EA046475B1 - METHOD FOR INHIBITION OF WATER PENETRATION INTO A PRODUCTION WELL OF HYDROCARBON FLUID FROM AN UNDERGROUND FORMATION - Google Patents

Description

The present invention relates to a method for inhibiting the penetration of water into a production well of a hydrocarbon fluid from a subterranean formation.

In particular, the present invention relates to a method of inhibiting water penetration into a production well of a hydrocarbon fluid from a subterranean formation, which includes injecting into the formation a near-wellbore treatment composition containing at least one chemical compound capable of swelling by selectively absorbing formation water present therein. (i.e., produced water) by changing the local permeability of the formation and thus blocking the penetration of additional water into the production well. The composition for treating the tree trunk zone is presented in the form of a dispersion of the aqueous phase in an oil dispersion medium. This formulation causes the injected compound to interact primarily or even exclusively with formation water rather than residual water, thus not affecting the mobility of the hydrocarbon fluid.

For purposes of this description, the expression hydrocarbon fluid means a fluid containing hydrocarbons or substantially containing hydrocarbons, in a gaseous, liquid or gas-liquid mixture form of natural origin, present in an underground or underwater rock formation, such as oil or natural gas. The oil may optionally contain water in dispersed form. Hereinafter, the terms petroleum and oil are used interchangeably.

For the purposes of this description, the expression residual water means the proportion of water present in the pores of a rock containing a hydrocarbon fluid, or in the spaces between grains of rock that make up that formation; Residual water, retained in the formation primarily by surface tension forces, is essentially not removed during the extraction of hydrocarbon fluid from the formation.

For purposes of this description, the expression formation water means the proportion of water present in a rock formation containing a hydrocarbon fluid that can be removed from the formation along with the recovered hydrocarbon fluid. Produced water (or produced water as an alternative term) can be formed, for example, by the infiltration of water from an aquifer located near the formation, or by the injection of water or steam into the subsoil to displace fluid towards the production well.

The presence of water in combination with hydrocarbon fluid extracted from a subterranean formation is a problem of great economic importance in the field of petroleum production and, generally, in the gas and oil industries.

Extracting a hydrocarbon fluid mixed with water reduces the efficiency of extracting the fluid itself, increases the cost and size of the equipment needed to separate the water, increases the overall cost of extracting the fluid, and finally creates the problem of disposing of separated water that is contaminated with hydrocarbons.

The extraction of water along with hydrocarbon fluid from an oil well, in addition to causing frequent interruptions in production operations to allow water containment measures to be implemented, may in some cases reach such an extent as to result in the well being shut in early, thereby preventing full exploitation of the oil field (for example, when the oil field is located near an aquifer).

In the modern world, various methods are known to reduce water extraction from an oil well. One of these methods involves injecting chemical compounds into the formation rock, such as polymers, gels and foams, that can form a mechanical barrier that is impermeable to water, blocking the preferential path of water in the rock to the production well. A mechanical barrier can be obtained by interaction in situ (in place), i.e. in a subterranean formation, two or more reactants, introduced separately, which form a water-tight barrier compound.

Currently known methods of inhibiting the penetration of water into a production well of hydrocarbon fluid from an underground formation have several disadvantages.

First, the effect of reducing water penetration is short-lived. This leads to frequent interruptions in production, which allows for further injection of the composition to treat the near-well zone into the formation with a subsequent reduction in production capacity.

Secondly, compounds introduced in accordance with methods of the prior art have low selectivity with respect to produced water. These compounds, in fact, can also interact with residual water or even water dispersed or emulsified in the oil, also causing a decrease in the mobility of the hydrocarbon fluid and, therefore, its recovery upon recovery.

To overcome the above-mentioned disadvantages, in the application WO 2016/166672 the applicant described a composition for treating the near-stem zone containing hydrogel particles with micrometric or nanometric dimensions. This tree trunk treatment composition contains a dispersion or emulsion in an organic solvent of a copolymer formed by at least one (meth)acrylic monomer and at least one comonomer containing at least one ethylene

- 1 046475 unsaturation and at least one polyoxyethylene chain. This near-wellbore treatment formulation is very effective in controlling water intrusion into hydrocarbon production wells due to the high water selectivity of the microgels and nanogels.

Despite the excellent performance demonstrated, the performance of the hydrogels described in WO 2016/166672 is influenced by the salt content of the water present in the formation. In fact, it has been observed that the above hydrogels exhibit high swelling properties, i.e. swelling due to water absorption when water salinity is in the range of 10-80 g/l. In waters with higher salt content (salinity > 80 g/L), hydrogels tend to absorb little water or displace water that has already been absorbed.

Another disadvantage of hydrogel-based compositions known in the art for treating the near-wellbore zone is that the adhesion of hydrogel particles to the surface of the formation rock is not always effective. In fact, in some cases, especially where formation fluids are produced under high pressure, it is possible that hydrocarbon fluid production operations performed after treating the well with near-wellbore treatment compounds based on the above-mentioned hydrogels also entail the recovery of the same hydrogels . Therefore, it is desirable to have compositions for treating the near-wellbore zone that can ensure longer and more durable placement of the hydrogel polymer material in the treated formation.

Taking into account the above-mentioned state of the art, the Applicant has set himself the main task of overcoming the above-mentioned disadvantages of the methods known at the state of the art, at least partially.

In this regard, it is an object of the present invention to provide a method for inhibiting the intrusion of water into a hydrocarbon fluid production well, which effectively reduces the amount of water produced with the hydrocarbon fluid, thereby eliminating the disadvantages associated with the activities of separating water from the hydrocarbon fluid and removing water, contaminated with hydrocarbons.

A second object of the present invention is to provide a method for inhibiting the penetration of water into a hydrocarbon fluid production well, which can be effectively used in formations characterized by rocks having different geological characteristics (eg, porosity, fractures, etc.).

It is yet another object of the present invention to provide a method for inhibiting the intrusion of water into a hydrocarbon fluid production well, which can be applied in the presence of formation water having a salinity over a wide range of values, and the method can be effectively applied, in particular, even in the presence of fresh water or water high in salt.

Applicant has now discovered that these and other objects, which will be better illustrated in the following description, can be achieved using a root zone treatment composition containing a micrometric or nanometric dispersion of an aqueous phase in oil, wherein the aqueous dispersed phase contains particles of a hydrogel containing chains of cationic polymer obtained, for example, from monomers containing at least one cationic group (for example, a primary, secondary, tertiary or quaternary ammonium group).

In fact, it has been observed that the presence of cationic groups on the polymer leads to the formation of hydrogels based on cationic polymers with high swelling ability with respect to water. Preferably, the water absorption and retention properties of these hydrogels are little affected by the degree of salinity of the water, particularly if the salinity is due to the presence of divalent cations (eg Ca ²⁺ , Mg ²⁺ ), which have a greater impact on the performance of prior art hydrogels.

Surprisingly, furthermore, hydrogels containing cationic polymers bind more strongly to carbonate rocks, likely due to electrostatic interactions that are established between the positive charges of the polymer and the negative charges present on the surface of the carbonate rocks. Thus, once placed within a formation, the materials of the present invention alter the permeability of the rock in a more stable and durable manner than prior art hydrogels.

The hydrogels described herein, in addition to their high water absorption capacity, are stable at water temperatures and salinities typical of an oil or gas reservoir (eg, temperatures in the range of 50-90°C).

In particular, water-swollen hydrogels can withstand prolonged contact with high-salinity water without undergoing significant structural degradation.

In accordance with a first aspect, the present invention therefore relates to a method for inhibiting the penetration of water into a production well of a hydrocarbon fluid from a subterranean formation, which includes supplying a water-in-oil emulsion containing an oil dispersion medium,

- 2 046475 an aqueous dispersed phase containing water and a plurality of particles of at least one hydrogel containing at least one cationic polymer, wherein said cationic polymer does not contain any anionic units/groups;

placing said water-in-oil emulsion in contact with said subterranean formation.

According to a second aspect, the present invention relates to a wellbore treatment composition for hydrocarbon fluid production wells, comprising a water-in-oil emulsion comprising an oil dispersion medium, an aqueous dispersed phase containing a plurality of particles of at least one hydrogel containing at least one cationic polymer, wherein said cationic polymer does not contain anionic units/groups.

The specified composition for treating the near-wellbore zone is effective in the present method, which makes it possible to reduce water content during operations to isolate aquifers in a production well of hydrocarbon fluid from an underground formation.

According to another aspect, the present invention relates to a method for producing a water-in-oil emulsion containing an oil dispersion medium, an aqueous dispersed phase containing a plurality of particles of at least one hydrogel containing at least one cationic polymer, the process comprising the following sequential steps:

supplying an oil dispersion medium containing at least one oily fluid;

supplying an aqueous dispersed phase containing water, at least one monomer having at least one cationic group, and optionally at least one comonomer;

emulsifying said aqueous dispersed phase in said oil dispersion medium in the presence of at least one surfactant and at least one radical polymerization initiator generating free radicals to polymerize said monomer having at least one cationic group and optionally said comonomer.

For purposes of this specification and claims, the verb include and all terms implied therefrom as used herein in the specification and claims also include the meaning of the verb consist of and terms implied therefrom.

The numerical limits and ranges expressed in the present specification and the accompanying formulas also include said numerical value or numerical values. In addition, all values and sub-intervals of a limit or numeric interval are to be treated as specifically included, as if they were explicitly mentioned.

For the purposes of this description, the term water-in-oil emulsion (also called invert emulsion) means a dispersion containing at least two immiscible phases. These immiscible phases include an oil dispersion medium (also called the external phase) and an aqueous disperse phase (also called the internal phase). The aqueous dispersed phase is dispersed in the dispersion medium in the form of droplets, if the phase is mainly liquid, as in the process of preparing a composition for treating the tree trunk zone, or in the form of particles, if the aqueous phase is mainly gel-like, as in the case of a composition for processing of the tree trunk zone obtained after polymerization. The term droplet or particle is used herein to refer to discrete portions of a dispersed phase in a dispersion medium without any implications regarding the shape, size, or other characteristics of the particles. Said droplets or particles in accordance with the present invention are also defined as micrometric or nanometric in terms of their sizes less than 1 mm and more than 1 μm or more than 10 nm and up to 1 μm, respectively.

For the purposes of this description, a hydrogel particle (or droplet) is a particle or droplet that contains a three-dimensional structure (network) of hydrophilic polymer chains that are substantially insoluble in water; said three-dimensional structure may be a colloidal hydrogel in which water is the dispersion medium. In the tree trunk treatment composition of the present invention, said droplets or individual hydrogel particles that comprise the emulsion, defined herein as water in oil, preferably contain a minimal amount of water by weight, more preferably less than or equal to the amount by weight of the cationic polymer. In this way, it is possible to obtain a hydrogel with a high concentration of polymer, which provides high swelling after placement in the desired location of the formation.

The method in accordance with the present invention improves the efficiency of recovery of a hydrocarbon fluid, such as oil or natural gas, preferably oil, from a subterranean formation.

The method in accordance with the present invention can be advantageously used to improve the recovery efficiency of both a liquid fluid, such as petroleum oil, and a gaseous fluid, such as natural gas.

The method in accordance with the present invention is based on placing less

- 3 046475 at least one water-in-oil emulsion containing a plurality of hydrogel particles containing at least one cationic polymer that is capable of selectively interacting with formation water, absorbing it in its three-dimensional structure. The swelling of the hydrogel after absorbing water prevents or at least slows down the penetration of hydrocarbon fluid into the production well.

The method of the invention can be applied to rocks having different geological characteristics. In particular, the method is suitable for reducing water penetration into predominantly fractured rocks or predominantly porous rocks.

In addition, the method of the invention is effective even for waters with relatively high salinity up to 150 g/l.

The water-in-oil invert emulsion of the present invention contains at least one oil continuous phase in which is dispersed an aqueous disperse phase containing the above-mentioned cationic polymers.

The water-in-oil emulsion of the present invention does not involve the use of any self-inverting agent such as a sulfosuccinate surfactant.

The oily dispersion medium may contain any oily fluid suitable for this purpose. The oil dispersion medium has the function of transporting the hydrogel particles in the rock until they come into contact with the formation water, crossing any petroleum oil that may be present.

The oily fluid used for the purposes of the present invention is substantially insoluble in water and soluble or partially soluble in oil. The term substantially insoluble in water means that the oily fluid has a solubility in water at 25°C of less than or equal to 5 g/L, preferably less than or equal to 1 g/L.

The term partially soluble in oil means that the oily fluid has a solubility in oil at 25°C equal to or greater than 100 g/l.

Preferably, the oily fluid is in a liquid state in the temperature range used in production wells, especially in the range from -5 to 90°C. The oily fluid may be polar or, preferably, non-polar.

Preferred examples of oily fluids suitable for the purposes of the present invention are: C6-C25 hydrocarbon solvents, more preferably _C10 - _C15 , aliphatic or aromatic (eg kerosene); amides with the number of carbon atoms from 7 to 25; alcohols with the number of carbon atoms from 7 to 25; ethers with a number of carbon atoms from 7 to 25 (for example, diethyl ether, dioctyl ether, diphenyl ether); ethers with the number of carbon atoms from 7 to 25; ketones with the number of carbon atoms from 7 to 25.

Hydrocarbon oily fluids are particularly preferred, for example the oily fluids marketed as LAMIX 30® (mixture of C11- _C14 hydrocarbons containing n-alkanes, isoalkanes, cyclic hydrocarbons (aromatic hydrocarbon content less than 2% by weight of the mixture)) and Versalis E -solv G® (mixture of aliphatic and aromatic hydrocarbons).

Other examples of oily fluids suitable for the purposes of the present invention are: naphtha, kerosene fractions, diesel and biodiesel fuels, aromatic solvents such as xylene, toluene and tetralin.

The oily dispersion medium may contain a mixture of two or more oily fluids.

The choice of oleaginous fluid may depend on several factors, such as the polarity of the hydrocarbon fluid being recovered, the compatibility of the oleaginous fluid with the environment, and other factors. One skilled in the art may also be able to select an oleaginous fluid suitable for a particular application of the present invention using the present disclosure.

In one embodiment, the oleaginous fluid may be present in the water-in-oil emulsion in an amount in the range of 50-99% by weight of the water-in-oil emulsion.

In one embodiment, the oil dispersion medium may be present in a weight ratio relative to the aqueous disperse phase ranging from 50:50 to 95:5.

The aqueous dispersed phase contains a plurality of particles of at least one hydrogel containing water and at least one cationic polymer.

Preferably, the cationic polymer contains at least one monomer unit corresponding to a water-soluble monomer having at least one polymerizable ethylene unsaturation and at least one cationic group, preferably an ammonium group. Preferably, the above ammonium group is a -N ⁺ -R ¹ R ² R ³ group, where R ¹ , R ² and R ³ , whether the same or different, represent an H or a C'i-Ci alkyl group.

The terms monomer and monomer unit corresponding to the specified monomer, as used herein in the description and in the claims, refer to the polymerizable compounds and the corresponding structural units obtained from them after polymerization, which bind with each other, leading to the formation of a polymer (or copolymer , if it is formed from monomers

- 4 046475 or consists of monomer units that differ from each other). In the polyaddition polymerization of ethylenically unsaturated monomers, the monomer and the corresponding monomer unit have the same starting formula.

Cationic monomers useful for forming polymer hydrogels in accordance with the present invention are preferably selected from water-soluble [2-(methacryloyloxy)ethyl]trimethylammonium salts, 2-(acryloyloxy)ethyltrimethylammonium salts, and mixtures thereof. Preferred water-soluble salts are halides, more preferably chlorides or bromides.

Cationic polymers can be cationic homopolymers or cationic copolymers. In a preferred embodiment, the cationic polymers are cationic copolymers prepared starting with one or more cationic monomers and one or more (hydrophilic comonomers) without cationic groups. The use of hydrophilic comonomers without cationic groups makes it possible to modulate the hydrophilic properties of the cationic polymer, and therefore the hydrogel, without introducing an excessive amount of positive charges on the polymer chain, which can make the emulsion unstable.

In one embodiment, the hydrophilic comonomer contains at least one ethylenic unsaturation and at least one polyoxyethylene chain.

For example, a hydrophilic comonomer may be a compound having the formula (I) below CH ₂ = SC ₁ -CO-X-(CH ₂ CH ₂ O} _I - r _{2 (t)} where R1 is H or CH ₃ ;

R2 is selected from H, ^-^-alkyl or acrylate group COCR ₃ =CH2, where R ₃ represents H or CH3;

X is O or NH;

n is an integer in the range from 0 to 500, preferably in the range from 0 to 200, even more preferably in the range from 4 to 100.

In a preferred embodiment, in the above formula (I) X represents an oxygen atom, the comonomer being acrylic or methacrylic acid or a (poly)oxyethyl ester of these acids.

In another preferred embodiment, in the above formula (I), X represents an NH group, the comonomer being an acrylamide monomer.

In a particularly preferred embodiment, the comonomer of formula (I) has only one ethylenic unsaturation, that is, the comonomer of formula (I) R1 is CH ₃ , R2 is selected from H and ^-^-alkyl, X is O or NH, and n represents an integer in the range 4-50.

In another preferred embodiment, the comonomer of formula (I) is a difunctional monomer containing at least two ethylenic unsaturations.

Preferably, the comonomer of formula (I) has a molecular weight in the range of 200-10000 Da, more preferably in the range of 200-5000 Da, even more preferably in the range of 200-3000 Da.

In a particularly preferred embodiment, the hydrophilic comonomer is selected from: poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) methyl ether methacrylate, acrylamide, methacrylamide, and mixtures thereof.

Poly(ethylene glycol) methyl ether acrylate or poly(ethylene glycol) methyl ether methacrylate preferably has a molecular weight in the range of 200-10,000 Da, preferably in the range of 200-5,000 Da, more preferably in the range of 200-3,000 Da.

In the present description, the molecular weights of the polymers are expressed as average weight (Mw), which can be determined, for example, using gel permeation chromatography (GPC).

Preferably, the ratio between the total weight of hydrophilic comonomers and the sum of the weight of cationic monomers and optional comonomers is in the range of 1 to 50%, preferably in the range of 3 to 40%, even more preferably in the range of 5 to 35%. In another embodiment, the weight ratio of said comonomer unit to said monomer unit is in the range of 5-50%, preferably in the range of 10-35%, even more preferably in the range of 20-30%.

For purposes of this description and the accompanying claims, unless otherwise indicated, the total weight of cationic monomers and optional comonomers does not include the weight of any cross-linking agents.

Hydrogel particles can have a wide range of average diameters. For example, in one embodiment, the hydrogel particles may have an average diameter in the range of 1-1000 microns, preferably in the range of 5-500 microns, more preferably in the range of 10-200 microns. For the purposes of this description, hydrogels having particles of these sizes are also called microgels.

The sizes of microgels are comparable to the sizes of cracks in fractured rocks. Thus, microgels in accordance with the present invention can be advantageously used to inhibit the penetration of water into a production well located in a fractured rock.

- 5 046475 layer.

In another embodiment, the hydrogel particles may have an average diameter in the range of 10,500 nm, more preferably in the range of 50-300 nm. For the purposes of this description, hydrogels having particles of these sizes are also called nanogels. Thus, nanogels in accordance with the present invention can be advantageously used to inhibit water penetration into a production well located in porous rock formations where the formation pores are on average in the order of nanometers in size.

The average particle diameter of the aforementioned microgels and nanogels can be determined using dynamic light scattering (DLS) measurements or, in the case of microgels, also using a compound microscope.

Water-in-oil emulsions in accordance with the present invention can be prepared using methods and devices known in the art. In particular, microgels can be prepared by inverse suspension polymerization or inverse miniemulsion polymerization.

In one embodiment, reverse suspension polymerization can be performed by emulsifying an aqueous dispersed phase containing water and at least one cationic monomer in an oil dispersion medium containing at least one oily fluid, in the presence of at least one surfactant and at least one radical polymerization initiator.

In the presence of a polymerization initiator and a surfactant, the monomer and comonomer react to form copolymer particles that remain enclosed in droplets forming the discontinuous phase of the emulsion.

The radical polymerization initiator is preferably a water-soluble or dispersible compound. Classes of initiators that can be used for the purposes of the present invention are, for example: halogen molecules, hydroperoxides, azo compounds and persulfates.

To obtain an invert emulsion, in which the hydrogel polymer particles have an average size of the order of 1-1000 micrometers (microgels), it is preferable to use thermally activated initiators of radical polymerization, i.e. compounds that, upon increasing temperature, decompose to form free radicals capable of initiating the polymerization reaction of monomers and comonomers, if any.

The polymerization reaction initiated by thermally activated initiators is preferably carried out at a temperature in the range of 30 to 120°C according to the type of initiator used, preferably at a temperature less than or equal to 90°C to avoid destruction of the polymer chains.

To obtain an invert emulsion in which the hydrogel polymer particles have an average size in the range from 10 to 500 nanometers (nanogels), it is preferable to use redox polymerization initiators. Redox initiators contain two compounds that can react with each other through an oxide reduction reaction to produce radicals necessary to initiate a polymerization reaction. An example of a redox pair used as a polymerization initiator is the persulfate/metabisulfite ion pair.

The polymerization reaction initiated by the redox couple preferably occurs at a temperature in the range of 0-50°C, more preferably 0-30°C.

In general, the total concentration of polymerization initiator is in the range of 0.1-10% by weight relative to the weight of the monomers that take part in the polymerization.

In the case of microgels, the initiator is preferably added to the aqueous phase in a concentration in the range of 0.1-2.5% by weight relative to the weight of the monomers that take part in the polymerization.

In the case of nanogels, preferably each of the two redox couple initiators is added to the corresponding oil dispersion medium and aqueous disperse phase at a concentration in the range of 1.0-3.0% by weight of the initiator, related to the weight of the phase to which it is added.

Reverse suspension or reverse miniemulsion polymerization is carried out in the presence of at least one emulsifier to stabilize the emulsion. The emulsifying agent may be included in the dispersion medium, in the dispersed phase, or in both phases.

Preferably, the emulsifying agent is a surfactant.

Preferably, the emulsifier is added to at least the oil dispersion medium.

To control the stability of the emulsion by adding surfactants, two or more surfactants having different HLB (hydrophilic-lipophilic balance) values can be preferably used. By varying the weight ratio of surfactants in the formulation, the desired HLB value can be achieved. Preferably, the HLB value of the surfactant-containing invert emulsion is in the range of 3-15. IN

- 6 046475 When preparing microgels, the HLB value is preferably in the range of 3-9. In the case of nanogels, the HLB value is preferably in the range of 5-10.

The surfactants used are preferably nonionic surfactants because the lack of electrical charges in this type of surfactant prevents them from reacting with the cationic groups of the polymer, promoting emulsion stability.

Preferred examples of non-ionic surfactants used for the purposes of the present invention are: polysorbate 80 (hydrophilic surfactant, HLB 15, eg TWEEN80®) and sorbitan monooleate (HLB 4.3, eg SPAN80®).

Emulsifying agents are present in the invert emulsion preferably in a total concentration in the range of 1.0-30% by weight relative to the weight of the invert emulsion, preferably in the range of 2.5-20% by weight.

To obtain hydrogels in cross-linked form, the invert emulsion may also contain at least one cross-linking agent, which is preferably added to the aqueous dispersed phase. Crosslinking agents known in the art useful for crosslinking the cationic monomers and comonomers used for the purposes of the present invention can be used without particular limitation. Typically, cross-linking agents are compounds having two or more ethylenic unsaturations.

Preferred crosslinking agents are: MI-methylene bis-acrylamide. ethylene glycol dimethacrylate, divinylbenzene, poly(ethylene glycol) diacrylate, 1-4-butanediol diacrylate, trimethylpropane triacrylate, 1-4-bis(4-vinylphenoxy)butane, bis(2-methacryloyl)oxyethyl disulfide.

The degree of cross-linking of the copolymer can be varied by adjusting the concentration of cross-linking agent in the formulation.

Preferably, the ratio between the total weight of the crosslinking agent and the total weight of cationic monomers is in the range of 0.1-5%, preferably in the range of 0.2-1.0%.

The emulsification phase of the dispersed phase and the dispersion medium can be performed using homogenizing devices known in the art, such as mechanical stirrers (eg a static mixer), sonicators (eg an ultrasonic sonicator) or by mechanical mixing at high pressure.

In the case of microgels, the emulsification phase is preferably carried out by mechanical stirring (reverse suspension polymerization).

In the case of nanogels, the emulsification phase is preferably carried out using ultrasound (reverse miniemulsion polymerization).

In a preferred embodiment, a thermally activated polymerization initiator is used and emulsification is carried out using a mechanical stirrer at a temperature equal to or higher than the activation temperature of said thermally activated initiator.

Additional additives may be present in the water-in-oil invert emulsions of the present invention provided they do not adversely affect the stability or other properties of the emulsions themselves. Examples of such additives are: wetting agents, thickeners, weighting agents, stabilizers, bactericides, corrosion inhibitors, oxidizing agents, and the like.

Additional information on reverse suspension or miniemulsion polymerization methods can be found, for example, in:

Dispersion polymerization in polar-solvents, SAENZ, J.M.; ASUA, J.M. (JOURNAL OF POLYMER SCIENCE, PART A-POLYMER CHEMISTRY; vol. 33 (1995), pp. 1511-1521;

Superabsorbent polymer materials: Review. Zohuriaan-Mehr, Mohammad J.; Kabiri, Kourosh; IRANIAN POLYMER JOURNAL; volume. 17(6) (2008), pp. 451-477.

As stated, an invert emulsion that includes hydrogels in accordance with the present invention can be used as a near-wellbore treatment composition to modify water permeability in a formation where the rock is of a generally porous or fractured type.

Without wishing to refer to any particular theory, in the case of nanogels it is believed that the possible mechanism of action is as follows.

Particles of nanogels containing a cationic polymer, having sizes compatible with the pore sizes of the rock, are transferred inside the above-mentioned pores. Dispersed phase particles containing a cationic polymer, due to the significant miscibility of petroleum fluids with petroleum oil, if present in the rock, until it comes into contact with formation water without undergoing significant changes.

Contact of the root zone treatment composition with water causes inversion or breakdown of the inverse emulsion or dispersion and, consequently, release of nanogel or microgel particles, which consequently begin to absorb water and swell. Swelling causes a significant increase in their volume (up to 10 times compared to the original volume), causing compression and immobilization

- 7 046475 tion in the pores and cracks of the rock and blocking or significantly slowing down the flow of the aqueous phase and possible rise to the production well. This creates an effective barrier to the passage of water.

Applicant has also unexpectedly discovered that the hydrogels of the present invention, characterized by cationic polarity, are able, in their swollen form, to bind more firmly to the rock surface with which they come into contact, thereby forming a barrier that is more pressure resistant and therefore more durable. stable with respect to the stresses to which the formation is subjected during production operations from the formation.

Since to obtain an inversion of the emulsion it is required that the droplets of the dispersed phase come into contact with a relatively large amount of water, then the contact of the droplets with residual water (present at the surface of contact with oil in dispersed form and in a much smaller quantity than formation water) or with any water , dispersed or emulsified in oil, does not cause nanogel release. A water-in-oil emulsion containing nanogels therefore acts selectively towards formation water, being active only at those points in the rock where the water/oil ratio is high enough.

In the case of invert emulsions containing microgels, the mechanism of action in the underground formation may be as follows.

Microgel particles, due to their larger size than nanogels, have a definite tendency to settle after a certain period of time if they are not kept under agitation in the emulsion. Once placed in a subterranean formation, the microgel particles, having dimensions compatible with the dimensions of the rock fractures, settle in the dispersion medium until they penetrate the aforementioned fractures, crossing any oil present until they reach the interface between it and water.

During deposition through oil, the hydrogel particles remain essentially unchanged, without interacting during the time required for deposition with either possible residual water or water that may be present in the oil in dispersed or emulsified form. Once they come into contact with the formation water, the hydrogel particles exert their absorptive effect on the bulk water with which they come into contact.

Therefore, even in the case of emulsions containing microgels, the release of the cationic polymer occurs selectively only at those points in the formation where formation water is present. This is believed to be possible due to the fact that water dispersed or emulsified in the oil is not present in sufficient quantity to activate the emulsion breaking process, i.e. to penetrate micelles containing microgels.

Given what has been described, one skilled in the art can appreciate the advantages that arise from the use of invert emulsions in accordance with the present invention.

In general, the invert emulsions described herein can be used as near-wellbore treatment compositions during the drilling, completion and maintenance phases of production wells.

In particular, the above-mentioned emulsions can be used to inhibit water penetration into a production well in accordance with the present description, both before the start of hydrocarbon fluid production operations and while the well is already in the process of production, i.e. when the reservoir is being exploited.

In particular, the method of inhibiting water intrusion into a production well can be advantageously applied to so-called mature production wells, that is, wells that have now reached production capacity, which are characterized by the recovery of significant quantities of water in combination with hydrocarbon fluid.

Placement of an invert emulsion into a formation, for example, can be achieved using equipment and in accordance with known technologies from the oil industry.

Placement of the invert emulsion into the formation can be accomplished either through a hydrocarbon fluid production well or through other wells commonly found in an oil field, such as wells for injecting steam, water, or other fluids (called injection wells) into the subsurface.

Thus, invert emulsions and the method in accordance with the present invention can be used in the context of secondary and tertiary hydrocarbon fluid recovery interventions, both in water blocking interventions (aquifer isolation) and in rock treatment (structure treatment).

The amount of invert emulsion injected into a subterranean formation can vary greatly depending on the specific geological structure of the formation.

The amount of invert emulsion to be injected can be readily determined by one skilled in the art based on the geologic characteristics of the formation and simple routine experimental testing as is routinely performed in the industry.

The placement of a water-in-oil emulsion containing cationic hydrogels may preferably

- 8 046475 precede the injection of a first aliquot of an oily fluid, preferably the same oily fluid (or mixture of oily fluids) used to prepare the continuous phase of the aforementioned water-in-oil emulsion.

It is equally advantageous that the placement of the invert emulsion into the formation may be followed by the placement of a second aliquot of oily fluid to facilitate penetration of the water-in-oil emulsion into the rock.

At the end of placement of the invert emulsion and possibly the first and second aliquots of oily fluid, hydrocarbon fluid production from the well may be initiated or resumed. Preferably, before proceeding to recover the hydrocarbon fluid by injecting the displacement fluid, wait (pause) a period of time sufficient for the invert emulsion to release the hydrogel polymer particles as soon as they come into contact with the formation water and obtain the desired mobility inhibition effect water.

If necessary, hydrocarbon fluid recovery can be interrupted to allow further injections of near-wellbore treatment compounds to further increase production well productivity.

The invert emulsions of the present invention can be prepared, if desired, by diluting a concentrated water-in-oil emulsion with petroleum to the desired concentration. The concentrated water-in-oil emulsion may have an oil/water ratio lower than the desired oil/water ratio for the end use.

The following embodiments are provided for the sole purpose of illustrating the present invention and are not to be construed as limiting the scope of protection as defined by the appended claims.

Example 1. Preparation of invert water-in-oil emulsions containing cationic microgels.

Water-in-oil emulsions containing cationic microgels were prepared by inverse suspension polymerization according to the following procedure.

The oily dispersion medium was prepared by mechanically mixing LAMIX 30 as an oily fluid and a mixture of commercial nonionic surfactants SPAN80 and TWEEN80. The weight ratio between the two surfactants was chosen to induce the polymerization reaction at the desired HLB value.

In the specific example of an HLB value of 6, SPAN80 surfactant was used at a high concentration, referring to the sum of the two surfactants being 84%.

The aqueous dispersed phase was prepared by dissolving in water using an ultrasonic sonicator and maintaining the temperature below 50°C the cationic monomer ([2-(methacryloxy)ethyl]trimethylammonium chloride - MADQUAT), a cross-linking agent (Y-methylenebis(acrylamide)MBA) and optionally (poly(ethylene glycol) methyl ether methacrylate comonomer with a molecular weight of 500 Da (PEGMEMA 500) or 2000 Da (PEGMEMA 2000).

An aqueous solution of 2,2'-azobis(2-methylpropianimidine) dihydrochloride (AAPH) (a thermally activated radical polymerization initiator) was prepared separately using a minimum amount of water sufficient to dissolve the compound.

The oil dispersion medium and the aqueous disperse phase were mixed in a 2 L reactor heated by a thermostatic oil bath. Mixing took place using a mechanical stirrer. The reactor was equipped with a water cooling jacket to remove heat generated during the polymerization reaction. During polymerization, the reactor was maintained at a constant flow of N2 to remove air within it.

The weight ratio between the aqueous dispersed phase and the total weight of the water-in-oil emulsion was chosen to be 16% for sample PEG2 and 18% for samples PEG4 and PEG11.

The polymerization reaction was initiated by pouring the AAPH initiator solution drop by drop into the reaction mixture, preheated to a polymerization temperature of 70 or 80°C. The reaction duration was chosen to be 2 or 2.5 hours.

In the next table. Figure 1 shows the compositions of the prepared invert emulsions of microgels.

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Table 1. Composition of microgel emulsions

Sample MADQU AT (%) ^a PEGMEM A 500 (%) ^a PEGMEM A 2000 (%) ^a MBA (%) ^a AAP H (%) ^c Surfactant (%) ^b H.L.B. 1(A4) ^d 100 - - 0.35 0.5 7.0 6 2 (PEG2) ^e 95 - 5 0.35 0.5 5.0 4.3 3 (PEG4) ^e 90 - 10 0.35 0.5 5.0 4.3 4 (PEGll) ^e 92.5 7.5 - 0.35 0.5 5.0 4.3

a: percentage by weight relative to the weight of the MADQUAT+PEGMEMA comonomers;

b: percentage by weight related to the total weight of the emulsion;

c: percentage by weight relative to the total weight of the comonomers MADQUAT+PEGMEMA+MBA;

d: polymerization temperature=80°C; polymerization duration 2.5 hours;

e: polymerization temperature=70°C; polymerization duration 2.0 hours.

Example 2. Preparation of invert water-in-oil emulsions containing cationic nanogels.

Water-in-oil emulsions containing cationic nanogels were prepared by inverse miniemulsion polymerization according to the following procedure.

The oily dispersion medium was prepared by mechanically mixing Eni LAMIX 30 in the form of an oily fluid and a mixture of commercial nonionic surfactants SPAN80 and TWEEN80. The weight ratio between the two surfactants was chosen to induce the polymerization reaction at the desired HLB value.

In the specific example of an HLB value of 10, SPAN80 surfactant was used at a high concentration, referring to the sum of the two surfactants being 47%. The aqueous dispersed phase was prepared by dissolving in water using an ultrasonic sonicator and maintaining the temperature below 50°C, cationic monomer ([2(methacryloxy))ethyl]trimethylammonium chloride-MADQUAT), cross-linking agent (K,K'-methylenebis(acrylamide)- MVA) and ammonium persulfate as the first initiator of the ammonium persulfate (APS)/sodium metabisulfite (SMBS) redox initiator pair.

After conditioning the oil dispersed phase in an ice bath (T equal to approximately 0-5°C), the aqueous dispersed phase was added to the oil dispersed phase, maintaining the mixture of the two phases under the influence of ultrasound. Then, the SMBS aqueous solution was added drop by drop to the mixture to initiate the polymerization reaction (polymerization duration 50 min).

In the next table. Figure 2 shows the compositions of the prepared invert emulsions of nanogels.

Table 2. Composition of nanogel emulsions

Sample MADQUAT (%) ^a MBA (%) ^b AP (%) ^b SMBS (%)b Surfactant (%) ^b H.L.B. 5(MZ17) 35 0.35 2.5 2.5 21 10

a: percentage by weight relative to the weight of LAMIX 30®;

b: percentage by weight relative to the total weight of MADQUAT.

3. Characteristics of emulsions of microgels and nanogels.

3.1. Swelling test.

The water absorption capacity of the prepared microgels was determined by measuring the average particle diameter using a compound light microscope before and after the swelling test. The swelling test was performed by placing a few drops of a water-in-oil emulsion into a flask previously filled with water of two different salinities or Lamix®. The samples were allowed to stand for 24 h to ensure thermodynamic equilibrium was reached. The samples were then observed under a microscope to determine the final microgel particle size.

The average particle diameter and polydispersity index (PDI) of the sample MZ17 nanogel polymer were determined using dynamic light scattering (DLS) measurements. The size distribution of nanogel particles was monomodal. The results of DLS measurements are given in table. 5.

In table Table 3 shows the chemical compositions of the salt waters used in the test.

In table Table 4 shows the microgel diameters determined in Lamix 30® and in the various waters tested.

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Table 3. Composition of salt waters

Na ⁺ (g/l) Ca ²⁺ (g/l) Mg ²⁺ (g/l) Field A 85 5.8 0.6 Field B 85 7.9 1.5

Table 4. Microgel diameter

Lamix (µm) Std. off (µm) Field B (µm) Std. off (µm) Field A (µm) Std. off (µm) A4 10.17 2.44 35.95 11.59 39.73 10.52 PEG2 9.37 5.63 32.77 11.74 30.93 13.77 PEG4 10.42 2.07 45.72 26.18 61.86 34.69 PEG11 9,904 2,372 67.22 33,381 63,916 29,087

It was observed that in samples placed in contact with Lamix 30®, the dimensions of the microgels before and after the swelling test were essentially identical; this shows that the microgels do not swell upon contact with oily fluids. On the other hand, in samples in contact with water, the sizes of microgels after the swelling test are larger than the sizes of the same microgels before the test.

Table 5. Nanogel diameter

Diameter (nm) Polydispersity (PDI) 5 (MZ17) 299.2 0.226

3.2. Assessing the compatibility of microgel emulsions with process fluids.

The following test was carried out to evaluate the behavior of cationic microgels in contact with process fluids (formation water and hydrocarbon fluids).

ml aliquots of salt water were placed in a glass container. A 2 g aliquot of oil was added to it. The container was closed and kept in an oven at a temperature of 85°C (to simulate the temperature of the bottom of the well). The sample was then removed from the oven and an emulsion containing microgels was added.

The tested emulsions having different concentrations of microgel particles were dosed into appropriate containers containing water and oil in such quantities as to obtain a concentration by weight of microgels equal to 26-28% relative to the weight of the mixture.

The following waters of varying salinity, originating from petroleum oil fields, were used in the test:

field C (total salinity: 2.3 g/l);

field D (total salinity: 84 g/l);

standard sea water (total salinity: 35 g/l).

In the tests, petroleum oil having a density of 1.012 to 1.017 g/cm ³ , also originating from a petroleum oil field, was used as the heavy oil.

Glass containers containing oil-water mixtures were placed in an oven and conditioned at a temperature of 85°C. At the end of conditioning, an emulsion containing microgels in the quantities indicated above was added to each container. The containers were then inverted several times to thoroughly mix all the ingredients and returned to the oven at 85°C for 24 hours.

At the end of thermal conditioning, the degree of separation of the water and oil phases, the deposition of microgels at the bottom of the container, and the volume of the container occupied by the microgels after swelling as a result of water absorption were visually assessed.

Samples 2, 3 and 4 showed good separation of water and oil phases and deposition of microgel particles with water absorption in all tests, i.e. with all three of the above waters varying in salinity. Sample 4, in particular, showed the best results for separating the aqueous and oil phases (a more transparent aqueous phase and a larger volume occupied by swollen microgels).

Thus, the test has proven that invert emulsions containing microgels are compatible with process fluids, in particular, their contact with these fluids does not lead to the formation of an oil-water emulsion that may be present, which in a real situation can deteriorate the efficiency of oil recovery, increasing amount of jointly produced water.

Tests also show the effectiveness of emulsions prepared in accordance with the present invention over a very wide range of water salinities.

3.3. Evaluation of microgel emulsions with process fluids in the presence of calcium carbonate.

To evaluate the effectiveness of the interaction of invert emulsions according to the present invention with carbonate rock, the following test was carried out.

10 g of solid calcium carbonate was weighed in one flask. Then 3 g of salted water was added to the flask

- 11 046475 water or 4.5 g (standard sea water with a total salinity of 35 g/l). An amount of 3 g was sufficient to completely cover the calcium carbonate present (Batch 1). An amount of 4.5 g created a condition of excess water (run 2). 2 ml of the oil phase (field D) slowly settled on the aqueous phase. The flasks were then placed in an oven and conditioned at 85°C. At the end of conditioning, the emulsion containing microgels was slowly added to each flask in an amount equal to 2 ml, being careful not to create turbulence.

The flasks were then placed back into the oven at 85°C for 24 hours.

Finally, it was visually assessed whether the microgel particles were able to cross the oil phase without emulsifying it, and where these particles were located. After 24 hours, the flasks were inverted to assess the degree of adhesion to calcium carbonate.

For comparison, the test was repeated with an invert emulsion of microgels containing copolymers of methacrylic acid (partially neutralized with NaOH) and poly(ethylene glycol) methyl ether methacrylate (HEMA-PEG, M _w = 2000 Da, 42 units of polyoxyethylene), prepared as described in example 2 WO 2016/166672.

In samples of series 1, added with emulsions containing cationic microgels No. 2, 3 and 4, complete penetration of microgel particles between the calcium carbonate grains was observed. This penetration was practically not observed in the comparison sample.

The observed penetration is likely explained by electrostatic attraction between the positive charges of the cationic microgels and the negative charges of calcium carbonate, as well as the smaller particle size of the cationic microgels (about 10 μm) relative to the comparative microgel particles (about 20 μm).

In addition, after inverting the flasks, it was noted that samples No. 2, 3 and 4 helped compact the carbonate grains together so that the solid phase remained solid at the bottom of the flask even when it was inverted. In contrast, in the comparative sample, when the flask was inverted, the calcium carbonate grains were observed to break down and slide downwards.

The same behavior of the cationic microgels according to the invention and comparative samples was observed in samples of series 2 containing excess water.

The test proved the greater ability of the emulsion microgel particles of the present invention to interact with carbonate rocks relative to prior art microgel emulsions.

4. Characteristics of nanogel emulsions.

4.1. Test 1: Washing cores saturated with oil and salt water.

The ability of Sample 5 containing nanogel particles to be introduced into a sandy environment (Berea Sandstone) and its ability to alter the permeability of the formation was assessed using porous media flow measurements. For this purpose, a cylindrical core with a length of 5.09 cm and a diameter of 2.47 cm, having a porosity of 16.5%, was used. The core was placed in a core holder under limiting pressure (40 bar) to avoid fluid leakage.

The core was initially filled with synthetic seawater (salinity: 33 g/L) and brought to a temperature of 40°C in an oven. The core was then washed with Lamix 30® until it reached a condition where water no longer formed (residually saturated core). At this point, sample 5 was injected at approximately 24 times the pore volume. The core was then left at 40°C for 24 h (pause) to allow the nanogels to act. At the end of the suspension period, the core was washed again with synthetic seawater to test the possible effect of reducing water permeability created by the cationic nanogels.

Sample 5 was easy to inject and no increase in pressure was observed during injection.

The final salt water rinse showed a reduction in core permeability to water compared to the water rinse prior to treatment with the invert emulsion of the invention. The initial water permeability value was actually 36 µm and dropped to 1.4 µm at the end of the test due to the desired behavior of the cationic nanogels.

Claims (18)

1. A method of inhibiting the penetration of water into a production well of a hydrocarbon fluid from an underground formation, including supplying a water-in-oil emulsion containing an oil dispersion medium, an aqueous dispersed phase containing a plurality of particles of at least one hydrogel containing at least one cationic polymer, and the specified the cationic polymer does not contain any anionic units/groups, where the cationic polymer is obtained starting from one or more cationic monomers and one or more hydrophilic comonomers without cationic groups, - 12 046475 wherein said cationic monomer is at least one water-soluble monomer that has at least one polymerizable ethylenic unsaturation and at least one cationic group, and wherein said hydrophilic comonomer without cationic groups contains at least one ethylenic unsaturation and at least one polyoxyethylene chain; and placing said water-in-oil emulsion in contact with said subterranean formation. 2. The method according to claim 1, wherein said at least one cationic group is a -N+-R ¹ R ² R ³ group, where R ¹ , R ² and R ³ , the same or different, represent H or C'i -Ci-alkyl group. 3. The method according to claim 1, where the specified cationic polymer contains at least one monomer unit corresponding to a monomer selected from water-soluble salts of [2-(methacryloyloxy)ethyl]trimethylammonium, 2-(acryloyloxy)ethyltrimethylammonium and mixtures thereof. 4. The method of claim 3, wherein said cationic polymer contains at least one comonomer unit corresponding to a monomer selected from poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) methyl ether methacrylate, and mixtures thereof. 5. The method according to claim 4, where the weight ratio of said comonomer unit and said monomer unit is in the range of 5-50%, preferably in the range of 10-35%, even more preferably in the range of 20-30%. 6. The method according to claim 4, wherein said poly(ethylene glycol) methyl ether acrylate or poly(ethylene glycol) methyl ether methacrylate has a molecular weight in the range of 200-10000 Da, preferably in the range of 200-5000 Da, more preferably in the range of 200-3000 Yes. 7. The method according to claim 1, wherein said cationic polymer is a cross-linked polymer. 8. The method according to claim 1, where the oil dispersion medium is present in a ratio relative to the aqueous dispersed phase in the range from 50:50 to 95:5 by weight. 9. The method according to claim 1, wherein said hydrogel particles have an average diameter in the range from 1 to 1000 micrometers. 10. The method according to claim 1, wherein said hydrogel particles have an average diameter in the range from 10 to 500 nanometers. 11. The method according to claim 1, including: a) placing a first aliquot of an oily fluid, preferably having the same oily fluid composition of an oil dispersion medium of said water-in-oil emulsion, in contact with said subterranean formation; b) placing said water-in-oil emulsion; c) placing a second aliquot of said oily fluid; d) injecting a displacement fluid to produce said hydrocarbon fluid. 12. A composition for treating the near-well zone of producing hydrocarbon fluids, containing a water-in-oil emulsion containing an oil dispersion medium, an aqueous dispersed phase containing water and a plurality of particles of at least one hydrogel containing at least one cationic polymer not containing any anionic units/groups, wherein the cationic polymer is prepared from one or more cationic monomers and one or more hydrophilic comonomers without cationic groups, wherein said cationic monomer is at least one water-soluble monomer having at least one polymerizable ethylene unsaturation and at least one cationic group, and wherein said hydrophilic comonomer without cationic groups contains at least one ethylenic unsaturation and at least one polyoxyethylene chain. 13. The composition for treating the near-trunk zone according to claim 12, where the specified cationic polymer contains at least one monomer unit corresponding to a monomer having at least one cationic group and at least one polymerizable ethylene unsaturation. 14. Composition for treating the tree trunk zone according to claim 13, where said at least one cationic group is a group -N+-R ¹ R ² R ³ , where R ¹ , R ² and R ³ , the same or different, represent H or a C1- _C4 alkyl group. 15. The composition for treating the near-trunk zone according to claim 12, where the specified cationic polymer contains at least one monomer selected from [2-(methacryloyloxy)ethyl]trimethylammonium halogen salt, 2-(acryloyloxy)ethyltrimethylammonium halogen salt and mixtures thereof. 16. A method for producing a water-in-oil emulsion containing an oil dispersion medium, an aqueous dispersed phase containing water and a plurality of particles of at least one hydrogel containing at least one cationic polymer not containing any anionic units/groups, said method comprising the following successive stages: - 13 046475 supply of an oil dispersion medium containing at least one oily fluid; supplying an aqueous dispersed phase containing water, at least one cationic monomer and at least one comonomer; wherein said cationic monomer is at least one water-soluble monomer having at least one polymerizable ethylenic unsaturation and at least one cationic group, and said comonomer is a hydrophilic comonomer without cationic groups that contains at least one ethylenic unsaturation and at least one polyoxyethylene chain; emulsifying said aqueous dispersed phase in said oil dispersion medium in the presence of at least one surfactant and at least one radical polymerization initiator generating free radicals to polymerize said monomer having at least one cationic group and said comonomer. 17. The method according to claim 16, where the specified initiator is thermally activated and the emulsification is carried out using a mechanical stirrer at a temperature equal to or higher than the activation temperature of the specified thermally activated initiator. 18. The method of claim 16, wherein said initiator comprises at least one pair of redox initiators comprising an oxidative initiator and a reductive initiator, wherein one of said oxidative initiator and reductive initiator is included in one of said oil dispersion medium and said aqueous a dispersed phase, with the remaining initiator being added to the water-in-oil emulsion during emulsification; This emulsification is carried out using ultrasound.