d i m e n t a t i o n p r o c e ss e s . T h i s e x p l a i n s t h e r e l a ti v e i n s i g n i fi c a n c e o f c ru d e o i l

v i s c o s it y b y i ts e lf . T h e w a t e r d r o p l e t c o a l e s c e n c e r a t e s e e m s t o b e r e l a t e d c l e a r l y

t o e m u l s i o n v i s co s it y , e s p e c ia l ly w h e n m e a s u r e d i n t e r m s o f th e c r u d e o i l v is -

c o s it y , a s in d i c a t e d b y E q n 4 ) . T h e f u ll i m p l i c a t i o n s o f t h i s o b s e r v a t i o n a r e

y e t t o b e u n d e r s t o o d , b u t f u r t h e r e x p e r i m e n t a l e f fo r ts , i n c l u d i n g c a re f u l ly d e -

s i g n e d m o d e l s y s t e m s , m a y b e o f g r e a t v a l u e , e s p e ci a ll y w h e n d i s c u s s in g a c o r -

r e l a t io n b e t w e e n i n t e r f a c i a l p r o p e r t ie s a n d e m u l s i o n v is c o si ty .

I n o r d e r t o s h o w t h e i m p o r t a n c e o f c h a n g e s i n t h e i n t e r fa c i a l fi lm , w e r e p o r t

i n s u b s e q u e n t w o r k s o n t h e i n f l u e n c e o f d e m u l s if i e rs o n f i lm p r o p e r t i e s a n d ,

f u r t h e r , o n t h e s t a b i li t y o f m o d e l c r u d e o i l e m u l s i o n s b u i lt u p b y s u r f a c t a n t s

w i t h d i f f e r e n t ty p e s o f a ss o c i a t io n p a t t e r n s .

A C K N O W L E D G E M E N T S

T h e I n s t i t u t e fo r S u r f a c e C h e m i s t ry Y K I ) a c k n o w l e d g es t h e f in a n c i a l s u p-

p o r t fr o m S t a to i l A / S C o n t r a c t n o . T . 9 01 5 ) , w h i c h m a d e t h e w o r k a t t h e

i n s t i t u t e i n t h e a r e a o f c r u d e o i l e m u l s i o n s p os s ib l e. V a l u a b l e c o m m e n t s b y

P r o f e s s o r P e r S t e n i u s o n a p r e l i m i n a r y m a n u s c r i p t a r e al so a c k n o w l e d g e d .

R E F E R E N C E S

1 F .G . C o t t r e l l , U .S . P a te n t 9 87 .1 1 4 1 9 1 1 ) .

2 F . G . C o t t r e l l a n d A . C h e e v e r , U . S . P a t e n t 9 87 .1 17 1 9 1 1 ) .

3 A .G . C o t t r e l l a n d J .B . S p e e d , U .S . P a te n t 9 87 .1 15 {1 9 1 1 ) .

4 A .G . C o t t r e l l a n d J .B . S p e e d , U .S . P a te n t 9 8 7.1 16 1 9 1 1 ) .

5 D .B . Do w, U .S . De p . C o m m. B u l l . , 2 5 0 1 9 2 6 ) .

6 G .B . S h e a , U .S . B u r . M in e s , B u l l . , 4 1 7 1 9 3 9 ) .

7 A .S .C . L a w re n c e , C h e m . In d . L o n d o n ) , 3 9 1 9 4 8 ) 6 15 .

8 J .L . W ig g in s , P e t . E n g . In t . , 2 9 B {1 9 57 ) 4 7.

9 F . S t e i n h a u f f , P e t r o l e u m L o n d o n ) , 2 5 1 9 6 2 ) 2 94 .

1 0 P .L . B a n s b a c h , O i l Ga s J . , 5 2 1 9 7 0 ) 87 .

11 C . M . B l a i r , C h e m . I n d . L o n d o n ) , 1 9 6 0 ) 5 38 .

1 2 J .E . S t r a s s n e r , J . P e t . T e c h n o l . , 2 0 1 9 6 8 ) 3 03 .

1 3 A .A . P e t r o v a n d S .S . B la to v a , T e c h n o l . T o p l io , M a s e l , 1 7 1 9 7 4 ) 3 2.

1 4 T . J . J o n e s , E . L . N e u s t a d t e r a n d K . P . W h i t t i n g h a m , J . C a n . P e t r . T e c h n o l ., 17 { 19 78 ) 1 0 0.

15 G . D . M . M a c K a y , A . B . M c L e a n , O . J. B e t a n c o u r t a n d B .D . J o h n s o n , J . In s t . P e t . L o n d o n ) ,

59 197 3) 164.

1 6 E . P a p i re r , C . B o u rg e o i s , B . S i f f e r t a n d H . B a la rd , F u e l , 6 1 1 9 8 2 ) 7 3 2 .

1 7 H . N . D u n n i n g , J . W . M o o r e a n d M . O . D e n e k a s , I n d . E n g . C h e m . , 4 5 1 9 5 3 ) 1 7 59 .

1 8 H .N . Du n n in g , J . C o l lo id S c i . , 8 1 9 5 3 ) 27 9 .

1 9 G . P . C a n e v a r i , P r o c e e d i n g s o f J o i n t C o n f e r e n c e o n P r e v e n t i o n a n d C o n t r o l o f O i l S p i l l s , A P I ,

New Y ork , 1969 .

2 0 A . L . B r i d i e , T . H . W a n d e r s , W . Z e g ve l d a n d H . B . v a n d e r H e i d e , M a r i n e P o l l u t . B u l l ., 11

1980) 343.

21 E.L. Neustadter, K.P. Wittingham and D.E. Graham, in D.O. Shah Ed.), Surface Phenom-

ena in Enhanced Oil Recovery, Plenum Press, New York, 1981, p. 307.

22 D.E. Graham, A. StockweU and D.G. Thompson, in P.H. Ogden Ed.), Chemicals in Oil

Industry, The Royal Society of Chemistry, London, 1983, p. 73.

23 E.D. Burger, T.K. Perkins and J.H. Striegler, J. Pet. Technol., 33 1981 ) 1075.

24 K.J. Lissant, Demulsification, Industrial Applications, Marcel Dekker, New York, 1983.

25 E.G. Richardson, Kolloid Z., 65 1933) 32.

26 S. Friberg, L. MandeU and M. Larsson, J. Colloid Interface Sci., 29 1969) 155.

27 S. Friberg and L. Rydhag, Kolloid Z. Z. Polym., 244 1971) 233.

28 S. Friherg Ed.), Food Emulsions, Marcel Dekker, New York, 1976.

29 B. Siffert, I. Bourgeois and E. Papirer, Fuel, 63 1984) 834.

30 J.J. Oren and G.D.M. MacKay, Fuel, 56 1977) 382.

31 For a review, see: J. SjSblom, P. Stenius and I. Danielsson, in M. Schick Ed.), Non-ionic

Surfactants: Physical Chemistry, 2nd edn, Surfactant Science Series, Vol. 23, Marcel Dekker,

New York, 1987, Ch. 7, p. 369.

Water-In-crude Oil Emulsions From the Norwegian Continental Shelf Part I. Formation,

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