Api report 82 45 1984 scan (american petroleum institute)

% polystyrene 900,000 molecular weight in carbon disulfide solution at temperature as indicated in each figure and run between parallel plates at 3% strain.Clark, et.al., Polym Preprin

Princeton University

Princeton, New Jersey 08544

V MATERIALS AND PREPARATION

V I RESULTS AND DISCUSSION

V I I KINETIC THEORY MODELING

VIII.RECOMMENDATIONS FOR FUTURE RESEARCH

I X RECOMMENDATIONS FOR INSTRUMENTATION

APPENDICES

A Wall S l i p Corrections f o r Coaxial C y l i n d e r Viscometer

B Impingement Mixer Schematic and P a r t s L i s t

C C a p i l l a r y Viscometer S c h e m a t i c a n d P a r t s L i s t

D Summary of Experiments P e r f o r m e d , p r e p a r e d by

D r John Cameron, API S t e e r i n g Committee Vice-chairman

S T D A P I / P E T R O 8 2 - 4 5 - E N G L O 7 3 2 2 9 U 0 5 7 7 b 8 2 8 2 2 E

2

I ,INTROD.$TION

T h i s is t h e f i n a l report on our research conducted under the American

Petroleum I n s t i t u t e ' s PRAC Project 82-45 e n t i t l e d " R h e o l o g i c a l C h a r a c t e r i z a -

t i o n of F r a c t u r i n g F l u i d s " The project was i n i t i a t e d by the American Petroleum

I n s t i t u t e (-1) because: 1) the e x p e n s e o f h y d r a u l i c fr a c t u r i n g makes it

d e s i r a b l e t o u n d e r s t a n d the process f u l l y , i n c l u d i n g the rheology of t h e f r a c -

t u r i n g f l u i d , t o e n s u r e a s u c c e s s f u l f r a c t u r i n g o p e r a t i o n , and 2 ) d u r i n g a round-robin t e s t i n g program by s e v e r a l l a b o r a t o r i e s t h e v i s c o s i t i e s reported

by t h e p a r t i c i p a n t s f o r i d e n t i c a l g e l f o r m u l a t i o n s v a r i e d by 1000%

The purpose of t h i s report t o t o p r o v i d e a working guide t o rheology of

guar g e l s We f i r s t provide, i n S e c t i o n 11, a summary of t h e s i g n i f i c a n t

r e s u l t s and conclusions from the f i r s t y e a r of t h i s i n v e s t i g a t i o n I n S e c t i o n

I11 dynamic o s c i l l a t o r y shear measurements, which are used t o study guar

r h e o l o g y a n d g u a r g e l s t r u c t u r e , are described Dynamic o s c i l l a t o r y s h e a r

measurements can be d i r e c t l y related t o t h e number of network c r o s s l i n k s

These measurements and their i n t e r p r e t a t i o n are d i s c u s s e d i n d e t a i l , s i n c e t h e y are probably less f a m i l i a r t o r e s e a r c h e r i n t h e o i l production research area

t h a n are steady shear measurements In Section I V we describe the r h e o l o g i -

c a l instruments used i n this s t u d y I n S e c t i o n V t h e p r e p a r a t i o n of guar

samples is d e t a i l e d The composition of the model g u a r g e l u s e d i n t h i s s t u d y

w a s s p e c i f i e d by the API S t e e r i n g Committee Our o b s e r v a t i o n s on t h e f a c -

t o r s c o n t r o l l i n g gel r h e o l o g y , in c l u d i n g c h e m i c a l e f f e c t s , sample p r e p a r a t i o n

e f f e c t s , a n d f l o w h i s t o r y effects are p r e s e n t e d i n S e c t i o n VI I n S e c t i o n V I 1 a model t h a t d e s c r i b e s t h e rheology o f g e l l i n g f l u i d s i s described The model i s based on the temporary network theories used t o d e s c r i b e t h e r h e o l o g y of

polymer melts and s o l u t i o n s To t h i s th e o r y we have incorporated the che-

m i c a l k i n e t i c s o f metal i o n a d s o r p t i o n o n t o the guar polymer backbone and

s u b s e q u e n t polymer-polymer c r o s s l i n k i n g I n t h e f i n a l s e c t i o n s recommendations

f o r r h e o l o g i c a l i n s t r u m e n t a t i o n a n d f o r f u t u r e r e s e a r c h are presented

A t the q u a r t e r l y m e e t i n g s w i t h t h e A P I Committee

s e v e r a l h u n d r e d p a g e s of e x p e r i m e n t a l data were

d a t a are n o t in c l u d e d in this report Rather the

drawn from t h o s e d a t a are p r e s e n t e d a l o n g w i t h

s u p p o r t t h o s e c o n c l u s i o n s The o r i g i n a l data are on

t i o n s d e p a r t m e n t and can be obtained through the API

have been used t o s t u d y

t h e r h e o l o g y of g u a r g e l s Dynamic o s c i l l a t o r y measurements have been used t o

s t u d y t h e slow h y d r a t i o n of g u a r polymer and t h e e f f e c t s of chemical composition and mixing on guar g e l s t r u c t u r e S t e a d y s h e a r measurements have been used t o

s i m u l a t e p r o c e s s c o n d i t i o n s Major c o n c l u s i o n s , p r e s e n t e d i n t h e body of t h i s report, i n c l u d e t h e f o l l o w i n g :

R e s u l t s from polymer k i n e t i c t h e o r y c a n be used t o r e l a t e the measured storage modulus, G ' , t o t h e c r o s s l i n k d e n s i t y i n t h e g u a r gel

Aged t i t a n a t e s o l u t i o n s p r o d u c e g e l s w i t h iower v a l u e s of G I ; and

t h e r e f o r e , dynamic o s c i l l a t o r y measurements can be used t o q u a n t i f y

t i t a n a t e r e a c t i v i t y

S T D - A P I I P E T R O 8 2 - 4 5 - E N G L 0 7 3 2 2 7 0 05'77b83 7 b 7

Adding d i k e t o n e ( t h a t is, a c e t y l a c e t o n e ) to modify the rate of r e a c t i o n

d o e s n o t j u s t s l o w down t h e r e a c t i o n , b u t it also p r e v e n t s t h e gel from

c r o s s l i n k i n g t o t h e same e x t e n t a t room temperature as g e l s w i t h o u t

added a c e t y l a c e t o n e Mixing i s shown to p l a y a crucial role i n t h e development of gel s t r u c -

t u r e Poor mixing appears t o produce microscopically inhomogeneous gel

networks that have h i g h e r l e v e l s of e l a s t i c i t y t h a n homogeneous gels

To P r o d u c e i n t i m a t e l y & x e d f l u i d s we have developed a novel impingement mixing device -

Measurements of the s t e a d y s h e a r v i s c o s i t y of gels i n d i c a t e t h a t wall

s l i p is occurring However, c o n v e n t i o n a l r h e o l o g i c a l t e c h n i q u e s f o r

c a l c u l a t i n g wall s l i p velocities h a v e g i v e n c o n t r a d i c t o r y r e s u l t s There i s a need f o r direct measurements of v e l o c i t y f i e l d s i n s h e a r flow t o c l a r i f y t h e mechanism of wall s l i p I n t h e next y e a r w e w i l l

be conducting laser doppler measurements t o address t h i s problem

Under q u i e s c e n t c o n d i t i o n s dynamic o s c i l l a t o r y measurements show t h a t

t h e g u a r c o n t i n u e s t o c r o s s l i n k o v e r a time scale of about 15 minutes The s t e a d y s h e a r measurements show t h a t s h e a r i n c r e a s e s the rate of

r e a c t i o n

A n o v e l network t h e o r y c o u p l e d w i t h c h e m i c a l r e a c t i o n k i n e t i c s is

proposed; material f u n c t i o n s c a n be expressed a n a l y t i c a l l y This model

p r o v i d e s a framework f o r modeling and p r e d i c t i n g r h e o l o g i c a l p r o p e r t i e s

of reacting g e l s

111 RHEOLOGICAL MEASUREMENTS

A Dynamic O s c i l l a t o r y Measurements

Dynamic o s c i l l a t o r y s h e a r e x p e r i m e n t s , which measure the l i n e a r visco-

e l a s t i c response of materials, are acknowledged t o be t h e most valuable probes

of g e l o r network s t r u c t u r e Though s t e a d y s h e a r measurements are necessary t o

d u p l i c a t e process c o n d i t i o n s , the o s c i l l a t o r y measurements give more i n s i g h t

i n t o the properties o f t h e g e l t h a n do s t e a d y s h e a r measurements When

i n t e r p r e t e d u s i n g classical n e t w o r k t h e o r y , l i n e a r viscoelastic measurements can

be used t o d e t e r m i n e t h e k i n e t i c s of g e l f o r m a t i o n , t h e c r o s s l i n k d e n s i t y of a gel, or t h e s h e a r d e g r a d a t i o n o f g e l s t r u c t u r e The g e l a t i o n of p o l y v i n y l alco-

h o l a n d g e l a t i n g e l s h a s b e e n s t u d i e d by a number of r e s e a r c h e r s ( 1 , 2 , 3 ) , and

a t P r i n c e t o n we have used these measurements t o study polyacrylamide gels used

as p e r m e a b i l i t y c o n t r o l a g e n t s i n enhanced o i l r e c o v e r y ( 4 , s ) For an introduc-

t i o n t o t h e f i e l d of l i n e a r v i s c o e l a s t i c i t y t h e reader i s r e f e r r e d t o t h e t e x t

by Ferry ( 6 )

I n a l i n e a r v i s c o - e l a s t i c measurement an o s c i l l a t o r y shear s t r a i n ,

y ( t ) , i s imposed on a sample,

S T D A P I / P E T R O 8 2 - 4 5 - E N G L PI 0 7 3 2 2 9 0 0 5 7 7 b A 4 h T 5 m

4

where Yo i s t h e maximum value of t h e s t r a i n

Experimentally this is accomplished by p l a c i n g a sample i n a cone and p l a t e geometry, a parallel plate geometry, o r between concentric cylinders i n a

Couette geometry, and then imposing a t o r s i o n a l o s c i l l a t i o n on one plate, cone,

o r cylinder The r e s u l t i n g stress on t h e s t a t i o n a r y plate, cone, o r c y l i n d e r

w i l l oscillate w i t h the imposed frequency w, b u t will be o u t of p h a s e w i t h t h e

f o r c i n g o s c i l l a t i o n The measured stress can be f a c t o r e d i n t o two components, one i n phase with the displacepent and one 90 d e g r e e s o u t of phase with the

displacement:

The in-phase stress d e f i n e s a s t o r a g e modulus G I t h a t gives information about

t h e e l a s t i c i t y and network structure, whereas the out-of-phase component d e f i n e s

a loss modulus G" t h a t gives i n f o r m a t i o n a b o u t t h e v i s c o u s o r d i s s i p a t i v e p r o -

p e r t i e s of t h e f l u i d The frequency and s t r a i n dependence of t h e s t o r a g e and

loss moduli, G I and G" r e s p e c t i v e l y , p r o v i d e i n f o r m a t i o n a b o u t t h e s t a t e of the

f l u i d For a n u n c r o s s l i n k e d g u a r s o l u t i o n b o t h G I and G" decrease with

decreasing frequency, w i t h G" l y i n g above G I As a g e l c r o s s l i n k s G I rises u n t i l

i t i s horizontal independent of frequency As an example, t h i s p r o g r e s s i o n i s

shown i n Fig 1 f o r t h e g e l a t i o n of a p o l y s t y r e n e / c a r b o n d i s u l f i d e s o l u t i o n as temperature is decreased As we will show i n S e c t i o n V I , G I can be monitored as

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

network s t r u c t u r e , t h e n G I will decrease with i n c r e a s i n g s t r a i n

Classical network theory ( 7 ) shows t h a t G ' , i n t h e low frequency region where G I i s independent of frequency, i s p r o p o r t i o n a l t o t h e number d e n s i t y of

c r o s s l i n k s i n t h e g e l :

where g i s a c o n s t a n t of o r d e r one, n i s t h e number d e n s i t y of c r o s s l i n k s , k is

t h e Boltzmann constant, T is the absolute temperature, and Ge is a c o n t r i b u t i o n

t o the modulus fram molecular entanglements For aqueous gels G e i s very small

It i s p o s s i b l e t o f o l l o w the k i n e t i c s of g e l formation by t a k i n g t h e time d e r i -

v a t i v e of Eq 3:

dn 1 d G '

d t kT d t

c = - -

Likewise, t h e d e s t r u c t i o n o f gel s t r u c t u r e by s h e a r can be monitored by

measuring G I a f t e r exposure t o steady shear The r e s u l t s c a n be i n t e r p r e t e d i n

terms of t h e breakdown i n t h e number of c r o s s l i n k p o i n t s

, Fig.1a-d Storage ((3') and loss (G") moduli as a function of frequency of a

: 8.5 wt % polystyrene (900,000 molecular weight) in carbon disulfide solution

at temperature as indicated in each figure and run between parallel plates

at 3% strain.(Clark, et.al., Polym Preprintrs 24,87( 1983))

- - -

5

I V ,EQUIPMENT

A Rheometrics System I V Rheometer:

Most of the measurements reported here were conducted on our Rheo-

metrics Inc System I V rheometer (Rheometrics, Inc., Piscataway, NJ) This

s t a t e - o f - t h e - a r t i n s t r u m e n t shown i n Fig 2 has s e v e r a l motor and transducer

o p t i o n s The i n s t r u m e n t i s f u l l y automated and a l l data a c q u i s i t i o n and manipu-

l a t i o n i s under computer control For measurements w i t h the Fluids Transducer

a c i r c u l a t i n g water bath i s a i a i l a b l e with a temperature range from -2OOC t o

8OoC

For most of the g u a r s o l u t i o n measurements a Fluids Transducer w i t h a

1 0 g-cm maximum t o r q u e and 100 g maximum normal force was used This F l u i d s Transducer allows s t e a d y shear measuremements of f l u i d v i s c o s i t y , dynamic

o s c i l l a t o r y s h e a r measurements, and, w i t h a some m o d i f i c a t i o n t o t h e d r i v e u n i t ,

s t e a d y shear followed by o s c i l l a t o r y shear For polymer s o l u t i o n s and g e l s t h e range of f r e q u e n c i e s and shear rates over which measurements can be made i s usually determined by t h e minimum torque range of the t r a n s d u c e r ( a b o u t 1/1000

t o 1/500 of the maximum t o r q u e ) F r e q u e n c i e s from 0.01 t o 100 rad/$ a r e

accessible and s t e a d y s h e a r rates from 0.01 t o 10,000 s-l The F l u i d s

Transducers can be run with cone-and-plate, parallel plate, or Couette

geometries

For dynamic o s c i l l a t o r y measurements on g u a r g e l s t h e 1 0 g-cm t r a n s -

d u c e r i s ideal; however, t h e t o r q u e r a n g e of this t r a n s d u c e r i s quickly exceeded

i f s t e a d y shear measurements are attempted on gels Therefore, f o r the bulk of

t h e gel measurements a Fluids Transducer with a 100 g-cm torque range was used

For our System I V rheometer we have a high temperature and pressure

c e l l t h a t allows measurement of f l u i d v i s c o s i t y and dynamic moduli under

p r e s s u r e s t o 4 5 0 p s i and t e m p e r a t u r e s t o 300'C However we generally found it more convenient to perform high temperature measurements on a Rheometrics

P r e s s u r e Rheometer, described below, rather t h e n on our System I V

B Rheometrics Inc Pressure Rheometer:

Measurements of gel properties a t e l e v a t e d t e m p e r a t u r e s were performed

o n a Rheometrics Pressure Rheometer located a t Rheometrics Inc laboratories i n

Piscataway, NJ The i n s t r u m e n t has a unique sealed sample chamber w i t h a C o u e t t e geometry Steady shear and dynamic o s c i l l a t o r y shear measurements over the same range of shear rates and frequencies spanned by the System I V Fluids Transducer

are p o s s i b l e The t o r q u e s e n s i t i v i t y of the P r e s s u r e Rheometer corresponds ap- proximately t o t h a t of the 100 g-cm Fluids Transducer It i s possible t o seal

a n d p r e s s u r i z e the sample c e l l t o run samples a t temperatures above the normal

b o i l i n g p o i n t of water It is somewhat awkward t o load and mount the sample cup the process takes 2-3 minutes Modifications t o allow o n - l i n e i n t r o d u c t i o n

of the sample t o the cup have b e e n s u g g e s t e d t o the manufacturer

Fig.2 S y s t e m I V R h e o m e t e r

S T D A P I / P E T R O B2-L.I5-ENGL m 0732270 0 5 7 7 b B d 2 4 0 SS

6

C Impingement Mixing Device:

The homogeneity achieved d u r i n g the mixing of the guar and t i t a n a t e

s o l u t i o n s and s h e a r h i s t o r y of the f l u i d as it c r o s s l i n k s d e t e r m i n e s the g e l properties The recommended p r o c e d u r e of mixing the g u a r s o l u t i o n a n d t i t a n a t e

s o l u t i o n i n a blender and then t r a n s f e r r i n g the preformed gel t o t h e v i s c o m e t e r

y i e l d s i r r e p r o d u c i b l e r e s u l t s T h i s will be discussed below To circumvent this problem, an impingement mixing d e v i c e was f a b r i c a t e d t h a t i n t i m a t e l y mixes the t

wo streams and i n j e c t s t h e m d i r e c t l y i n t o the rheometer t e s t c e l l (Fig 3 ) The

d e v i c e c o n s i s t s of a s t a i n l e s s ' s t e e l double a c t i n g p n e u m a t i c c y l i n d e r that is mechanically coupled t o a-microliter glass syringe The pneumatic cylinder i s

p r e s s u r i z e d w i t h n i t r o g e n at 200 p s i t o f o r c e g u a r s o l u t i o n i n the c y l i n d e r a n d

t i t a n a t e s o l u t i o n i n the syringe through an impingement mixing head; t h e mixture then flows through a packed bed mixing section The packed bed c o n s i s t s of t h r e e

i n c h e s of a 1/4" OD s t a i n l e s s s t e e l tube packed with 24-32 mesh (0.71 - 0.50 mm)

sand During i n j e c t i o n through the sand pack the Reynolds number is about one, based on a mean h y d r a u l i c radius f o r the sand pack and t h e v i s c o s i t y of t h e

uncrosslinked guar The c o n n e c t i o n s i n the device are made w i t h 1/8" t e f l o n

t u b i n g A three-way valve is used t o d i v e r t f l u i d either to waste or t o t h e rheometer cell The f l u i d fhws d i r e c t l y i n t o the rheometer c e l l and the dynamic

o s c i l l a t o r y measurement can be i n i t i a t e d e v e n b e f o r e t h e f l u i d f i l l s the gap The t o t a l time between the i n i t i a l c o n t a c t i n g of t h e g u a r and metal i o n s o l u -

t i o n s and t h e start of a dynamic o s c i l l a t o r y e x p e r i m e n t is on t h e order of 5 t o

1 0 seconds For a s t e a d y shear experiment the tube connecting the impingement mixer and the rheometer cup must be disconnected so that time t o i n i t i a t e a n experiment i s less t h a n 1 minute The schematic and parts l i s t f o r the impinge- ment mixer is g i v e n i n Appendix 8

D C a p i l l a r y Viscometer:

A p r e l i m i n a r y capillary viscometer has been designed and assembled The

s h e a r h i s t o r y d e p e n d e n c e of these gels, as shown i n S e c t i o n VI, convinced us

t h a t r a t h e r t h a n making a c i r c u l a t i n g loop u s i n g a pump, a better d e s i g n f o r o u r

v e r y small scale l a b work would be a l o n g c a p i l l a r y i n which the f l u i d i s pumped back and f o r t h I n t h i s way the f l u i d is u n d e r c o n s t a n t s h e a r ( e x c l u d i n g the

s h o r t times needed t o reverse t h e d i r e c t i o n of t h e f l o w ) The viscometer is

b e i n g c o n t r o l l e d by a n IBM p e r s o n a l computer with a Tecmar Inc A/D and D/A

board F u r t h e r d e t a i l s and r e s u l t s on t h i s d e v i c e will be p r e s e n t e d i n f u t u r e

p r o g r e s s r e p o r t s u n d e r n e x t y e a r ' s r e s e a r c h p r o j e c t The schematic of the

c a p i l l a r y v i s c o m e t e r i s g i v e n i n Appendix C

The e x a c t f o r m u l a t i o n of the guar g e l was s p e c i f i e d by the API Committee monitoring this project Special l o t s of hydroxypropyl guar and Tyzor AA t i t a -

n a t e were r e s e r v e d f o r this s t u d y by Celanese and DuPont, r e s p e c t i v e l y The

f o l l o w i n g f o r m u l a t i o n was used t o produce a 4 0 lb/Mgal g e l :

500 m l d i s t i l l e d water

2.4 g hydroxypropyl guar (Celanese SCN 9574)

0 6 g sodium d i a c e t a t e b u f f e r ( C e l a n e s e SCN 9744)

10 g a n a l y t i c a l g r a d e KCL ( F i s h e r l o t 722797)

0.1 25 m l 25% glutaraldehyde i n water ( E a s t n a n Kodak l o t

E l 1 A )

2 m l of ( 9 : l ) s o l u t i o n by volume isopropyl alcohol

( J T Baker) and Tyzor AA t i t a n a t e (DuPont)

The base guar ( w i t h & c r o s s l i n k i n g a g e n t ) is prepared using an Osterizer

blender s e t a t low speed, A timer and variac are connected with the blender i n series t o c o n t r o l mixing t i m e and speed The s o l u t i o n i s prepared i n t h e f o l -

lowing way The blender, w i t h 500 m l of water i n t h e p i t c h e r , is s e t a t a low

speed t o produce a shalluw vortex The hydroxypropyl guar is sprinkled slowly on

t h e f r e e s u r f a c e t o produce a uniform dispersion The potassium chloride, sodium

d i a c e t a t e and glutaraldehyde are q u i c k l y added The t o t a l mixing time i s three minutes The s o l u t i o n i s then t r a n s f e r r e d t o a n o t h e r c o n t a i n e r and allowed t o

mix f o r a b o u t 20 hours on a l o w shear tumbling mixer

To prepare crosslinked guars 'for rheological s t u d i e s two procedures were used During t h e f i r s t h a l f y e a r t h e s o l u t i o n s were mixed by hand, and i n t h e

l a s t half year the impingement mixing device was used In mixing by hand, 10 m l

of base guar solution i s placed i n a beaker, followed by a p r o p o r t i o n a l amount

of Tyzor AA ( d i l u t e d w i t h i s o p r o p a n o l ) The s o l u t i o n i s stirred vigorously with

a g l a s s s t i r r i n g rod for 30 seconds and t r a n s f e r r e d i n t o t h e rheometer cup The rheometer stage is t h e n c l o s e d t o s e t the proper gap and t h e t e s t begins This technique proved more r e p r o d u c i b l e t h a n mixing the guar and t i t a n a t e i n a

blender, The good r e p r o d u c i b i l i t y of dynamic o s c i l l a t o r y measurements f o r

samples mixed by hand i s shown i n Fig 4 However, v a r i a t i o n i n t h e hand mixing resulted in inadequate homogenization and t i m e delays which caused v a r i a t i o n s i n

s t e a d y s h e a r measurements This l e d t o our development of t h e impingement

mixer Subsequent studies with the impingement mixer have shown t h a t mixing

also influences dynamic o s c i l l a t o r y measurements (Section VI.B.la) Because it '

was n o t possible t o g e t the c r o s s - s e c t i o n s of the guar cylinder and t i t a n a t e

s y r i n g e i n e x a c t l y t h e correct ratios, extra isopropanol was added to t h e t i t a -

n a t e s o l u t i o n s t o o b t a i n the correct t i t a n a t e volume for the syringe The added isopropanol d i d n o t a f f e c t the g e l a t i o n k i n e t i c s ( S e c t i o n V.A.5) I n a l l cases

t h e Tyzor AA c o n c e n t r a t i o n i n the f i n a l g e l corresonded t o t h a t s p e c i f i e d i n t h e

r e c i p e above

F o r e x p e r i m e n t s l a s t i n g more than about 10 minutes, t h e f r e e l i q u i d s u r f a c e

is covered with mineral o i l t o prevent evaporation The mineral o i l i s

immiscible i n t h e g u a r s o l u t i o n and does n o t a f f e c t the t o r q u e s i g n a l s Between runs the rheometer tools are cleaned with water, followed by alcohol Thorough

c l e a n i n g i s required t o remove o i l films or the g e l will prematurely s l i p a t t h e

t o o l s u r f a c e s d u r i n g measurement,

F i g 4 Test of reproducibility of gel mixing and formation at diffent times

by different operators Samples were 48% HP guar (Gf K 3 N) mixed with Tyzor AA (.04%) by hand Tests 'began immediately after mixing at l.rad/sec 100% strain (runs 51983 3, 61083 4 8, 61583 1)

VI ,MSULTS - AND DISCUSSIOEJ

The properties of g u a r gels depend on the chemistry chosen, the mixing of

t h e components, and s h e a r h i s t o r y of the g e l I n this s e c t i o n we p r e s e n t the

r e s u l t s o f s t u d i e s on t h e s e effects

A summary of a l l of the measurements performed this y e a r and reported t o

t h e A P I Committee a t quarterly review meetings has been prepared by D r John Cameron, the Committee Vice-chairman (Appendix D l The s i g n i f i c a n t c o n c l u s i o n s are p r e s e n t e d h e r e

h y d r a t e the g u a r D u r i n g h y d r a t i o n m i c r o c r y s t a l l i n e c e l l u l o s e domains are

dissolved, t h e c e l l swells, and f i n a l l y t h e c e l l wall r u p t u r e s r e l e a s i n g t h e

guar The rate a t which this occurs depends on pH, temperature, and the osmotic

p r e s s u r e d i f f e r e n c e across the c e l l wall An experiment was conducted t o t e s t how l o n g it took t o f u l l y h y d r a t e t h e g u a r A g u a r s o l u t i o n was prepared and mixed i n the b l e n d e r f o r 30 minutes under strong agitation Immediately there-

a f t e r dynamic o s c i l l a t o r y laeasurements were run as a f u n c t i o n of s t r a i n ampli-

tude The r e s u l t s i n Fig 5 show that G I d e c r e a s e s as s t r a i n a m p l i t u d e i n -

creases This i n d i c a t e s t h a t there are t h r e e - d i m e n s i o n a l s t r u c t u r e s i n s o l u t i o n ,

p r o b a b l y a r i s i n g f r m association of the unhydrated guar domains, t h a t are

e a s i l y broken d m by shear This is not observed i f the guar i s allowed t o age

where, f o r t h e s o l u t i o n mixed 30 m i n u t e s , t h e s t e a d y s h e a r v i s c o s i t y i n c r e a s e s

a t es h e a r rates, whereas for t h e a g e d s o l u t i o n the v i s c o s i t y r e a c h e s a

Newtonian p l a t e a u This i n c r e a s e i n low s h e a r v i s c o s i t y a l s o i n d i c a t e s a g g r e g a -

t i o n a n d s t r u c t u r e i n s o l u t i o n I t i s i m p o r t a n t t o n o t e t h a t a t h i g h e r s h e a r rates t h e viscosities of t h e t m f l u i d s are i d e n t i c a l s i n c e moderate s h e a r

f i e l d s c a n d i s r u p t these weak a g g r e g a t e s We see t h a t dynamic o s c i l l a t o r y or low s h e a r r a t e measurements are s e n s i t i v e p r o b e s of s t r u c t u r e i n s o l u t i o n

2 Order of Addition

We were surprised t o f i n d t h a t the order of a d d i t i o n of i n g r e -

d i e n t s t o t h e o r i g i n a l base g u a r s o l u t i o n had an e f f e c t on t h e gels t h a t were

u l t i m a t e l y formed D r William S t i v e r s of Celanese ( 8 ) h a s s u g g e s t e d t h a t t h i s might be related t o t h e h y d r a t i o n of the g u a r , t h e o s m o t i c p r e s s u r e i n t h e s o l u -

t i o n d u r i n g h y d r a t i o n , and the number of cells t h a t f a i l t o r u p t u r e The o r d e r

of a d d i t i o n of t h e sodium diacetate b u f f e r (N), potassium c h l o r i d e (K), and guar

( G ) was v a r i e d i n a series of tests Though no d i f f e r e n c e s i n t h e r h e o l o g y of the g u a r s o l u t i o n s prepared u s i n g d i f f e r e n t o r d e r s of a d d i t i o n c o u l d be

measured, c e r t a i n orders of a d d i t i o n l e d t o gels with l o w e r l e v e l s of network

s t r u c t u r e (i.e., lower G I ) me r e s u l t s are shown i n Fig 7 f o r d i f f e r e n t

o r d e r s o f a d d i t i o n The d i f f e r e n c e s i n G' a r e q u i t e n o t i c e a b l e , though G" d a t a

0 96 strain 300 Fig 5- Storage(G') and loss (G") moduli as a function of strain of a 48%

HP War solution '(30 minutes agitation) at 10 rad/sec : (run 21 783 2)

Fig.6 Viscosity (Q) as a function of shear rate of 48% HP guar solutions

at different ages (runs 21683 and 21883 2)

Fig.7 Effect of order of addition on GJ am and G" of 48% I HP guar mixed with TYzor AA by hand Measurements began immediately after mixing

at 1 radlsec and 100% strain (runs 61583 1, 61583 2, 61583 5 & 7683 2)

S T D - A P I I P E T R O B Z - V 5 - E N G L M 0 7 3 2 2 9 0 0 5 7 7 b 9 5 480

98

are similar f o r a l l runs We ha7s not a t the time of this report d u p l i c a t e d

these runs with t h e impingement mixing technique For a l l s u b s e q u e n t s t u d i e s we

used the mixing order [G+K+N] F x t h e r work on t h i s phenomenon i s underway

3 Aging of Tyzor AA S o l u t i o n s

W z o r AA s o l u t i o n s change color from l i g h t y e l l o w t o o r a n g e or

brown o v e r a period of time D r Donald P u t z i g of DuPont has suggested three

mechanisms of Tyzor aging ( 9 ) :

a Photo-reduction of T i t a n i u m This will g i v e a green/blue

Color Keeping s o l u t i o n s i n brown b o t t l e s e l i m i n a t e s t h i s problem

b Oxidation of Acetylacetone by Oxygen This will g i v e an orange color However, D r P u t z i g d i d n o t t h i n k t h i s would a f f e c t t h e c r o s s l i n k i n g

smaller v i a l s and s e a l e d Brown vials were used and molecular seives (W.R Grace 3A) were added t o t h e v i a l t o scavenge water This worked w e l l and gave repro-

d u c i b l e r e s u l t s t h a t d i d n o t show the e f f e c t s of aging over a p e r i o d of months

4 Dike tone Addition The most s t r a i g h t f o r w a r d way of m e a s u r i n g g e l a t i o n k i n e t i c s i s t o measure the maximum slope i n t h e p l o t of G' v e r s u s time and t o a p p l y 4 4, as

w e have done p r e v i o u s l y i n o u r s t u d y o f p o l y a c r y l a m i d e / C r ( I I I ) g e l a t i o n ( 5 )

However, as can be s e e n from Figs 4, 7-9, and 13-14, t h e r e a c t i o n r a t e of t h e s e

g u a r / t i t a n a t e g e l s i s so f a s t t h a t t h e maximum r a t e cannot be determined with

c o n f i d e n c e it occurs a t t o o s h o r t a time

I t h a s b e e n s u g g e s t e d t h a t d i k e t o n e s c a n be used t o slow the rate

of c r o s s l i n k i n g ( 1 1 ) Our r e s u l t s , t a k e n a t room temperature, show t h a t n o t o n l y

does the a d d i t i o n o f a c e t y l a c e t o n e ( a d i k e t o n e ) s l o w t h e r e a c t i o n rate, b u t it

also p r e v e n t s t h e g e l from c r o s s l i n k i n g f u l l y With the a d d i t i o n of diketone,

a s shown i n Fig 9, t h e f i n a l v a l u e of t h e s t o r a g e modulus i s decreased It has

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

c r o s s l i n k i n g Further s t u d i e s of delayed crosslinking are being pursued

-~

S T D - A P I / P E T R O 82-45-ENGL D 0 7 3 2 2 9 0 0577b9b 317 Bp

Fig.8 Storage (G‘) and loss {G”I ,.moduli of HP guar gel (.48% guar

(G + K + N) and 04% Tyzor Aqmade from a newly opened bottle of Tyzor AA and from a bott1.e that had been used for several months Impingement device

was used and tests began immediately after mixing at 10 rad/sec 100% strain (runs 121583 1 & 122983 31

Fig.9 Effect of diketone on G' and G" of HP guar gel (.48% guar

(G -I .K+ N) and 04% Tyzor AA) Tests began immediately after mixing by hand at I radisec and 100% strain (runs 52483 2, 52483 4 4% 6 1583' 1)

could be varied within reasonable limits as long as t h e same t o t a l amount of

t i t a n a t e was delivered This A k e s matching t h e cross s e c t i o n s of the guar

syringe and t h e t i t a n a t e s y r i n g e i n the impingement mixer less c r i t i c a l

6 Temperature The data reported here were taken a t room temperature (2352OC)

T e s t s were run on the Rheometries Pressure rheometer a t 110'and 1 2OoC, but

e r r o r s fran wall s l i p c a u s e us t o q u e s t i o n t h e v a l i d i t y of t h e i n i t i a l d a t a I n

t h e next year extensive experiments a t elevated temperatures are planned

.%eology of .Gyar

In this s e c t i o n w e p r e s e n t the main r e s u l t s on the rheology of guar

g e l s i n dynamic o s c i l l a t o r y and steady shear flows The dynamic o s c i l l a t o r y measurements a r e used t o c h a r a c t e r i z e the network s t r u c t u r e , whereas the steady

s h e a r measurements a r e i n t e n d e d t o measure g e l v i s c o s i t y under process con-

d i t i o n s

1 Dynamic O s c i l l a t o r y Measurements

a Mixing The degree of homogenization a t a microscopic level i s cru-

c i a l i n determining the f i n a l gel s t r u c t u r e The problem of mixing r e a c t i v e titanium and guar solutions is i n many ways analogous t o problems encountered i n

reaction i n j e c t i o n molding of polyurethanes in the p l a s t i c s i n d u s t r y ( 1 2, 1 3 )

Thorough mixing i n the impingement mixing d e v i c e r e s u l t e d i n g e l s with lower values of G' t h a n g e l s made with hand mixing For example, t h e t o r q u e s i g n a l i n

a dynamic o s c i l l a t o r y test €or a g e l mixed by hand would be 1.1 g-cm, whereas

f o r a g e l made i n the impingement mixer the torque would be 0.6 g-cm Guar polymer chain s c i s s i o n d u r i n g flaw through the mixing device is i n s i g n i f i c a n t

W believe the e higher levels of e l a s t i c i t y noted f o r t h e hand mixed samples a r e caused by the inhomogeneous gel s t r u c t u r e t h a t is produced by incomplete mixing

During hand mixing i n t e r f a c e s are developed between s t r i a t i o n s o r l a y e r s of bulk guar solution and t h e v e r y c o n c e n t r a t e d t i t a n t a t e s o l u t i o n The r e a c t i o n rate i n

t h e s e i n t e r f a c i a l r e g i o n s is very h i g h w i t h t h e r e s u l t t h a t r e g i o n s of dense

c r o s s l i n k s t r u c t u r e are developed The f i n a l g e l formed contains microscopic

threads or sheets of more h i g h l y c r o s s l i k e d g u a r t h a t are e l a s t i c , imparting t o

t h e g e l a higher level of G' t h a n would be predicted i f t h e c r o s s l i n k s were homogeneously d i s t r i b u t e d C h a r a c t e r i z a t i o n of the s t a t e of mixedness during the production of g e l s i n t h e l a b o r a t o r y o r f i e l d i s critical

0 time(min.1

S T D A P I / P E T R O 82-45-ENGL 0 7 3 2 2 7 0 0 5 7 7 7 0 0 b 7 8

11

b Storage Modulus Versus S t r a i n Amplitude Figure 11 shows t h e e f f e c t of s t r a i n on guar gels produced i n

t h e impingement mixer, i n t r o d u c e d i n t o t h e gap between parallel plates, and

allowed t o s i t f o r 1 5 m i n u t e s b e f o r e t h e dynamic o s c i l l a t o r y test a t 10 rad/s was begun A t l o w s t r a i n s the v a l u e of G I i s above G" As t h e s t r a i n amplitude

i s i n c r e a s e d G' d r o p s d r a m a t i c a l l y i n d i c a t i n g t h a t the g u a r g e l s t r u c t u r e is

b e i n g d i s r u p t e d by s t r a i n or t h a t wall s l i p i s occurring In this experiment

t h e s t r a i n i s f i r s t i n c r e a s e d fo 500 % and t h e n decreased Hysteresis can be

obgerved i n d i c a t i n g t h a t i n the time scale of t h e s e e x p e r i m e n t s t h e gel does n o t

r e h e a l The n e c e s s i t y of having adequate t o r q u e s i g n a l s r e q u i r e s t h a t most of

our experiments were run at 100 % s t r a i n I t should be k e p t i n mind that a t

t h e s e s t r a i n s some d i s r u p t i o n of g e l network s t r u c t u r e o c c u r s I n t h e n e x t y e a r

o f t h i s s t u d y a new sensitive t r a n s d u c e r will be a v a i l a b l e t o a l l o w measurements

a t lower s t r a i n s The s t r a i n s e n s i t i v i t y of guar gels is i n s h a r p c o n t r a s t t o

t h e p e r f e c t l y e l a s t i c behavior of polyacrylamide gels formed with chromium

c r o s s l i n k s ( 5 ) shown i n Fig 12 The value of GI i s unaffected by s t r a i n s as

l a r g e as 500 % f o r p o l y a c r y l a m i d e g e l s

C Storage Modulus Versus Frequency The storage a n d l o s s moduli of guar gels produced i n t h e impingement mixer, allowed t o s i t f o r 20 minutes, and measured a t 100 % s t r a i n

are as shown i n Fig 13 The s t o r a g e modulus, GI, is above t h e loss modulus,

G " , and GI becomes c o n s t a n t at l o w frequencies as is i n d i c a t i v e of a c r o s s l i n k e d gel

d S t o r a g e Modulus Versus Time: Chemical K i n e t i c s

As d e s c r i b e d i n S e c t i o n 111, by measuring t h e time depen- dence of t h e s t o r a g e modulus d u r i n g c r o s s l i n k i n g it is p o s s i b l e t o f o l l o w t h e

c h e m i c a l k i n e t i c s of the g e l a t i o n r e a c t i o n The equilibrium modulus, which i s

e q u a l t o t h e s t o r a g e modulus G' a t zero frequency and z e r o s t r a i n , is propor-

t i o n a l t o t h e number d e n s i t y of c r o s s l i n k s From t h e data showing t h e s t r a i n and frequency dependence of these guar g e l s it should be remembered t h a t a t 10 rad/s t h e a c t u a l v a l u e of G' a t z e r o s t r a i n i s h i g h e r t h a n t h e measured value

A second e f f e c t acts i n o p p o s i t i o n t o t h e decrease i n G' w i t h s t r a i n t h e

measured G I a t 10 rad/s i s a c t u a l l y h i g h e r t h a n t h e e q u i l i b r i u m modulus of the

g e l as can be s e e n from Fig 13 Most measurements were taken a t 10 rad/s and 100% s t r a i n b e c a u s e t h o s e v a l u e s y i e l d e d a d e q u a t e t o r q u e s i g n a l s and a f a s t d a t a

a c q u i s i t i o n time so t h a t r e a c t i o n dynamics could be followed

A series of measurements of t h e s t o r a g e modulus v e r s u s time

were made while varying guar a n d t i t a n a t e c o n c e n t r a t i o n s ( F i g s 14 and 1 5 ) The

g e l s were produced i n t h e impingement mixer and introduced directly into the gap

between p a r a l l e l p l a t e s The time between t h e mixing of t h e g u a r and t i t a n a t e streams and t h e f i r s t datum p o i n t i s approximately 10 8 Measurements were con- ducted a t 1 0 rad/s and 100% s t r a i n The s u r p r i s i n g t h i n g a b o u t t h e r e s u l t s is

t h e speed of t h e r e a c t i o n W e were unable t o measure a n i n d u c t i o n p e r i o d b e f o r e

t h e network formed The maximum rate of r e a c t i o n (i.e maximum s l o p e i n GI vs t )

occurs b e f o r e t h e f i r s t data p o i n t Using t h e e n t i r e shape of the G' versus

time c u r v e , a n d i n t e r p r e t i n g this curve using the polymer k i n e t i c t h e o r y model developed i n S e c t i o n V I I , it s h o u l d be p o s s i b l e t o d e t e r m i n e r e a c t i o n k i n e t i c s

1 oa

1

FiQ.11, Effect of 8train on 0' and 0" of HP guar Qel (.48% guar

( 0 -t- K 4- N) and 04% fyror AA) produced in the impingement device

Mixture was allowed to 8it for 15 minutes before tests began at

10 tadhec (tun 113083 l)* Arrow indicates the direction of strain sweep

Fig.12- Effect of strain on 0' and 0" of polyacrylamide

formed withchromhm /Erocrslinks.(5)

- ~ - - - ~ -

oels

S T D A P I / P E T R O 82-45-ENGL W 0 7 3 2 2 9 0 0 5 7 7 7 0 4 2 1 3

immediately after mixing in the implngement device Only the values of

0" of HP guar (.0.48%) with -04% Tytor AA is shown because 0" are

the same for all runs.(runs 122883 2, 122803 1, 122803 4, 122883 3,

-

122983 2,& 122983 3)

-

S T D A P I / P E T R O 82-45-ENGL = 0 7 3 2 2 7 0 0 5 7 7 7 0 5 L 5 T

Fig.15, Effect of HP guar (Gf K+N) concentration on gel formation at

a constant fyzor AA concentration, .08% Tests began immediately after mixing in the impingement device (runs 122883 4, 1484 3, 1484 1,

& 1584 1)

- - _ " _ ,

S T D - A P I I P E T R O 8 2 - 4 5 - E N G L m 0 7 3 2 2 9 0 0 5 7 7 7 0 b 0 7 b

12

These data can be used t o show the sensitivity of guar gel

p r o p e r t i e s t o guar and titanium concentrations It i s possible t o obtain the same values of G' from s o l u t i o n s having d i f f e r e n t compositions However, these

g e l s may show d i f f e r e n t time, temperature, and shear stabilities

2 Steady Shear kasureme.nt.s

a Gels Mixed by Hand

Our i n i t i a l ' steady shear experiments were on guar gels

mixed by hand and introduced to the rheometer t e s t c e l l This process takes on the order of 2 minutes t o accomplish The quiescent period before steady shear

is imposed, we now believe, has a dominant e f f e c t on the viscosity that i s

measured The s t r e s s versus time behavior f o r gels being sheared a t 100, 500,

and 1000 s-l ,respectively were investigated Several series of t e s t s were run

where the gels were allowed to s i t 2.5, 3.5, and 4.5 minutes before shear was

i n i t i a t e d I n a l l of the steady shear experiments the asymptotic s t r e s s a t

long times ( 1 5 0 0 s) i s roughly the same - independent of shear rate When the

s t r e s s d a t a i s divided by shear r a t e t o obtain a viscosity, n,.,,, a log-log p l o t of viscosity versus shear rate has a slope of -0.96 shown i n Fig 16 This slope

i s u n r e a l i s t i c f o r a polymer f l u i d (which normally has a slope between -0.6 and

-0.31, and i s much more suggestive of wall s l i p Each qco datum point on Fig 16 represents a new experiment Stepping up or down i n shear rate to obtain nco a t several shear rates for the same gel introduces shear h i s t o r y e f f e c t s and will produce d i f f e r e n t r e s u l t s A standard procedure t o t e s t for the presence of

w a l l s l i p i s t o take two sets of measurements w i t h d i f f e r e n t gap s e t t i n g s I f ,

a t the same shear stresses, the shear rates are the same w i t h both gaps, then

w a l l s l i p i s thought not t o occur; b u t i f , a t the same shear stresses, the shear

r a t e i n t h e narrower gap i s greater, then s l i p is occurring We performed steady

shear measurements a t 25 s-' w i t h gaps of 0.75 m m , 1.5 mm, and 3.0 mm as shown

i n Fig 17 I n a l l cases the s h e a r s t r e s s e s a t long times were identical within experimental uncertainty This i n d i c a t e s s l i p is not occurring The interpreta-

t i o n of these observations is uncertain Resolution will require direct measure- ment of the velocity field We consider t h i s a major research need a t t h i s

point

b Impingement Mixing: Effect of Shear on Reaction Rate

B y using the impingment mixer it i s possible t o introduce solutions i n t o the rheometer and begin measurements before the f l u i d completely gels A s e r i e s of measurements a t 25, 100, and 500 s-' were run and the results

of s t r e s s versus time a r e shown i n Fig 18 I n the r u n s a t 25 and 100 s-l the stress increases linearly for 100-200 s as the guar network gels A t the gel

p o i n t t h e f l u i d can no longer flow and the stress rises sharply I t then f a l l s

j u s t as sharply, as would be observed i f the gel broke away from the p a r a l l e l plate surfaces and began to slip After the drop i n s t r e s s i t remains essen-

t i a l l y constant for 1500 S The location of the rise i n s t r e s s and also the

slope of the stress versus time p l o t s f o r 25 and 100 s-' increases w i t h i n -

creasing shear rate The conclusion i s that shear increases the rate of reac- tion We may assume t h a t f o r t h e measurement a t 500 the jump i n s t r e s s a t very short times corresponds t o the gel point which i s seen more c l e a r l y a t the lower shear rates

S T D A P I / P E T R O 8 2 - 4 5 - E N G L SS 0 7 3 2 2 9 0 0 5 7 7 7 0 7 T 2 2 iass

= * a

Fig.16 Effect of shear rate on viscosity ( r) ) of 48% HP guar

(0 t K + N) gels with 04% Tyror AA produced by hand mixing Tests began after the gels were allowed to sit 2.5 , 3.5 and 4.5

0

minutes Solid line is a least squar fit of these points (runs

Fig.17, Steady shear measurements with parallel plates geometry with gaps

Of 0.75mm 1.5mm a 3.0mm on $8% guar (G t K f N gels (.04% Tyzor AA) produced in the impingement device Tests began 'immediately aftter mixing

at 25/sec.(runs 1 1084 1, 1 1 184 1 S 1 1 184 2)

- , _ _