OTC 24470

Wettability Alteration in Carbonates By Surfactants: The Effects of Interfacial Tension on this Process and Reflex in Porous Media Behavior M. F. Pinto, Petrobras.

Copyright 2013, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference Brasil held in Rio de Janeiro, Brazil, 29–31 October 2013. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.

Abstract

Most rocks of carbonate reservoirs is preferably lipophilic, this feature of rock-fluid interaction, also known

as wettability and is closely linked at low oil recovery rates. The application of surface modifying agents is a way to

changing the wettability of carbonates, making them preferentially hydrophilic and thereby favoring the reduction of

residual oil saturation (Ros).

Actually reservoirs with heterogeneous permeability, which have regions of low permeability and presence

of fractures and high permeability channels, there is a tendency that the injection water to flow preferentially

through these channels with high permeability. This type of reservoir, the oil recovery process is improved by

capillary forces, spontaneous process known as imbibition, where water tends to soak the smaller pores, expelling

the oil to the larger pores. This phenomenon retard “breakthrough” and reducing the residual oil saturation (Ros).

However, spontaneous imbibition only occurs appreciably in water wet reservoir. In the oil wet formations, the

water has less affinity for the wall of the pores and the capillary forces are small and in many cases could be

negative.

The paper presents results of Enhanced Oil Recovery (EOR) Group from Cenpes/ Petrobras, evaluating

two anionics and one cationic surfactants, with different interfacial tension (IFT) and their ability to increase

hydrophilicity of carbonates. The results showed that the anionic surfactant with higher IFT values was responsible

for increased to make the carbonate preferably hydrophilic, keeping in high values the capillary pressure.

The results were demonstrated by the core flow tests, which showed higher oil relative permeability and

Ros reduction; spontaneous imbibition test, presents higher oil recovery and contact angle evaluated, which

showed lower adhesion of the oil phase on the surface of carbonate.

The agent wettability modifying can be applied as a chemical method of EOR, as well as around the

producing well. In this last one, could be created convergence zones for oil and be increased the effective oil

permeability near the oil production well.

2 OTC 24470

Introduction

The oil reservoir carbonates, due to its complex diagenesis, exhibit peculiar characteristics when

compared to the sandstone reservoirs. The intense lithological transformations suffered by the carbonates are

inherent to their high reactivity, which results in atypical petrophysical features, this features may be caused by the

water originated from the formation and/or meteorical waters (underground water originated by rain), which

solubilize and recrystallizes in new carbonates, in order to keep the chemical equilibrium of the ions in the

reservoir. These mechanisms can create high permeability channels (super K) or cementing in the porous spaces.

Another component which alters the morphology of reservoirs is the stress caused by continuous overlaying of

land during your diagenesis, commonly seen in ultra deep reservoirs such as the Pre-Salt reservoir, which is

capable of significantly altering the porous medium of the reservoir through the reduction of the porosity or

fracturing.

Wettability is notoriously know as yet another factor which influences the behavior of reservoir fluids

(water/oil/gas) and is closely linked to the recovery rates of an oil reservoir, due to the influence of wettability in the

distribution and in the flow of fluids presents. Wettability is defined in petroleum industry as the “tendency of a fluid

of adhering to the surface of a solid material when in the presence of another immiscible fluid” (AGBALAKA et al.,

c2008). In oil-wet (OW) reservoirs, generally, it is observed a reduction of the relative permeability and leads to

higher values of residual oil saturation (Ros), when compared to preferably water-wet (WW) reservoirs

(STANDNES and AUSTAD, c2000). This phenomenon occurs because the arrangement of the fluids in lipophilic

rocks is organized with the oil phase occupying the smaller pores and covering the walls of the bigger pores,

resulting in negative capillary pressures

The capillary forces is very important for to the oil recovery process in matrixes which have preferential

channels or fractures, seeing that the injection water can only recover oil through those high permeability regions.

However, in cases in which a rock is WW, as soon as the capillary pressure in the pores becomes positive, water

can penetrate the small pores, thereby expelling the oil to the bigger pores and afterwards towards preferable

channels to the production well.

The lipophilic or hydrophilic feature of a reservoir depends upon a series of factors, some of them being

the composition of the rock (sandstone or carbonates) (CHILINGAR and YEN, c1983), the presence of

heteroatoms in the composition of the oil, such as oxygen, sulfur and nitrogen (asphaltenes, resins and

thiophenes) (Mc GEE et al, c1985), the pH of the reservoir, as well as the composition of water in the formation

(TREIBER et al, c1972).

The injection of surfactants with the intention of making the rock in the reservoir preferably hydrophilic is a

widely studied chemical EOR method. The modification of the wettability by surfactants can be differentiated by

some types of mechanisms, including the adsorption of the surfactant in the surface of the rock. In this case, the

modification of the wettability depends not only on the capability of the surfactant of being adsorbed in the surface

but also on the molecular structure (hydrophilic lipophilic balance) and the orientation in which it processes the

adsorption, i.e., whether from the polar or nonpolar part of the surfactant (SOMASUNDARAM, c2006). Another

hydrofilization mechanism is the formation of ionic pairs from the oil surfactant agents, which has be responsible

for increasing the lipophilic feature of the reservoir rock (STANDNES and AUSTAD, c2000).

OTC 24470 3

Experiments In all tests were used carbonate outcrop sample, the plugs were previously cleaned in a toluene and

methanol flow, after dried in a laboratory oven. The products tested were diluted with synthetic sea water (Table 1).

Table 1. Chemical composition of the synthetic seawater used in this work.

Ion Sea water (mg/L)

Sodium (Na+) 11000

Potassium (K+) 395

Magnesium (Mg2+) 670

Calcium (Ca2+) 255

Barium (Ba2+) 0.2

Strontium (Sr2+) 5

Iron (Fe2+) 0.15

Chloride (Cl-) 19600

Bromide (Br-) 64

Sulfate (SO42-) 106

Bicarbonate (HCO3-) 42

Acetate (CH3COO-) 6.65

Equal Salinity in NaCl. 32297

Interfacial tension (Spinning drop Video tensiometer)

The purpose of this test is to compare the interfacial tension (IFT) between the EWM-11, a anionic product

it was developed at Cenpes/Petrobras by the EOR and Flow Assurance groups, with the cationic commercial

surfactant Dodecyl Trimethyl Ammonium Bromide (DTAB) and the anionic surfactant lauryl alcohol ethoxylate

phosphate esters (C12H25(EO)10PO4). All this products were diluted in synthetic seawater; the assays were made in

range 25º and 60ºC and using decane as a nonpolar phase. The equipment used was the Spinning drop Video

tensiometer 20 (SVT) by Dataphysics® and the analyses were made at 6000 rpm.

The spinning drop method consists in the insertion of a drop of a liquid on another immiscible liquid, which

is located in a capillary. The capillary spins around its axis at a constant speed, deforming the drop under the effect

of centrifugal acceleration. This deformation results from the IFT between the fluids, which is related to the density

of the liquids present, temperature and rotation of the system. (Equation 1) (COUPER et al., c1983).

Equation 1. Equation for calculating the interfacial tension.

The interfacial tension is expressed in the International System of Units, in mN/m. This unit indicates that

the interfacial tension of water, for example, is equivalent to the free energy per area unit in the frontier between

water and the other fluid.

4 OTC 24470

Spontaneous Imbibition test Spontaneous imbibitions are ruled mainly by capillary forces, which influence the process of oil recovery in

reservoirs. The test consists of comparing two immiscible fluids regarding their affinity with a certain surface, as the

fluid with higher affinity on the surface of the rock will imbibe it spontaneously, thereby removing the previously

present fluid.

The spontaneous imbibition test gives a quick but aproximate idea of the wettability, is a quantitative

method of estimating the affinity of the rock with the aqueous or organic phases through the quantity of oil is

displaced by brine in imbibition process.

For this test, 5 limestone carbonate outcrop plugs were used. This mineral is primarily composed of calcite

and aragonite, which are composed of calcium carbonate (CaCO3) but only differ from each other due to the format

of their crystalline reticle (DUNHAM, c1962). The plugs were previously cleaned in a toluene and methanol flow

and dried in a laboratory oven. Then, they underwent a lipophilization process through treatment with a mixture of

decane and cyclohexane pentanoic acid 1.5 wt%. This lipophilization process was done collectively, and the plugs

were saturated in vacuum for the same amount of time and in the same solution of decane with naphthenic acid.

this way is guaranteed homogeneity lipophilic character of plugs.

One of the plugs did not receive the naphthenic acid treatment (NA), i.e., it kept its original wettability. This

procedure was adopted in order to create a benchmark sample (control α) and correlate the efficiency of the

treatment and increasing the lipophilic feature of plugs.

The plugs were acclimatized in the imbibitions cells (Figure 1). The performance of the following products

diluted in sea water was evaluated:

Lauryl alcohol ethoxylate phosphate esters (C12(EO)10PO4) (L(10EO)P);

Dodecyl trimethyl ammonium bromide (DTAB);

EWM-11 anionic surfactant, developed at Cenpes/ Petrobras by the EOR and the Elevation and

Channeling Technology Teams.

Figure 1. Imbibition cell (Amott). Adapted from the Petrobras, COMEP 2010 institutional video.

The products were diluted in sea water at 0.5 wt% (5000ppm). The imbibition cells were stored in an oven

at 60ºC for 35 days, and the volume of oil produced was periodically recorded. The choice of the commercial

surfactants for this study was based on the studies of Standnes and Austad (c2000), and the cationic and anionic

ROCK WETTED BY WATER

ROCK WETTED BY OIL /

CARBONATE WETTABILITY INVERSION

OTC 24470 5

products were selected due to its features, which presented the best performance in imbibition tests. The studies

showed a direct relationship between the efficiency of the anionic surfactant during imbibition and its degree of

ethoxylation (STANDNES and AUSTAD, c2000). The surfactants were compared with an EWM-11 surfactant,

which has a relatively low capability of reducing the interfacial tension (IFT), as seen further below.

Contact angle

The measurement of the contact angle is a quantitative method used to determine the wettability degree

according to the contact angle (θ), is resulting from the balance between the interfacial tensions of the fluids

involved (oil and water) and the solid surface (GOLABI, c2009) (KSHITIJ, c2009). The contact angle can be easily

interpreted when the surface is smooth, but a very rough surface may lead to a misinterpretation of the contact

angle, also known as the apparent contact angle, which can be different from the actual contact angle (ABDALLAH

et al., c2007). However, this type of deviation is only relevant when the compared contact angles are very similar.

During the imbibition process, some differences in the contact angle between the decane and the

carbonate surface in the cells A0 and A1, both immersed in sea water and A3 immersed in at EWM-11, could be

observed (Table 3).

This contact angle variation was influenced by the pre-treatment intended for enhancing the lipophilicity of

the carbonate, as well as for the contact with the products evaluated in the spontaneous imbibition tests.

The effects of wettability on relative permeability

The aim of the test is to evaluate the capacity of the EWM-11 product in modifying the wettability of the

carbonate through the values of the terminal saturation points (Swi and Sor) and the oil and water relative

permeability.

In summary, ion oil-wet rocks, expected the higher permeability to water in the residual oil saturation

(Krw@Sor) than in water wet rocks. In a preferably hydrophilic porous medium, water will also permeate through

the smaller and consequently less permeable pores, the inverse behavior occurs when the relative permeability to

oil is measured in WW rocks, thereby the oil flowed through the bigger pores, showing better permeabilities

(GOLABI et al, c2009) (ANDERSON, c1987b).

In this assays were compared three carbonate outcrop plugs with similar petrophysical properties. These

properties were previously measured in the basic petrophysical parameters for reservoir characterization (porosity,

absolute permeability and porous volume) (Table 3). After that, two of these plugs (M11 and M12) did not contact

any surface agent and the M13 plug was pre-treated in flow, recirculating 4 porous volumes (VPs) of the EWM-11

product in solution at a 3000ppm concentration for 3 days at a 0.025cc/min flow rate. This way, about 5 porous

volumes were recycled by the sample every 24h. The system was placed in an oven at 70ºC during the test (Figure

2).

After this stage the same procedure below was used for the relative permeability evaluation for all 3 plugs.

This procedure consisted of: saturating the plugs with synthetic seawater; confining the plugs in a holder at 2000

psi; water flow and measure absolute water permeability (Kw); injection of white mineral oil (µ = 4,5cP) to take the

sample to Swi, to obtain the oil relative permeability (Kro@Swi) and finally the injection of water to obtain Ros and

Krw@Ros.

6 OTC 24470

The absolute permeability to water must show values close to the absolute permeability to gas, thereby

ratifying the efficiency in the saturation. Discrepancies between these permeability values may help detect the

presence of internal air within the pores.

Figure 2. Recycle system in core flow media.

Results and discussions

Interfacial tension (IFT) evaluation

The process of imbibition in porous media is influenced by the capillary diameter (r), by the capillary forces

and the gravity-driven process (GRUPTA et al, c2008). It is important to mention that the use of surfactants in EOR

generally cause a significant reduction in the interfacial tension (𝛿𝛿) (IFT), consequently reducing the effect of

capillary forces (Equation 2). In some cases the effect of the reduction of the IFT can be minimized when the

surfactant is also capable of increasing the water wettability of the carbonate. This effect is indicated by the

reduction of the contact angle (θ<90°) and represented in Equation 2 by “cos θ”, resulting in an enhancement of

the capillary forces.

𝑃𝑃𝑃𝑃 =2 ∗ 𝛿𝛿 ∗ cos 𝜃𝜃

𝑟𝑟

Equation 2. Capilar pressure equation

The IFT of different products was measured with the use of decane as an oil phase. The EWM-11 cause a

small reduction in the IFT (26mN/m), when compared to the tension between the pure seawater and the decane

(32mN/m). The IFT value presented by the EWM-11 surfactant was significantly high when compared to

commercial surfactants L(10EO)P and DTAB, which reduced the interfacial tension to 3 and 4 mN/m respectively

(Table 2) (Figure 3).

OTC 24470 7

Table 2. IFT test (mN/m) in temperature range.

Temp (ºC) 25 ºC 30 ºC 40 ºC 50 ºC 60 ºC

Brine 35.0 35.0 35.0 33.0 32.0

EWM-11 (0.1% p/p) 29.0 29.0 29.0 27.0 26.0

L(10EO)P (0.1% p/p) 4.5 4.5 3.0 3.0 3.0

DTAB (0.1% p/p) 5.2 5.5 4.0 4.0 4.0

Figure 3. Interfacial tension by Spinnig drop tensiometer.

Spontaneous imbibition evaluation

The out crop plugs (Table 3) were immersed in solutions as previously mentioned and according to the

following arrangement:

A0) Non-treated carbonate with NA (original wettability), Control sample α;

Solution: synthetic seawater;

A1) Carbonate treated with NA (lipophilic); Control sample β;

Solution: synthetic seawater;

A2) Carbonate treated with NA (lipophilic);

Solution: Lauryl alcohol ethoxylate phosphate esters (L(10EO)P); 0.5 wt%;

A3) Carbonate treated with NA (lipophilic);

Solution: EWM-11; 0.5% wt%;

A4) Carbonate treated with NA (lipophilic);

Solution: dodecyl trimethyl ammonium bromide (DTAB); 0.5% wt%;

Between the volumes of oil produced by the benchmark sample A0 (WW) and sample A1 (OW), 34.5%

and 2.2% respectively, both immersed in pure seawater, it is observed a discrepancy in the recovery factors due to

such distinct wettabilities (Figure 4). As expected, the imbibition occurred much less intensely in plug A1, treated

with NA, thereby ratifying the efficiency of the treatment in increasing the lipophilicity of rocks.

Plug A0, benchmark sample, was not in contact with NA, and represented the degree of oil wettability

equivalent to the original of the studied samples. Therefore, one may assumed that the pre-treated rocks with NA

(A1, A2, A3 and A4), when attaining an imbibition value close to 34.5% after being immersed in surfactants, it

would be as if the rock had returned to its original wettability.

8 OTC 24470

The anionic surfactants can act as wettability modifier through the adsorption of the lipophilic grouping

(nonpolar) at the surface of the MO rock (lipophilic), exposing the hydrophilic part (polar) of the surfactant, thereby

reducing the interaction between the oil (nonpolar) and the surface of the rock (CHEN et al., c2000) (VARADARAJ

et al, c1994). The adsorption may occur too with the formation of more than double-layer at the surface.

Furthermore, the anionic surfactants act by strongly reducing the IFT and favoring the formation of smaller oil

droplets, thereby increasing the mobility of oil in the reservoir (SEETHEPALLI et al, c2004).

Table 3. Basic petrophysical properties: Samples A0, A1, A2, A3 and A4.

Cor

e

Dia

met

er (c

m)

Leng

th (c

m)

Wei

ght (

g)

Abs

olut

e

perm

eabi

lity

(mD

)

Por

e vo

lum

e

(cm³)

Sat

urat

ed w

eigt

h

(g)

PV

W*

(cm³)

Sat

urat

ion

inde

x

(%)

A0 3.802 6.480 168.21 3.83 9.73 174.99 9.29 95.45

A1 3.801 6.786 170.84 4.15 9.58 177.43 9.03 94.21

A2 3.787 6.554 172.62 4.05 10.30 179.46 9.37 91.00

A3 3.797 6.466 168.16 3.97 10.36 175.20 9.64 93.11

A4 3.792 6.378 168.19 4.50 9.66 174.75 8.99 93.03

* PVW, pore volume by weight, difference between the saturated weight and the dry plug weight, divided by the density of the fluid used in the

saturation.

A negative aspect of this mechanism would be the formation of more stable emulsions between water and

oil, which would demand the insertion of specific demulsifying in the water/oil separation basins. Besides, the

formation of emulsions are generally very viscous and undesirable in the vicinities of the injector well (FAROUQ

and COLOMONT, c1977).

When comparing the oil recovery between the anionic surfactants EWM-11 (IFT= 26mN/m) and L(10EO)P

(IFT= 3mN/m), 22.8% and 5.3%, respectively, one may assume that the low IFT value of the product L(10EO)P

was a factor which hindered the imbibing process, since a low IFT causes a reduction in the capillary pressure of

the porous medium. Such effect is especially stronger for the low permeabilities plugs, whose absolute

permeability to gas are close to 4 mD (Table 3), a low permeability is a scenario in which prevails the oil recovery

mechanism through capillary forces over gravitational forces (GRUPTA et al, c2008).

For a cationic surfactant such as DTAB, the inversion mechanism is processed through the desorption of

the surface agents present in the oil which make the carbonate oil wet, followed by the formation an elestrostatic

bond (ion-pair) between the surface agent in the oil and the cationic surfactant. Carboxylates (RCOO-) are the

examples of surface agent composites present in oil and often present in the molecular structures of asphaltenes

and resins.(STANDNES and AUSTAD et. al c2000).

Among the products evaluated, the surfactants DTAB and L(10EO)P showed the major decrease of IFT,

but presented different values of imbibitions. This behavior reveals that only the reduction of IFT is not enough to

increase the imbibitions process and reveals the importance in the kind of mechanism wettability inversion in oil

OTC 24470 9

recovery, this mechanism is the predominant factor for enhanced oil recovery, when capillary forces are reduced

by reducing the IFT.

With the comparison of the imbibitions process of the cationic product DTAB (IFT= 4mN/m) and the anionic

product EWM-11 (IFT= 26mN/m), with IFT distinct, similar recovery values at the end of the 35th day can be

observed. However, up to the 22nd day, the chart presents higher imbibed volume for product EWM-11. This

behavior suggests that the different mechanisms between anionics and cationics surfactants result in a higher

imbibing velocity for EWM-11 and consequently a higher wettability inversion time rate for the carbonate, this

behavior it was noticed by Milter and Austad (c1996a).

Figure 4. Spontaneous imbibition test.

Contact angle evaluation During the imbibing process, different contact angles could be observed between the decane and the

surface of the carbonates OW and WW. This contact angle variation was influenced by the pre-treatment applied in

order to make the carbonate oil-wet, and the products in the imbibing tests were evaluated in terms of their

capability of altering the wettability of the rock (KSHITIJ, c2009) (SHAW, c1992).

As previously mentioned, the plug A0 was not treated with naphtenic acid with the purpose of making it

OW. Therefore, it has kept its original wettability. According to Anderson (c1987a), the process of cleaning of plugs

can make them slightly oil wet or make them neutraly wet (θ= 90º), as observed during the test (Figure 5).

Plug A1, immersed in synthetic seawater was pre-treated with naphthenic acid, presenting a contact angle

(θ) higher than 90º between the decane and carbonate. In Figure 6, a wider spread of the oil droplet can be

observed on the surface of the carbonate, which ratifies the effectiveness of the pre-treatment in order to make the

rock lipophilic and also justifies the low volume of water imbibed during the spontaneous imbibition test.

The samples immersed in the EWM-11 solution (Figure 7) presented a significant reduction in the contact

angle between the oil phase and the carbonate, which demonstrates a reduction of the affinity of the carbonate to

the oil phase after its contact with the EWM-11.

10 OTC 24470

Figure 5. Decane droplets in the surface of plug A0 (original wettability), immerse in synthetic seawater.

Figure 6. Decane drop on the surface of plug A1 (pre-treated with naphtenic acid), immersed in synthetic seawater.

Figure 7. Decane droplets on the surface of plug A3 (pre-treated with naphtenic acid) and immersed in EWM-11

solution (0.5%).

The effects of wettability on relative permeability evaluation A significant increase of oil permeability could be observed in plug M13 (Ko@Swi = 85%), treated by

recirculation of the solution of the EWM-11 when compared to plugs M11 (Ko@Swi= 56.7%) and M12 (Ko@Swi=

61.1%). The oil permeability increase is the result of an increase of the rock's affinity to water, at Swi.

In a preferably hydrophilic environment, the water creates a thin layer over the pores of the rock and the

organic phase occupies the internal part of the bigger pores. Such distribution of fluids within the plug reflects the

effective oil permeability value, which will be relatively high (3.8 mD), in this case close to the absolute permeability

to gas (4.44 mD) (Table 4) and higher than the absolute permeability to water (2.7 mD), as evidenced in the M13

sample test (Figure 8).

In WW rocks, the water flow permeates the rock through its pores with small or medium sizes, flowing in

uniform manner and causing a piston effect, which promotes a more efficient drag in the oil phase, consequently

improving the scanning efficiency and reducing the Ros value (ANDERSON, c1987b) (STANDNES and AUSTAD,

c2000).

OTC 24470 11

Table 4. Basic petrophysical properties: samples M11, M12 and M13.

Cor

e

Dia

met

er (c

m)

Leng

th (c

m)

Sam

ple

Wei

ght

(g)

Abs

olut

e

Per

mea

bilit

y (m

D)

Por

ous

Vol

ume

(cm³)

Sat

urat

ed w

eigh

t

(g)

Por

ous

Vol

. per

Wei

ght (

VP

P) c

m3

Sat

urat

ion

Inde

x

(%)

M11 3.78 4.71 119.94 4.97 8.78 128.55 8.44 96.13

M12 3.79 4.68 122.03 2.56 8.11 129.59 7.38 91.03

M13 3.79 4.75 121.15 4.44 8.08 129.10 7.79 96.41

The modification of the wettability in plug M13, caused by the treatment with EWM-11, reflected in the

values of the terminal saturation points (Swi and Ros) (Table 5). Plugs M11 and M12 presented 28.4% and 38.2% of

Swi respectively. An M13 sample presented a higher Swi value (48.6%). The explanation for that can the increase in

water wettability after the treatment with the EWM-11 product. This WW feature increased the capillary pressure of

the system, as the water, as a wetting fluid, started to imbibe the smaller pores which were, until then,

inaccessible, thereby increasing the Swi value.

Table 5. Relative permeability results and terminal points of saturation (Swi and Ros) of samples M11, M12 and M13. M11 K (mD) Kr %

Kg 4.5 100.0

Kw 3.0 66.7

Ko@Swi_____ Swi = 38.4% 2.6 56.7

Kw@Sor_____ Sor =35.5% 0.7 15.6

M12 K (mD) Kr %

Kg 2.56 100.0

Kw 1.90 74.2

Ko@ Swi______ Swi = 28.2% 1.56 61.1

Kw@ Sor ____ Ros = 37.9% 0.25 9.7

M13 K (mD) Kr %

Kg 4.44 100.0

Kw - 1 2.70 60.81

Recycle: 60mL_EWM-11 (3000ppm)

Kw’ - 2 1.7 38.3

Ko@ Swi _______ Swi = 48.6% 3.8 85.1

Kw@ Sor ______ Ros = 16.7% 0.3 7.1

The reduction in the residual oil saturation (Ros) value was another consequence of the increase of

hydrophilicity of plug M13. When compared to plugs M11 and M12, which obtained Ros s similar to 35.5% and

37.95% respectively, plug M13 presented an Ros of 16.7%, a reduction of nearly 50% in the rock’s capability of

retaining oil during the injection of water (Table 5).

12 OTC 24470

Figure 8. Influence of the EWM-11 treatment in the relative permeability.

Conclusions

Evaluation of outcrop carbonates with low permeability:

The anionic surfactant EWM-11 was effective in increasing the hydrophilicity of the carbonate and

enhanced oil recovery without significantly reducing the IFT.

Evaluating the anionics surfactant EWM-11 and L(10EO)P, the product EWM-11 has higher IFT, keeping

capillary pressure high of the porous medium, had enhanced recovery of oil.

The DTAB (cationic) and L(10EO)P (anionic) show similar behavior in relation to IFT change, but showed

different results for oil recovery. Notes that only reduced IFT (for values presented), does not explain the high

levels of oil recovery.

Products EWM-11 and DTAB, both were efficient in reversing the wettability of carbonate, however acting

through distinct mechanisms. The EWM-11 has higher IFT and showed higher velocity for oil recovery by

spontaneous imbibitions process.

The contact with product EWM-11 increases the hydrophilicity of the carbonate surface, reflecting in

increment of the Swi and Ros, as well the relative permeability to oil.

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After recycle with EWM-11

OTC 24470 13

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