Immiscible Microemulsion Flooding

ROBERT N. HEALY EXXON PRODUCTION RESEARCH CO.

RONALD L. REED HOUSTON
MEMBERS SPE-AIME

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ABSTRACT microemulsion flooding.
The first of these papers 1 identified micellar
Economical microemulsion flooding in·evitably structures above the binodal curve and showed how
involves microemulsion phases that are immiscible the region of miscibility could be maximized at the
with water, oil, or both. Oil recovery is largely expense of the multiphase region, thereby prolonging
affected by displacement efficiency in the locally miscible displacement. This was accom-
immiscible regime. Therefore, it is pertinent to plished by varying salinity, and the notion of
study this immiscible aspect in relation to variables optimal salinity was introduced as that which
that affect phase behavior and interfacial tension minimized the extent of the multiplrase region.
between phases. This is accomplished through core Interfacial tensions within the multiphase region
flooding experiments wherein microemulsions were measured and found to vary nearly three orders
immiscible with oil and/or water are injected to
of magnitude, depending on WOR and surfactant
achieve enhanced oil recovery. One advantage of concentration. Careful isothermal pre-equilibration
such an immiscible microemulsion flood is that
of bulk phases was a requisite to all interfacial
s~rfactant concentration can be small and slug
tension measurements.
szze large, thereby reducing deleterious effects
The second paper 2 emphasized core flooding
of reservoir heterogeneity,· a disadvantage is that
b~havior and distinguished locally miscible
the temporary high oil recovery accompanying
displacement before slug breakdown, from immiscible
locally miscible displacement before slug breakdown
displacement occurring thereafter. Fractional oil
is reduced.
flow was correlated with capillary number 3-6 and
Final oil saturation remaining after lower, middle-,
it was found that an effective immiscible displace-
and upper-phase microemulsion floods is studied as
m~nt. cannot be distinguished from the locally
a function of salinity, cosolvent, temperature, and
m1sc1ble case. Further, during an effective flood,
surfactant structure; and results are related to
the greater part of the oil was recovered during the
interfacial tension, phase behavior, and solubiliza-
immiscible regime. Finally, it was shown that
tion parameters. A conclusion is that immiscible
micellar structure within the miscible region is not
microemulsion flooding is an attractive alternative
of itself an important variable.
to conventional microemulsion processes.
Oil recovery obtained from microemulsion slugs Having determined that the immiscible aspect of
is correlated with capillary number based on what a microemulsion flood was important and dominant,
zs called the controlling interfacial tension. the third paper7 dealt extensively with the
Physically, this means the least effective of the multiphase region. Microemulsions were classified
displacement processes at the slug front or rear as lower-phase (l), upper-phase, (u), or middle-phase
determines the flood outcome. (m) in equilibrium with excess oil, excess water,
Finally, a screening procedure is developed that or both excess oil and water, respectively.
is useful for either immiscible or conventional Transitions among these phases were studied and
microemulsion floods and that can reduce the number systematized as functions of a number of variables.
of core floods required to estimate oil recovery Solubilization parameters for oil and water in
potential for a candidate microemulsion sys tern. microemulsions were introduced and shown to
correlate interfacial tensions. The middle-phase
INTRODUCTION was identified as particularly significant because
microemulsion/ excess-oil and microemulsion/
This ls the fourth 1n a sequence of papers excess-water tensions could be made very low
dealing with miscible and immiscible aspects of simultaneously.
In this paper, the sequence is continued by
Original manuscript received in Society of Petroleum Engineers
office Jan. 16, 1976. Paper accepted for publication Nov. 3, introducing the notion of an immiscible microemulsion
1976. Revised manuscript received Dec. 9, 1976. Paper (SPE flood as one having an injection composition in the
5817) was first presented at the SPE-AIME Fourth Symposium
on Im~roved Oil Recovery, held in Tulsa, March 22-24, 1976. © neighborhood of the multi phase boundary. 8 The
Copynght 1977 American Institute of Mining, Metallurgical, and primary fluids injected are micro emulsions that, for
Petroleum Engineers, Inc.
This paper will be included in the 1977 Transactions volume. all practical purposes, are immiscible with oil

APRIL, 1977 129

and/ or water. Interfacial tensions can be extremely that microemulsion effectively displace oil at the
low and oil recoveries high, so that immiscible slug front and be effectively displaced by water at
microemulsion flooding is considered to have the slug rear. Both aspects are essential. For an
practical as well as academic value. immiscible microemulsion floodin·g process to meet
Remarkably, study of the multi phase region has these requirements, the microemulsion-oil interfacial
not only assisted in understanding immiscible tension (ym 0 ) and the microemulsion-water interfacial
aspects of microemulsion flooding but, as will be tension (y mw ) must both be low. 7
seen, in understanding certain of the miscible Although both y mo and Ym w influence the outcome
aspects as well. of an immiscible microemulsion flood, the concept
of controlling interfacial tension, y c, defined by
EXPERIMENTAL PROCEDURE Yc = max(Ymo' Ymw), finds application. Thus,
y c = Ymo for lower-phase microemulsions; Yc = Ymw
Microemulsions were always prepared by for upper-phase microemulsions; and for middle-
isothermal equilibration of the over-all composition

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phase microemulsions, y c may be either y mw or
3 percent 63/37 MEACNOXS/ co solvent,* Y percent Ymo, depending on which is greater. It is of
brine and (97- Y) percent oil (Appendix A). Carbon interest that Yc is minimized when Ymo = Ymw. The
number of the alkyl side chain, N, was either 9 or controlling interfacial tension is particularly
12, and cosolvent was t-amyl alcohol, unless important s1nce it enables development of
stated otherwise. The WOR used to prepare the correlations between oil recovery and capillary
microemulsion was unity; that is, the over-all number. These correlations then serve as a guide
composition corresponds to 48.5-percent brine and in screening microemulsions for oil-recovery
48.5-percent oil, unless otherwise stated. Brine potential.
salinity (percent NaCl) is a variable.
Floods were conducted in 4-ft x l-in. x l-in. CORRELATIONS OF OIL RECOVERY
horizontally disposed cores, cut from a single slab WITH CAPILLARY NUMBER
of Berea rock. The average of the absolute brine
permeabilities of all cores used was 492 ± 96 md, CONTINUOUS INJECTION
and the average of the core residual oil saturations Lower-, middle-, or upper-phase microemulsions
was 33.6 ± 1.5 percent PV. Cores used in 74 °F having N = 9 or 12 were used in core flooding
floods were cast in epoxy, while those used at experiments wherein microemulsion was injected
150 °F were mounted in a Hassler-type holder. The continuously. The floods were conducted at constant
entire flooding procedure, from initial brine rate in the range 0.5 to 2.3 ft/D, and fractional
saturation to termination of the microemulsion flows of oil, f0 , and water, f w, during production
flood, was performed isothermally using an air of the stabilized oil bank were measured. Flooding
bath. rate, brine salinity, microemulsion type and
The cores always contained discontinuous viscosity, interfacial tension, capillary number, f 0 ,
residual oil and continuous brine at the start of and /, are tabulated for these floods in Table 1.
microemulsion injection. The same volume of w
Fractional flow data can be correlated wlt 'h
surfactant was used in all floods employing capillary number, Nc , provided Nc is calculated
microemulsion slugs. Accordingly, bank sizes were using the controlling interfacial tension; that is,
selected so that B x C5 = 32, where B is bank size Nc = Vf1/y c. However, the fractional flow that
in percent PV and C5 is concentration of correlates depends on whether microemulsion-oil or
MEACNOXS in volume percent. microemulsion-water tension is controlling. If
Mobility control was considered in all floods, Yc = Ymo, f 0 increases with Nc (Fig. la); and if
and is discussed in Appendix B. Unless otherwise Yc = Ymw, fw increases with Nc (Fig. lb). Data in
stated, microemulsion slugs were displaced through Fig. 1 also show that neither correlation depends
continuous injection of brine containing 1 ,000-ppm significantly on N.
XC biopolymer. All floods were conducted at a con- It has been established that fractional flow of
stant velocity (q/A cp) of about 1 ft/D unless otherwise oil or water during stabilized oil-bank production
specified. Also, in every case, core residual oil depends on the amount of water and oil bypassed
was the same as oil used to form the microemulsion, by microemulsion.9 Results in Fig. 1 suggest that
and core resident brine was the same as brine used
when y c = Ymo, nearly all the resident water is
to prepare microemulsion and thickened drive water.
displaced by microemulsion; and / 0 depends then
This mode of operation enabled results to be
on the amount of bypassed oil which, in turn, is a
interpreted more easily than otherwise.
function of Ymo. Similarly, when Yc = Ymw, nearly
all the residual oil is displaced; then fw depends
CONTROLLING INTERFACIAL TENSION on the amount of bypassed water, which is a
It has been conjectured that an efficient function of y mw·
immiscible microemulsion flooding process requires
SLUG INJECTION
Slugs of lower-, middle-, and upper-phase
*Unless otherwise stated, all concentrations except for salt microemulsions having N = 12 were injected at
concentrations refer to volume percent. Salt concentrations are
in gm/100 ml, reported as percent. constant rates in the range 0.5 to 1.3 ft/D and final

130 SOCIETY OF PETROLEUM ENGINEERS JOURNAL

 TABLE 1 -CONTINUOUS MICROEMULSION INJECTION FLOODS
Microemulsion
v Salinity Microemulsion Viscosity at Ymo Ymw Yc
N (ft/D) (percent NaCI) Type 23 sec- 1 (cp) (dyne/em) (dyne/em) (dyne/em) Vf-1/Yc fo fw
9 0.8 2.0 I 2 2.7X 10- 1 0.0 2.7 X 1o- 1 2.1x1o-s 0.00 1.00
9 0.5 7.0 u 3 0.0 6.0 X 1o- 2 6,0 X 10- 2 8.8 X 1o- 5 0.63 0.37
9 1,0 1.0 2 6.5x 10- 1 0,0 6.5X 10- 1 1.1x1o-s 0,00 1.00
9 1.1 2.0 2 2.7 X 1o- 1 0.0 2.7 X 10- 1 2.9 X 1o- 5 0.07 0.93
9 1.0 3.0 4 9.0 X 10- 2 0.0 9.0 X 1o-2 1.6 X 1o- 4 0,23 0.77
9 1.2 3.8 m 12 2.2 X 10- 2 1.0x1o- 2 2.2 X 1o- 2 2.3 X 1o- 3 0,33 0.67
9 1' 1 5.0 m 26 1.2 X 1o- 2 2.2 X 10- 2 2.2 X 10- 2 4.6 X 10- 3 0.39 0.61
9 1.0 7.0 u 3 0.0 6.0 X 10-2 6.0 X 10-2 1.8 X 10-4 0,69 0.31
9 1,0 8.0 u 5 0.0 1.2x1o- 1 1.2x1o- 1 1.5x 1o-4 0,59 0.41
9 2.3 2.0 2 2.7 X 10- 1 0.0 2.7x1o- 1 6.0 X 10- 5 0,09 0.91

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9 2.0 7.0 u 3 0.0 6.0 X 1o-2 6.0 X 10-2 3.5 X 10-4 0.71 0,29
12 0.5 0.5 3 4.5 X 1Q-2 0.0 4.5 X 10-2 1.2x1o-4 0,13 0.87
12 0.5 1.25 12 8.0 X 10-3 0.0 8.0 X 10- 3 2.6 X 1o- 3 0.40 0.60
12 0.5 2.5 u 6 0.0 4.0 X 1o-2 4.0 X 10-2 2.6 x 1o-4 0.62 0.38
12 0.9 0.5 3 4.5 X 1o- 2 0.0 4.5 X 10-2 2.1 X 1o- 4 0.13 0.87
12 1.0 1.0 3 1.5 X 1Q-2 0.0 1.5 X 10-2 7.0 X 1Q-4 0.18 0.82
12 1 .. 0 1.25 12 8.0 X 10-3 0.0 8.0 X 10-3 5.3 X 1o-~ 0.32 0.68
12 1.0 1.4 m 11 1.0x1o- 3 5.0 X 10-4 1.ox 1o- 3 3.9 X 1o- 2 0.37 0.63
12 1.0 1.5 m 10 7.0 X 10-4 3.0 X 1o- 3 3.0 x 1o-3 1.2.x 10- 2 0.42 0.58
12 1.0 1.75 m 13 3.0 x 1o-4 2.7 X 1o-2 2. 7 X 1o-2 1.7X 10- 3 0.43 0.57
12 1.0 2.5 u 6 0.0 4.0 X 1o-2 4.0 X 1o-2 5.3 X 1o-4 0.52 0.48
12 1.0 3.0 u 4 0.0 6.1x1o- 2 6.1 X 1o-2 2.3 X 1o- 4 0.65 0.35
12 2.2 0.5 I 3 4.5 X 1o-2 0.0 4.5 X 10-2 5,1 X 1o- 4 0.13 0,87

oil saturation, sof' was determined from surfactant retention. Although the correlation is
expected to depend on properties of the specific
system of interest, it is conjectured that so/
decreases with Nc for all systems having favorable
A summary of these floods appears in Table 2 mobility, provided surfactant retention does not
where salinity, microemulsion type and viscosity, dominate oil-recovery behavior.
interfacial tension, bank size, flooding rate, and A possible physical interpretacion of results from
S 0 1 are given. Microemulsion compositions can be these slug floods is that Ymo determines the
calculated from information in the table. Fig. effectiveness of the displacement of oil b'y
2 shows that S0 / broadly decreases with Nc, but microemulsion at the slug front,· while displace-:-
the correlation depends on which tension is ment of microemulsion by drive water at the slug
controlling. The scatter was anticipated in view of rear is cOii'ltrolled by Ymw' The least effective of
changing injection composition, mobility ratio, and these displacements determines the outcome.

0.5 a OIL RECOVERY IN RELATION

...I TO SEVERAL VARIABLES
~ 0.4 •N=9
o3: •N=12 Some effects of salinity, surfactant and cosolvent
~
(.)LL
g 0.3
molecular structures, temperature, and composition
<(...I on oil recovery were determined using immiscible
a:-
u..O
microemulsion slugs .
...,o
0 SALINITY
10-6 10-1
Lower-, middle-, and upper-phase microemulsions
0.7 b
. having N = 9 or 12 were used to evaluate the effect

/
0.61- •N=9 of salinity on oil recovery. Physicochemical and
...I •N=12
<(3: 0,51-
zo ~ 40~-----------------------------------,
0....1 0,41- w
~ LL
Ua: • • 6...Ia..ffi
N=12 - • Yc=Ymo
<(W 0.31- • •
30 ... - - • Yc=Ymw

fE~ Yc=Ymw
~ z 20
~3: 0,21- _o ...
.... ~~
0,11- oa:
CIJ::::>
•
0
10-6
o1
1~ 1~ 1r 1~
,I ol

1~
~
CIJ
OL-~--~~~u_--~~~LU~--~~~~~
10-4 10-3 10-z io-,
Nc, CAPILLARY NUMBER= v11/yc Nc, CAPILLARY NUMBER=vJ-1/Yc

FIG. 1 - FRACTIONAL FLOW FOR CONTINUOUS FIG. 2 - OIL-RECOVERY /CAPILLARY -NUMBER

FLOODS. CORRELATION FOR SLUG FLOODS, N = 12.

APRIL, 1977 131

 TABLE 2 - MICROEMULSION SLUG FLOODS, N = 12
Microemulsion
v Salinity Microemulsion Viscosity at Slug Size Ymo Ymw Yc Sot
(ft/D) (percent N aCI) Type 23 sec- 1 (cp) (percent PV) (dyne/em) (dyne/em) (dyne/em) Vf1/Yc (percent PV)
0.7 0.5 I 3 10 4.5 X 1o-2 0.0 4.5 X 1o- 2 1.6x1a-4 22
0.8 1.0 I 3 11 1.5 X 10-2 0.0 1.6x1o-2 5.6 X 10-4 9
0.5 1.5 m 10 10 7.0 X 10- 4 3.0 X 10- 3 3.0 X 1() 3 5.8 X 10- 3 15
0.6 2.0 u 10 11 0.0 5.8 X HJ- 2 5.8 X 1o- 2 3.6 X 1a- 4 12
0.6 3.0 u 4 10 0.0 6.1x1o-2 6.1x1o-2 1.4X10-4 21
1.1 0.2 3 9 1.0 X 10- 1 0.0 1.0X1CJ
1
1.2X 1CJ 4 13
1.3 0.5 3 10 4.5 X 1Q-2 0.0 4.5 X 1o-2 3.0 X 10-4 10
0.9 1.0 3 11 1.5 X 1o- 2 0.0 1.5x1o-2 6.3 X 1CJ4 7
1.2 1.25 12 12 8.0 X 10- 3 0.0 8.0 X 10- 3 6.3 X 10- 3 8
1.2 1.4 m 11 11 1.0 X 10-3 5.0 X 10-4 1.0 X 10-3 4.6 X 1o- 2 8
1.5 m 10 10 7.0 X 10-4 3.0 X 10- 3 3.0 X 10- 3 1.4X 1o- 2 6

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1.2
1.0 2.0 u 10 11 0.0 5.8 X 10- 2 5.8 X 1a- 2 6.0 X 1CJ 4 13
1.3 2.5 u 6 10 0.0 4.0 X 10- 2 4.0 X 1CJ 2 6.8 X 1()4 16
0.9 3.0 u 4 10 0.0 6.1 X 1o- 2 6.1x1a- 2 2.1 X 1o- 4 28

TABLE 3 - MICROEMULSION SLUG FLOODS, N =9

Microemulsion
v Salinity Microemulsion Viscosity at Slug Size Ymo Ymw Sot
(ft/D) (percent NaCI) Type 23 sec- 1 (cp) (percent PV) (dyne/em) (dyne/em) (percent PV)
1.1 1.0 I 2 9 6.5 X 10- 1 0.0 30
1.0 1.5 2 9 0.0 31
1.2 2.0 2 10 2.7 X 10- 1 0.0 27
1.0 2.5 3 10 0.0 26
1.0 3.0 4 10 9.0 x 1o-2 0.0 20
1.1 3.8 m 12 4 2.2 x 1o- 2 1.0 X 10-2 21
1.0 4.5 m 12 4 28
1.0 5.0 m 26 3 1.2 X 10-2 2.2 X 10-2 30
1.0 7.0 u 3 9 0.0 6.0 X 1o- 2 30
1.0 8.0 u 5 9 0.0 1.2x 1o- 1 29
*Interfacial tension not measured.

flooding data pertinent to these experiments are NaCl and S 0 / = 0.06. These results are consistent
included in Tables 2 and 3. with the fact that both Cy and interfacial tension
For N = 9, Fig. 3 gives S0 / and interfacial at Cy decrease with N. 7
tension as functions of salinity. Even though
variables such as mobility control and surfactant COSOLVENT
retention undoubtedly influenced these floods, Immiscible microemulsion floods were conducted
there is, nevertheless, a connection between S of corresponding to N 12 and two different
and interfacial tension. The salinity corresponding cosolvents, t-amy 1 alcohol (TAA) and t-buty 1 alcohol
to minimum S 0 I is termed optimal salinity for oil
2
recovery, and is denoted by C*. Previously, (.)
........
interfacial-tension optimal salinity, Cy, was defined w
2
as the salinity corresponding to Ymo = Ymw .7
c>
Results in Fig. 3 show that, for N = 9, C* = 3.0-percent ;i 10-1
NaCl and Cy = 4.4-percent NaCl. Fig. 4 shows So/ 0
and interfacial tension as functions of salinity Cii
2
for N = 12; C* = 1.5-percent NaCl and Cy = 1.4-percent w
1-
NaCl. ...J
<(
Results in Figs. 3 and 4 indicate. that for N = 9 c:;
or 12, C* ~ Cy- Since Yc is minimized at Cy, an ~
alternative description is that minima of so/ and a:
w 1-
1- 2
Yc occur at nearly the same salinity. Evidently, 2 w
both Ymo and Ymw must be low if high oil recovery 32 ...J ~
is to be achieved.
28 ~<(2~
SURFACTANT STRUCTURE 24 2 0
U:::i=
A comparison of graphs of S0 / vs salinity for .<(
20 b a:
N = 9 and 12 appears in Fig. S. Pertinent data are UJ::J
tabulated in Tables 2 and 3. Oil recovery is ~_L~~~~_L~~_L~~~16 <(1-
0 2 3 4 5 6 7 8 CJ)
strongly dependent on surfactant structure. For SALINITY, % NaCI
N = 9, C* = 3-percent NaCl, corresponding to a
FIG. 3 - INTERFACIAL TENSION AND OIL
minimum of S0 / = 0.20. For N = 12, C* = 1.4-percent RECOVERY, N = 9.

132 SOCIETY OF PETROLEUM ENGINEERS JOURNAL

 TABLE 4 - MICROEMULSION SLUG FLOODS, N = 12, TBA
Microemulsion
v Salinity Microemulsion Viscosity at Slug Size Ymo Ymw sol
(it/D) (percent NaCI) Type 23 sec-1 ( cp) (percent PV) (dyne/em) (dyne/em) (percent PV)
1.3 0.5 I 2 9 1.2 X 10- 1 0.0 13
1.1 1.0 2 9 0.0 8
1.1 1.5 17 10 1.5X 10- 2 0.0 6
1.2 2.0 m 11 9 4.0 X 1o-3 1.3 X 10- 3 9
1.2 2.25 m 11 9 1.8 X 10- 3 1.5 X 10- 3 12
1.0 2.5 m 21 8 9.0 X 10-4 5.0 X 1o- 3 22
1. 1 2.75 m 19 10 4.0 X 10-4 8.0 X 10-3 24
1.0 3.0 u 9 10 0.0 24
0.9 4.0 u 5 10 0.0 29
*Interfacial tension not measured.

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TABLE 5 - MICROEMULSION SLUG FLOODS, 150°F
Microemulsion
v Salinity Mlcroemulsion Viscosity at Slug Size Ymo Ymw sol
N (ft/D) (percent NaCI) Type 23 sec- 1 (cp) (percent PV) (dyne/em) (dyne/em) (percent PV)
9 0.9 3.4 I 3 9 7.8 X 10- 2 0.0 30
9 1.0 4.0 I 2 9 9.9 X 10-2 0.0 29
9 1.1 5.2 m 7 3 3,5 X 10-2 1.2 X 10- 2 20
9 1.0 6.0 m 4 4 2.0 X 10- 3 4.1 X 10- 2 24
9 0.8 7.0 m 6 3 3.0 X 10- 3 6.6 X 10- 2 29
9 0.9 8.0 m 9 1 3.0 x 1o-3 4.2 X 10- 2 28
9 1.0 12.0 u 2 9 0.0 1.9 X 10- 1 30
12 1.1 1.0 9 7.7 X 10-2 0.0 24
12 1.1 2.0 m 8 7 4.0 X 10-3 * 19
12 0.9 2.4 m 8 6 4.0 X 10-3 3.0 X 1o- 3 15
12 0.9 2.8 m 10 6 2.0 X 10- 3 4.0 x 1o- 3 19
12 1.2 3.2 u 7 10 7.0 X 1o-4 2.3 X 1o-2 24
12 0.8 4.4 u 13 9 0.0 1.2 X 10- 1 25
* lnterfaci al tension not measured.

(TBA) (Tables 2 and 4). Graphs of S0 ! as functions core floods at 7 4 and 150 °F using microemulsions
of salinity for these cosolvents are quite similar for which N = 9 or 12. Physicochemical and flooding
(Fig._6). For both alcohols, C* = 1.4-percent NaCl data are included in Tables 2, 3, and 5.
and S0 f = 0.06 there. This is consistent with the Final oil saturation for N = 9 is graphed as a
similarity between the graphs of interfacial tension function of salinity for 7 4 and 150 °F in Fig. 7. C*
vs salinity for these alcohols. 7 increases with temperature, consistent with the
fact that Cy,. for this system also increases with
TEMPERATURE temperature. 7 Furthermore, S 0 at C* is 0.20 and is
Temperature effects were studied by conducting independent of temperature. This is expected since
interfacial tension at Cy is only weakly

I
,_
...._--.r-"'
,. temperature-dependent for this system. 7

35~----------------------------~
I 1-
I zw
/Ymw (J
--I a:
w
f D.
I z
0
i=
<t
28 1-
a:
2 ::>
24 ..J
w
(J ~
en
20 °~
..J
<( 2
..J
0
..J
16 ~ Q <t
12 ~
..::.
z
Oa: u::
8 CJ) ::> .j:..
0
~ en
L____l~---'-_l__l____L__l___J____L_.l~-,-J--:--'---::-~--=-'-::--'--=-' 4 CJ) 0
0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.4 0 9
SALINITY,% NaCI SALINITY,% NaCI
FIG. 4 - INTERFACIAL TENSION AND OIL FIG. 5 - EFFECT OF SURFACTANT STRUCTURE ON
RECOVERY, N = 12. OIL RECOVERY.

APRIL, 1977 133

 TABLE 6 - MICROEMULSION SLUG FLOODS, N = 12, WOR = 90/7
Microemulsion
v Salinity Microemulsion Viscosity at Slug Size 8ot
(ft/D) (percent NaCI) Type 23 sec- 1 (cp) (percent PV) (percent PV)
1.2 0.2 s 2 17 29
0.9 0.5 s 2 17 11
1.1 1.0 s 2 17 12
1.0 1.25 s 2 17 11
1.1 1.5 s 4 17 5
1.0 1.75 I 3 17 11
1.0 2.0 u 51 5 9
1.1 2.5 u 84 3 21
1. 1 3.0 u 84 3 25
*s = single-phase over-all composition.

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For N = 12, Fig. 8 shows that both C* and 50 / at
C* increase with temperature. This is consistent 35
with the corresponding interfacial-tension behavior. 7 1-
2
COMPOSITION
w
(J
All the floods considered thus far used a:
w
microemulsions formed by equilibrating over-all a..
compositions having WOR = 1. At salinities near
..
2
C*, these microemulsions usually have a high oil 0
concentration of 30 to 70 percent. It is an economic ~
advantage to reduce oil content; therefore, oil <t
a:
recovery was examined for microemulsions formed ::::>
by equilibrating over-all compositions having WOR 1-
<t
>>I. en
Microemulsion properties and flooding conditions ...J
for tests wherein N = 12 and WOR = 90/7 are given 0
in Table 6. High microemulsion viscosities at 2.0-, ...J
2. 5-, and 3.0-percent NaCl required using 1, 500-
<t
2
ppm XC biopolymer in the drive water to insure a u::
favorable displacement at the slug rear for these ..:.
0
salinities. Fig. 9 shows a comparison between a en
0
0 2 4 6 8 10 12 14
35
1- SALINITY, o/o NaCI
zw
(.)
a:
w
c.. /
,.
TBA
FIG. 7 - EFFECT OF TEMPERATURE ON OIL
RECOVERY, N = 9.

35
... / 1-
z zw
0 (.)
c:r: 74° F
w
~
a:
c..
z
~
1-
<(
(/)
_.
0
~
c:r:
:::>
''' \
\
0
~
_. 10
(/)
...J
<( 0
z ...J
<t
u:: z
....0 u:::
.....
(/) 0
(/)
0 0
0 1 4 5 0 6
SALINITY, % NaCI SALINITY, % NaCI
FIG. 6 - EFFECT OF COSOLVENT ON OIL FIG. 8 - EFFECT OF TEMPERATURE ON OIL
RECOVERY, N = 12. RECOVERY, N = 12.

134 SOCIETY OF PETROLEUM ENGINEERS JOURNAL

 graph of S0 ! as a function of salinity for N = 12 suggests that, for these systems, C* can be
and WOR = 90/7, and the corresponding graph for estimated from solubilization parameters.
WOR = 1. The two curves are quite similar, and it Further, it is conjectured that oil recovery from
is noteworthy that in both cases C* = 1.5-percent slug injection is maximized with respect to any
NaCl. Also, for both WOR's, S 0 ! at C* is 0.06. variable of interest (X) when Ymo ~ y mw· It has
Evidently, for this system, oil recovery is only been shown 7 for several variables that Xy e:t X¢·
weakly dependent on WOR. This is consistent with Hence, it is conjectured that X* :::::X¢· This finds
a similar finding for injection compositions in the
application in the following development of a
single-phase region when surfactant concentration
screening method.
and bank size were constant. 2

SUMMARY SCREENING METHOD

Final oil saturation from immiscible micro emulsion For a given system, results presented here

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core floods using slug injection was determined as suggest a method that can be applied to reduce the
a function of salinity, surfactant structure, and number of laboratory core floods needed to
temperature. In every instance, there was an evaluate oil-recovery behavior. Specifically, the
optimal salinity where S0 ! achieved a relative screening method is used to estimate the value of
minimum. Fig. 10 provides a convenient summary a variable corresponding to maximum oil recovery
of these floods; it shows relationships among the from slug injection. In addition, the method is
variables C*, temperature, S0 !, and N. Several useful for estimating oil-recovery potential. The
trends are evident. For constant N, C* increases approach is developed in terms of immiscible
with temperature. At constant temperature, increas- microemulsion flooding; however, as described
ing N corresponds to decreasing both C* and Sof· later, it also finds application in locally miscible
These trends are consistent with previously microemulsion flooding. 2, 10,11
reported relations among Cy, temperature, optimal It is assumed that X*-:::: X¢ and oil recovery from
interfacial tension, and N. 7
slug injection depends on N c (y c). Situations may
For all the systems wherein oil recovery from
microemulsion slug injection was determined as a
function of salinity, maximum recovery corresponded 6
to Ymo c: Ymw ; or, alternatively, oil recovery was
uco •• S 0 f, FINAL OIL SATURATION, PERCENT
...
z
~
maximized when salinity was in the neighborhood
of Cy. It has been previously established that Cy :::::!. ...~ >a:
0~

-----'N=9
-- -- - - - - 20.0

C¢, where C¢ is the salinity where the solublizauon

parameter for oil in microemulsion (V0 /V 5 ) equals
<(
en w
...1
<(
>
0 "'20.;
---
2 (.)
w
the solubilization parameter for water in i= a:
a..
microemulsion (V w /Vs ).7 Therefore, it follows that 0
...1
0 6.0
C* e:t C¢>. Fig. 11 shows that, for slug floods con- *' a:
(.)
0
ducted to determine the effects of salinity, surfactant LL 0
and cosolvent molecular structure, and temperature, 60
TEMPERATURE, °F
C* is indeed approximately equal to C¢. This
FIG. 10 - EFFECT OF TEMPERATURE, SALINITY,
AND SURFACTANT STRUCTURE ON FINAL OIL
SATURATION.
35 6~-------------------------------,
1-
zw
(..)
WOR=1/1 (3
a:
~~
0
w
a.
z '
\
\
\WOR=90/7
1/
z'#.
:::i>
<(a;:
~ \ enw
a:
::>
\
\
...J>
<(0
~~
•
~
en \ 1-a::
ll....J Vrv1 FT/DAY
...J \ o-
*. 0 B x C5 =32
0
...J ua:: WOR=1/1
<( 0
z LL
u:::
~
0
en 1 2 3 4 5 7
0 Ccf>, OPTIMAL SALINITY
0 3.5
SALINITY, % NaCI FROM PHASE BEHAVIOR, % NaCI
FIG. 9-EFFECT OF WOR ON OIL RECOVERY, N = 12. FIG. 11 - CORRELATION BETWEEN C"' AND C cp·
APRIL, 1977 135
arise wherein variables such as mobility control or advantage. In this case, X¢ is determined as above;
surfactant retention influence oil recovery in such but the best oil recovery is established from core
a way that these assumptions are invalid; neverthe- floods using microemulsions equilibrated at high
less, we have found the approach applicable to a WOR in the over-all mixture. In one case reported
number of anionic surfactant systems. here, maximal oil recovery and C* were independent
A set of samples is prepared having a fixed of WOR.
over-all composition of surfactant, cosolvent, brine,
and oil, where some variable is changed in a CONNECTION BETWEEN LOCALLY
monotonic manner. Among variables of interest are MISCIBLE AND IMMISCIBLE
surfactant and cosolvent molecular structure, MICROEMULSION FLOODING
temperature, salinity, and oil composition. In many
of the examples considered here, the selected The immediate vicinity of the multi phase boundary
over-all composition was 3-percent 63/37 surfactant/ is the demarcation between injection composj tions
for miscible-type,lO high-concentration,l2 or

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cosolvent, 48.5-percent oil, and 48.5-percent
X-percent NaCl, where X was varied. A WOR of soluble-oilll microemulsion floods, on the one hand,
unity is preferred because it enables easy and and immiscible microemulsion floods on the other.
accurate determination of solubilization parameters. It has been pointed out that minimizing height of
Samples are thoroughly mixed and allowed to remain the multiphase boundary prolongs locally miscible
undisturbed at constant temperature until the initial microemulsion displacement,l,2 whereas decreasing
opaque emulsion completely disappears, and controlling interfacial tension enhances immiscible
distinct translucent phases remain. Graphs of~ /V s microemulsion displacement. A question arises as
and Vw /V5 as functions of X are then prepared, to whether these two considerations are related or

X¢ is determined, and the viscosity of each quite independent. The following developments
microemulsion phase is measured. According to the answer this question and make use of the result.
hypothesis, oil recovery should be maximal in the INTERFACIAL TENSION - SOLUBILIZATION
neighborhood of Xc:p. PARAMETER CORRELATION
Values of Vf1/y c for the various microemulsion Figs. 12a and 12b show correlations between
phases are determined and used to provide estimates Ymo and V0 /V5 and between Ymw and Vw/V5 ,
of oil-recovery potential. The value of Nc that is
respectively. These data were published previously,
sufficiently large for good oil recovery depends on
and a large number of anionic surfactant systems
the specific system. The Ym 0 -V0 /V5 and Ymw-
were found to exhibit this general behavior.7 The
Vw /V5 correlations 7 are used to reduce the number
solid curves shown result from fitting these data
of interfacial tension measurements required. If N c
with the equations
is sufficiently large in the neighborhood of X¢.,
laboratory core floods are run to determine oil
recovery as a function of X. A graph of S0 ! vs X
determines X* and the minimum value of S01 . If N c
is not sufficiently large, no core flooding and
experiments are needed smce none of the
microemulsions has good oil-recovery potential.
A modification of the screening method sometimes
using the parameters,
can be applied to develop effective high-water-
content microemulsions, which have an economic

~ a
a: ~ 10° b
W(.)
..... ~ .............
-w <(W
o2
3:~
2'>
c 10-1 I c 10-1
0 2 ..
-2 02
~0 -o
(/)_
::::>Ci) ....1(/)
~ 2 10-2 ::::> 210-2
ww ~w
Ol- wl-
a: ....I 0....1
(.)<( a:<(
~ 0 10-3 ~ ~ 10-3
.. ~ ~LL
oa: .. a:
Ew ~w
>--t- El-
2 10-4 >-. 210-4
- 0 2 4 6 8 10 12 14 16 - 0 2 4 6 8 10 12 14 16 "18 20
Vo/Vs Vw/Vs
FIG. 12- INTERFACIAL-TENSION/SOLUBILIZATION-PARAMETER CORRELATIONS.

136 SOCIETY OF PETROLEUM ENGINEERS JOURNAL

 a = 6.285 b = 12.167 microemulsion floods are also favorable to locally
log Ymo' = -7.058 log Ymw' = -12.856 miscible microemulsion floods; therefore,. the
screening method developed here is applicable to
m 0 = 0.04477 mw = 0.01280.
both approaches to oil recovery.
Note that in the limits of zero V0 /V8 or Vw /V5 ,
the intercepts are 0.17 and 0. 20 dyne/ em, SUMMARY AND CONCLUSIONS
respectively. There is sufficient scatter that these
Immiscible microemulsion flooding is defined
data could have been easily fit with indentical
and studied using lower-, middle-, and upper-phases
intercepts. The value of the intercept is of the
in core floods where several variables of interest
same order of magnitude as the interfacial tension
are changed. Data from more than seventy 4-ft core
between excess water and excess oil at Cy-
floods are presented and interpreted in terms of
INTERFACIAL TENSION AND HEIGHT OF Ymo and Ymw· Results provide support for our prior

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THE MULTIPHASE BOUNDARY contention 1,2, 7 that immiscible microemulsion
Along any line passing through C s = 1, (that is, displacement of residual oil and water is related to
100-percent surfactant), Vw/V0 is a constant, say interfacial tension measured between phases that
e. Since C0 + Cw + C5 = 1, then Cw/C 0 = Vw /V 0 , previously have been bulk equilibrated. Further,
the concept of a controlling interfacial tension,
C0 /C 5 = V0 /V5 , and Cw/C 5 = Vw/V 8 • It follows
that Yc = max (Ymo' Ymw), is introduced and found
useful.
a . . . (3) The following statements pertain to continuous

(l:o ~)C ~scs) +1

microemulsion injection.
1. If Ymo controls, f 0 increases with N c; most
of the resident water is displaced; and f 0 depends
on the amount of bypassed oil, which is a function
b . . ( 4)
~)c- cs)
of Ymo·
(mw
1+e cs
+1 2. If y mw controls, f w increases with N c; most
of the residual oil is displaced; and f w depends on
Eq. 3 applies to a lower- or middle-phase the quantity of bypassed water, which is a function
microemulsion. Eq. 4 applies to an upper- or of Ymw·
middle-phase microemulsion. If a middle-phase A number of floods using microemulsion slugs
occurs, then C 5 is the same in Eqs. 3 and 4, so were run where salinity, micro emulsion type and
that viscosity, interfacial tension, and flooding rate
were varied. It was found that final oil saturation,
mw e = -1 + b/log(Ymw1Ymw') • (5)
So/' decreased with Nc. Physically, this means
m0 -1 + a/log(y molY mo')
10-1 c - - - - - - - - - - - - - - - - - - - - ,
Eq. 5 can be used to determine the jump in
interfacial tension between Ymo and Ymw for a
middle-phase.
For a fixed WOR, e,
Eqs. 3 and 4 relate height ~
of the multi phase region cs (e) to y mo and y mw· (.)

These equations are graphed for e

= 1 in Fig. 13,
........
w
2
using parameters estimated from Figs. 12a and 12b. >
0
Also shown in Fig. 13 is the y - C s path followed
when a variable is changed monotonically so that 2
0 I
the microemulsion phase undergoes the transition
l ~ m ~ u. Every point on Path ABCD corresponds
(i)
2
w I;
II
to a different ternary diagram. Along Path AB, all 1-
...I
microemulsions are lower-phase, and interfacial
<C
tension, y mo' decreases as the height C 5 decreases. C3
At Point B, the multiphase region having the least
height at e
= 1 is achieved, and a middle-phase
forms having the two tensions Ymo (B) and Ymw (C).
<C
LL
a:
w
1-
2
10-4 I
Once past the optimum, Cs,min' microemulsions
along Path CD are upper-phase, and interfacial
tension, Ymw' increases as the height C 5 increases. Cs, min
In summary, for surfactants studied here, 10-5
interfacial tensions are decreasing functions of 0 4 8 12 16 20 24
solublization parameters. When this is the case, C5 , SURFACTANT
at any fix~d WOR, interfacial tension decreases as CONCENTRATION, o/o MEAC120XS
height of the multiphase region decreases. It FIG. 13 -INTERFACIAL TENSION AS A FUNCTION
follows that ternary diagrams favorable to immiscible OF HEIGHT OF BINODAL CURVE AT WOR = 1.

APRIL, 1917 137

that the least effective of the displacement C* optimal salinity for oil recovery, percent
processes at the front or rear of the microemulsion NaCl
slug determines the outcome. Good oil recovery oil concentration in microemulsion, volume
requires that both Ymo and Ymw be low. fraction
Immiscible micro emulsion slugs were injected
surfactant concentration in microemulsion,
under varying conditions of salinity, surfactant
volume fraction or volume percent
and cosolvent structure, temperature, and composi-
tion, to determine how these variables affect oil cs,min surfactant concentration in microemulsion
recovery. For these experiments the following were corresponding to minimal height of
concluded: multiphase region, volume percent
3. The salinity, C*, where S0 / was a minimum, water concentration in microemulsion,
nearly coincided with the minimum of y c· volume fraction
4. As surfactant alkyl chain length, N, increased, optimal salinity for interfacial tension,

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C* decreased and oil recovery improved. percent NaCl
S. Oil recovery as a function of salinity was optimal salinity for phase behavior,
nearly the sam~ for TBA and TAA cosolvents. percent NaCl
6. C* increased with temperature for N = 9, but fractional oil flow, dimensionless
sof there was nearly temperature-independent,
consistent with a weak dependence of y c on fractional water flow, dimensionless
temperature. For N = 12, y c depends more strongly relative permeability to oil, dimensionless
on temperature, so both C* .and S0 / (C*) increased relative permeability to water, dimension-
with temperature. less
7. Oil recovery was insens1t1ve to a change constant, dimensionless
in over-all WOR (used to prepare microemulsions) constant, dimensionless
from 1 to 90/7. carbon number of alkyl side chain
The foregoing trends. and conclusions were used
capillary number (vJliYc), dimensionless
to develop a screening method that helps reduce
volumetric flow rate, ml/ sec
the number of core floods needed to evaluate a
microemulsion system. Briefly, the method assumes final oil saturation, dimensionless
that when the solubilization parameters are graphed velocity, em/ sec or ft/D
vs a variable X, their intersection is approximately volume of oil in microemulsion,. ml
the value X*, where oil recovery is a local maximum. volume of oil initially contained in core,
Oil-recovery magnitude can be estimated from the ml
capillary-number correlation. Laboratory core floods
vo,inj volume of oil injected, ml
are then run to improve the estimate of X*, and S0 /
there. vo,p volume of oil produced, ml
Interfacial-tension/ solubilization-parameter data V0 /V 5 solubilization parameter for oil 1n micro-
were fit with empirical equations so that, at fixed emulsion, volume ratio of oil to
WOR, interfacial tensions could be calculated as surfactant in microemulsion phase
functions of height of the multiphase region. A core pore volume, ml
result was that decreasing the height of the volume of water in microemulsion, ml
multiphase region, a trend favorable to conventional solubilization parameter for water in
microemulsion flooding, results 1n decreased microemulsion, volume ratio of water
interfacial tensions for over-all compositions to surfactant in microemulsion phase
within the multiphase region, a trend favorable to
variable
immiscible microemulsion flooding. Hence, the
foregoing screening process is useful for both types optimal X for oil recovery
of floods. optimal X for interfacial tension
Finally, it should be observed that oil recoveries optimal X for phase behavior
in relation to· surfactant requirements are sufficiently variable
good that immiscible microemulsion flooding can be
Yc controlling interfacial tension, dyne/ em
considered an attractive alternative to conventional
microemulsion flooding, particularly since lower Ymo microemulsion-oil interfacial tension,
surfactant concentrations permit larger bank sizes dyne/em
needed for heterogeneous reservoirs. constant, dyne/ em
Ymw = microemulsion-water interfacial tension,
NOMENCLATURE dyne/em
constant, dyne/ em
a constant, dimensionless
J1 viscosity, cp or poise
A cross-secti~::>nal area, sq em
flo oil viscosity, cp
b constant, dimensionless
flw water viscosity, cp
B microemulsion bank size, percent PV
¢ porosity, dimensionless
138 SOCIETY OF PETROLEUM ENGINEERS JOURNAL
 ACKNOWLEDGMENTS sulfonate 13 was supplied by Exxon Chemical Co.,
U.S.A., and is designated Sulfonate FA-400. The
We wish to acknowledge the efforts of Patsy Gee
specific dodecyl sulfonate used was specially
and G. W. Runberg, who did the experimental work.
prepared and was about 92-percent active. Inactive
components were unreacted oil and salt.
REFERENCES
The nony 1 surfactant was laboratory-synthesized
1. Healy, R. N, and Reed, R. L.: "Physicochemical
specifically for this work by Exxon Research and
Aspects of Microemulsion Flooding," Soc. Pet. Eng.
], (Oct, 1974) 491-501; Trans., AIME, Vol. 257. Engineering Co. It was about 75-percent active;
2. Healy, R. N,, Reed, R, L., and Carpenter, C. W.:
inactives were about 2-percent salt and 23-percent
''A Laboratory Study of Microemulsion Flooding,'' unreacted oil. All surfactant concentrations reported
Soc. Pet. Eng. ], (Feb. 1975) 87-103; Trans., AIME, here are on a 100-percent-active basis.
Vol. 259. Alcohol co solvents were c c Baker Analyzed''
3. Stegemeier, G. L.: "Relationship of Trapped Oil tertiary butyl (TBA) and tertiary amyl (TAA)

Downloaded from http://onepetro.org/spejournal/article-pdf/17/02/129/2158292/spe-5817-pa.pdf by Universitatea Petrol-Gaze Ploiesti user on 22 February 2023

Saturation to Petrophysical Properties of Porous reagents obtained from J. T. Baker Chemical Co.
Media," paper SPE 4 7 54 presented at the SPE-AIME
Third Symposium on Improved Oil Recovery, Tulsa,
In all cases, a volumetric mixture of 63-percent
April 22-24, 1974. surfactant and 37-percent alcohol cosolvent (63/37
4. Taber, J, ], : "Dynamic and Static Forces Required MEACNOXS/ alcohol) was used.
to Remove a Discontinuous Oil Phase From Porous
Media Containing Both Oil and Water," Soc. Pet. OIL
Eng. ]. (March 1969) 3-12. The oil used throughout this work was a volumetric
5. Taber, J. ],, Kirby, J. C., and Schroeder, F. U.: mixture of 90-percent lsopar M and 10-percent Heavy
''Studies on the Displacement of Residual Oil: Aromatic Naphtha (90/10 1/H), chosen to simulate
Viscosity and Permeability Effects," Paper 4 76
presented at Symposium on Transport Phenomena in
a specific crude of interest. Isopar M and Heavy
Porous Media, 71st National AIChE Meeting, Dallas, Aromatic Naphtha are trade names for refined
Feb. 20-23, 1972. paraffinic and aromatic oil, respectively, sold. by
6. Foster, W. R.: "A Low-Tension Waterflooding Exxon Co., U.S.A.
Process," ]. Pet. Tech. (Feb. 1973) 205-210; APPENDIX B
Trans., AIME, Vol. 255.
7. Healy, R. N., Reed, R. L., and Stenmark, D. G.: MOBILITY CONTROL
"Multiphase Microemulsion Systems," Soc. Pet. Eng.
], (June 1976) 147-160; Trans., AIME, Vol. 261. Requirements for adequate mobility control for
8. Reed, R. L., Healy, R. N., Stenmark, D. G., and an immiscible microemulsion slug process are that
Gale, W. W.: "Recovery of Oil Using Micro- the microemulsion mobility be less than or equal to
emulsions," U. S. Patent No. 3,885,628 (May 27, the mobility of the stabilized oil bank, and that the
1975). mobility of the viscous drive water be less than or
9. Davis, J, A. and Jones, S. C.: "Displacement equal to the microemulsion mobility.
Mechanisms of Micellar Solutions," ]. Pet. Tech. Mobility control is often designed on the basis of
(Dec. 1968) 1415-1428; Trans., AIME, Vol. 243.
the mm1mum expected oil-bank total relative
10. Gogarty, W. B. and Tosch, W. C.: "Miscible-Type
Waterflooding: Oil Recovery With Micellar Solutions," mobility 14 (kr 0 / flo + krwlflw). For floods discussed
]. Pet. Tech. (Dec. 1968) 1407-1414; Trans., AIME, here, minimum total relative mobility determined
Vol. 243. from Berea core oil-water relative-permeability data
11. Holm, L. W.: "Use of Soluble Oils for Oil Recovery," was 0.082 cp-1. Since maximum relative permeability
]. Pet. Tech. (Dec. 1971) 1475-1483; Trans., AIME, to microemulsion is about 0.5, 2 a viscosity 2. 6 cp
Vol. 251. should give a favorable displacement at the slug
12. Gogarty, W. B.: "Status of Surfactant or Micellar front.
Methods," ]. Pet. Tech. (Jan. 1976) 93-102.
For some of the floods discussed here, micro-
13. Prillieux, M. and Tirtiaux, R.: ''Enchancing the
emulsion viscosity was less than 6.1 cp; in these
Recovery of Oil From Subterranean Formations,"
U, S. Patent No, 3, 799,263 (March 26, 1974). instances no attempt was made to adjust viscosity,
14. Gogarty, W, B., Meabon, H. P., and Milton, H. W., since this would have required altering compositional
Jr.: ''Mobility Control Design for Miscible-Type variables that we preferred to maintain constant.
Waterfloods Using Micellar Solutions," ]. Pet. Tech. Nevertheless, for these floods, the displacement at
(Feb. 1970) 141-147. the slug front may have been favorable, because for
APPENDIX A an immiscible microemulsion flood wherein not all
CHEMICALS the resident water and residual oil are displaced by
microemulsion, microemulsion viscosity necessary
SURFACTANT AND COSOLVENTS for a unit-mobility-ratio displacement is less than that
Anionic surfactants were monoethanol am1ne calculated on the basis of minimum oil-bank mobility
salts of alkyl-orthoxylene sulfonic acid, where the and maximum relative permeability to microemulsion.
alkyl side chain was predominantly either nonyl or Relative mobility of XC biopolymer solutions
dodecyl. These will be designated by MEACNOXS, flowing in Berea rock was determined as a function
where the predominant carbon number (N) of the of frontal velocity and XC concentration. These
alky 1 side chain is either 9 or 12. Side-chain data were used to select concentration of XC
molecular weight distributions for these surfactants biopolymer needed in the drive water to g1 ve a
have been reported elsewhere. 7 Dodecyl orthoxylene favorable displacement at the slug rear. ¥¥¥

APRIL, 1977 139