StructureâPerformance Characteristics of Surfactants in Contact with

Downloaded by UNIV OF MASSACHUSETTS AMHERST on September 15, 2016 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch016

Chapter 16

Structure—Performance Characteristics of Surfactants in Contact with Alkanes, Alkyl Benzenes, and Stock Tank Oils Thomas A. Lawless and John R. Lee-Snape Winfrith Petroleum Technology Centre, Winfrith AEE, Dorchester, Dorset, England The assessment o f surfactant structures and optimal mixtures f o r p o t e n t i a l use i n t e r t i a r y flooding strategies i n North Sea f i e l d s has been examined from fundamental investigations using pure oils. The present study furthermore addresses the physico-chemical problems associated with r e s e r v o i r oils and how the phase performance o f these systems may be correlated with model o i l s , including the use o f toluene and cyclohexane in stock tank oils t o produce synthetic l i v e reservoir crudes. Any dependence o f surfactant molecular structure on the observed phase properties o f proposed o i l s o f equivalent alkane carbon number (EACN) would render simulated l i v e o i l s as unrepresentative. Both commercial grade and pure nonionic and anionic surfactants have been evaluated by phase inversion and optimal s a l i n i t y screening procedures t o e s t a b l i s h relationships t o t h e i r molecular structures.

The optimal structure o f surfactants f o r p r a c t i c a l and e f f i c i e n t EOR flooding strategies i n North Sea o i l r e s e r v o i r s remains largely unresolved. Previous research studies (1-4) have attempted t o assess surfactant performance p o t e n t i a l using pure synthesised materials. These have been successful i n focussing on molecular structural benefits and i d e n t i f y i n g some shortcomings associated with d i f f e r i n g functional moieties. The present study attempts t o probe the r e l a t i o n s h i p between structure and performance o f 8 surfactants; 7 o f which are commercial i n o r i g i n . Cosurfactants have not been employed i n the present study. However, surfactants from canmercial sources w i l l contain isomers and manufacturing impurities. Nevertheless, a major aim o f t h i s study has been t o address the performance c h a r a c t e r i s t i c s o f commercial formulations. Wherever appropriate, hydrophobic 0097-6156/89A)396-0305$06.00A) Published 1989 American Chemical Society Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

OIL-FIELD CHEMISTRY


306

s t r u c t u r a l assemblies were selected that were a v a i l a b l e i n both anionic and nonionic form. Variations i n the ethoxylate chain length, the degree o f anionic substitution, inorganic s a l t content and unreacted products w i l l a l l a f f e c t performance behaviour, and therefore demand c a r e f u l attention. A methodical assessment of a l l surfactant formulations has been undertaken using the technique o f conductivity t o determine the temperature or s a l i n i t y required f o r phase inversion t o occur. Of d i r e c t i n t e r e s t i s the EACN concept (5) and how pure o i l s may be r e l a t e d to r e s e r v o i r crudes. Furthermore the a b i l i t y of c e r t a i n aromatics and c y c l i c s t o a c t as separator gas equivalents i s a l s o addressed. The influence of ethoxylate i n c l u s i o n t o the surfactant hydrophile and the observed concomitant equivalences, f o r toluene and cyclohexane have been investigated t o follow the a p p l i c a b i l i t y of such concepts. These optimal c o r r e l a t i o n s and their inherent sensitivities a i d the interpretation of formulation p o t e n t i a l f o r f i e l d i n j e c t i o n . Experimental ; Materials and Methods Oils The n-alkane s e r i e s Cg-C^, toluene and cyclohexane were purchased from BDH, Poole, UK, each with a stated p u r i t y of 99%; reagents were used as received. Crude o i l samples were obtained from two North Sea f i e l d s ; one located i n the Norwegian sector and the other from the UK sector. Stock tank o i l from the Gullfaks f i e l d was supplied by S t a t o i l , Norway and the other stock tank o i l from an undisclosed source. Both crude o i l s are derived from sandstone formations with r e s e r v o i r temperatures of 70° and 101 °C respectively. Brines A n a l y t i c a l grade sodium chloride, p u r i t y 99.9% was obtained from BDH and used throughout the study. Water was p u r i f i e d by reverse osmosis, and deionised i n a Milli-Q-Reagent system immediately p r i o r t o use. Surfactants Information on the pure and commercial grade surfactants studied with regard t o structures, contaminations and a c t i v i t i e s i s d e t a i l e d i n Table I. A l l surfactants were used as received. Cloud Point Measurements Cloud points were recorded by the v i s u a l observation of aqueous solutions containing 1% W/V surfactant. The measurement defines the temperature a t which the system under t e s t shows a c h a r a c t e r i s t i c t r a n s i t i o n a l change from a c l e a r s o l u t i o n t o an opalescent or cloudy state. A l l cloud points were recorded i n both ascending and descending temperature cycles t o ensure data confidence. The influence of s a l t and/or o i l s on the cloud point were systematically evaluated. Phase Inversion The phase inversion o f b r i n e / o i l / s u r f a c t a n t systems was established routinely by measuring s o l u t i o n conductivity employing a Jenway FWA 1 meter and c e l l . The process i d e n t i f i e s the range over which a large decrease i n conductivity occurs as the sytem under t e s t i s converted from an o i l i n water emulsion t o a water i n o i l emulsion. Phase

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


3

3

2

5

n

2

2

3

2

1|

7

3

100

35

* 8* unsulphonated o i l r e p o r t e d present

2

2

(CH (CH ) CH(C H )CH ) C 0 C^H S0 Na

m

SIGMA ENGLAND

2

DIOCTYL SULPHOSUCCINATE

3

CH (CH ) CH=CH(CH ) S0 Na

MITSUBISHI JAPAN

2

LEONOX I.O.S. (MOL WT = 375)

3

85

H

1]

13-15 27-31(E°)30CH C0 Na

C

3

2

ICI ENGLAND

A3C

i n this

100

-

100

formulation

- 100

- 35

~ 60

-

-

~ 25

- 9

100

-

100

- 26

100

-

100

35

2

100

NONIONIC %

-

ANIONIC %

NATURE OF SURFACTANT COMPOSITION

100

% SURFACTANT ACTIVITY

Bu Ph(EO) S0 Na

7

10

HOECHST W GERMANY

2

6

5^27-31 (EO)yOH

8

D3620

3

CH (CH ) CH=CH(CH ) (EO) OH

SIGMA ENGLAND

POE10

1?

C H Ph(EO) OH

ICI ENGLAND

NP6

9

C-j

ICI ENGLAND

10

A7

3

Bu PL(EO) OH

CHEMICAL FORMULA OF MAJOR SYNTHESISED PRODUCT

HOECHST W GERMANY

SUPPLIER

SURFACTANT SAMPLES UNDER OBSERVATION

T100

TRADE NAME

TABLE I


-

7

-

*53

8

60

-

5

-

-

-

WATER CONTENT/*

-

-

-

INORGANIC SALT CONTENT/*

308

OIL-FIELD CHEMISTRY

inversion temperatures were measured i n w e l l s t i r r e d systems undergoing a temperature change o f t y p i c a l l y 1 K min" . Cooling p r o f i l e s were a l s o recorded and only when the conductivity measurements i n the heating and cooling cycles matched were the data recorded. S a l i n i t y loadings necessary f o r phase inversion a t a s p e c i f i c temperature were a l s o evaluated. Because o f p o t e n t i a l l y undesirable e f f e c t s such as g e l formation, test temperatures o f 40° o r 60° C were selected f o r these experiments. Aqueous solutions containing e i t h e r 150 o r 300 g dm" NaCl were prepared and used as t i t r a n t s t o promote phase inversion i n oil/water/surfactant systems. Care was taken t o maintain the water t o o i l r a t i o as close t o 1 as possible. The surfactant loadings necessary t o produce such phase inversions were r e l a t e d t o anticipated requirements f o r a l l pure o i l s and stock tank oils. For the purpose o f standardisation most t e s t s were performed on systems containing 5% W/V surfactant. 1


3

RESULTS NONIONIC SURFACTANTS Cloud Points The influence o f added NaCl on the observed cloud points o f 1% W/V solutions o f the four nonionic surfactants under observation are given i n Figure 1. Approximately l i n e a r correlations were observed as the aqueous NaCl l e v e l was increased, with negative c o e f f i c i e n t s recorded between 0.22 - 0.3 K.g~ dm . Higher loadings o f surfactant were found t o increase the cloud point. I t was observed a l s o that the i n c l u s i o n o f small quantities o f o i l s t o surfactant solutions could e i t h e r elevate o r depress the cloud point. The s i g n i f i c a n c e o f t h i s f a c t w i l l be developed l a t e r . 1

3

Phase Inversion Temperatures I t was possible t o determine the Phase Inversion Temperature (PIT) f o r the system under study by reference t o the condurtivity/teirperature profile obtained (Figure 2). Rapid declines were i n d i c a t i v e o f phase preference changes and mid-points were conveniently i d e n t i f i e d as the inversion point. The alkane s e r i e s tended t o y i e l d PIT values within several degrees o f each other but the estimation o f the PIT f o r toluene occasionally proved d i f f i c u l t . Mole f r a c t i o n mixing r u l e s were employed t o a s s i s t i n the p r e d i c t i o n o f such PIT values. Toluene/decane blends were evaluated r o u t i n e l y f o r convenience, as shown i n Figure 3. The construction o f PIT/EACN p r o f i l e s has y i e l d e d l i n e a r relationships, as d i d the mole f r a c t i o n o i l blends (Figures 4 and 5). The compilation and assessment o f a l l experimental data enabled the s i g n i f i c a n t parameters, a t t r i b u t a b l e t o such surfactant formulations, t o be tabulated as i n Table I I . The PIT dependence p r o f i l e s generated f o r the nonionic surfactants i n contact with alkanes are given i n Figure 6. T h e i r l i n e a r c o r r e l a t i o n s allow s u i t a b l e c o e f f i c i e n t s t o be extracted from these data which may be used i n l a t e r , derivable i n t e r relationships. I t was observed that v a r i a t i o n s i n the water t o o i l r a t i o (W0R) affected the recorded PIT (Figure 7). The


16. LAWLESS AND LEE-SNAPE

Characteristics of Surf octants


(AQUEOUS SURFACTANT LOADINGS =1%W/V)

* • O A

SIGMA POE 10 HOECHST T100 ICI A7 ICI NP6

NaCl SALINITY/g 100cm'

Figure 1. Cloud point variation for different (Aqueous surfactant loadings = 10 g/dm )

salinities

3

TEMPERATURE/C

Figure 2. alkanes

Conductivity/temperature

p r o f i l e s for the


309

OIL-FIELD CHEMISTRY


310

< Q_

01 0

Figure 4. alkanes

1

1 1 1 i I i I i I i 2 U 6 8 10 EQUIVALENT ALKANE CARBON NUMBER

I

12

i

14

Phase inversion temperature variation for the


Characteristics of Surfactants

16. LAWLESS AND LEE-SNAPE


60

SURFACTANT = ICI NP6 (AQUEOUS SURFACTANT) = WATER : OIL RATIO = 1 AQUEOUS SALINITY z 1 %

0-2 0-4 0-6 08 MOLE FRACTION TOLUENE IN DECANE

Figure 5. Phase inversion temperature v a r i a t i o n for toluene/decane blends

^80

SYNPERONIC NP6 SAP0GENAT T100 SYNPERONIC A7 POE 10 0LEYL ETHER

20

LU

3 J

2

J

L_

i

L

6 8 10 12 EQUIVALENT ALKANE CARBON NUMBER

U

14

Figure 6. Variation of phase inversion temperature with equivalent alkane carbon number


311


d PIT

35

50

3.4

2.3

5.2

10

50

200

HOECHST T100

SIGMA POE 10 OLEYL ETHER -

-

23

14

24

*62

65

61.5

-

74

-

32

9

23

GULLFAKS CRUDE

-

CYCLO HEXANE

35

TOLUENE

*62

65

60.5

74

20

NINIAN CRUDE

OIL PIT/°C (MEASURED OR EXTRAPOLATED)

7.6

-

7.9

- 16

-

- 12

- 16

TOLUENE

StructureâPerformance Characteristics of Surfactants in Contact with

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