EP3898883A1

EP3898883A1 - Kinetically stable nanoemulsions, processes for the preparation thereof and their use in petroleum and natural gas storage reservoirs, and in thermal water storage reservoirs, in well base treatment and bed stimulation processes

Info

Publication number: EP3898883A1
Application number: EP19858681.0A
Authority: EP
Inventors: Sándor Puskás; Imre DÉKÁNY; Ádám JUHÁSZ; Gyula KÁLMÁN
Original assignee: MOL Magyar Olaj- es Gazipari Nyilvanosan Muekodo Reszvenytarsasag
Current assignee: MOL Magyar Olaj- es Gazipari Nyilvanosan Muekodo Reszvenytarsasag
Priority date: 2018-12-18
Filing date: 2019-12-13
Publication date: 2021-10-27
Also published as: WO2020128543A1; EA202191551A1

Abstract

The present invention relates to a nanoemulsion with an oil outer phase and complex aqueous solution internal phase, having delayed-action, containing inorganic and/or organic acids, said nanoemulsion being suitable for treating and stimulating hydrocarbon and thermal water storage layers, and for cleaning the base of wells. More particularly, the present invention relates to a nanoemulsion comprising a complex aqueous solution as an emulsified phase in an organic dispersion medium as defined herein, wherein the emulsifier is a surfactant mixture of nonionic surfactants as defined herein, which is generated in an interfacial layer said interfacial layer providing for kinetic stability of the nanoemulsion. The nanoemulsion comprises in the emulsified aqueous phase one or more of the compounds described herein for use as a layer enhancer, in particular an acid improving rock permeability acid or a mixture of acids, optionally a corrosion inhibitor, a Fe 3+ ion binding agent and a clay swelling inhibitor.

Description

KINETICALLY STABLE NANOEMULSIONS, PROCESSES FOR THE

PREPARATION THEREOF AND THEIR USE IN PETROLEUM AND NATURAL GAS STORAGE RESERVOIRS, AND IN THERMAL WATER STORAGE

RESERVOIRS, IN WELL BASE TREATMENT AND BED STIMULATION

PROCESSES

The present invention relates to a nanoemulsion with an oil outer phase and complex aqueous solution internal phase, having delayed-action, containing inorganic and/or organic acids, said nanoemulsion being suitable for treating and stimulating hydrocarbon and thermal water storage layers, and for cleaning the base of wells. More particularly, the present invention relates to a nanoemulsion comprising a complex aqueous solution as an emulsified phase in an organic dispersion medium as defined herein, wherein the emulsifier is a surfactant mixture of nonionic surfactants as defined herein, which is generated in an interfacial layer said interfacial layer providing for kinetic stability of the nanoemulsion. The nanoemulsion comprises in the emulsified aqueous phase one or more of the compounds described herein for use as a layer enhancer, in particular an acid improving rock permeability acid or a mixture of acids, optionally a corrosion inhibitor, a Fe³⁺ ion binding agent and a clay swelling inhibitor.

DESCRIPTION OF THE STATE OF THE ART

Emulsions have played an important role in many industries for decades. They are used in significant quantities in the food and cosmetics industry and in health care. In addition, the oil industry represents a particularly important field of application, which in itself would justify research on emulsions in terms of volume. Simplifying technologies for emulsion production and stabilization and reducing the cost of methods employed in each of these areas is a current and necessary task. Interest in emulsions containing droplets in the nanometer-scale has become increasingly important since the 1980s. Compared to the known and used macro and micro emulsions, these systems have improved properties due to their extremely small droplet size. Nanoemulsions have emerged as a rapidly expanding field of science in the development of pharmaceuticals, cosmetics and food products, and in plastic and petrolchemical research. Their promising potential is their use as a nanoscale chemical reactor or drug delivery system [M. Porras et ak, Coll. And Surf. A: Physchem. Eng. Asp. 270-271 (2005) 189-194). One of the potential uses of nanoemulsions in the oil industry is the transport/storage of chemicals used in oil recovery, and their targeted delivery. In this way, the substances dissolved in the internal emulsified phase do not come into contact with the equipment used for transport and storage, and thus for example, materials with corrosive properties, can be easily delivered. Removal of deleterious deposits from wells and ducts can thus be solved without damaging the structural materials [T. Del Gaudio et al., Society of Petroleum Engineers, SPE International Symposium on Oilfield Chemistry, Houston, Texas, USA, February 28-March 2, 2007].

Emulsions are multiphase dispersed systems consisting of two liquids which are not miscible or only slightly miscible with each other. One of these liquids is a lipophilic liquid (mineral or vegetable oil, paraffin, etc.), the other is usually water or hydrophilic liquid (e.g. alcohol). The emulsions contain a continuous outer phase (dispersant) and at least one inner phase (dispersed part). According to the nature of the liquid constituting the medium of the emulsion, an oil-in-water (O/V) or water-in-oil (V/O) emulsion can be distinguished. In addition to the above two types, complex emulsions are known in which the emulsified droplets themselves also form an emulsion, in which the liquid constituting the emulsion medium is dispersed therein (LL Schramm, Emulsions, Foams, and Suspensions, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (2005)].

In addition to the nature of the dispersion medium, the emulsions may be further classified according to their droplet size, mode of their formation, and the number of components, thus macro, micro, and nanoemulsions are known. Macro-emulsions are non-spontaneously forming and non-equilibrium dispersed systems, which, in the absence of a suitable stabilizing agent, separate their phases by coagulation and then coalescence. In their case, the average size of the emulsified droplets is well over 0.5 micrometers. Microemulsions are spontaneously generated thermodynamically equilibrium systems containing co-surfactant (usually an alcohol with higher number of carbon atoms) in addition to polar and apolar fluids and surfactants, in which the droplet diameter can vary from 10 to 250 nm. Due to the small droplet size, microemulsions are transparent or translucent. Their important feature is that they are equilibrium systems (thermodynamically stable) against macroemulsions without co-surfactants, which are formed spontaneously.

Nanoemulsions, like macroemulsions, do not contain co-surfactant, and, due to their low average droplet size of less than 200 nm, exhibit extremely high kinetic stability. Because, in contrast with microemulsions, they are not equilibrium systems, they do not form spontaneously, but require significant external energy input. Therefore, not only the droplet size of the dispersed phase, but also thermodynamic instability is a defining characteristic of the term nanoemulsions. [M. Porras et al, Coll and Surf. A: Physchem. Eng. Asp., 270-271 (2005) 189—194) es L·. Del Gaudio et al, Society of Petroleum Engineers, SPE International Symposium on Oilfield Chemistry, Houston, Texas, USA, February 28-March 2, 2007]. Physical chemical explanations for emulsion formation can be found, among others, in L. Del Gaudio et at Society of Petroleum Engineers, SPE International Symposium on Oilfield Chemistry, Houston, Texas, USA, (2007) February 28-March 2, and T. Tadros et at Adv. in Coli. and Int. Sci., 108-109 (2004) 303-318 Without providing a detailed explanation, an overall picture can be obtained by examining the work required for emulsification at a given temperature and pressure, which is necessary to create the increased interface. At this point, the change in interfacial free enthalpy (G°) can be defined, which, based on the work needed to increase the interface, can be expressed using the correlation below [Ghosh, L.; Das, K.P.; Chattoraj, D.K. Thermodynamics of adsorption of inorganic electrolytes at air/water and oil/water interfaces. J. Colloid Interface Sci. 1988, 121, 278—288], in which the g proportionality factor, surface tension, appears. j &G dA_s = j fdA_s

Surfactants, so-called amphipathic type compounds, contain a longer chain hydrophobic group and a hydrophilic atom group, which different proportions gives asymmetric polarity to the molecule. The numerical measure introduced to quantify the varying degree of asymmetric polarity and consequent variability in solubility and association (micelle formation) due to the different chemical structures is the so-called HLB value [Schott H, Solubility Parameter and Hydrophilic- Lipophilic Balance of Nonionic Surfactants, Journal of Pharmaceutical Sciences, 1984 vol: 73 (6) pp: 790-792] Due to their different polarity, these molecules are oriented at the interface with the apolar moiety turning towards the apolar phase and the polar head group toward the polar phase (Figure 1).

Due to their enrichment in the interfacial phase and their special location, the surfactants reduce the interfacial tension, thereby enabling the formation of emulsions and stabilizing the resulting dispersion system. Despite the stabilization, except for microemulsions, these systems show only kinetic stability. As a result, the emulsions cease to exist over a shorter or longer period of time, and the separation of the liquid phases which constitute them, continues to become mutually saturated, separated solution phases (Figure 3). Stabilizing surfactants can reduce the rate of separation to such an extent that the system can remain stable for months, with no change in droplet size distribution. [L·. L. Schramm , Emulsions, Foams, and Suspensions, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (2005) and D. M_jers, Surfaces, Interfaces and Colloids, John Wiley & Sons, Inc. New York, (1999)]. The exact definition implies that nanoemulsions are not equilibrium systems and are not spontaneously formed, but exhibit significant kinetic stability and can be formed at lower surfactant concentrations than microemulsions. The kinetic stability is due to the fact that due to the small size of the droplets, these systems are less subject to gravity-driven sedimentation (sedimentation due to the difference in density of the two phases). In these systems, due to the very small droplet size, Brownian motion is able to overcome the gravitational pull. The thickness and flexibility of the adsorption layer formed at the interface and the size of the droplets are extremely important for maintaining these properties. The properties and stability of the nanoemulsions are critically influenced by the method of preparation, the nature of the surfactant employed and the nature of the materials constituting the continuous and dispersed phases [L·. Del Gaudio et al, Society of Petroleum Engineers, SPE International Symposium on Oilfield Chemistry, Houston, Texas, USA, (2007) February 28 - March 2; I. Sole et al, Coll and Surf. A: Physchem. Eng. Asp., 288. (2006) 138- 143 and C. Solans et al, Current Opinion in Coll. & Int. Sci., 10 (2005) 102-110].

In the oil industry, what is termed bed stimulation is to increase the flow rate of fluid stored in the storage bed by creating new flow channels and increasing the fluid conducting capacity of existing channels. As a result of these processes, the permeability (in other words throughput potential) of the storage rock is increased from the storage layer in the direction of the well in the case of a production well, and from the well to the storage bed in the case of an injection well.

The prior art bed stimulation process uses acids (e.g., HC1, HF, acetic acid) to improve the permeability of the rock in the immediate vicinity of the base of well (the deepest point in the well), and thereby increase the amount of fluid entering the well, or injected in the well. In this case, the acid and / or its mixture with other solvents is discharged to the base of well, which, upon leaving the well, reacts immediately with some of the components of the storage rock or with bed damaging and permeability reducing agents, precipitated and deposited in the pores of the rock, said materials agents, such as limescale or a a mixture of limescale and high-carbon solid hydrocarbons, e.g. of paraffins, asphaltenes, resins. As a result of this reaction, these components are released from the rock and thus high permeability caverns, or channels, known as wormholes are formed in the rock. The so-called matrix acidification may also cause such a degradation of the bedrock that causes the base of well to collapse. Some rocks are particularly susceptible to such interventions, such as lime yellow, which is typically very low in permeability but can store large amounts of oil. The effect of this bed stimulation is typically limited to the well area.

One solution of the prior art attempts to mitigate the effects described above by incorporating the acid used in a system containing a viscoelastic surfactant which, due to the increased pH by the reaction of the acid, becomes gelatinous state, and diverts the unreacted acid towards the still intact parts of the reservoir (VDA, viscoelastic diverting acid - commercially available material and process, available from Schlumberger oil service company, reference patent: US 6667280 B2). As an improved version of this solution, the acid system containing the viscoelastic surfactant is used in a foamed form, whereby the diverting action of the viscoelastic gel and the foam is used together (US 7148184 B2). In these processes, the formation of gels may slightly reduce the formation of caverns, but due to the rapid reaction between the acid and the rock, the active ingredient cannot be delivered to deeper parts of the reservoir, so its effect still remains limited to the base of the well.

Alternatively, delaying the action of the acid is accomplished by delivering the acid in the reservoir in emulsified form by providing the stability of the emulsion with a suitable surfactant and an acid-insoluble solid nanoparticle (clay, quartz, carbon nanotube, etc.) of about 1000 nm (US 2012/0090845 Al). However, the size of these nanoparticles represents a lower size limit as to the diameter of the pores in which the active ingredient can be introduced; and impedes the flow of the emulsion described in the present invention in low permeability compacted storage rocks. Another problem may be the viscosity of these emulsions (30-200 mPa*s), which also makes it difficult to penetrate the parts of the storage rock further from the well. Due to the particle size of the solid and the viscosity of the emulsion, this product is more suitable for use in layer fracturing processes.

In addition to matrix acidification, another option for increasing fluid inflow is hydraulic fracturing of the reservoir by forming a system of fluid facilitating fluid flow in the reservoir with a suitable fracturing fluid which is pressed into the reservoir at or above the fracturing pressure of the rock. The formation of fractures can be caused by the above-mentioned process but cannot be controlled.

WO2018075147 international patent application discloses an acidic stimulating fluid which is an external emulsion of an oil, composed of hydrocarbon based fluid, an acidifying agent and a surfactant, and which may contain other excipients commonly used in the oil industry. The surfactant is a mixture of relatively high molecular weight imide compounds, which is a reaction product of a hydrocarbon-substituted acylating agent (such as a fatty acid derivative or a long-chain polycarboxylic acid), and a nitrogen-containing compound capable of reacting with the acylating agent (such as an alkyl polyamine or a heterocyclic compound containing more than one N), which is prepared during the preparation of a stimulation solution in situ in a hydrocarbon based solvent. The acidifying component is an organic or inorganic acid, or a mixture of these; typically hydrochloric acid. The disclosed solution differs substantially from the present invention in the surfactant used. According to the two-step process of the Russian patent No. RU2579044, anionic, cationic or nonionic surfactant, or a mixture thereof, and an anti-corrosion agent are first introduced into the layers in a hydrocarbon-based fluid containing a light oil fraction also containing aliphatic alcohol, followed by injection of a sulfuric acid solution. The disclosed solution differs from the present invention in that the delivery is not simultaneously with the solvent flooding and is not in the form of a nanoemulsion.

In WO2013148760 international patent publication document an O/V type microemulsion helping reflux is disclosed for use with stimulating fluids said microemulsion comprising: a) an oil like phase comprising at least one nonionic surfactant having an HLB of less than 9, which may be selected from the group consisting of alkoxylated alcohols, alkoxylated alkyl phenols, glycerol esters; glycol esters, polyglycerol esters, sorbitol esters, ethylene oxide/propylene oxide copolymers or combinations thereof; b) a water-soluble organic solvent; c) at least one water-soluble or dispersible nonionic surfactant other than the nonionic surfactant used in the oil-like phase; d) at least one further surfactant, which is selected from anionic, cationic, amphoteric materials, and combinations thereof; e) a demulsifier, which may be a crosslinked ethylene oxide/ propylene oxide copolymer or a mixture of a crosslinked ethylene oxide/propylene oxide copolymer and a polyethylene imine alkoxylate; and f) water. The disclosed solution differs substantially from the present invention in that it uses an oil-in-water microemulsion.

The general preparation of a water-in-oil nanoemulsion is described in U.S. Patent No. 8431620, wherein said nanoemulsion has dispersed phase droplets having a diameter of 1-500 nm. According to the disclosed process, a homogeneous water/ oil mixture (I) having a surface tension of less than 1 mN/m, containing 30-70% by weight of water and at least two different HLB surfactants, is prepared in the first step. Said surfactants are selected from the group consisting of nonionic, anionic and polymeric surfactants and are present in an amount of 5 to 50% by weight. In the second step of the process, the mixture (I) is dispersed in a dispersing phase comprising oil and a nonionic, anionic or polymeric surfactant as surfactant, and the amount of the dispersing phase and surfactant is sufficient to obtain a nanoemulsion having an HLB value, which differs from that of the mixture (I).

Mandal et al , („Characterization of Surfactant Stabilized Nanoemulsion and Its Use in Enhanced Oil Recovery”, Conference Paper, June 2012 SPE 155406, Copyright 2012, Society of Petroleum Engineers), report that based on their physico-chemical properties, the nanoemulsions are expected to be successful in the use after primary and secondary recovery processes to recover residual oil trapped in fine pores through capillary forces. It is stated that oil-in-water nanoemulsion can reduce the oil-in-water interface tension (IFT) by a factor of 3 to 4, and can therefore be advantageously used. The advantage or applicability of the water-in-oil nanoemulsions according to the present invention is not mentioned in the publication.

Agi et al. , " [„Mechanism governing nanoparticle flow behaviour in porous media: insight for enhanced oil recovery applications”, International Nano Letters (2018) 8:49-77] discuss the effect of silicate-containing nanoparticles in aqueous systems, in an oil-in-water interface in that, whether they are suitable for aiding the conversion of oil-wetted rocks to water-wetted.

Mohammed et al, [„Wettability alteration: A comprehensive review of materials /methods and testing the selected ones on heavy-oil containing oil-wet systems”, Advances in Colloid and Interface Science 220 (2015) 54-77] review the carbonate and sandstone based reservoirs for methods and materials for modifying the wetting properties of oil storage rocks. The effect of the acidic components originally present in the crude oil is discussed only from this point of view.

Sun et al, („Application of Nanoparticles in Enhanced Oil Recovery: A Critical Review of Recent Progress”, Energies 2017, 10, 345) provide a detailed review of the results of research into the use of nanoparticles in enhanced oil extraction. Although the use of nanoemulsions is mentioned, nanoemulsions containing acid to increase the permeability of rocks are not disclosed.

US20150329767 Al. U.S. patent publication document discloses a layer-stimulating emulsion having an emulsified phase having a droplet size of 10-100 nm and containing two different surfactants in certain proportion, and HC1 as an acid. However, the emulsion disclosed is a microemulsion which is a homogeneous, thermodynamically stable single-phase system, is formed spontaneously and is therefore explicitly distinguished from thermodynamically unstable emulsion systems, such as the nanoemulsions according to the present invention, which are significantly dependent on the energy investment performed by intense stirring. Further, according to the cited document, the second surfactant is macromolecules (polyamines, polyimines, polyesters and resins), which may also be polyelectrolytes. Due to their structure and size, these materials can provide only steric stabilization and, due to the properties described above, have only a certain amount of surfactant properties. In contrast to the document cited, the present invention is a nanoemulsion which is thermodynamically unstable, its preparation requires a high level of energy investment, and has kinetic stability. Furthermore, the present invention uses a mixture of low molecular weight, nonionic surfactants, not macromolecules, which, by virtue of their association ability, ensure the formation of the resulting nanoemulsion. US20020155084 Al. U.S. Pat discloses an emulsion composition for drug delivery systems, wherein the emulsion comprises two or more surfactants. Although the cited document refers to the system described as nanoemulsion, it is a thermodynamically stable system, spontaneously formed without external energy input, i.e. microemulsion, based on the features as disclosed herein.

US20060110418 Al U.S. patent publication document discloses a water-in-oil emulsion comprising water nanoclusters and one or more surfactants. The spatial extent of the water nanoclusters is less than 10 nm in at least one direction. The purpose of the disclosed composition is to deliver a stable water nanocluster composition to the top layer of human skin. The document cited does not disclose that the emulsion disclosed is used to transport acids. In this case too, although the document mentions nanoemulsion, the document mentions that it is a thermodynamically stable system, so it can be assumed that the emulsion according to the document has the characteristics of microemulsions. In addition, the document reveals that the composition may contain so-called auxiliary or co-surfactant. This name is misleading in itself, since the auxiliary surfactant is actually a longer-chain asymmetrically polar molecule (usually a straight chain alcohol or carboxylic acid) which, although is a surfactant, does not form an association colloid. The nanoemulsion of the present invention does not contain such auxiliary surfactant.

THE PROBLEM TO BE SOLVED BY THE INVENTION

The technical problem to be solved by the invention is to increase the fluid inflow into the well or the injection of fluid into the reservoirs during the rock stimulation process so that the rock is not destroyed or damaged in the immediate vicinity of the base of the well, but at the same time, the bed stimulation be applicable not only in the vicinity of the base of the well, but it be effective also in distant storage compartments. It is a further object of the present invention to provide a solution for the stimulation of compact storage rocks having extremely low porosity, which makes it impossible, or only to a limited extent, to inject the bed stimulating agents used in the prior art. The invention is also suitable for increasing the permeability of storage rock in the immediate vicinity of a well (well base cleaning).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: Water (left) or oil drop (right) stabilized by surfactant (tenside). H represents the hydrophilic head group of the surfactant molecule and A represents the hydrophobic alkyl chain V = water and O = oil. Figure 2: Changes in surface tension of the air/liquid interface as a result of the formation of a mixed adsorption layer of surfactants of different chemical structure and of the change of the critical concentration of the surfactant mixture in the solution phase as a function of the composition of the mixture.

Figure 3: Ways to cease emulsions: 1: phase separation (supernatant, sedimentation); 2: Ostwald aging; 3: aggregation processes (coagulation, coalescence); 4: phase inversion.

Figure 4: Mean droplet size of nanoemulsions containing different emulsified phases as a function of their transmittance.

Figure 5: Droplet size distribution curve of nanoemulsion containing hydrochloric acid prepared with alkyl polyglucoside based surfactant.

Figure 6: Flow curve of a nanoemulsion containing hydrochloric acid prepared with alkyl polyglucoside based surfactant at 25 °C

Figure 7: Temperature dependence of the viscosity of a nanoemulsion containing hydrochloric acid prepared with alkyl polyglucoside based surfactant.

Figure 8: Droplet size distribution curve of a nanoemulsion containing hydrochloric acid prepared with a silicone polyether based surfactant.

Figure 9: Flow curve of a nanoemulsion containing hydrochloric acid prepared with a silicone polyether based surfactant at 25 °C.

Figure 10: Temperature dependence of the viscosity of a nanoemulsion containing hydrochloric acid prepared with a silicone polyether based surfactant.

Figure 11: Droplet size distribution curve of nanoemulsion containing hydrochloric acid prepared with ethoxylated nonylphenol based surfactant.

Figure 12: Flow curve of hydrochloric acid-containing nanoemulsion prepared with ethoxylated nonylphenol based surfactant at 25 °C.

Figure 13: Temperature dependence of viscosity of nanoemulsion containing hydrochloric acid prepared with ethoxylated nonylphenol based surfactant.

Figure 14: Photographs of the entrance and exit sides of a limestone rock core treated with VDA acid gel containing hydrochloric acid.

Figure 15: Photographs of the entrance and exit sides of a limestone rock core treated with nanoemulsion containing hydrochloric acid. Figure 16: Electron microscopy images of VDA acid-gelated treated limestone rock core containing hydrochloric acid.

Figure 17: Electron microscopic images of limestone rock core treated with nanoemulsion containing hydrochloric acid.

Figure 18: Photograph of effluent leaving rock core during a pilot bed enhancement experiment with nanoemulsion containing hydrochloric acid.

Figure 19: Photograph of effluent leaving rock core during a pilot bed enhancement experiment with VDA acid gel containing hydrochloric acid.

DISCOVERY SERVING AS THE BASIS OF THE INVENTION

The present invention achieves the above-mentioned object by the solutions based on the following discoveries:

a) if an agent enhancing the permeability of the rock, i.e. the acid or mixture of acids according to the present invention, is encapsulated in a special, controlled release carrier having the ability of phase inversion (phase-reversible), then the active agent can be delivered to the part of the reservoir further away from the well, thereby increasing the volumetric efficiency of the treatment;

b) dispersing the drug-containing carrier in the form of droplets of 10-400 nm in a medium of opposite polarity, i.e. forming a low-viscosity nanoemulsion, can also deliver the active agent to low permeability rocks;

c) when the active ingredient is introduced into the reservoir in the form of a nanoemulsion, leaving the base of the well, the active agent does not react immediately with the reservoir or with deposited sediments such as bed damaging agents, which had been deposited in the pores of the reservoir, such as, e.g. limestone, asphaltenes, paraffins, resins, etc., but has delayed effect due to the presence of the dispersion medium, so that it can be delivered to storage areas further from the base of the well; d) if said nanoemulsion is formed by a mixture of two or more surfactants having a defined HLB_mx value, the kinetic stability of the nanoemulsion and the droplets of the emulsion is lost by introducing the nanoemulsion into the rock at the temperature prevailing in the rock; undergoes phase inversion due to fusion of emulsified droplets and the presence of bed water, thereby release of the active agent takes place; e) if said nanoemulsion is composed of components that are kinetically stable, alone or in the presence of other components forming the nanoemulsion, at high temperatures, the nanoemulsion retains its stability and can be used over a wide range of temperature range;

f) when the active ingredient is applied in the form of a nanoemulsion, it can significantly reduce the corrosion of the devices used in the bed enhancement operation, and prevent the local enrichment of the active agent in the storage bed due to the homogeneously distributed active ingredient.

The subject of the present invention can be applied in case of carbonate reservoirs or low permeability reservoirs, said permeability reduced by bed damaging agents, where the carbonate content of said reservoirs is in the range of from 65 to 100%, and the clay content is in the range of from 0 to 35%. The composition of the nanoemulsion according to the present invention can be optimized for the particular rock or bed damaging agent, having regard to the composition of the rock to be treated, or the bed damaging depositied agent. In the practice of the invention, the determination of rock composition and rock type is within the skill of one of ordinary skill in the art of geological sciences.

By the method of the present invention, due to the action mechanism of the delayed release of active agent provides a capillary channel network extending in depths around the well bed, in contrast to the caverns and fractures and wormholes formed by the processes according to the state of the art, which increases by orders of magnitude the permeability of the rock, preferably from 0.1 mD up to 100 mD (mD = millidarcy). The invention is also capable of exerting a bed-stimulating effect on reservoir areas further away from the well base, and the use of the active ingredient in the form of nanoemulsion, in contrast to prior art solutions, also ensures delivery of the active agent into compact rock with very low porosity.

Due to the small droplet size of the nanoemulsion produced by the process of the present invention, it is capable of delivering the emulsified active agent (hydrochloric, formic, acetic, phosphoric and hydrofluoric acid solutions or mixtures thereof) to low porosity rocks. As a result of the subsoil temperature increase (geothermal gradient), the kinetic stability of the nanoemulsion at the temperature of the layer is lost; due to the decomposition of the nanoemulsion in the porous system the emulsified active agent releases, thus delayed release of the active agent takes place in the reservoir rock. In addition, the phase inversion in the storage bed (the water-in-oil nanoemulsion converts to oil-in-water macroemulsion), due to contact with the reservoir bed water, also promotes release of the active ingredient. The active agent, which is homogeneously distributed in the nanoemulsion, exerts its macroscopic effect through the structural transformation of the nanoemulsion in the porous system, limited and evenly distributed by the expansion of the capillary system. As a result, increasing the permeability of the rock can be achieved by avoiding the local enrichment of the active agent and the consequent formation of so-called "wormholes".

BRIEF DESCRIPTION OF THE INVENTION

1. A water-in-oil nanoemulsion providing a fracture-free bed enhancement, said composition comprises the following components:

(a) a first non-ionic surfactant having a hydrophobic character or a hydrophobic mixture of non ionic surfactants, dissolved in an organic solvent as a dispersion medium; b) one or more second nonionic surfactants dissolved in a complex aqueous solution as dispersed phase, containing one or more acids, optionally a corrosion inhibitor, a clay anti-swelling agent and a Fe³⁺ ion-binding agent; wherein said nonionic surfactants are low molecular weight surfactants (less than 500 g mol⁴), and wherein said nonionic surfactants form a mixture of surfactants in the interfacial layer on the surface of the drop;

and wherein said nonionic surfactants have an HLB_mx value in the range of 7-11 (preferably 8); and wherein the nanoemulsion behaves like a Newtonian fluid at a temperature in the range of from 20 to 90 °C, its viscosity measured by the rotary viscometer at room temperature not exceeding 10 mPas; and wherein the first nonionic surfactant used in the surfactant mixture has an HLB value less than the second nonionic surfactant HLB value.

2. The nanoemulsion according to Item 1, wherein the surfactant mixture enriched in the interfacial layer gives 10-15%, preferably 12-14% by weight the weight of the nanoemulsion.

3. The nanoemulsion according to Item 1 or 2, wherein the organic solvent used as the dispersion medium is a mixture of C10-C14 aliphatic hydrocarbons, which gives 72-77% by weight the weight of the nanoemulsion.

4. The nanoemulsion according to any one of Items 1 to 3, wherein the possible components of the acid/acid mixture are selected from the group consisting of inorganic acids, in particular hydrogen halides (preferably HF, HC1), phosphoric acid, sulfuric acid, nitric acid, boric acid, fluoroboric acid; organic acids, especially mono carboxylic acids (preferably formic acid, acetic acid); dicarboxylic acids (preferably oxalic acid, malonic acid, glutaric acid), tricarboxylic acids, aminocarboxylic acids, sulfonic acids, chloroacetic acid, hydroxyacetic acid.

5. A nanoemulsion according to any one of Items 1 to 4, wherein the possible components of the acid/ acid mixture are selected from the group consisting of HF, HC1, phosphoric acid, formic acid, acetic acid, sulfuric acid or nitric acid.

6. A nanoemulsion according to any one of Items 1 to 5, wherein the acid is HC1.

7. A nanoemulsion according to any one of Items 1 to 6, wherein the first nonionic surfactant is selected from the group consisting of sorbitan ester based surfactants, preferably sorbitan monoesters, more preferably sorbitan mono-fatty acid esters, in particular sorbitan monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan monopalmitate.

8. A nanoemulsion according to any one of the Items 1 to 7, wherein the second nonionic surfactant is selected from the group consisting of a) ethoxylated sorbitan ester based surfactants, preferably ethoxylated sorbitan monoesters containing 10 to 30, preferably 20 ethoxy groups, more preferably ethoxylated sorbitan mono-fatty acid esters containing 10 to 30, preferably 20 ethoxy groups, especially ethoxylated sorbitan monooleate (preferably with 20 ethoxy groups), ethoxylated sorbitan monolaurate (preferably with 20 ethoxy groups), ethoxylated sorbitan monostearate (preferably with 20 ethoxy groups), ethoxylated sorbitan monopalmitate (preferably with 20 ethoxy groups);

b) alkoxylated alcohols, preferably ethoxylated propoxylated alcohols according to formula I below

CO

wherein R is C8-C18 alkyl, n is 5 to 80 and m is 0 to 5, preferably R is C8-C18 alkyl, n is 5 to 10 and m is 2 to 5;

c) alkoxylated alkyl phenols, preferably ethoxylated alkyl phenols according to formula II below wherein R is C8-C18 alkyl, n is from 5 to 80, preferably R is C8-C18 alkyl, n is 5 to 12, more preferably R is nonyl, n is 9; d) alkyl polyglucosides according to formula III below

wherein R is C6 -C14 alkyl, DP is from 1.3 to 1.7; preferably R is C8-C14 alkyl, DP is from 1.3 to e) silicone polyethers according to formula IV below

(IV),

wherein x is 0 to 1, y is 1, w is 6 to 9 and z is 0 to 5, preferably x is 0, y is 1, w is 6 to 9 and z is 0.

9. A nanoemulsion according to any one of Items 1 to 8, wherein the complex aqueous solution used as the dispersed phase gives 9 to 14% by weight the weight of the nanoemulsion.

10. The nanoemulsion according to any one of Items 1 to 9, wherein the complex aqueous solution present as the dispersed phase comprises, by weight, based on the weight of the nanoemulsion: (i) not more than 3%, preferably 2.98% acid/ acid mixture in concentration of 32%, ii) up to 0.7%, preferably 0.65%, of a clay swelling inhibitor agent, which is a strong electrolyte, preferably potassium halide, more preferably KC1;

iii) in the range of 0 to 0.15%, preferably 0.13%, of a corrosion inhibitor, in particular hydrazine, an amine, preferably hexamethylene tetramine;

iv) in the range of 0 to 0.1%, preferably 0.06%, of Fe³⁺ binding agent, preferably citric acid.

11. Process for the preparation of the nanoemulsion according to Items 1 to 10, comprising the following steps: a) dissolving the one or more first nonionic surfactants in the organic solvent as a dispersion medium to obtain an organic precursor; b) dissolving the one or more second nonionic surfactants, the one or more acids, optionally a corrosion inhibitor, a clay swelling inhibitor agent and a Fe³⁺ -binding agent, in water to obtain an aqueous precursor; c) gradually adding the aqueous precursor to the organic precursor with constant stirring; to obtain a nanoemulsion, which is characterized by its rheological behavior as a Newtonian fluid at temperatures in the range of 20 to 90 °C, and its viscosity measured by rotary viscometer does not exceed 10 mPas at room temperature; wherein said nonionic surfactants form a surfactant mixture in the interfacial layer at the drop surface;

and wherein said nonionic surfactants have an HLB_mx value in the range of 7-11 (preferably 8); and wherein the first nonionic surfactant used in the surfactant mixture has an FiLB value less than the second nonionic surfactant FiLB value.

12. The method according to Item 11, wherein the nanoemulsion is produced in a high performance homogenizer within less than 24 hours prior to use.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the present invention, the term "nanoemulsion" refers to a colloidal system consisting of two liquids and emulsifiers which are not or only slightly miscible with each other, in which the inner phase of the emulsion (also known as dispersed part) emulsified in the outer phase of the emulsion (also called dispersion medium) has an average droplet size of up to 400 nm, and thermodynamically unstable, but practically stable kinetically. For the purposes of the present invention, the term "rock permeability" or "permeability" refers to the fluid conductivity of a rock, as described in Darcy's Law:

q m

^{K =} A Dr Lr¹ where K is the permeability (measured in Darcy, D), q is the volume of fluid flow per unit of time, m is the viscosity of the fluid, Dr is the pressure drop across the sample length, A is the rock sample cross section and L is the rock sample length.

For purposes of the present invention, the term "bed stimulation process" refers to a process for increasing yields in oil and gas wells and geothermal storage wells, to provide economical hydrocarbon production from low permeability layers and to improve absorptivity in water injection wells.

For the purposes of the present invention, "kinetically stable nanoemulsion" means a nanoemulsion which is capable of withstanding droplet stability for 24 hours, i.e., it is resistant to the processes of droplet confluence and aggregation.

For purposes of the present invention, the "kinetically stable nanoemulsion" can be classified as Newtonian fluids after its production, as evidenced by the flow curve recorded by rotation technics in Figure 7.

For the purposes of the present invention, HLB_mx is the cumulative ratio of surfactants present in the nanoemulsion, the value of which is calculated by the following formula:

wherein X_t is the mass fraction of surfactant“I” in the surfactant mixture and HLB is the F1LB of surfactant“I”. In the correlation X, is the mass fraction calculated from the sum of the cumulative amounts of the surfactants dissolved in the aqueous and oily phases of the emulsion and enriched at the interface, which must be distinguished from the mass fractions formed after emulsification, X,^v, X^® and ^~X °, which characterize the composition of the aqueous, oily and interfacial surfactant mixture, respectively. It is not possible to calculate the mass fractions of the latter (X,^v, X^® and X°), and at the current state of the art, for different interfaces of liquid phases (including emulsions), it is only certain that the molar ratio of surfactants present in the interfacial layer differs from the molar ratios of equilibrium block phases. The present invention relates to a nanoemulsion containing a complex aqueous solution of an organic dispersion medium as an emulsified phase, wherein the emulsifier is a mixture of nonionic surfactants and the nanoemulsion comprises one or more compounds suitable for bed stimulation in the emulsified aqueous phase, in particular an acid or a mixture of acids which increases the permeability of the rock, corrosion inhibitor, Fe³⁺+ ion-binding agent, and clay swelling inhibitor additive.

The surfactant mixture present in the nanoemulsion as an emulsifier consists of at least two nonionic surfactants of different HLB values, which form a layer providing minimal interfacial energy. The unique HLB value of surfactants is a function of their chemical structure, thus the value determined and guaranteed by the manufacturer of the surfactant, which is unchanged during the production of nanoemulsion, whereas HLB_mx a measure characterizing the mixture formed by mixing surfactants of different chemical structures, which can be modified by changing the mixing ratio.

The exact composition of the mixed interfacial layer (Fig. 2) is unknown and cannot be experimentally determined in the state of the art as its composition, since said composition, in addition to the material quality of the surfactants and solvents constituting the emulsion, is determined by the dynamic distribution equilibrium and temperature between the oily and aqueous phases so that only the weight ratio of the surfactants used in the production can be defined. The HLB_mx value of the surfactant mixture used in the nanoemulsion of the present invention falls in the range of 7-11, it is preferably 8. For HLB_mx values outside this range, the droplet size of the dispersed phase increases to such an extent that the formation of nanoemulsion is no longer possible. The surfactants are required to be stable in the presence of an acid at the temperature of the reservoir being treated.

Accordingly, the present invention relates to the following.

7. A nanoemulsion according to any one of Items 1 to 6, wherein the first nonionic surfactant is selected from the group consisting of sorbitan ester based surfactants, preferably sorbitan monoesters, more preferably sorbitan mono-fatty acid esters, in particular sorbitan monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan monopalmitate. 8. A nanoemulsion according to any one of the Items 1 to 7, wherein the second nonionic surfactant is selected from the group consisting of a) ethoxylated sorbitan ester based surfactants, preferably ethoxylated sorbitan monoesters containing 10 to 30, preferably 20 ethoxy groups, more preferably ethoxylated sorbitan mono-fatty acid esters containing 10 to 30, preferably 20 ethoxy groups, especially ethoxylated sorbitan monooleate (preferably with 20 ethoxy groups), ethoxylated sorbitan monolaurate (preferably with 20 ethoxy groups), ethoxylated sorbitan monostearate (preferably with 20 ethoxy groups), ethoxylated sorbitan monopalmitate (preferably with 20 ethoxy groups); b) alkoxylated alcohols, preferably ethoxylated propoxylated alcohols according to formula I below

CO

wherein R is C8-C18 alkyl, n is 5 to 80 and m is 0 to 5, preferably R is C8-C18 alkyl, n is 5 to 10 and m is 2 to 5; c) alkoxylated alkyl phenols, preferably ethoxylated alkyl phenols according to formula II below

wherein R is C8-C18 alkyl, n is from 5 to 80, preferably R is C8-C18 alkyl, n is 5 to 12, more preferably R is nonyl, n is 9; d) alkyl polyglucosides according to formula III below

wherein R is C6 -C14 alkyl, DP is from 1.3 to 1.7; preferably R is C8-C14 alkyl, DP is from 1.3 to

1.7; e) silicone polyethers according to formula IV below

(iv),

10. The nanoemulsion according to any one of Items 1 to 9, wherein the complex aqueous solution present as the dispersed phase comprises, by weight, based on the weight of the nanoemulsion:

(i) not more than 3%, preferably 2.98% acid/ acid mixture in concentration of 32%,

ii) up to 0.7%, preferably 0.65%, of a clay swelling inhibitor agent, which is a strong electrolyte, preferably potassium halide, more preferably KC1;

11. Process for the preparation of the nanoemulsion according to Items 1 to 10, comprising the following steps: a) dissolving the one or more first nonionic surfactants in the organic solvent as a dispersion medium to obtain an organic precursor; b) dissolving the one or more second nonionic surfactants, the one or more acids, optionally a corrosion inhibitor, a clay swelling inhibitor agent and a Fe³⁺ -binding agent, in water to obtain an aqueous precursor;

c) gradually adding the aqueous precursor to the organic precursor with constant stirring; to obtain a nanoemulsion, which is characterized by its rheological behavior as a Newtonian fluid at temperatures in the range of 20 to 90 °C, and its viscosity measured by rotary viscometer does not exceed 10 mPas at room temperature;

wherein said nonionic surfactants form a surfactant mixture in the interfacial layer at the drop surface; and wherein said nonionic surfactants have an HLB_mx value in the range of 7-11 (preferably 8); and wherein the first nonionic surfactant used in the surfactant mixture has an HLB value less than the second nonionic surfactant HLB value.

It is a crucial aspect that the lower HLB surfactant be dissolved in the hydrocarbon mixture forming the dispersion phase and the higher HLB surfactant be dissolved in the aqueous mixture when mixing the organic and aqueous phases in course of preparation of the nanoemulsion.

During the preparation, the organic and aqueous precursors are first prepared. For the preparation of the organic precursor, the first surfactant is dissolved in the hydrocarbon mixture forming the dispersion medium. The aqueous precursor is prepared by dissolving the second surfactant, the clay anti-swelling agent, the corrosion inhibitor and the Fe³⁺ ion-binding agent, and the acid or mixture of acids in water. The aqueous precursor is then gradually added to the organic precursor with constant stirring.

The nanoemulsion according to the present invention can be prepared under laboratory conditions and in the well area, preferably within a time period prior to use that does not exceed the criterion of stability of the nanoemulsion (24 h). The nanoemulsion is prepared in a high performance homogenizer both in laboratory, and field conditions. During production, especially under field conditions, flow parameters of organic and aqueous phases and mixing speed are determined by the power and capacity of the homogenizer used; the precise determination of these manufacturing parameters is within the skill of the art without undue experimentation.

The nanoemulsion composition of the present invention is characterized by its rheological behavior as a Newtonian fluid at temperatures between 20 and 90 °C, and its viscosity measured at rotary viscometer does not exceed 10 mPas even at room temperature.

The nanoemulsion composition of the present invention is characterized in that its average droplet size determined by dynamic light scattering is in the range of 10-400 nm, preferably 10-160 nm, for example: 12 nm, 30 nm, 54 nm, 70 nm, 97 nm, 106 nm, 118 nm, 124 nm. nm, 133 nm, 147 nm, 158 nm.

There is a relationship between the droplet size and the spectral properties of the nanoemulsion. The correlation between the average droplet size determined by dynamic light scattering and the transmittance allows the field-produced nanoemulsion to be quickly and safely qualified for its droplet size. The reference nanoemulsion was produced in the laboratory so the spectral properties of the field sample may not be completely identical due to the contamination of the field sample, thus, in the field qualification, the only requirement for nanoemulsion is that the percentage transmittance in the visible range should be one hundred percent within the wavelength range of 400 to 600 nm.

The ability of the nanoemulsion according to the present invention to bed stimulation is investigated by liquid permeation on consolidated rock cores with a permeability of at least 1 mD at a temperature appropriate to the bed to be treated, at a back pressure of 4 to 10 bar and at a flow rate of 0.5 to 4 ml/min. The parameter recorded during the test is the pressure drop between the entrance and exit sides of the rock core, in addition to the amount of fluid injected, which allows, using Darcy's law, to calculate the mobility of fluid flowing through the rock core (in M, mD/cP units) :

K q L

M =— =

m A A

Knowing the viscosity of the fluid, the permeability (K) of the rock for a given fluid can be determined.

The first step in the measurement is to determine the initial permeability and mobility with 5% KC1 solution and petroleum, followed by injection of the nanoemulsion at a volume of 10 to 15 times the pore volume of the applied rock sample measured with a fluid. After injection of the nanoemulsion, the mobility measured with the 5% KC1 solution and petroleum was re-determined in the same direction as that of the injection and in the opposite direction.

The practical examples and results detailed below illustrate the applicability of the composition of the invention and are not intended to limit the applicability of the subject invention.

EXAMPLES

Example 1: Preparation of 100 g of a nanoemulsion based on alkyl polyglucoside containing hydrochloric acid Components required to prepare the nanoemulsion:

7.00 g of Span 80 (Fluka, HLB=4.3) sorbitan monooleate surfactant

14.00 g Glucopon 650 EC (BASF, F1LB=11.9; 50% surfactant formulation) alkyl polyglucoside based surfactant.

73.10 g Dunasol 180/220 (MOL, boiling range 180-220 °C) C10-C13 aliphatic hydrocarbon mixture as organic dispersion medium

• 0.06 g of citric acid as Fe³⁺ ion binding agent

0.13 g of hexamethylene tetramine as a corrosion inhibitor

• 0.65 g KC1 as an clay anti-swelling agent

• 2.08 g water

2.98 g of 32% hydrochloric acid.

The surfactant mixture had an FILB_^ value of 8.1. Dissolve Span 80 in Dunasol to prepare the organic phase. The aqueous phase is prepared by dissolving Glucopon 650 EC in water, citric acid, hexamethylenetetramine and KC1, and then adding hydrochloric acid. The nanoemulsion is blended at 8000 rpm with a high performance homogenizer by gradually adding the aqueous component to the organic component.

The droplet size distribution curve of the nanoemulsion thus produced is shown in Figure 5, which demonstrates that the average droplet size is 13 nm. The viscosity of the nanoemulsion at 25 °C is 6.1 mPas. The flow curve at 25 °C shown in Figure 6 demonstrates that the nanoemulsion exhibits Newtonian behavior after production. The viscosity curve of the nanoemulsion at a temperature range of 20-90 °C using a constant speed gradient is illustrated in Figure 7, whereby the nanoemulsion behaves like a Newtonian fluid in the temperature range under study and its viscosity decreases as the temperature increases such that within a temperature range of 80 to 90 °C, it approximates a viscosity of water of 1.0 mPas at 20 °C.

Due to the thermal stability properties of the alkyl polyglucoside surfactant, the nanoemulsion of the composition described above can be used in reservoirs at temperatures not exceeding 100 °C.

Example 2: Preparation of 100 g of a silicone polyether based nanoemulsion containing hydrochloric acid

Components required to form a nanoemulsion: 4.00 g of Span 80 (Fluka, HLB=4.3) sorbitan monooleate surfactant

• 10.00 g Silsurf A008 UP (Siltech, HLB> 10) silicone polyether surfactant

76.10 g Dunasol 180/220 (MOL, boiling range 180-220 °C) C10-C13 aliphatic hydrocarbon mixture

• 0.06 g of citric acid as Fe³⁺ ion binding agent

0.13 g of hexamethylene tetramine as a corrosion inhibitor

• 0.65 g KC1 as a clay anti-swelling agent

• 6.08 g water

2.98 g of 32% hydrochloric acid

The surfactant mixture had an HLB_^ value of 8.4. Span 80 surfactant was dissolved in Dunasol to prepare the organic phase. The aqueous phase was prepared by dissolving Silsurf A008 surfactant, citric acid, hexamethylenetetramine and KC1 in water and then adding hydrochloric acid. The nanoemulsion is blended at 8000 rpm with a high performance homogenizer by gradually adding the aqueous component to the organic component.

The droplet size distribution curve of the nanoemulsion thus produced is shown in Figure 8, which demonstrates that the average droplet size is 158 nm. The viscosity of the nanoemulsion at 25 °C was 1.74 mPas. The flow curve at 25 °C in Figure 9 demonstrates that the nanoemulsion exhibits Newtonian behavior. The viscosity curve of the nanoemulsion over a temperature range of 20-130 ° C using a constant speed gradient is shown in Figure 10, which demonstrates that the nanoemulsion behaves like a Newtonian fluid in the temperature range under study and as the temperature increases, the viscosity decreases to near the viscosity of water of 1.0 mPas at 20°C, and then at an even lower value, at a higher temperature.

The applicability of the nanoemulsion having the composition described above has an upper temperature limit of 140 °C.

Example 3: Preparation of 100 g of ethoxylated nonylphenol based hydrochloric acid containing nanoemulsion

Components required to form a nanoemulsion:

• 6.9 g of Span 80 (Fluka, HLB = 4.3) sorbitan monooleate surfactant

• 5.1 g Lutensol AP9 (BASF, HLB = 13) ethoxylated nonylphenol surfactant • 74.80 g Exxsol D80 (Exxson Mobil, boiling range: 200-250 °C) aromatized hydrocarbon mixture

• 0.07 g of citric acid as Fe³⁺ ion binding agent

• 0.13 g of hexamethylene tetramine as a corrosion inhibitor

• 0.66 g KC1 as a clay anti-swelling agent

• 9.47 g water

• 2.88 g of 32% hydrochloric acid

The surfactant mixture has an HLB^ value of 8. The Span 80 surfactant is dissolved in Exxsol D80 to prepare the organic phase. The aqueous phase is prepared by dissolving Lutensol AP9 surfactant, citric acid, hexamethylenetetramine and KC1 in water and then adding hydrochloric acid. The nanoemulsion is blended at 8000 rpm with a high performance homogenizer by gradually adding the aqueous component to the organic component.

The droplet size distribution curve of the nanoemulsion thus produced is shown in Figure 11, which demonstrates that the average droplet size is 31 nm. The viscosity of the nanoemulsion at 25 °C was 3.95 mPas. The flow curve at 25 °C shown in Figure 12 demonstrates that the nanoemulsion exhibits Newtonian behavior after production. The viscosity curve of the nanoemulsion at a temperature range of 20-90 °C using a constant speed gradient is illustrated in Figure 13, whereby the nanoemulsion behaves like a Newtonian fluid at the temperature range tested and the viscosity decreases with increasing temperature such that at a temperature range of 80-90 °C. it approximates the viscosity of water of 1.0 mPas at 20°C.

Example 4: Preparation of 100 g nanoemulsions based on alkyl polyglucoside containing of various acids

Components required to prepare nanoemulsions:

• 7.00 g of Span 80 (Fluka, F1LB=4.3) sorbitan monooleate surfactant

• 14.00 g Glucopon 650 EC (BASF, HLB=11.9; 50% surfactant formulation) alkyl polyglucoside based surfactant

• 73.10 g Dunasol 180/220 (MOL, boiling range 180-220 °C) C10-C13 aliphatic hydrocarbon mixture as organic dispersion medium • 0.06 g of citric acid as Fe³⁺ ion binding agent

0.13 g of hexamethylene tetramine as a corrosion inhibitor

• 0.65 g KC1 as a clay anti-swelling agent

• 2.08 g water

• 2.98 g of 32% acid according to Table 1

The surfactant mixture had an HLB_mx of 8.1. Dissolve Span 80 surfactant in Dunasol to prepare the organic phase. The aqueous phase is prepared by dissolving Glucopon 650 EC surfactant, citric acid, hexamethylenetetramine and KC1 in water and mixing the acid solution. The nanoemulsion is blended at 8000 rpm with a high performance homogenizer by gradually adding the aqueous component to the organic component. The droplet size and viscosity at 25 °C of the resulting nanoemulsion are shown in Table 1.

Table 1: Droplet size and viscosity at 25 °C of alkyl polyglucoside based nanoemulsions containing various acids.

Due to the thermal stability properties of the alkyl polyglucoside surfactant, the nanoemulsions of the above-described compositions are suitable for use in reservoirs at temperatures not exceeding 100 °C.

Fluids are called Newtonian fluids, in which the laminar flow speed gradient of the fluid layers is directly proportional to the shear stress it produces, so that the viscosity of the Newtonian fluids does not change as the shear stress increases.

The low viscosity of the nanoemulsions shown presents a very favorable condition for injection into the reservoir, and a further decrease in viscosity due to temperature is particularly advantageous for injection into higher bed temperature reservoirs.

Example 5: Bed stimulation model experiments According to the experimental procedure detailed above, bed stimulation model experiments were carried out with a nanoemulsion containing hydrochloric acid, which is the subject of the present invention, and by comparison with a state-of-the-art bed-stimulating solution, i.e. VDA acid gel containing hydrochloric acid. The data presented in the following comparison are the results of model experiments performed on limestone cores from the same core drilling at 65 °C. In the model experiment with VDA acid gel, the mobility values obtained from the registered parameters are shown in Table 2, a photograph of the entrance and exit sides of the treated rock core is shown in Figure 14. The mobility and permeability values obtained in the model experiment with the form of nanoemulsion as shown in Example 3 are shown in Table 3, and a photograph of the entrance and exit sides of the treated rock core is shown in Figure 15. Figure 16 shows electron microscopy images of the acid gel and Figure 17 the electron microscopy images after nanoemulsion treatment. An important result in connection with the present invention is that due to the properties of the nanoemulsion of the invention, it is also capable of releasing hydrocarbon from the rock containing oil, as shown in Figure 18, whereas VDA acid gel does not show such effect (Figure 19).

Table 2: Mobility and permeability values obtained from a VDA acid gel layering model experiment on a limestone rock core

Table 3: Mobility and permeability values obtained from the limestone rock core in the nanoemulsion bed stimulation model experiment of the present invention

According to the mobility values, the nanoemulsion of the present invention achieves greater permeability as compared to the acid gel process. The reason is that although the large diameter caverns formed during the acid gel process increase the permeability of the rock core, but this effect is limited to the rock area around the caverns, while the nanoemulsion according to the invention nanoemulsion forms multiple channels of smaller diameter or capillary channel system covering a larger volume of rock, thereby allowing fluid inflow from larger rock volumes.

Example 6: Field experiments

One embodiment of the present invention, namely the nanoemulsion of the composition described in Example 1, was subjected to a three-time running experiment in which the nanoemulsion was pressed into a well at a temperature of 70 °C in a deepened limestone well. During the first operation experiment, 8.5 m³ of nanoemulsion was pressed into the designated well. After injection, the well was put into production. The production data obtained after the layer treatment is shown in Table 4. Following the bed stimulation operation, we observed an increase in the well production of the wells and a significant increase in the amount of gas accompanying the oil. In the second run experiment, the bed was treated with 100 m³of nanoemulsion. The effect of bed stimulation is shown in Table 5, which shows a significant increase in fluid production after injection of a larger volume of nanoemulsion, while no significant change in the amount of oil accompanying gas.

Table 4: Production data before and after the 8,5 m³ nanoemulsion bed treatment

Table 5: Production data before and after 100 m³ of nanoemulsion bed treatment

INDUSTRIAL APPLICABILITY

The nanoemulsion according to the present invention increases the fluid inflow in the oil, natural gas and thermal water storage layers by stimulating the fluid in such a way that the rock in the immediate vicinity of the well is not destroyed, but smaller diameter channels or capillary channel systems are formed that cover a larger volume of rock, thereby providing fluid inflow from the larger rock volume.

Claims

WHAT IS CLAIMED IS

(a) a first non-ionic surfactant having a hydrophobic character or a hydrophobic mixture of non ionic surfactants, dissolved in an organic solvent as a dispersion medium;

b) one or more second nonionic surfactants dissolved in a complex aqueous solution as dispersed phase, containing one or more acids, optionally a corrosion inhibitor, a clay anti-swelling agent and a Fe³⁺ ion-binding agent; wherein said nonionic surfactants are low molecular weight surfactants (less than 500 g mob¹), and wherein said nonionic surfactants form a mixture of surfactants in the interfacial layer on the surface of the drop; and wherein said nonionic surfactants have an HLB_mx value in the range of 7-11 (preferably 8); and wherein the nanoemulsion behaves like a Newtonian fluid at a temperature in the range of from 20 to 90 °C, its viscosity measured by the rotary viscometer at room temperature not exceeding 10 mPas; and wherein the first nonionic surfactant used in the surfactant mixture has an HLB value less than the second nonionic surfactant HLB value.

2. The nanoemulsion according to Claim 1, wherein the surfactant mixture enriched in the interfacial layer gives 10-15%, preferably 12-14% by weight the weight of the nanoemulsion.

3. The nanoemulsion according to Claim 1 or 2, wherein the organic solvent used as the dispersion medium is a mixture of C10-C14 aliphatic hydrocarbons, which gives 72-77% by weight the weight of the nanoemulsion.

4. The nanoemulsion according to any one of Claims 1 to 3, wherein the possible components of the acid/acid mixture are selected from the group consisting of inorganic acids, in particular hydrogen halides (preferably HF, HC1), phosphoric acid, sulfuric acid, nitric acid, boric acid, fluoroboric acid; organic acids, especially mono carboxylic acids (preferably formic acid, acetic acid); dicarboxylic acids (preferably oxalic acid, malonic acid, glutaric acid), tricarboxylic acids, aminocarboxylic acids, sulfonic acids, chloroacetic acid, hydroxyacetic acid.

5. A nanoemulsion according to any one of Claims 1 to 4, wherein the possible components of the acid/ acid mixture are selected from the group consisting of HF, HC1, phosphoric acid, formic acid, acetic acid, sulfuric acid or nitric acid.

6. A nanoemulsion according to any one of Claims 1 to 5, wherein the acid is HC1.

7. A nanoemulsion according to any one of Claims 1 to 6, wherein the first nonionic surfactant is selected from the group consisting of sorbitan ester based surfactants, preferably sorbitan monoesters, more preferably sorbitan mono-fatty acid esters, in particular sorbitan monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan monopalmitate.

8. A nanoemulsion according to any one of the Claims 1 to 7, wherein the second nonionic surfactant is selected from the group consisting of a) ethoxylated sorbitan ester based surfactants, preferably ethoxylated sorbitan monoesters containing 10 to 30, preferably 20 ethoxy groups, more preferably ethoxylated sorbitan mono-fatty acid esters containing 10 to 30, preferably 20 ethoxy groups, especially ethoxylated sorbitan monooleate (preferably with 20 ethoxy groups), ethoxylated sorbitan monolaurate (preferably with 20 ethoxy groups), ethoxylated sorbitan monostearate (preferably with 20 ethoxy groups), ethoxylated sorbitan monopalmitate (preferably with 20 ethoxy groups); b) alkoxylated alcohols, preferably ethoxylated propoxylated alcohols according to formula I below

CO

c) alkoxylated alkyl phenols, preferably ethoxylated alkyl phenols according to formula II below

1.7; e) silicone polyethers according to formula IV below

CH₃ CH3 CH 3 CH 3

CH₃-Si(-0-¾_s(-0-St ₇-0-Si-CH₅

CH₃ CH₃ (CH₂) CH 3

3

(0 CH₂CH₂)_W-(0-CH₂CH)_Z0H

CH₃

(IV),

9. A nanoemulsion according to any one of Claims 1 to 8, wherein the complex aqueous solution used as the dispersed phase gives 9 to 14% by weight the weight of the nanoemulsion.

10. The nanoemulsion according to any one of Claims 1 to 9, wherein the complex aqueous solution present as the dispersed phase comprises, by weight, based on the weight of the nanoemulsion:

11. Process for the preparation of the nanoemulsion according to Claims 1 to 10, comprising the following steps: a) dissolving the one or more first nonionic surfactants in the organic solvent as a dispersion medium to obtain an organic precursor; b) dissolving the one or more second nonionic surfactants, the one or more acids, optionally a corrosion inhibitor, a clay swelling inhibitor agent and a Fe³⁺ -binding agent, in water to obtain an aqueous precursor;

wherein said nonionic surfactants form a surfactant mixture in the interfacial layer at the drop surface;

and wherein said nonionic surfactants have an HLB_mx value in the range of 7-11 (preferably 8); and wherein the first nonionic surfactant used in the surfactant mixture has an HLB value less than the second nonionic surfactant HLB value.

12. The method according to Claim 11, wherein the nanoemulsion is produced in a high performance homogenizer within less than 24 hours prior to use.