Bound Water in Shaly Sand - American Chemical Society

Chapter 33

Bound Water in Shaly Sand

Downloaded by UNIV OF LIVERPOOL on November 30, 2016 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch033

Its Determination and Mobility Ying-Chech Chiu Department of Chemistry, Chung Yuan Christian University, Chung-Li, Taiwan 32023, Republic of China Specific ion electrodes were used for anion-free water determination of clay minerals at equilibrium with e l e c t r o l y t e solutions. A new equation was developed for determining anion-free water. Mobility of the anion-free water was determined by compaction experi ments with pressure up to 10,000 p s i . At NaCl concen trations of 0.2 M or higher, the anion-free water i s immobile. At lower concentrations, it i s movable under high pressure. Under ordinary flowing conditions, the anion-free water gives a good indication of the immo b i l e water. At high pressure, the amount of the immo b i l e water seems to be related to the porosity of the rock. The actual amount of the immobile water can be found by the method described i n this paper. Through compaction of the clay-water slurry, bound water can be concentrated i n the sample to facilitate NMR meas urements and other studies. Recent interest i n clay hydration water and i t s effect on various petrophysical properties of shaly sand (1-13) has prompted the author to reinvestigate the subject of "bound water". It has long been sug gested that water associated with the clay mineral surfaces causes deviations from the normal petrophysical measurements (14-16). Since bound water exists i n the i n t e r f a c i a l region between l i q u i d and s o l i d , i t i s quite d i f f i c u l t to obtain accurate and meaningful results concerning the nature and amount of water i n this region. In the past, information concerning bound water has mainly been extracted from vapor phase adsorption of water (8,9,17,18). In recent years, NMR studies have provided much insight into the problem. I t i s generally recognized now by NMR study that some water molecules are p r e f e r e n t i a l l y oriented at the clay surfaces (10,13,19-21). The mobility of water i n the i n t e r f a c i a l region depends on the type of clay and the amount of sorbed water (22-24). Many authors believe that the t i g h t l y bound water occupies only a small f r a c t i o n of a monolayer (25-27). L i t t l e d i r e c t , quantitative measurement has been done on bound water existing i n equilibrium with clay mineral substances i n 0097-6156/89/0396-0596$06.00/0 o 1989 American Chemical Society Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


33. C H I U


597

aqueous solution. Dmitrenko (28) was the f i r s t to devise a method for determining bound water i n natural sediments. The method i s based on the determination of "nonsolvent water". By assuming the bound water a nonsolvent and assuming chloride ion adsorption neg l i g i b l e , Dmitrenko (28) calculated the amount of bound water after chemical analysis and material balance of water and chloride i n the sample. H i l l et a l . (2), using the Dmitrenko method i n conjunction with the "anion exclusion (29-31) technique" based on e l e c t r i c a l double layer theory, determined the amount of bound water i n twentyeight samples from six f i e l d s . They called the water determined by this method "anion-free water" and assumed this water to be the clay hydration water (2). By using the amount of anion-free water and assuming that the anion-free water i s immobile for normal flow pro cesses, H i l l et a l . (2) developed procedures for (1) obtaining an estimate of brine permeability, (2) correcting mercury i n j e c t i o n curves to estimate oil-water or gas-water c a p i l l a r y curves, (3) ob taining a more r e a l i s t i c estimate of information water s a l i n i t y from core water s a l i n i t y and (4) calculating o i l or water saturations for pre d i c t i n g whether o i l or water w i l l be produced. This paper discusses the use of s p e c i f i c ion electrodes for de termining the anion-free water. This method i s simpler and more accurate at low e l e c t r o l y t e concentration than ordinary chemical methods. I t i s p o t e n t i a l l y useful for o i l f i e l d application and laboratory automation. The mobility of this water i s also examined under forced conditions with pressure gradients. I t i s expected that by using the methods developed i n this paper, one may obtain a better understanding of the clay properties.

Experimental Bound Water Determination. A modified method of H i l l et a l . (2) was used i n determining the bound water (anion-free water). No separa tion of s o l i d and l i q u i d was made during this determination. The ion concentrations were measured by s p e c i f i c ion electrodes. The major equipment consisted of an Orion Model 801 d i g i t a l pH/mv meter, a Beckman 39278 sodium electrode, an Orion 94-17 chloride electrode and an Orion 90-01 reference electrode. Glen Rose Shale (Baroid Division of NL Industries supplied this sample i n a fine powder) was used as the sample. Samples i n bottles were weighed and dried at 110°C overnight. A known quantity of d i s t i l l e d water or NaCl solution was added to the b o t t l e . After shaking with a floor shaker for 2 hours, the clay and sand were allowed to s e t t l e overnight. The ion poten t i a l was measured by placing the electrode i n the clear l i q u i d on top. A l l experiments were carried out at 24±1°C. The electrodes were calibrated with NaCl solutions of known concentration. The concentration of the unknown solution was determined from the c a l i bration curves. The amount of anion-free water was calculated by a material balance of chloride and water i n the system. The calculation can be simplified by using volume concentrations. Details of the c a l c u l a tion are i l l u s t r a t e d i n Appendix I. Compaction Experiments and Other Related Measurements.

After the

Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


598

OIL-FIELD CHEMISTRY

anion-free water was determined, the shale-electrolyte s l u r r y was poured into a f i l t r a t i o n or a compaction c e l l . Gas or hydraulic pressure was applied to force the water out of the system. A Millipore f i l t e r (No. 4004700) or a Fann F i l t e r press was used when the gas pressure was below 100 p s i . Hydraulic pressure of 400 to 10,000 psi was applied through a compaction c e l l having a configuration as described by Darley (32). The solution forced out of the c e l l was c o l l e c t e d , weighed, and i t s chloride concentration was determined. When no more l i q u i d could be forced out, the mineral cake was weighed and dried at 110°C to constant weight. The amount of water i n the cake i s taken as the residual water i n clay. The volume of the cake was also measured. The pore size d i s t r i b u t i o n of the dried sample was measured by a Aminco 60,000 p s i Mercury-Intrusion Porosimeter. The NMR measurement on water retained i n the compacted sample was performed by using a Bruker CXP-200 NMR Spectrometer. Some properties of the rock used i n this study were measured : The cation exchange capacity (cec) was determined by the barium sulfate method as described by Mortland and Mellor (33). Surface area was measured by using a Digisorb Meter (Micromeritics Instrument Corporation) through nitrogen adsorption. Estimation of mineral composition and i n d e n t i f i c a t i o n of the rock were performed by X-ray diffraction.

Results and Discussion Bound Water Determination at Low E l e c t r o l y t e Concentration. From the theoretical and experimental investigation of the anion-free water i n the l i t e r a t u r e , i t i s most reasonable to conclude that the anion-free water i s the water inside the e l e c t r i c a l double l a y e r . This concept has been discussed i n more d e t a i l s using the "dual water model" (1) in which the anion-free water i s referred to as the "clay water". Figure 1 compares the experimentally determined anion-free water contents. The three c i r c l e s i n Figure 1 are data taken from Ref. 2 determined i n the NaCl concentration region 0.228 -5.41 M. The other data are taken from this investigation i n the low concentration region. Ws i s the anion-free water i n g/100 g rock. The cec value and other properties of the sample, Glen Rose Shale, are given i n Table I . In order to chech the agreement between the values obtained in Ref. 2 and p.n this study, four points have been gathered around 0.2 M NaCl (CQ^=2A). A l l the points coincide well and are shown as one point i n Figure 1. The agreement between the two studies i s good. A straight l i n e passing through the o r i g i n correlates a l l the points in Figure 1. At extremely high e l e c t r o l y t e concentrations, f l o c c u l a t i o n of clay should occur. Therefore, when C Q ^ = 0 , W S = 0 . Figure 2 compares data from this investigation with those from the l i t e r a t u r e . Most l i t e r a t u r e data i n Figure 2 are from Figure 3 of Ref. 2. The equations mentioned i n Figure 2 have the following forms : Equation 1 comes from Schofield (29) and Bolt et a l . (30-31),




33. CHIU

0

Figure 1.

1

2

3

A

5

6

599

7

8

9

10

11

12

Anion-free Water As A Function of NaCl Concentration.

Co

Figure 2. Hydration Water As A Function of Concentration and Method of Determination.



13.73

5.0

Fithian Illite 51.5 (Ward's)

Rochester Illite 19.0 (Ward's)

10.83

13.33

cec meq/ lOOg

0.45

16.8

42.7

2

Surface Area m /g

0.97

Berea Sandstone

Glen Rose Shale

Grundite Illite (Magcobar)

Sample

Properties

2.63

2.66

4.65

6.45

3.11

45

40

80

45

48

25

3

2

2

s

a

5

5

p

r

o f the Rock Sample

50

50

15

20

50

90

10

60

10

20

40

90

30

layer

80

70

Illite

Surface C o m p o s i t i o n , % from X-Ray D i f f r a c t i o n Charge Quartz Dolomite FeldDensity Calcite Pyrite clay Clay (meq/m*) Illite Kaolinite x 1()3 Chlorite Mixed

T a b l e I.


33. CHIU


601

where X~ i s the n e g a t i v e a n i o n a d s o r p t i o n , C has the same meaning as the e q u i l i b r i u m s o l u t i o n c o n c e n t r a t i o n , S i s the a r e a of the charged s u r f a c e , and B i s a c o n s t a n t . By assuming c e c / S t o be c o n s t a n t and X ~ / C t o be e q u i v a l e n t to Ws, H i l l e t a l . (2) d e f i n e d equation 2, Q

0

— cec

= ACo** °

B


where A and B are c o e f f i c i e n t s a f f e c t e d by the r a t i o , c e c / S . f i t t i n g t h e i r d a t a i n t o e q u a t i o n 2 , H i l l et a l . (2) o b t a i n e d 3 i n t h i s form :

cec

= 0.084 Co"** + 0.22

(2) By equation

(3)

Data from t h i s study seem to c o i n c i d e b e t t e r w i t h the d a t a o f B o l t e t a l . . A s t r a i g h t l i n e p a s s i n g through the o r i g i n b e s t f i t s a l l the p o i n t s i n F i g u r e 2. T h i s l i n e has the f o l l o w i n g form :

cec

= 0.31

h

CZ °

(4)

S u r f a c e Charge D e n s i t y . In the p r e v i o u s s e c t i o n , i t was assumed t h a t the s u r f a c e charge d e n s i t y , c e c / S , i s a c o n s t a n t . Table I gives the s u r f a c e charge d e n s i t y f o r f i v e s a m p l e s . I t v a r i e s from 2.63 x 10"3 to 6.45 x 10~3 meq/m*. F i g u r e 3 shows a p l o t of t h e s e p o i n t s . Four of the p o i n t s can be f i t t e d c l o s e l y by a s t r a i g h t l i n e w i t h a s l o p e o f 2.9 x 10~3 meq/m^. One p o i n t d e v i a t e s from the l i n e . P a t c h e t t (35) has p l o t t e d some cec v s . S f o r n i n e API s t a n d a r d c l a y s on a l o g - l o g p a p e r . The b e s t l i n e r e p r e s e n t i n g the 9 p o i n t s has a s l o p e o f 2.4 x 10~3 meq/m^. When the d a t a i n F i g u r e 3 were p l o t t e d i n P a t c h e t t ' s d i a g r a m , the f i v e p o i n t s l i e around h i s l i n e w i t h about the same degree of s c a t t e r i n g as h i s own d a t a . I t appears t h a t the assumption o f c e c / S b e i n g a c o n s t a n t i s a r e a s o n a b l e assumption f o r many r o c k s . M o b i l i t y o f The A n i o n - F r e e W a t e r . I t i s w e l l known t h a t water i n the e l e c t r i c a l d o u b l e l a y e r i s under a f i e l d s t r e n g t h of 10^-10^ V/cm and t h a t the water has low d i e l e c t r i c c o n s t a n t s ( 3 6 ) . Since anion-free water i s thought to be the water i n the e l e c t r i c a l d o u b l e l a y e r between the c l a y and the b u l k s o l u t i o n , at h i g h e l e c t r o l y t e c o n c e n t r a t i o n s , the d o u b l e l a y e r i s c o m p r e s s e d ; t h e r e f o r e , the water i n s i d e i s l i k e l y quite immobile. A t low e l e c t r o l y t e c o n c e n t r a t i o n s , the e l e c t r i c a l double l a y e r i s more d i f f u s e , the a n i o n - f r e e water i s e x p e c t e d to be l e s s i m m o b i l e . S i n c e the e v a l u a t i o n of the s h a l y f o r m a t i o n p r o p e r t i e s r e q u i r e s the knowledge of the immobile w a t e r , experiments were conducted to f i n d out the c o n d i t i o n s f o r the a n i o n f r e e water to become m o b i l e . By d e f i n i t i o n , the a n i o n - f r e e water i s f r e e o f s a l t . When p r e s s u r e i s a p p l i e d to a c l a y - b r i n e s l u r r y to f o r c e out water (as t h a t d e s c r i b e d i n the e x p e r i m e n t a l s e c t i o n ) , the s o l u t i o n t h a t f l o w s out of the c e l l s h o u l d m a i n t a i n the same c h l o r i d e c o n c e n t r a t i o n as the b r i n e ' s i f the a n i o n - f r e e water i s i m m o b i l e . O t h e r w i s e , the c o n c e n t r a t i o n o f the c h l o r i d e d e c r e a s e s . P r e s s u r e f o r c e s water to f l o w through the p o r e s w i t h a c e r t a i n v e l o c i t y ; meanwhile, the pore s i z e


OIL-FIELD CHEMISTRY


602

i s reduced. By accounting material balances during the experiment, useful information was deduced. Table I I shows the result of compaction experiments with Glen Rose Shale. Column 2 gives the equilibrium NaCl concentration of the solution before the compaction experiment. Column 3 gives the anionfree water calculated as shown i n Appendix I. Column 4 gives the amount of the bulk solution which has the NaCl concentration given i n Column 2. Column 5 gives the t o t a l amount of f l u i d flowing out of the c e l l . Column 6 indicates the pressure applied and Column 7, the i n i t i a l flow rate. The flow rate decreased with time and could be measured or estimated from equations (37). Column 8 gives the water retained i n the clay sample after compaction by determining the weight loss after heating at 110°C. Porosity of the dried clay sample was determined by comparing the volume of residual water and t o t a l volume of the sample and i s given i n Column 9. Water density was assumed to be lg/cm^. Column 10 gives the average pore diameter of the dried clay sample. Experiments No. 1,2 and 3 were performed at gas pressure begin ning at 15 p s i and stepping up to 77 p s i . The t o t a l f l u i d collected was less than the bulk solution i n the system. The concentration of chloride i n the f l u i d collected i n these three runs was about the same as the values given i n Column 2. It was concluded that under these conditions, the anion-free water was immobile. It was observed that under the same applied pressure, the higher the NaCl concentra tion, the faster the flow rate — consistent with observations re ported by Engelhardt and Gaida (38). In order to increase the flow rate without too much pressure, Experiment 4 was performed with a Fann f i l t e r press which has a wider cross sectional area. A constant a i r pressure of 100 p s i was applied, the flow rate was 26 times that of Experiment 1 while the NaCl concentration was only s l i g h t l y higher than that of Experiment 1. Although the flow rate was much increased i n Experiment 4, the result was similar to Experiment 1. The water retained i n the clay (Column 8) determined by drying was found to be close to the amount of anionfree water. The porosity of the sediment was 0.4 and the average pore diameter was 4466 X. It was concluded from this experiment, that the anion-free water was immobile even at 100 p s i and 7.4 ft/day. The pore size d i s t r i b u t i o n o f the sample showed 90% of the pores to have a diameter above 350 A and less than 3% of the pores to have a diameter below 100 X (Figure 4). It was decided to increase the pressure i n subsequent experi ments to push the anion-free water out. Experiments 5 and 6 were performed at 400 p s i at a NaCl concentration around 0.01 M. Experi ments 5-10 were performed i n the compaction c e l l as described i n the experimental section. This apparatus was rated for 10,000 p s i . The pressure regulation at 400 p s i region was about ± 100 p s i . Some evaporation occurred that made the t o t a l f l u i d c o l l e c t i o n less than expected from t o t a l material balance. NaCl concentration of the collected f l u i d could not be measured accurately. However, the amount of f l u i d collected and the amount of water retained i n the sediments i n Experiments 5 and 6 c l e a r l y indicated some anion-free water was mobilized. Experiment 7 was the f i r s t run under 400 p s i hydraulic pressure followed by 10,000 p s i . Most of the f l u i d was collected at the low Q


33. CHIU

603



u

Surface

F i g u r e 3. Area.

a r e a , m^/g

C a t i o n Exchange C a p a c i t y As A F u n c t i o n of

Surface

0.40-

o Pore Diameter, A

F i g u r e 4.

Pore S i z e D i s t r i b u t i o n

By Mercury

Intrusion.


604

OIL-FIELD CHEMISTRY CO ^ r-lO«J O

vO vO

(30 CM CM

o

u o


o

i—l

O

CO CO CO

00

ON

o

•8

4J

a

Tj CD •H H M 3 rH

rH

ON

CM

o

U O *H o

»H cd

o ,o

cd

3 CO cd cd

u

& cd

w

CO

CM

ON

00

00

rH 00

o

O

CO

vO

CM CO

CM CO

ON

O

00

o

CM

rH CD CD U

MH

60

a * •H

cd 3 cd cd

•H rH

CM

vO

O

CO

o

CD ^ o

O

O

s-/ cd

vO

o o o

•H rH

N ^ 91 N O B ) I m CM CD CO

no CD

vO CM o o

o

rH A

o CM

m CO

vO

00

vO 00

vO

rH

m

CM

00

m

vO

ON

rH

rH

rH

rH

rH

rH

O

Bound Water in Shaly Sand - American Chemical Society

Recommend Documents