BACKGROUND
[0001] The present invention relates to emulsions and methods of using such
emulsions. More particularly, the present invention relates to emulsion stabilizing agents and
their uses in subterranean applications.
[0002] Emulsions usually comprise two immiscible phases. The two immiscible
phases may include a continuous (or external) phase and a discontinuous (or internal) phase.
The discontinuous phase may comprise the secondary fluid that usually exists in droplets in the
continuous phase. Two varieties of emulsions are oil-in-water and water-in-oil. Oil-in-water
emulsions usually include a fluid at least partially immiscible in an oleaginous fluid (usually an
aqueous-based fluid) as the continuous phase and an oleaginous fluid as the discontinuous
phase. Water-in-oil emulsions are the opposite, having the oleaginous fluid as the continuous
phase and a fluid at least partially immiscible in the oleaginous fluid (usually an aqueous-based
fluid) as the discontinuous phase. Water-in-oil emulsions may be also referred to as invert
emulsions.
[0003] Such emulsions have been used in various oil and gas applications. For
instance, emulsions may be used in the oil and gas industry for subterranean treatment
applications, including drilling, production, and completion operations. Invert emulsions may
be used because oleaginous-based treatment fluids (also known as muds) may have desirable
performance characteristics when compared with water-based muds in some situations, e.g..
when there is an abundance of water reactive materials in a well bore. These performance
characteristics may include, e.g., better lubrication of the drilling strings and downhole tools,
thinner filter cake formation, and better hole stability.
[0004] A water-in-oil type emulsion, that does not have an emulsifying agent
capable of stabilizing the fluid that is at least partially immiscible in the oleaginous fluid
typically will undergo natural degradation processes, such as droplet coalescence and Ostuald
ripening, until the two phases which are at least partially immiscible separate and the emulsion
no longer exists. Having an unstable in\crt emulsion may be problematic hecause if the
emulsion destabilizes, il ma\ not have tonsislcnl. reliable propcnic-:. Iliis prohlcin tna_\ be
exacerbated b\ ilic physical lorcc^ U::)i the eniul^iU'ii ma\ UIKL.;uo wiicii bciuL! used in
•subterranean upplicatioiis. such ,A li. rinai. mechanical, and chcn^ici ^i)\'--c- ' MMJsi.in
^^•bili/ing aijciUs. sonictimc- •'•.••••: ['.' as cniui-.l'icrs. m;i\ be u ,• ':! •••, ,;'!M!-s i.-. ••.,
3
stabilizers, especially when used in subterranean applications. The term "emulsion stabilizing
agent" or emulsifier as used herein may refer to any compound capable of lowering the
interfacial tension between an oleaginous tluid and a fluid at least partially immiscible in the
oleaginous fluid.
[0005] Some traditional emulsion stabilizing agents are surfactant-based.
Surfactant-based emulsion stabilizing agents usually comprise a hydrophobic part that interacts
with the oil phase and a hydrophilic part that interacts with the non-oleaginous phase. These
interactions generally decrease the surface tension of the interface between the water droplet and
the oil, which may slow the natural tendency of the two immiscible phases to separate.
SUMMARY
[0006] The present invention relates to emulsions and methods of using such
emulsions. More particularly, the present invention relates to emulsion stabilizing agents and
their uses in subterranean applications.
[0007] According to a first aspect of the present invention, there is provided a
stabilized emulsion composition comprising: an oleaginous fluid, a fluid that is at least partially
immiscible with the oleaginous fluid, and an emulsion stabilizing agent, wherein the emulsion
stabilizing agent comprises a first ionic compound soluble in the oleaginous fluid or the fluid
that is at least partially immiscible with the oleaginous fluid, and a second ionic compound with
a charge of opposite sign of the first ionic compound and that is at least partially soluble in the
opposite fluid as the first ionic compound.
[0008] In an embodiment, the first ionic compound, the second ionic compound,
or both comprise an ionic surfactant.
[0009] In an embodiment, the first ionic compound, the second ionic compound,
or both comprise an ionic polyelectrolyte.
[0010] In an embodiment, one of the first ionic compound and the second ionic
compound comprises an ionic surfactant and the other of the first ionic compound and the
second ionic compound comprises an ionic polyelectrolyte.
[0011] In an embodiment, the ionic surfactant comprises an anionic surfactant.
[0012|ln an embodiment, the anionic surfactant comprises ai least one
compound selected Ironi the group consisting of: an alk\l carboxylate. an alk\!clher
carboxx laic. a N-ac\ laminoacid. a N-ac\lglutamalc. a N-acylpol_\ peptide. ,in
alk\ Ibcii/ciicsullonalc. a parainnic sulionate. an (/-r.!cnnsui!<>n,ilc. a hgnosuHate. a dori\al!\',:
4
of a sulfosuccinate. a polynapthylmethylsulfonate, an alkyl sulfate, an alkylethersulfate. a
monoalkylphosphate, a polyalkylphosphate, a fatty acid, an alkali salt of an acid, an alkali salt of
a fatty acid, an alkaline salt of an acid, a sodium salt of an acid, a sodium salt of a fatty acid, an
alkyl ethoxylate. a soap, a combination thereof, and a derivative thereof
[0013] In an embodiment, the ionic surfactant comprises a cationic surfactant.
[0014] In an embodiment, the cationic surfactant comprises at least one
compound selected from the group consisting of: an alkyl amine, an alkyl amine salt, a
quaternary ammonium salt, an ethoxylated quaternary ammonium salt, an amine oxide, an
alkyltrimethyl amine, a triethyl amine, an alkyldimethylbenzylamine, a derivative thereof, and a
combination thereof.
[0015] In an embodiment, the ionic polyelectrolyte comprises an anionic
polyelectrolyte.
[0016] In an embodiment, the anionic polyelectrolyte comprises at least one
compound selected from the group consisting of: a polymer or copolymer comprising a
carboxylate group, a sulfonate group, a phosphate group, a phosphonate group, an acrylate
monomer, a methacrylate monomer, a styrene carboxylate, a vinyl sulfonate, a 2-acrylamine-2-
methyl-propyl sulfonate, a 3-acryIamide-3-methyl butanoate, a sah of malic acid, a polyacrylic
acid, a partially-hydrogenated polyacrylamide, a carboxy methyl cellulose, a cellulose modified
with an anionic functional group, a polysaccharide modified with an anionic functional group, a
galactomannan modified with an anionic functional group, a derivative thereof, and a
combination thereof.
[0017] In an embodiment, the ionic polyelectrolyte comprises a cationic
polyelectrolyte.
[0018] In an embodiment, the cationic polyelectrolyte comprises at least one
compound selected from the group consisting of: a polyethylene imine. a polyamide amine, a
polyamine. a vinyl benzyl trimethyl ammonium chloride, a dimethyldiallyl ammonium chloride,
a 3-acrylamido-3-methyl butyl trimethyl ammonium chloride, a polyvinylpyrrolidone, chitosan
modified with a cationic functional group, a gelatin modified with a cationic functional group, a
galactomannan modified with a cationic functional group, a cellulose modified with a cationic
functional group, a derivati\c thereof, and a combination thereof
lOOl*^)] In an embudimcni. ihc oleaginous fluid comprises at least one tluid
sckctcd from the group citnsisting oi': ii dicscl oil. a crude oil. a parailln oil. a mineral oil. a low
uixiLilN niiiicral oil. an oicllr;. .ai CNICI. an aiiiidc. an aniinc. a pol\ulefm. a
5
polydiorganosiloxane, a siloxane, an organosiloxane. an ether, an acetal, a dialkylcarbonate, a
hydrocarbon, a derivative thereof, and a combination thereof.
[0020] hi an embodiment, tlie fluid that is at least partially immiscible with the
oleaginous fluid comprises at least one fluid selected from the group consisting of: glycerin, a
glycol, a polyglycol amine, a polyol, fresh water, sea water, salt water, a brine, a derivative
thereof, and a combination thereof
[0021 ] According to another aspect of the present invention, there is provided a
method comprising: providing a stabilized emulsion composition formed by combining
components that comprise: an oleaginous fluid, a fluid that is at least partially immiscible with
the oleaginous fluid, and an emulsion stabilizing agent, wherein the emulsion stabilizing agent
comprises a first ionic compound soluble in the oleaginous fluid or the fluid that is at least
partially immiscible with the oleaginous fluid, and a second ionic compound with a charge of
opposite sign of the first ionic compound and that is at least partially soluble in the opposite
fluid as the first ionic compound, and placing the stabilized emulsion composition in a
subterranean formation as part of a subterranean application. The stabilized emulsion
composition may comprise one or more of the embodiments described above.
[0022] According to another aspect of the present invention, there is provided a
method comprising: providing a stabilized emulsion composition comprising: an oleaginous
fluid, a fluid that is at least partially immiscible with the oleaginous fluid, and an emulsion
stabilizing agent, wherein the emulsion stabilizing agent comprises a first ionic compound
soluble in the oleaginous fluid or the fluid that is at least partially immiscible with the
oleaginous fluid, and a second ionic compound with a charge of opposite sign of the first ionic
compound and that is at least partially soluble in the opposite fluid as the first ionic compound,
and drilling a well bore in a subterranean formation using the stabilized emulsion composition.
The stabilized emulsion composition may comprise one or more of the embodiments described
above.
[0023] Yet another aspect of the present invention comprises a method of
preparing a stabilized emulsion composition comprising: providing an oleaginous fluid:
providing a fluid that is at least partially immiscible with the oleaginous fluid; providing an
emulsion stabilizing agent, wherein the emulsion stabilizing agent comprises: a flrst ionic
cumpound soluble in the oleaginous fluid or the fluid ihul is al least partialK' immiscible uith
the oleaginous fluid, and a second ionic compound with a charge ol'opposite sign (if the flrst
lOiiie eoiVipounJ, ;jnd th,!i is a! le,is! pp.nialK soluble ui llie opposite fluid as the flrst iiMiie
6
compound; and combining the oleaginous fluid, the fluid that is at least partially immiscible
with the oleaginous fluid, and the emulsion stabilizing agent to form a stabilized emulsion
composition. The stabilized emulsion composition may comprise one or more of the
embodiments described above.
[0024] The features and advantages of the present invention will be apparent to
those skilled in the art. While numerous changes may be made by those skilled in the art, such
changes are within the scope of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The present invention relates to emulsions and methods of using such
emulsions. More particularly, the present invention relates to emulsion stabilizing agents and
their use in subterranean applications.
[0026] While there are many advantages to the present invention, only some are
disclosed herein. The emulsion stabilizing agents provided by the present invention may be
advantageous because it is believed that the electrostatic interactions of the molecules may serve
to anchor the surfactants to the interface between the two phases present in the emulsion or
invert emulsion, potentially resulting in an increased surfactant or polyelectrolyte concentration
at the interface. This may result in an improved stability of the emulsion and allow a relatively
low amount of the emulsion stabilizing agent to be used to achieve a stable emulsion.
[0027] The present invention provides emulsion stabilizing agents that comprise
a pair of charged surfactant or polyelectrolyte compounds of opposite charge. The emulsion
stabilizing agents of the present invention may be used beneficially to stabilize emulsion
compositions. Such emulsion compositions that comprise the emulsion stabilizing agents of the
present invention may be referred to herein as the "stabilized emulsion compositions" of the
present invention. These stabilized emulsion compositions are formed by combining
components that comprise an oleaginous fluid, a fluid that is at least partially immiscible with
the oleaginous fluid, and an emulsion stabilizing agent of the present invention. After mixing,
these components may or may not be separately identifiable, depending on the sophistication of
the technique used. The stabilized emulsion compositions may be suitable for use in a variet\ of
subterranean applicatie)ns wherein ciil-in-water or a water-in-oil emulsions are suitable. These
ma> include subterranean applications comprising stiinulatit^n operations such as fracturing and
.\ai!c;i water, salt water, and brines [ci^.. saturated salt waters).
8
Any brine may be used with the emulsions of the present invention that does not interfere with
the emulsion stabilizing agents. One of ordinary skill in the art will appreciate that detrimental
interactions may occur between some components of some brines and charged surfactants or
polyelectrolyte pairs. Suitable brines may include heavy brines. Heavy brines, for the purposes
of this application, include brines that may be used to weight up a fluid, such as a treatment
fluid, instead of using traditional weighting agents. Brines may comprise H2O soluble salts. In
certain exemplary embodiments, suitable H2O soluble salts may comprise sodium chloride,
calcium chloride, calcium bromide, zinc bromide, potassium carbonate, sodium formate,
potassium formate, sodium acetate, potassium acetate, calcium acetate, ammonium acetate,
ammonium chloride, ammonium bromide, sodium nitrate, potassium nitrate, ammonium nitrate,
calcium nitrate, sodium carbonate, potassium carbonate, and combinations thereof In other
exemplary embodiments, the H2O soluble salt may be any salt which reduces the water phase
activity of the emulsion. Factors that determine what partially immiscible fluid will be used in a
particular application may include cost, availability, and which oleaginous fluid has been
chosen. Another factor that may be considered is the application of the emulsion. For example,
if the application needs an emulsion with a heavy weight, a zinc bromide or calcium chloride
brine may be chosen. One skilled in the art with the benefit of this disclosure in view of the
considerations will be able to choose a particularly suitable partially immiscible fluid for a
particular application.
[0030] As noted above, the stabilized emulsion compositions of the present
invention also comprise an emulsion stabilizing agent of the present invention. The emulsion
stabilizing agents comprise at least a pair of compounds that may generally comprise two
surfactant molecules, polyelectrolyte molecules, or any combination thereof that have opposite
charges, which may or may not be of the same magnitude. In general, the members of the pair
will be either cationic or anionic. The charge on one or both of the compounds may result from
one or more ionic functional groups. As used herein, the term "ionic" or "ionic functional
group" may refer to any compound capable of carrying at least a partial positive or negative
charge, whether inherent in the chemical structure or formed due to the presence of any other
components in a mixture. Such compounds may include ionic groups or compounds, polar
groups or compounds, amphoteric groups or compounds, or any other type of material capable
ofcarrNing or dc\ eloping a charge. In some embcKliments. the anit)nic member of the pair ma_be at icasi pariiall} soluble in ihc oleaginous phase while the cationic member ma\ be at least
p.irtialK siMubU- ip; the lltiid thai i> al least partialh immiscible in the oleagiiuuis fiLiid. hi other
9
embodiments, the cationic member of the pair may be at least partially soluble in the oleaginous
phase while the anionic member may be at least partially soluble in the fluid that is at least
partially immiscible in the oleaginous fluid. While not wishing to be limited by theory, it is
believed that the electrostatic interactions may occur at the interface between the oleaginous
phase and the fluid that is at least partially immiscible in the oleaginous fluid. While each
member of the emulsion stabilizing agent pair may be soluble in one of the phases, the
combined component formed by the electrostatic interactions may be at least partially insoluble
in both phases. The resulting emulsion stabilizing agent pair may remain at the interface
between the phases, resulting in an improved stability of the emulsion.
[0031] In an embodiment, a member of the emulsion stabilizing agent pair may
be a surfactant that may carry an anionic or cationic charge. In an embodiment, a surfactant
useful with the emulsion stabilizing agent disclosed herein may comprise at least one ionic
functional group. Exemplary functional groups may include carboxylates, sulfonates, sulfates,
amines, imines, phosphates, and phosphonates. Exemplary cationic surfactants may include, but
are not limited to, alkyl amines, alkyl amine salts, quaternary ammonium salt, ethoxylated
quaternary ammonium salts, amine oxides, alkyltrimethyl amine, triethyl amine,
alkyldimethylbenzylamine. Exemplary anionic surfactants may include, but are not limited to,
alkyl carboxylates, alkylether carboxylates, N-acylaminoacids, N-acylglutamates, Nacylpolypeptides,
alkylbenzenesulfonates, paraffmic sulfonates, a-olefmsulfonates,
lignosulfates, derivatives of sulfosuccinates, polynapthylmethylsulfonates, alkyl sulfates,
alkylethersulfates, monoalkylphosphates, polyalkylphosphates, fatty acids, alkali salts of acids,
alkali salts of fatty acids, alkaline salts of acids, sodium salts of acids, sodium salts of fatty acid,
alkyl ethoxylate, and soaps. One of ordinary skill in the art would be able to determine the
phase to which the ionic surfactant should be added, which may be based on the composition of
each phase in the emulsion, the solubility of the component in each phase, the operating
conditions (e.g.. temperature), and any additives present in either phase (e.g., salts). For
example, anionic surfactants may react with any calcium present in the fluid that is at least
partially immiscible in the oleaginous fluid to form compounds that may not be effective
stabilizers. As such, one of ordinary skill in the art may avoid the use of anionic surfactants in
the fluid that is at least partiall) inimiscible in the oleaginous fluid when calcium ions are
present.
|<)032| In aii cinhiKlimcnt. a member of the emulsion stabilizing agent pair nia'x; :.i piii\eicctiui\ic iH.u nuiv Cdii) im anionic oi cationic charge. As used herein, a
10
polyelectrolyte may be a polymer whose repeating units comprise an electrolyte group. These
groups may dissociate in solutions comprising an aqueous fluid, allowing the polymers to carry
a formal charge to some degree. For example, a poKmer may be prepared that contains an
anionic monomer to impart an anionic character to the molecule. Exemplary anionic
polyelectrolytes include, but are not limited to, polymers or copolymers derived from anionic
monomers containing carboxylates, sulfonates, phosphates, phosphonates, acrylate monomers,
methacrylate. 2-acrylamine-2-methyl-propyl sulfonate, 3-acrylamide-3-methyl butanoate,
styrene carboxylate, vinyl sulfonate, salts of malic acid, polyacrylic acid (PAA), partiallyhydrogenated
polyacrylamide (PHPA), carboxy methyl cellulose, derivatives of cellulose,
polysaccharides {e.g.. xanthan, arable gum), and galactomannans modified with anionic
functional groups. Non-ionic monomers may be included in these compounds, e.g., as in a
copolymer between an anionic monomer and a neutral monomer. Exemplary cationic
polyelectrolytes include, but are not limited to, polymers or copolymers comprising cationic
groups such as imines, amines, and copolymers with neutral monomers. Specific examples may
include, but are not limited to, polyethylene imine, polyamide amine, polyamines, vinyl benzyl
trimethyl ammonium chloride, dimethyldiallyl ammonium chloride, 3-acrylamido-3-methyl
butyl trimethyl ammonium chloride, and polyvinylpyrrolidone. For example, polymers
comprising chitosanes, gelatins, galactomannans and cellulose may be modified with cationic
monomers to form cationic polyelectrolytes. The polyelectrolytes useful with the emulsion
stabilizing agents disclosed herein may be prepared by any method known to one of ordinary
skill in the art.
[0033] In an embodiment, the emulsion stabilizing agent may be added to the
stabilized emulsion composition in any amount capable of stabilizing the emulsion to a desired
degree. The emulsion stabilizing agent pair may be added on a charge balanced basis. For
example, if the anionic member of the emulsion stabilizing agent pair carried a formal charge
equal to twice that of the cationic member of the emulsion stabilizing agent pair, then the
anionic member of the emulsion stabilizing agent pair may be added in an amount equal to half
of the total amount of the cationic member of the emulsion stabilizing agent pair on a mole
basis, in other embodiments, the members of the emulsion stabilizing agent pair may be added
in a ratio not related to the charge on the emulsion stabilizing agent pair members. For example,
if it is expected that one incinber ol'tlie pair max interact with other components of the stabilized
emulsion, then more or less ol' that member of the pair may be added to compensate for the
inltraclion. hi an cmhodiiiienl. the vinulsion stahili/in!.: ULicnt nia_\ be added to a stabilized
11
emulsion composition in an amount ranging from about 0.1 pounds per barrel (Ib/bbl) to about
12 Ib/bbl (about 0.29 kg/metre^ to about 34 kg/metre^) of the stabilized emulsion composition.
In another embodiment, the emulsion stabilizing agent may be added to a stabilized emulsion
composition in an amount ranging from about 0.25 Ib/bbl to about 4 Ib/bbl (about 0.71 kg/metre"'
to about 11 kg/metre"*) of the stabilized emulsion composition.
[0034] The stabilized emulsion compositions of the present invention may
optionally contain a variety of additives. Examples of additives useful in the stabilized
emulsions may include, but are not limited to, solids, weighting agents, inert solids, fluid loss
control agents, emulsifiers, salts, dispersion aids, corrosion inhibitors, emulsion thinners,
emulsion thickeners, viscosifiers, and any combination thereof
[0035] In some embodiments, a weighting agent may be used to increase the
density of the stabilized emulsion. The weighting agents, which serve to increase the density of
the stabilized emulsions, may be any solids known to those skilled in the art as useful for such
purpose that do not adversely interact with the emulsion stabilizing agent composition.
Examples of weighting agents may include, but are not limited to, barite, calcite, ilmenite,
mullite, gallena, manganese oxides, iron oxides, mixtures of these and the like. For example, a
ground barium sulfate additive having the tradename BAROID® available from Halliburton
Energy Services, Inc. in Houston, Tex., U.S.A. may be used as a weighting agent. The
weighting material may typically be added in order to alter the density of the stabilized
emulsion. The density of the fluid may be less than about 20 (about 2400 kg/metre'^), or less
than about 15 (about 1800 kg/metre ), or alternatively less than about 10 pounds per gallon
(about 1200 kg/metre^). One of ordinary skill in the art would be able to determine the amount
of weighting agent to add to produce a stabilized emulsion with a desired density.
[0036] In an embodiment, the stabilized emulsion may comprise lluid-loss
control additives, emulsifiers, or both. Fluid loss control agents such as modified lignite,
polymers, oxidized asphalt and gilsonite may also be added to the stabilized emulsion. Usually
such fluid loss control agents may be employed in an amount which is at least about 0.1. at least
about 1. or at least about 5 percent by weight of the total fluid. For example, an additive having
the trade name ADAPTA'^^' available from Halliburton Energy Services. Inc. in Houston. Tex..
U.S.A. may be used as a fluid los.s control additi\e. Alkali may also be used, preferably lime
(calcium hydm.xide or calcium o.xidc). to bind or react with acidic gases {e.i^.. C"(): and H2S)
cntouniercd during drilling in the lonnation so long as the alkali does not interfere with the
emulsion siiibili/mg ;,gciils disc'rscJ iiercin. The quantilx of ti'ce lime in a drilling tluid ma12
range from about 1 to about 10 Ibs/bbl (about 2.9 kg/metre"' to about 29 kg/metre ), or more
preferably about 1 to about 4 ibs/bbl (about 2.9 kg/metre"' to about 11 kg/metre'^), although lower
ranges such as less than about 2 Ibs/bbl (about 5.7 kg/metre^) are preferred for certain esters that
tend to hydroiyze in the presence of alkaline compounds as will be known to those skilled in the
art. Other suitable agents as an alternative to lime may also be used to adjust and/or stabilize the
emulsions with respect to acids.
[0037] Various supplemental surfactants and wetting agents conventionally used
in emulsions may optionally be incorporated in the stabilized emulsions. Such surfactants may
be, for example, fatty acids, soaps of fatty acids, amido amines, polyamides, polyamines,
imidazoline derivatives, oxidized crude tall oil, organic phosphate esters, alkyl aromatic sulfates
and sulfonates, as well as, mixtures of the above. Generally, such surfactants may be employed
in an amount which does not interfere with the use of the stabilized emulsions. For example, the
surfactants or wetting agents may be used in an amount that does not interfere with the ability of
an a stabilized emulsion to act as a drilling fluid or drill in fluid and remove cuttings from the
well bore.
[0038] Further, the stabilized emulsion may have added to it or mixed with the
stabilized emulsion, other fluids or materials. Such materials may include for example additives
to reduce or control temperature rheology or to provide thinning, such as, for example, additives
having the tradenames COLDTROL®, RHEMODTM L, ATC®, and OMC 2™; additives for
providing temporary increased viscosity for shipping (transport to the well site) and for use in
sweeps, such as, for example an additive having the tradename TEMPERUS''"'^ (modified fatty
acid); additives for bridging porous rock, such as, for example additives having the tradename
BARACARB* 50; additives for high temperature high pressure filtration control (HTHP
FILTRATE) and emulsion stability, such as, for example, additives having the tradename
FACTANT"'"'^ (highly concentrated tall oil derivative); and supplemental additives for
emulsification, such as. for example additives having the tradenames EZ MULT"^ NT or LE
SUPERMUL™ (polyaminated fatty acids). Blends of thinners such as the OMC 2^^^,
COLDTROL". and ATC" may also be effective in stabilized emulsions of the invention. All of
the aforementioned trademarked products are available from Halliburton Elnergy Services. Inc.
in 1 louston. Tex.. U.S.A.
|0()39| Viscosifx ing agents may oplionally he employed in the stabilized
i^nuilsinns ol'thc prcsciil iiuculicMi. Lsualh. \iseosilying agents such as oil and water soluble
poKmcis. |\)l_\aniidc resin-;. |x>i;c>iri\.\\ lie acids and latt_\ aciJ soaps ma\ be ciiipioycd, I he
13
amount of viscosifying agent used in the composition will necessarily vary depending upon the
end use of the composition. Usually such viscosifying agents are employed in an amount which
is at least about 0.1. at least about 2, or at least about 5 percent by weight of the total fluid. For
example. TAU-MOD™ or BARAZAN" D PLUS, both available from Halliburton Energy
Services, Inc. in Houston, Tex., U.S.A., may be used as a viscosifying agent.
[0040] Still further, dispersion aids, corrosion inhibitors and/or defoamers may
be used. These and other suitable auxiliaries and additives are used in amounts known to those
skilled in the art depending on the conditions of the particular well bore and subterranean
formation.
[0041] Generally, the stabilized emulsions of the present invention may be
formed using any technique known in the art. For example, the components may be mixed
together in any order under agitation condition. A representative method of preparing the
stabilized emulsion may comprises mixing an appropriate quantity of the fluid that is at least
partially insoluble in the oleaginous fluid and an appropriate quantity of the emulsion stabilizing
agent and any optional additives during continuous, mild agitation. An oleaginous fluid may
then be added while mixing until a stabilized emulsion is formed. If weighting agents, such as
those described above, are to be added, then the weighting agents are typically added after the
stabilized emulsion is formed. Alternatively, the stabilized emulsions of the present invention
may be prepared by simply adding the emulsion stabilizing agent to an existing stock of drilling
fluid. The effectiveness of this treatment may depend on the constituents of the fluid.
[0042] An example of a method of the present invention is a method of treating a
subterranean formation comprising the steps of providing a treatment fluid comprising a
stabilized emulsion comprising an oleaginous fluid, a fluid that is at least partially immiscible
with the oleaginous fluid, and an emulsion stabilizing agent; and treating the subterranean
formation. In certain exemplary embodiments of the present invention, a method of treating a
subterranean formation includes a well completion operation or a drilling operation. In other
exemplary embodiments of the present invention, a method of treating a subterranean formation
includes a stimulation operation. Examples of stimulation operations of the present invention
include fracturing operations and acid stimulation opertitions. like matrix acidizing and a
fracturing acidizing processes. In ofhcr exemplary embodiments of the present invention, a
method of treating a subterranean formation includes a sanJ control operation such as installing
a graxc! pack.
14
[0043] Another example of a method of the present invention is a method of
drilling a well bore in a subterranean formation using a stabilized emulsion drilling fluid
comprising an oleaginous fluid, a fluid that is at least partially immiscible with the oleaginous
fluid, and an emulsion stabilizing agent.
[0044] An exemplary method of the present invention is a method of emulsifying
crude oil comprising the steps of providing crude oil, a fluid that is at least partially immiscible
with the crude oil and an emulsion stabilizing agent; and mixing the crude oil, the fluid that is at
least partially immiscible with the crude oil and the emulsion stabilizing agent so as to form a
stabilized crude oil emulsion.
[0045] To facilitate a better understanding of the present invention, the following
examples of certain aspects of some embodiments are given. In no way should the following
examples be read to limit, or define, the scope of the invention.
EXAMPLES
[0046] In order to demonstrate the stabilization of an emulsion with the emulsion
stabilizing agents disclosed herein, several samples of stabilized emulsions were prepared and
allowed to age different time periods. In this example, 1.5 Ib/bbl of polyelectrolyte (EZ-MUD®
GOLD, available from Halliburton Energy Services of Houston, Texas) and 6 Ib/bbl of a
filtration control agent (N-DRIL® HT PLUS, available from Halliburton Energy Services of
Houston, Texas) were mixed with 3% KCl salt water using a multi-mixer for 5 minutes followed
with 1.0 Ib/bbl of hydrophobic surfactants (Octadecylamine with a technical grade of 90%) for
another 5 minutes. An amount of diesel comprising 20% of the overall fluid volume was added
and mixed for another 30 minutes. The resulting mixture was hot-rolled for 16 hours at 230°F
(110°C) to form a sample labeled "Sample 1." A second batch of the fluid was prepared
according to the same procedure and labeled "Sample 2." The second batch of fluid was
viscosified with a viscosifier (BARAZAN* D PLUS, available from Halliburton Energy
Services, of Houston, Texas) and hot-rolled for 16 hours. The fluid appearance showed little to
no phase separation after 24 hours and 72 hours. The rheological properties of the 8.0 lb/gal
fluids are shown Table 1.
liible L Formulation and Properties of'DiescI in an Aqueous Fluid
. . . . . , .^ Sample Sample
Description Inits .' '
I 2
15
Table 1. Formulation and Properties of Diesel in.an Aqueous Fluid
„ . ^. ,, .^ Sample Sample
Description Units ^
Density lb/gal (kg/metre-^) 8.0 (960) 8.0 (960)
Water bbl (metre'^) 0.789 (0.094) 0.789 (0.094)
BARAZAN^ D PLUS lb (kg) 0 0.5 (0.2)
N-DRIL™ HT PLUS lb 6 {2.1) 6 {1.1)
Emulsifier Blend lb 2.5(1.1) 2.5(1.1)
Diesel | bbl | 0.199(0.0316) | 0.199(0.0316)
Rheological Properties
Hot-rolled at 120°F Vhx \ 0 \ f6
(49°C)
Remixed on a Multi- min 3 3
mixer
Plastic viscosity cP (gram/cm.second) 29 (0.29) 37 (0.37)
Yield Point lb/100ft2 (kPa) 71 (34) 53 (25)
10 Sec gel lb/100ft2(kPa) 11(5.3) 5 (2.4)
10 Min gel lb/100ft2 (kPa) 14(6.7) 4(1.9)
Fann 35 Readings @120°F (49°C)
600 rpm \ 129 \ 127
300 rpm ToO 90
200 rpm 86 71
100 rpm 66 46
6 rpm 18 6
3 rpm 13 4
[0047] A fluid sample prepared according to the procedure described above was
prepared and allowed to age for approximately six weeks. A visual inspection of the fluid
confirmed that little to no phase separation had occurred. This result demonstrates that the
emulsion is capable of remaining stable for extended periods of time using the emulsion
stabilizing agents disclosed herein. Further, the stable emulsion offered the opportunity to
adjust the viscosity of the fluid with BARAZAN'* D PLUS without adversely affecting the
stability of the emulsion.
[00481 Therefore, the present invention is well adapted to attain the ends and
adxantages mentioned as well as those that are inherent therein, fhe particular embodiments
disclosed aho\e are illuslialixe OVL\\\ as the present in\ention nia\ he modified aiul practiced in
dirfLivm but ec!iii\alenl niaiHicis apparenl to those skilled in the art ha\ing the henelu t>f tlie
16
teachings herein. Furthermore, no limitations are intended to the details of construction or
design herein shown, other than as described in the claims below. It is therefore evident that the
particular illustrative embodiments disclosed above may be altered or modified and all such
variations are considered within the scope of the present invention. While compositions and
methods are described in terms of "'comprising," '"containing," or "including" various
components or steps, the compositions and methods can also "consist essentially o f or "consist
of the various components and steps. All numbers and ranges disclosed above may vary by
some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed,
any number and any included range falling within the range is specifically disclosed. In
particular, every range of values (of the form, "from about a to about b," or, equivalently, "from
approximately a to b," or, equivalently, "from approximately a-b") disclosed herein is to be
understood to set forth every number and range encompassed within the broader range of values.
Moreover, the indefinite articles "a" or "an", as used in the claims, are defined herein to mean
one or more than one of the element that it introduces. Also, the terms in the claims have their
plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. If there
is any conflict in the usages of a word or term in this specification and one or more patent or
other documents that may be incorporated herein by reference, the definitions that are consistent
with this specification should be adopted.

WE CLAIM
1. A stabilized emulsion composition comprising: an oleaginous fluid, a tluid that is at least
partially immiscible with the oleaginous fluid, and an emulsion stabilizing agent, wherein the
emulsion stabilizing agent comprises a first ionic compound soluble in the oleaginous fluid or
the fluid that is at least partially immiscible with the oleaginous fluid, and a second ionic
compound with a charge of opposite sign of the first ionic compound and that is at least partially
soluble in the opposite fluid as the first ionic compound.
2. A stablized emulsion composition according to claim 1, wherein the first ionic
compound, the second ionic compound, or both comprise an ionic surfactant.
3. A stablized emulsion composition according to claim 1 or 2, wherein the first ionic
compound, the second ionic compound, or both comprise an ionic polyelectrolyte.
4. A stablized emulsion composition according to claim 2 or claim 3 when dependent on
claim 2, wherein the ionic surfactant comprises an anionic surfactant.
5. A stablized emulsion composition according to claim 4, wherein the anionic surfactant
comprises at least one compound selected from the group consisting of: an alkyl carboxylate, an
alkylether carboxylate, a N-acylaminoacid, a N-acylglutamate, a N-acylpolypeptide. an
alkylbenzenesulfonate, a paraffinic sulfonate, an a-olefinsulfonate, a lignosulfate, a derivative
of a sulfosuccinate, a polynapthylmethylsulfonate. an alkyl sulfate, an alkylethersulfate. a
monoalkylphosphate. a polyalkylphosphate, a fatty acid, an alkali salt of an acid, an alkali salt of
a fatty acid, an alkaline salt of an acid, a sodium salt of an acid, a sodium salt of a fatty acid, an
alkyl ethoxylate. a soap, a combination thereof, and a derivative thereof
6. A stablized emulsion composition according to claim 2 or any claim dependent on claim
2. wherein the ionic surfactant comprises a cationic surfactant.
7. A stabli/cd emulsion, coniposilion according to claim 6. wherein the cationic surfactani
comprises al least one compiuind seicLlcd from the group consisting of: an alkyl amine, an alk\ I
uiiiiiic salt, li qu.iternarx rniinuiniimi suit, an etlioxxlaied qiiaternar} ammonium sail, an amine
18
oxide, an alkyltrimethyl amine, a triethyl amine, an alkyldimethylbenzylamine, a derivative
thereof, and a combination thereof.
8. A stablized emulsion composition according to claim 3 or any claim dependent on claim
3. wherein the ionic polyelectrolyte comprises an anionic polyelectrolyte.
9. A stablized emulsion composition according to claim 8, wherein the anionic
polyelectrolyte comprises at least one compound selected from the group consisting of: a
polymer or copolymer comprising a carboxylate group, a sulfonate group, a phosphate group, a
phosphonate group, an acrylate monomer, a methacrylate monomer, a styrene carboxylate, a
vinyl sulfonate, a 2-acrylamine-2-methyl-propyl sulfonate, a 3-acrylamide-3-methyl butanoate, a
salt of malic acid, a polyacrylic acid, a partially-hydrogenated polyacrylamide. a carboxy methyl
cellulose, a cellulose modified with an anionic functional group, a polysaccharide modified with
an anionic functional group, a galactomannan modified with an anionic functional group, a
derivative thereof, and a combination thereof.
10. A stablized emulsioncomposition according to claim 3 or any claim dependent on claim
3, wherein the ionic polyelectrolyte comprises a cationic polyelectrolyte.
11. A stablized emulsion composition according to claim 10, wherein the cationic
polyelectrolyte comprises at least one compound selected from the group consisting of: a
polyethylene imine, a polyamide amine, a polyamine, a vinyl benzyl trimethyl ammonium
chloride, a dimethyldiallyl ammonium chloride, a 3-acrylamido-3-methyl butyl trimethyl
ammonium chloride, a polyvinylpyrrolidone, chitosan modified with a cationic functional group,
a gelatin modified with a cationic functional group, a galactomannan modified with a cationic
functional group, a cellulose modified with a cationic functional group, a derivative thereof, and
a combination thereof.
12. A stablized emulsion composition according to any preceding claim, wherein the
oleaginous tluid comprises at least one fluid selected from the group consisting of: a diesel oil. a
crude oil. a paraftln oil. a mineriil oil. a low toxicit\ mineral oil. an olefin, an ester, an amide, an
amine, a polxolefin. a poKditirganosilo.xane. a siloxane. an organosiloxane. an ether, an acetal. a
dialk_\ Icarboiiatc. a li\ Jrocarboii. a clciiNatixc thereof, and a combinalion thereof.
19
13. A stablized emulsion composition according to any preceding claim, wherein the fluid
that is at least partially immiscible with the oleaginous fluid comprises at least one fluid selected
from the group consisting of: glycerin, a glycol, a polyglycol amine, a polyol, fresh water, sea
water, salt water, a brine, a derivative thereof, and a combination thereof.
14. A method comprising: providing a stabilized emulsion composition according to any one
of claims 1 to 13; and placing the stabilized emulsion composition in a subterranean formation
as part of a subterranean application.
15. A method comprising: providing a stabilized emulsion composition according to any one
of claims 1 to 13; and drilling a well bore in a subterranean formation using the stabilized
emulsion composition.
16. A method of preparing a stabilized emulsion composition, the method comprising:
providing an oleaginous fluid; providing a fluid that is at least partially immiscible with the
oleaginous fluid; providing an emulsion stabilizing agent, wherein the emulsion stabilizing
agent comprises: a first ionic compound soluble in the oleaginous fluid or the fluid that is at
least partially immiscible with the oleaginous fluid, and a second ionic compound with a charge
of opposite sign of the first ionic compound and that is at least partially soluble in the opposite
fluid as the first ionic compound; and combining the oleaginous fluid, the fluid that is at least
partially immiscible with the oleaginous fluid, and the emulsion stabilizing agent to form a
stabilized emulsion composifion.
17. A method according to claim 16. further comprising placing the stabilized emulsion
composition in a subterranean formation as part of a drilling operation.