Enhanced Oil Solubilization Using Microemulsions With Linkers - SPE-164131-MS

7/17/2019 Enhanced Oil Solubilization Using Microemulsions With Linkers - SPE-164131-MS

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SPE 164131

Enhanced Oil Solubilization Using Microemulsions with LinkersGianna Pietrangeli, SPE and Lirio Quintero, SPE, Baker Hughes

Copyright 2013, Society of Petroleum Engineers

This paper was prepared for presentation at the SPE International Symposium on Oilfield Chemistry held in The Woodlands, Texas, USA, 8–10 April 2013.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not beenreviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, itsofficers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission toreproduce 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 SPE copyright.

AbstractIn recent years, applications of microemulsion technology have increased in the drilling and production industry. Some of

these applications include oil-based drilling fluid displacement to water-based fluid, near-wellbore remediation, well

stimulation, enhanced oil recovery and flow-back recovery in shale gas wells.Microemulsion formulations for these applications need to have high oil solubilization and very low interfacial tension,

which is achieved with relatively high concentration of surfactants. High-performance microemulsion systems with lower

surfactant concentrations are desired to optimize the cost of the technology application.

The reduction of surfactant concentration could be achieved by introducing linker additives in the formulations. The

addition of linker molecules enhances the microemulsion solubilization property, which increases the hydrophilicity and/or the

lipophilicity behavior of surfactants. Previous studies indicate the addition of a linker substance could double the solubilization

of the system by segregating at the interface. The linker molecules create chaos, avoid formation of organized structure and

decrease the viscosity, which helps to pack surfactants more efficiently at the interface. Some examples of linker additives

include amines, acids, alcohols and phenols.

This paper presents systematic studies that have been carried out to determine the influence of lipophilic and hydrophilic

linkers in an anionic/nonionic surfactant mixture when exposed to olefin-based oils that are used in synthetic-based drilling

fluids.

The results of the study include phase behavior of a microemulsion system, interfacial properties and kinetic diffusion

under several temperatures, as well as evaluation of the system with and without the addition of linker molecules for cleanupof synthetic and oil-based drilling fluids.

IntroductionThe oil and gas industry has been using microemulsion technology in downhole operations with the objective of maximizing

production and optimizing wellbore construction. This application includes near-wellbore cleanup to prevent or remediate

formation damage, and effective displacement of synthetic or oil-based mud to water-based fluids to minimize non-productive

time, reduce waste volume, prevent cement failures and reduce the risk of tool complications during the completion of a well

(Penny et al. 2005; Lavoix et al. 2007; Quintero et al. 2005; Quintero et al. 2009).

The microemulsion fluids for these applications need to have very low interfacial tension between the microemulsion and

the OBM filtrate or the crude oil, and high oil solubilization to restore or increase the water-wet condition of the solid surfaces

(e.g., rock formation, downhole tools, casing) (Quintero et al. 2007; Quintero et al. 2012). Microemulsions with these

properties produce good cleaning/removal of organic material with minimum mechanical energy input and, at the same time,

enhance the water-wet condition encountered in the majority of reservoirs.

To obtain microemulsion formulations that are effective in a broad range of conditions that match the well and reservoir variables (e.g., type and concentration of brine, t ype of oil use in drilling fluids, t ype of crude oil, oil/water ratio and reservoir

temperature), studies of phase behavior of the brine-surfactant(s)-oil microemulsion systems and their properties are required

(Quintero et al. 2011; Quintero et al. 2012). Even if proper selection of surfactant blend, co-surfactants and solvents are made,

the microemulsion systems used in applications in oil and gas wells typically require high concentrations of surfactants to

reach high oil solubilization, which limits the use of these fluids in certain wells for economic reasons.

Fundamental studies of various research results (Sabatini et al. 2003; Salager et al. 2005; Acosta et al. 2003) proved that

the concentration of surfactants in microemulsions could be significantly reduced by adding small concentrations of certain



2 SPE 164131

molecules that act as linkers at the interface between polar and nonpolar fluids. These linkers enhance the solubilization

capability of the microemulsion system.

Although there are various papers describing the fundamentals of formulations using linker molecules, the concept has not

been applied to microemulsion systems for maximizing production and optimizing wellbore construction. This paper discusses

solubilization of microemulsions and t he effect of linker and co-surfactant additives. Laboratory studies (phase behavior,

interfacial tension, fluids compatibility and cleaning tests) using microemulsion systems with linker molecules for applications

in oil and gas wells are discussed.

Fundamentals of MicroemulsionsMicroemulsions are thermodynamically stable fluids consisting of aqueous and oleic phases stabilized by an interfacial film of

surfactant molecules (Ezrahi et al. 1999; Salager and Anton 1999; Xie et al. 1992). They can be prepared with little or no input

of mechanical energy. These systems could have optional additives such as co-surfactants, acids, lipophilic and hydrophilic

linkers.

In 1954, Winsor introduced three categories of microemulsions defined according to phase behavior studies. The threecategories (Winsor I, Winsor II and Winsor III) are determined based on the concept of the ratio of interactions (R) between

the surfactant, oil, and water phases to determine the convexity of the interface and the resulting phase behavior (Winsor

1968).Winsor I microemulsion systems consist of oil-swollen micelles in a water phase in equilibrium with excess oil. Winsor II

microemulsion systems consist of water-swollen reverse micelles in an oil phase in equilibrium with excess water. Winsor III

systems are a middle-phase bicontinuous microemulsion, in equilibrium with excess water and oil. The surfactant(s) in the

bicontinuous microemulsions have equal affinity for the water phase and the oil phase. A single-phase microemulsion (Winsor

IV) is obtained when a sufficient amount of surfactant is added to a Winsor III system to solubilize the excess oil and water

into the microemulsion (Ezrahi et al 1999; Salager and Anton 1999). A single-phase microemulsion (Winsor IV) is obtained by increasing the surfactant concentration of a Winsor III microemulsion fluid (Schulman and Rile y 1948; Salager et al. 2005;

Salager and Anton 1999). Fig. 1 shows a photograph of test tubes with Winsor I, Winsor III and Winsor II microemulsions

phase behavior. Systematic studies of phase behavior are usually made to select the appropriate microemulsion system and

composition that fit the need for a particular purpose. Some of the variables included in the phase behavior studies are

concentration of brine, type and concentration of co-surfactants, surfactants, types and concentration of oil, solvents, linkers,

and temperature.

Fig. 1 Phase behavior of water-surfactant-oil system obtained by variation of salinity

The results obtained from phase behavior studies are used to build phase diagrams of the microemulsion systems. Fig. 2

shows an example of the type of ternary phase diagram that could be obtained with the phase behavior for oil-water-surfactant

systems when the formulation variables are sistematically changed. There is a characteristic progression from two-phase to

three-phase to two-phase coexistence of an oil-water surfactant system with the systematic change of formulation variables.

For example, at low salinity an oil-in-water microemulsion coexists with an excess of oil (Winsor I). At high salinity, a water-

in-oil microemulsion coexists with an excess of brine (Winsor II). At intermediate salinities a bicontinuous microemulsion

coexists with excess of water phase and oil phase (Winsor III) (Winsor 1954; Clausse et al. 1981; Holmberg 1998; Bellocq

1999).

Winsor I Winsor IIWinsor III



SPE 164131 3

Fig. 2 Phase behavior and types of microemulsion according to Winsor’s definition.

Solubilization of Microemulsions

Solubilization in microemulsions results from the equilibrium coexistence of oil and water in the presence of surfactants and

cosurfactants that form the swollen micelles. The increase of interactions between surfactant and oil and surfactant and water

in a microemulsion system increases their solubilization. This can be quantified in terms of t he solubilization parameter (SP).

The solubilization parameter is the amount of oil solubilized in the core of the swollen micelles per unit mass of surfactant(Salager et al. 2005).

A high concentration of surfactant(s) in the microemulsion systems is typically required to reach high solubilization levels.

The addition of co-surfactants, such as short-chain alcohols, modifies the phase behavior of microemulsion formulations and

improves the solubilization (Salager et al. 2005). However, the solubilization capacity of microemulsion systems could beincreased by using lipophilic linkers, and/or hydrophilic linkers.The effect of linker molecules on microemulsion solubization,

(Salager et al. 2005) demonstrates that the surfactant concentration can be considerably reduced by adding linkers to the

system.

Microemulsion with Linkers

Lipophilic and hydrophilic linkers are amphiphilic molecules that segregate near the interface in microemulsion systems

(Sabatini et al. 2003). Hydrophilic linkers are hydrophobic enough to segregate near the surfactant head group at the oil/water

interface while avoiding strong interactions with the oil (Salager et al. 2005; Yaghmur et al. 2002). The lipophilic linkers

segregate near the hydrophobic tail.

The amphiphilic nature of linkers enables them to interact with the tails or polar heads of the surfactant monolayers at the

interface, thereby affecting the packing and structural assembly of surfactants at the interface.

Lipophilic linkers serve as links between oil molecules and the surfactant tails (Salager et al. 2005; Graciaa et al. 1993a

and 1993b). Examples of lipophilic linkers are phenols, fatty esters and long-chain alcohols, such as alcohols with more than

eight carbons. These molecules act as lipophilic linkers in microemulsion systems because they have a relatively good

interaction with the oil molecules but do not adsorb at the interface. They exhibit very weak hydrophilicity compared to the

head groups of the surfactant molecule. They exhibit lipophilicity about the same as the tails of the surfactant molecule. In

most cases, alcohols having between three and six carbons behave as co-surfactants because they interact strongly with the oil

but retain their adsorption at the oil-water interface; whereas, short-chain alcohols with less than three carbons show a co-

solvent effect that tends to decrease the surfactant-surfactant interaction.

The concept of hydrophilic linker was introduced later by adding a surfactant-like molecule that segregates near or at the

oil-water interface, but that due to its short tail offers little interaction with the oil phase (Uchiyama et al. 2000). The addition

of a hydrophilic linker increases the space between the headgroups of the surfactant molecules, thus allowing for more a

flexible surfactant membrane, which translates into faster coalescence and solubilization kinetics (Salager et al. 2005).

Combinations of hydrophilic and lipophilic linkers can produce a surfactant-like system. The proper combination of lipophilic and hydrophilic linkers has been found to significantly increase the solubilization capacity of microemulsions for

different oils (Sabatini et al. 2003; Uchiyama et al. 2000; Acosta et al 2003). The linker approach has been used to formulate

microemulsions in applications such as environmental remediation and detergent formulations (Acosta et al. 2003;

Tongcumpou et al. 2003).

Microemulsions with Co-Surfactant

Molecules such as alcohols can be used as co-surfactants in microemulsion systems to modify its phase behavior to bring the

microemulsion into the required experimental window of composition and temperature.

Formulation variable (e.g.Salinity)

Winsor I Winsor III Winsor II



4 SPE 164131

The addition of small concentrations of co-surfactants such as short-chain alcohols (e.g., methanol, isopropanol, or n-

butanol) can increase the total interfacial area at low alcohol concentrations, thus increasing the solubilization (Bellocq 1999;

Hou et al. 1998). At high alcohol concentrations, the interdroplet interaction increases and produces a phase separation. The

optimal concentration of alcohol is determined by phase behavior studies to formulate microemulsion fluids with maximum

solubilization capacity. The addition of an optimal amount of alcohol and salinity, together with the effect of the composition

of the oil phase, may lead to the largest possible solubilization capacity of a given microemulsion system.

Experimental Procedures

Microemulsion formulations were studied using the components described in Table 1. Many components were screened tocreate the best combination under specific requirements, keeping in mind that the microemulsion or treatment fluid will be

used to remediate or prevent formation damage and to displace oil or synthetic-based fluid to water-based fluid in oil and gas

wells.

Table 1 Microemulsion components.

Components Range of

concentration, wt%

Surfactant blend 2-20

Solvent/co-Solvent 1-10

Brine/Water 30-70

Organic Acid 0-15

Lipophilic linker 0-3

The process of selecting a microemulsion formulation capable of solubilizing synthetic-based oil was done in a systematic

study. The selection process includes studies of phase behavior and pseudoternary phase diagrams of various surfactant-water-

oil systems, dynamic interfacial tension, crude oil/microemulsion compatibility, and synthetic-based mud cleaning evaluation.

Phase behavior studies are performed under specific conditions of salinity, temperature, surfactant concentration, and

water/oil ratio. Each data point in the ternary phase behavior diagram represents a test tube under unique conditions at the

same specified temperature. The test tubes contain different surfactant concentrations and water/oil ratios; however, the

salinity remains constant. The regions were delineated in the pseudoternary diagram performed isothermally at 180°F at

constant salinity, as follows:

First, variation of water/oil ratio from 10/90 to 90/10 at fixed surfactant mixture concentration;

Second, variation of surfactant concentration from 5% to 50% at fixed water/oil ratio and

Third, change of water/oil ratio from 10/90 to 90/10 and surfactant concentration variation from 5% to 50% with

and oil/lipophilic linker fixed ratio.

The test tubes were prepared, mixed and placed at the specified temperature until they reached equilibrium. Informationrelevant to the type of phase formed (Winsor I, Winsor II or Winsor III) was read at the equlibrium condition.

Dynamic interfacial tension (IFT) is measured as function of time, when two immiscible fluids are in contact and one of

them contains surface-active material. The interfacial tension measurements were made using a SVT20 model Dataphysics

Spinning Droplet Tensiometer. In these tests, interfacial tensions were measured until t hey reached equilibrium or until the

drop of crude oil was completely solubilized by the microemulsion fluid.

Crude oil/microemulsion compatibility evaluation is determined by blending crude oils with the microemulsion fluid in a

50/50 ratio. The mixtures are vigorously mixed by hand-shaking in a graduated cylinder. The cylinder is then allowed to rest at

a predetermined temperature while separation of the fluids is observed. Crude oil with gravities ranging from 10 °API degrees

to 35 °API was used for compatibility evaluations.

Cleaning evaluation for synthetic or oil-based mud is performed to evaluate the effectiveness of the microemulsion to clean

the filter cake formed with drilling mud. A high-pressure/high-temperature (HPHT) double-ended filter cell is used to prove

the ability of the treatment fluid to clean-up filter cake and to remove viscous water-in-oil emulsions under wellbore

conditions. Fig. 3 shows the equipment setup used to perform the test. Discs of various micron-size discs are available in the

market. For the tests discussed in this paper, a 40-micron aloxite disk was used. The cleaning test procedure for the synthetic- based mud began with the filter cake deposition. The mud-off takes place for 3 hours at 500 psi at the desired temperature.

Then, the treatment fluid replaces the excess mud in the cell and soaks the filter cake for 24 hours at 200 psi at the desired

temperature. After 24 hours, the cell is depressurized and the soak solution is poured out. The aloxite disk is removed from the

cell and the residual filter cake solids on top of the disk are assessed for water-wetness and disperability.



SPE 164131

Fig. 3 Schematic of HPHT

Results and Discussion

Pseudoternary Phase Diagram study

The solubilization of the system was studied b

map is not easy because of the four componeFig. 4 shows the schematic quaternary phas

microemulsion systems and three dimension

water-surfactant(s)-oil microemulsion system

of the microemulsion system. Fig. 4b shows t

Fig. 4 Schematic quaternary system of a

Fig. 5a and Fig. 5b show pseudoternary

system. The phase behavior results obtained

The area with the blue dots corresponds to th

(WII) phase behavior are represented with b

oil/water occurred and Winsor III microemul

pseudoternary phase diagram, representing WI

The pseudoternary diagram Fig. 5a represFig. 5b represents the pseudoternary phase di

linker/oil ratio.

The development of a WIII region in F

solubilization in the oil/water/surfactant syst

Salager et al. (2005) the optimum formulatio

adding a lipophilic or/and hydrophilic linker.

parameter obtained (Graciaa et al. 1993; U

dodecanol as a lipophilic linker.

Surfactant

Blend

LipophilicLinker

test setup used in synthetic or oil-based mud cleaning evalu

y mapping the phase behavior as a function of compositi

ts of the microemulsion system and the three dimensiondiagrams that are usually used to study phase diagra

. Fig. 4a shows an example with a bidimentional cut

without lipophilic linker. The dark color region corresp

he example of the microemulsion system with the additio

microemulsion system (a) without lipophilic linker and (b)

diagrams obtained for the surfactants/water/oil/lipophili

rom the series of test tube studies are plotted onto the

e observed Winsor I (WI) phase behavior. The glass tub

lack dots. The red dots symbolize the glass tubes whe

sion was obtained. As a result, three patterns can be ob

, WII, and WIII.

ents the phase behavior of the microemulsion system inagram when a lipophilic linker was added to the system

ig. 5b, compared to no WIII region in Fig. 5a, sho

em when the lipophilic linker was incorporated to the

could be reached by slightly modifying the surfactant

The present results corroborate the reported enhancem

hiyama et al. 2000), when anionic and nonionic surf

Oil

ater

Surfactant

Blend

Water

LipophilicLinker

5

ation.

n. To create the correct

s of the phase diagram.s for four-component

of the diagram using a

nds to the composition

n of lipophilic linker.

ith lipophilic linker.

c linker microemulsion

hase diagrams as dots.

es presenting Winsor II

re the solubilization of

erved in Fig. 5b in the

the absence of a linker.at a constant lipophilic

s the enhancement of

system. According to

film at the interface by

nt in the solubilization

ctants are mixed with

Oil



6 SPE 164131

Fig. 5 Pseudoternary phase diagram at 180˚F of a microemulsion system (a) without lipophilic linker and (b) with lipophilic linker.

Effect of Temperature on Microemulsions with Linker

A microemulsion system for cleaning synthetic-based mud from wellbore surfaces was mixed with a hydrophilic linker to

change or improve its properties. Fig. 6 shows that the range of temperature where the microemulsion is formed could shift

from lower to higher temperature by changing the type of hydrophilic linker. Hydrophilic linker 1 is a glycol and hydrophiliclinker 2 is an alcohol.

For example, at 20% of nonionic surfactant in the surfactant package, the impact of a glycol (a polyol) is to confer a lower

susceptance to temperature effects than using an alcohol. The property shift is due to the important interaction between the

surfactant molecule and the linkers. This theory can be supported by the studies performed by Salager et al. (2005) and

Yaghmur et al. (2002), where they conclude that the amphiphilic nature of linkers with a hydrophilicity tendency enables them

to interact with the surfactant head group monolayers at the interface, thereby affecting the head group packing. In this case,

the hydrophilic linker could be used as a tuning parameter to increase the flexibility of the surfactant film, lowering the density

of surfactant head groups in the surface monolayer and enhancing certain properties. This entropic effect, occurring on the

molecular scale, results in a geometric rearrangement of the surfactant headgroups at the interface that tends to change the

average size of the micelles, changing the effective curvature of the interfacial film surface, with resulting lower observed IFT.

Fig. 6 Temperature effect of hydrophilic linkers in microemulsions.

Dynamic Interfacial Tension

Achieving a very low interfacial tension between the oily substance or crude oil encountered in the well and the treatment fluid

is the main aim for the microemulsion system, to prevent and remove in-situ water-in-crude oil emulsions, as well as to

remove any formation damage caused by the oily materials used in downhole operations.When an extra component is added to the microemulsion, for example a lipophilic linker, the molecule will not adsorb at

the interface; instead, it will stay in the oil phase and concentrate near to the interface because of the van der Waals long-range

forces (Spernath et al. 2006). The new addition will interact with the lipophilic surfactant tail and will rearrange the tail

causing an increase in the solubilization by increasing the transition zone thickness.

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8

T e m p e r a t u r e ,

º C

Nonionic/Anionic surfactant fraction

1Φ

1Φ

Hydrophilic Linker 1Hydrophilic Linker 2



SPE 164131 7

Fig. 7 shows the effect of adding a lipophilic linkeron the dynamic interfacial tension of microemulsion systems. The

microemulsion treatment fluid that contains an anionic/nonionic surfactant blend, oil and water shows low values (~0.1 mN/m)

for the microemulsion interfacial tension at the beginning of the test. However, the same microemulsion system with the

addition of a lipophilic linker resulted in a reduction of interfacial tension at the initial contact between the crude ol and the

microemulsion (< 0.01 mN/m). After one hour of contact with the crude oil, the interfacial tension for the system with the

lipophilic linker is one order of magnitude lower than observed for the microemulsion without the lipophilic linker. At the end

of the test, the IFT for the microemulsion with the lipophilic linker was two orders of magnitude lower than the fluid without

the linker molecules.

Fig. 7 Dynamic interfacial tension between crude oil and microemulsion formulated with and without lipophilic linker.

Fig. 8 shows the interfacial tension (IFT) between 30°API crude oil sample and the microemulsion formulation with

lipophilic linker using various types of co-surfactants.

Without any co-surfactant, the interfacial tension is approximately 0.25 mN/m. When the microemulsion is mixed with co-

surfactant 1, the IFT decreases by one order of magnitude. In the case of the microemulsion mixed with co-surfactant 2, the

IFT decreases by more than 3 orders of magnitude during the 4-hour dynamic test. The difference between the two co-

surfactants is the carbon chain length. Co-surfactant 1 has a shorter carbon chain than co-surfactant 2.

The segregation and interaction of the lipophilic linker with the co-surfactant and/or surfactant is apparently better with the

system containing co-surfactant 2. This means that a reduction of the IFT value is due to something happening close to the

interface and due to interactions between the tail or head of the surfactant molecules with the co-surfactant and the lipophilic

linker. Co-surfactant 2 may be acting as an intermediate hydrophilic linker.The addition of co-surfactants and lipophilic linkers show enhanced behavior of the assembled surfactant system at the

interface. The combination has a higher solubilization capacity than the surfactant mixture alone, as a result of a smoother

transition between the non-polarity of the oil and the polarity of the water.

Fig. 8 Dynamic interfacial tension between crude oil and a microemulsion with two different co-surfactants.

0.001

0.01

0.1

1

10

0.0 0.5 1.0 1.5 2.0 2.5 3.0

I n t e r f a c i a l T e n s i o n , m N / m

Time, hours

Without LipophilicLinker

With LipophilicLinker

0.0001

0.001

0.01

0.1

1

0.0 1.0 2.0 3.0 4.0 5.0

I n t e r f a c i a

l t e n s i o n , m N / m

Time, hours

Whitoutco-surfactant

With Co-surfactant 1

With Co-surfactant 2



8 SPE 164131

Crude oil/Microemulsion Compatibility Evaluation

Interactions between the crude oil and components of the drilling or completion fluid may generate in-situ emulsions and/or

formation damage. Depending on its composition and nature, the crude oil could contain natural surfactant molecules capableof forming in-situ water-in-crude oil emulsions with the drilling or completion fluids. It is important to test the compatibility of

the microemulsion treatment fluid with a representative crude oil sample before field application, to minimize the risk that this

problem could arise. Fig. 9 shows results of the emulsion risk test using a 30°API crude oil with the microemulsion treatment

fluid in a ratio of 50/50.

Within 5 minutes, all the crude oil was completely separated, indicating good compatibility with the microemulsion fluid

and confirming the effectiveness in preventing and breaking in-situ emulsions. The results agree with theory (Salager et al.2009) whereby the system shows ultra-low interfacial tension, minimum emulsion stability and optimum solubilization

parameter at the optimum formulation.

(a) (b) (c) (d)

Fig. 9 Fluids compatibility: (a) before agitation, (b) after agitation and (c) after 5 min of agitation and (d) fluids separation as functionof time.

Synthetic-based Mud Cleaning Evaluation

A modified HPHT filtration test is performed to evaluate the effectiveness and cleaning power of the microemulsion with

synthetic-based filter cake. Evaluation of treatment fluid in a HTHP double-ended filter cell is used to demonstrate the ability

of the microemulsion to cleanup and break viscous emulsions under wellbore conditions.

The main parameters to be evaluated are the filter cake characteristics before and after treatment and the water wettability

of the residual filter cake solids after treatment. Fig. 10 shows the untreated filter cake from a synthetic-based mud.

Fig. 10 Untreated synthetic-based mud filter cake.

The treatment fluid with lipophilic linker was evaluated at 100°F and 180°F. Fig. 11a and Fig. 11b show pictures of the

aloxite disc with the residual filter cake, after treatment. The data indicate that the system at 100°F is too far from optimum

solubilization point, despite the presence of the lipophilic linker (Fig. 11a). However, when the temperature was raised from

100°F to 180°F, the system approached the optimum solubilization point, resulting in the incorporation of the oil from the mud

to the microemulsion. In addition, the solids changed from oil-wet to water-wet condition (Fig 11b). Temperature played a

significant role in the thermodynamic condition of the system, affecting the interfacial tension and the solubilization

parameter.

Fig. 11a. clearly shows an oil-wet condition of the residual filter cake. Notice the bright color characteristic of the oily

material on top of the disc, indicating that the cleaning was not completed and that the residual solids on top of the disk are not

0

20

40

60

80

100

120

0 3 6 9 12 15

M i c r o e m u l s i o n s e p a r a t i o n ,

%

Time, minutes



SPE 164131 9

dispersible in water. A water-wet condition is shown in Fig. 11b where almost all of the filter cake was removed. Only clean

drill-cutting solids remained on the disc after the treatment. Notice the complete dispersability of the remaining solids in water.

Fig. 11 Cleaning performance of microemulsion fluid at two different temperatures (a) 100°F and (b) 180°F.

Summary and Conclusions

The combination of linker molecules with the microemulsion system produces a higher solubilization capacity than the

original surfactant blend, as demonstrated in the pseudoternary phase diagram studies. Results of interfacial tension measurements of the microemulsion systems with linkers prove that the linker molecules

produce a reduction of the IFT, increasing the solubilization capacity of the microemulsion fluids.

A very small amount of linker added to the microemulsion (between 1 and 2 %) can reduce the IFT by various orders

of magnitude.

In summary, the results discussed in this paper give evidence that the microemulsion system with linkers: (1)

significantly decreases the interfacial tension between crude oils and the treatment fluid, (2) is compatible with the

crude oil, (3) efficiently cleans synthetic-based mud, and (4) completely water-wets the solids, which is a step

improvement in the use of microemulsions for applications to maximize production and to optimize wellbore

construction.

AcknowledgmentWe thank the management of Baker Hughes for allowing us to publish this paper. Special thanks to Dr Jean-Louis Salager and

Dr Ana Forgiarini for their advice and contribution on the studies.

NomenclatureIFT = interfacial tension

mN/m = milli Newton per meter

°F = temperature in Fahrenheit

°C = temperature in Centigrade

° = degree

°API = specific gravity of crude oil in degree

W I = Winsor I

W II = Winsor II

W III = Winsor IIII

W IV = Winsor IV

Φ = phase

% = percentage

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Acosta, E.J., Mai, P.D., Harwell, J.H., et al. 2003. “Linker modified microemulsions for a variety of oils and surfactants,” J. SurfactantsDeterg, 6 (4): 353-363.

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Filter cake after

treatment

Filter cake after

treatment

Residual filter cake

solids in water

Residual filter cake

solids in water

(a) (b)



10 SPE 164131

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SI Metric Conversion Factors(°F-32)/1.8 = °C

mN/m x 1.0 E +03 = kg/s2

hour x 2.8 E -04 = s

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Enhanced Oil Solubilization Using Microemulsions With Linkers - SPE-164131-MS