WO2024134373A1

WO2024134373A1 - New foaming agent with high thermal stability and biocompatibility

Info

Publication number: WO2024134373A1
Application number: PCT/IB2023/062607
Authority: WO
Inventors: Massimo BRUNO; Tatiana ZOCCARATO; Umberto CIARDI; Andrea VOLPONI; Michele BANCONE; Milena Mantarro; Andrea QUARANTA
Original assignee: Chimec S.P.A.
Priority date: 2022-12-20
Filing date: 2023-12-13
Publication date: 2024-06-27

Abstract

The present invention refers to a foaming product, and its use, with high thermal stability (up to 130°C for some weeks) and with an excellent environmental toxicity profile which makes it suitable for offshore applications, wherever low environmental impact. The new formulation is used in a method for the removal of the liquid column which depresses or eliminates the production of gas wells (Gas Well Deliquification). The product tolerates the presence of hydrocarbon very well and has the ability to reduce the density of the hydrostatic column of the well, generating foam, and ensuring that the gas production is then able to reach the surface.

Description

NEW FOAMING AGENT WITH HIGH THERMAL STABILITY AND BIOCOMPATIBILITY

FIELD OF INVENTION

The present invention refers to a mixture of surfactants, a foaming product, and the related use, wherein said mixture and said product have a high thermal stability (up to 130°C for some weeks) and with an excellent environmental toxicity profile which makes them suitable for offshore applications, wherever a low environmental impact is necessary.

The new formulation is used in a method for the removal of the liquid column which depresses or eliminates the production of gas wells (Gas Well Deliquification). The product tolerates the presence of hydrocarbon very well and has the ability to reduce the density of the hydrostatic column of the well, generating foam, and ensuring that the gas production is then able to reach the surface.

STATE OF THE ART

The production of gas wells is usually limited by the accumulation of water and light hydrocarbons (usually called "condensates") produced together with the gas, a phenomenon that amplifies with the aging of the well itself. In "mature" wells, the decrease in the pressure of the gas being formed and in the speed of the gas itself causes the invasion of the bottom of the well due to the deposition of liquids called "loading". Liquid loading of a gas well occurs when the downhole pressure is not sufficient to displace the liquids produced (condensate and especially water, which is often very saline and therefore high density). The liquids, accumulating, obstruct the passage of gas from the productive formation to the well, causing a progressive decrease in production and a reduction in the life of the well itself. There are various methods for unloading the well, some of these are called: Gas Lift, ESP, Beam pumps, Plunger Lift, PCP. The choice depends on technical reasons (operability) and economic reasons. The method chemical removal through foam (Foam Assisted Lift (FAL)) involves the use of foaming agents capable of creating a foam that lightens the weight of the hydrostatic column, thus allowing the pressure of the reservoir reserve to continue the supply of gas from the well. See for example W02008/109216 or WO 2011/064292. The FAL is an integral part of the management programs for the operation of low production wells, although it is very difficult in case of high condensate:water ratios. In fact, traditional foamers can be ineffective if the concentration of condensate is high. The foam has the effect of reducing the critical velocity needed for the gas to transport the liquid to the wellhead. Foaming agents, which fall into the class of surfactant substances, can be of any nature. For example, they are of the cationic surfactant type, such as quaternary ammonium salts, which however have a biocidal action and are therefore toxic for marine environments. Another type concerns anionic surfactants, such as carboxylated or sulfonated compounds, which however do not show high thermal stability and therefore would not be suitable for application in gas wells where temperatures reach high values (>100°C), they also suffer of loss of effectiveness when the formation water present in the well has a high salt content. Also worth mentioning are amphoteric surfactants, such as Betaines, which are widely known and used in the FAL field for their high efficiency, but have a biocidal function, and are therefore no longer interesting given their lack of eco- compatibility, furthermore they tend to degrade and therefore they become ineffective when they are subjected to temperatures above 100°C for a long time. Finally, there are non-ionic surfactants, such as polyglucoside derivatives, which represent a good compromise between eco-compatibility and thermal stability but have low foaming power.

The reduction of the surface tension and density of the liquid head effected by foaming determines a decrease of approximately 2/3 of the critical speed. Typical dosages are between 4,000 and 10,000 ppm referring to the total volume of liquid produced. The foam can be formed through the interaction of the chemical product (foamer) with a gas, which is normally the hydrocarbon gas produced by the well itself; however, when the well's gas production is already very low and would not be sufficient to form the necessary quantity of foam, other gases can be added. The usable gases are nitrogen, carbon dioxide, methane, natural gas or other hydrocarbon gases.

There are essentially three main methods of applying foamer into the well:

- throwing solid soap (soap sticks) into the tubing: it costs little, is easy to apply and does not require additional equipment. The success rate is low, however, as there are difficulties in quickly dissolving the solid soap in the well.

- batch treatment in the annulus, i.e. the space between the production tube and the well wall. They can be carried out in wells without a packer (i.e. hydraulically sealed sealing device for an oil well) where the treatment fluid can be pumped from the annulus. - continuous or batch downhole injection (i.e. at the bottom of the well). Technique that allows for an injection of foaming agent at any depth of the well through a capillary string consisting of a small diameter tube inserted inside the well production tube. This system can also be used in wells equipped with a well safety valve (SCSSV).

The three methods are based on the use of similar chemistries, but solve different well situations. Although they are all normally applied, the third methodology is considered the best because it allows a direct and controlled injection directly at the bottom of the well.

The techniques described so far can be used to free the lines that transport the gas from the accumulation of associated liquids; as happens in the well, the accumulation of water and condensate can greatly increase the pressure losses generated by the transport of gas in the pipeline. A line can easily fill with liquids if the stretch it has to travel is uphill or in correspondence with topographical depressions; the pressure drops resulting from this situation counteract the production pressure at the wellhead. If a well is now mature, the production pressure will be low and the pressure drop due to liquids in the line can lead to a significant loss of production or, in the worst case, shutdown of the well.

The production liquids can therefore accumulate both at the bottom of the well (raising the hydrostatic head) and in the gas transport lines, in the absence of separators located at the wellhead or, even if the latter were present, if they are in any case inadequate for the total reduction of liquids associated with gas production.

Those “liquid loading" phenomena can be partially or totally eliminated through various techniques, including the use of foaming agents.

The traditional use of foamers involves the batch or continuous addition of the product, which must be able to develop the foam following the flow of the production gas and the turbulence caused by it.

The foam formed lowers the surface tension of the water present in the pipe which is therefore transported, always by the same gas, more easily than the water itself. At the end of the run, the foam reaches the production field and the main separators, where it must be broken down, before entering the separator, with a special anti-foam additive, in order to avoid entrainment of liquid in the gases produced. In the case of continuous injection of the foaming agent at the bottom of the well, the addition to the accumulated water will be gradual, as the injection method involves low dosages via " capillary string” for very long times or even in continuous.

The low dosages are due to the small diameter of the well production tube, which does not allow additions of large quantities in a short time; in the case of foamers with additives in continuous mode (dosages of 5 - 10 ppm), the concentration in the accumulation water will increase over time and only when the critical concentration is reached, foam will form which will allow the accumulated liquids, which clog, to escape, the passage of the gas, resulting in an increase in production and an extension of the life of the well itself.

On the use of foams, see the following literature:

JF Lea, HV Nickens, MR Wells “Gas Well Deliquification" Second Edition, Gulf Drilling Guides, Gulf Professional Publishing, Elsevier provides guidance on the deliquification of gas in wells.

Kalman Koczo, Oleg Tselnik and Benjamin Falk, Momentive Performance Materials Inc. “Silicon- Based Foamants For Foam Assisted Lift of Aqueous-Hydrocarbon Mixture”, SPE 141471, 2011 reports a study of silicone-based polyether foams in different hydrocarbon/water ratios.

BP Price and B. Gothard, SPE & Multi- Chem “Foam-Assisted Lift: Importance of Selection and Application”, SPE 106465, 2007 reports the issues relating to the “ Foam assisted lift” to be considered for long-term goals, i.e. 1) correct well diagnostics, 2) correct foaming agent selection, and 3) correct application and evaluation.

D. Orta, S. Ramanchandran, J. Yang, M. Fosdick, T. Salma, J. Long, J. Blanchard, Baker Petrolite Corp, and A. Allcom, C. Atkins and O. Salinas, Shell E&P “A Novel Foamer for Deliquification of Condensate- loaded Wells,” SPE 107980, 2007 describes the performance of a new foaming agent specifically designed to discharge condensate from wells. Parameters for well selection are described, as well as operational processes to maximize continuous production, which resulted in a significantly higher average daily gas production rate and shifted the daily on:off production cycle from 1:1 at 11 :1. This minimized downtime and increased overall daily production averages by 60%. M. Pakulski ’’Testing Gas Well Deliquification Chemicals at Real Downhole Conditions ”, SPE 121564, 2008 describes technologies for measuring the liquefaction capacity of foaming agents at temperatures above 100°C.

CAM Veeken and SPC Belfroid “New Perspective on Gas- Well Liquid and Unloading,” SPE 134483, 2010 describes the multiphase flow mechanism responsible for gas-well liquid loading, and reports gas well deliquitification methodologies that specifically target delay the reversal of the film flow.

S. Campbell, S. Ramachandran and K. Bartrip, Baker Petrolite “ Corrosion Inhibitor I Foamer Combination Treatment to Enhance Gas Production”, SPE 67325, 2001 reports a mechanistic description for predicting the performance of chemical foaming agents developed on measurable parameters demonstrating that the dominant factor is the density of the foam. Saleh and M. Al- Jamae'y, Colorado Scholl of Mine “Foam- Assisted Liquid Lifting in Low Pressure Gas Wells,” SPE 37425, 1987 reports experimental equipment, procedures, and results of a test program to study foam technology lift”.

The techniques described so far can be used to free the lines that transport the gas from the accumulation of associated liquids; as happens in the well, the accumulation of water and condensate can greatly increase the pressure losses generated by the transport of gas in the pipeline.

Such “liquid loading" phenomena can be partially or totally eliminated through various techniques, including the use of foaming agents.

The foam formed lowers the surface tension of the water present in the pipe which is therefore transported, always by the same gas, more easily than the water itself.

What is reported in the literature still leaves the question open on the applicability of foaming products in high temperature conditions for a long period, combined with the fact that the product itself has a low environmental impact, in particular for marine ecosystems, respecting the criteria agreed by the countries registered in the 'OSPAR and expressed by the CEFAS body (https://www.cefas.co.uk/).

In fact, the CEFAS body itself has established an ecotoxicological analysis protocol, from which it is possible to obtain a classification of the chemical product in question. The highest possible classification, which establishes the use of the product in any onshore and especially offshore installation without any limitation, is called "GOLD Without Substitution Warning”.

When looking for a foaming product that is highly biocompatible and performs at high temperatures, there are currently no literature works that report such properties for foaming agents.

SUMMARY OF THE INVENTION

The Authors of the present invention have surprisingly found that the combination of particular surfactants, mixed according to appropriate weight ratios, allows to obtain a foaming agent useful for the removal of the hydrostatic column of liquid that is formed in wells for gas extraction, allowing further gas to be recovered even from wells considered almost exhausted.

This foaming agent has excellent foam generation and stability capabilities, and has been characterized through the parameters "Foam formation time" (ability to generate a certain volume of foam in a given time interval) and "Foam half-life time" (ability of the foam to resist more than 50% of its volume without collapsing). Furthermore, the foaming agent of the present invention allows the exploitation of gas deposits in Oil&Gas fields in all countries, in particular in those countries where local legislation requires the use of products with low environmental impact, requiring, for example, the CEFAS GOLD No Substitution Warning classification. Combined with this high environmental compatibility, the foaming agent of the invention has the peculiarity of being usable in systems where high thermal stability is required, since it keeps its performance unchanged in terms of "Foam formation time" and " Foam half -time” even when the foam is exposed up to 130°C for more than 1 week.

Therefore, this invention fills the gap in the identification and use of heat-resistant and "green" foaming agents for natural gas production installations, extending the production period of gas wells that are now in decline or even "dead".

The restoration of declining or even “dead” wells, also without environmental damage, is particularly important in this historical moment in which a very strong energy crisis is felt worldwide.

Advantageously, the foaming agent object of the present invention has the ability to generate foam in gas wells wherein the hydrostatic column of liquid that has accumulated over time (whether composed of water alone, hydrocarbon alone, or a mixture of the two in any ratio) limits or completely blocks the production of gas towards the surface. In this case, the application of the foaming agents of the invention allows to recover important quantities of gas from those wells wherein production has now stopped or is reduced to a minimum, so as to restore productivity in those wells wherein the extraction of gas is no longer considered economically and technically convenient.

One of the greatest advantages of the invention concerns the environmental impact that the foaming agents of the present invention have on marine ecosystems when used on offshore installations. This is because, often, the water that is produced together with the gas after extraction is treated directly on the platform and then thrown back into the sea, or because accidents on the product injection systems or on the gas production can cause part of the foam (normally toxic to marine and aquatic ecosystems in general) flows directly into the sea.

Another advantage is the thermal stability of the foaming agent of the invention which, being sent to the bottom of the well, must resist high temperatures even for long residence times, depending on the intervention method.

The present invention fills the need to have foaming agents that do not show toxicity for marine ecosystems and that are stable at high temperatures for long exposure times. This makes the products covered by the invention suitable for application anywhere, in particular on those assets where attention to environmental impact is an essential parameter, such as offshore installations in the North Sea.

The technical effect obtained from the combination of the surfactants, in the selected proportions, of the present invention is a surprising and unexpected effect.

In fact, it will be demonstrated below that the selected surfactants do not have the technical characteristics necessary for use as a foaming agent alone and that only some, selected, ratios between the first and second surfactant satisfy these requirements.

The foaming agent object of the invention is made up of a mixture of surfactant substances whose eco-toxicological characteristics are known and attributed according to protocols universally recognized and described and regulated by the CEFAS body (https://www.cefas.co.uk/data-and-publications/ocns/ocns-ecotoxicology-testing/), such as to obtain the maximum possible classification regarding the eco-compatibility of these substances and of the resulting foaming agent, wherein said substances are mixed with precise ratios in weight identified by the authors of the invention.

These surfactant substances can be traced back to two classes of compounds:

• A surfactant belonging to the class of carboxy -methylated, -ethylated, - propylated, -butylated polyoxyethylene alkyl ethers / esters having formula (I),

wherein:

- X is an integer from 6 to 12;

-Y is an integer from 1 to 4;

-Z is H, CH₃, C₂H₅, C₃H₇or C₄H₉;

-n is a number ranging from 2.5 to 10 said surfactant can aiso be used in the form of a sait, in particuiar an alkali meta! sait or an organic salt

And

- A surfactant belongs to the derivatives of alkyl glucosides and fatty alcohols with formula (II) and a molecular weight of less than 1000Da.

Wherein: n is an integer from 6 to 18, m is an integer from 1 to 3.

The characteristic of these classes of compounds is their high biocompatibility for example: Bioaccumulation - LogPow : <3

Biodegradability: >60%

Toxicity on Algae: >10mg/l

Toxicity on Invertebrates: >10mg/l

Fish toxicity: >10mg/l

Furthermore, the data obtained by the authors of the invention have also demonstrated that these substances have an advantageous resistance to high temperatures (130°C for over 7 days).

In fact, during the tests carried out, the study of the combination of the products reported above in particular reciprocal quantitative ratios showed completely unexpected results wherein particular combinations were more performing than other combinations and the same substances taken individually. In fact, it has emerged that the particular combination of surfactants selected must be subject to a certain weight ratio range between the two surfactants used, outside of which the performance as a foaming agent becomes poor.

The performance as a foaming agent is, as mentioned above, evaluated through the Foam Formation Time, wherein, depending on the time, expressed in seconds, necessary for the development of the foam, the foaming product is defined as Good, Moderate and Poor, the values in seconds for this definition are shown in the table below:

Table 1

and through the half-life time of the foam wherein, depending on the time, expressed in seconds, necessary for 50% of the foam to decompose (i.e. to exit the "foam" state), the foaming product is defined as Good (good), Moderate (medium) and Poor (poor), the values in seconds for this definition are shown in the table below:

Table 2

As is easy to imagine, the best product is the one classified as "Good" both in terms of foam formation time and chilling time indicated by the half-life. For each individual product, these tests were repeated on the fresh chemical product and after thermal aging, for example at 130°C for 1 week. The results of the tests reported below for times greater than 120" (in the case of the foam formation time) were not monitored as they were not of interest and therefore the limit value is reported.

The presence of hydrocarbon in the water was considered a mandatory presence to evaluate the performance as a foaming agent suitable for use in gas wells with a water column as a minimum amount of hydrocarbons is always present in the water columns of these wells.

Therefore, all performance tests were conducted on water and 5% hydrocarbon (hydrocarbons with different characteristics were tested).

In the table below, it is possible to see how the weight percentage ratio between two surfactants belonging to the classes of substances indicated above has an optimal range of values outside of which the desired effects are not obtained.

Table 3

Efficiency test carried out on a medium salinity water column and 5% LAWS (Low Aromatic White Spirit) hydrocarbon

As reported in the tables above, the performance indicators are divided into: Poor, Moderate and Good).

Those foaming agents whose performance in terms of foam formation time and foam half-life fall within the definition of Good or Moderate according to tables 1 and 2 are considered of interest for the present invention, i.e. those foaming agents which show a of foam from <80 seconds to <120 seconds and a foam half-life of >180 seconds to >60 seconds.

These evaluations can be carried out as described in the examples part, on water columns of different salinities including hydrocarbons in low quantities.

The authors also verified that the same performances were maintained even after thermal aging of the mixtures in the same ratios, at 130°C for at least 1 week.

Therefore, the authors observed an unexpected and advantageous synergistic effect between the two surfactants of an exclusive nature since the properties of the mixtures tested are not the sum of the properties of the individual substances (far from it), and the properties considered of interest (Good or Moderate) for both evaluation criteria, occur only when the tested surfactants are mixed in precise ratios disclosed in this description. Without being bound to theories, the authors assume that in reports resulting in foaming properties that fall under the definition of Good or Moderate, the surfactants used have a chemical interaction such that the lamellae of foam formed from the ethoxylated methylated fatty acid ester (surfactant of formula I), which would collapse given the presence of hydrocarbon, would be stabilized by the alkyl glucoside (surfactant of formula II) which therefore manages to give body and structure to the foam.

The following are therefore the subject of the invention:

-A mixture comprising a surfactant of formula (I) and a surfactant of formula (II) having a molecular weight lower than 1000Da wherein said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio ranging from 70:30 to 99:1;

-A foaming agent comprising the aforementioned mixture in any of the embodiments described below and one or more solvents and/or additives.

-A process for removing a hydrostatic column of liquid accumulated in a gas well or in the transportation pipelines of such well,, said process comprising one or more steps of introducing the foaming agent according to the present description into said well, wherein said foaming agent is introduced in batches or in continuous or by throwing said foaming agent in solid form into said well, so to obtain the development of foam in the pipes of said well; the foam thus generated has, as is known, the effect of reducing the critical speed necessary for the gas to transport the liquid to the well head.

- Use of a foaming agent in any of the embodiments described below, in a method for removing the hydrostatic column of liquid accumulated in a gas extraction well.

-Use of the mixture as defined in any of the embodiments as described below for the preparation of a foaming agent.

Further advantages and/or embodiments of the present invention will be evident from the following detailed description.

GLOSSARY

The term “foaming agent’ or simply ‘'foamer is commonly used in the literature to define an agent containing or consisting of a surfactant or surfactant or mixtures thereof. The foaming agent composition normally includes the surfactant or mixture of surfactants, water and other elements including: solvents and co-solvents necessary for the stability of the formulation, acids or bases or salts to modify the pH of the mixture or to improve performance of surfactants. For the purposes of the present invention the words "tenside" and "surfactant" are considered synonymous.

The term “non-/on/c surfactant ” refers to surfactants that have no charges when dissolved in water; the hydrophilic part of the molecule that acts as a solubilizer is generally represented by the oxygen of ethylene oxide which shows affinity towards water thanks to the formation of hydrogen bridges. In addition to ethylene oxide adducts, sugar esters and fatty acid alkyl amides also belong to the class of non-ionic surfactants.

The terms “upstream” and “downstream" are intended, in the present invention, to refer to the direction of gas flow flowing from the wellhead to a peripheral station. The two expressions identify a position that respectively precedes or follows another position on the line.

The expression “alkylglucoside” refers to a compound having the formula

The term “number of moles of EO” refers to the number of moles of ethylene oxide present in the carboxy- methylated, -ethylated, -propylated, -butylated polyoxyethylene (EO) alkyl ether /ester polymer. The number of moles of EO indicates the ionic character of the substance wherein they are present.

The expression "Foam formation time" according to the present invention indicates the time, expressed in seconds, necessary for the development of the foam

The expression “Foam half-life” or foam half-life time according to the present invention, indicates the time necessary, expressed in seconds, for 50% of the foam to decompose (i.e. to exit the “foam” state).

The term “petroleum spirit” according to the present invention, indicates a compound of light hydrocarbons derived from the fractional distillation of petroleum with a boiling range of 40-60°C. The term “Low Aromatic White Spirit (LAWS)” defines a mixture of light hydrocarbons with a distillation range of 150-205°C and a very low aromatic content (<5ppm).

The expression "fatty acids" in the present invention has the meaning commonly used in the state of the art and refers to molecules constituted by a chain of carbon atoms, called aliphatic chain, with a single carboxyl group (-COOH) at one end.

DETAILED DESCRIPTION

The present invention refers to a mixture comprising a combination of two surfactants, wherein said surfactants are:

A surfactant having formula (I),

wherein:

- X is an integer from 6 to 12;

-Y is an integer from 1 to 4;

-Z is H, CH₃ C₂H₅, C₃H₇ or C₄H₉, _;

-n is a number ranging from 2.5 to 10 or a salt thereof a surfactant having formula (II) and a molecular weight lower than 1000Da

wherein: n is an integer from 6 to 18, m is an integer from 1 to 3 wherein said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight percentage ratio ranging from 70:30 to 99:1.

Throughout the present invention, the average molecular weight of the surfactant is intended as the average molecular weight measured by the standard technique of gel permeation chromatography.

For example, protocol ASTM D6474 (Standard Test Method for Determining Molecular Weight Distribution and Molecular Weight Averages of Polyolefins by High- Temperature Gel Permeation Chromatography), ASTM D5296 ( Standard Test Method for Molecular Weight Averages and Molecular Weight Distribution of Polystyrene by High Performance Size Exclusion Chromatography) or ISO 13885-1 Protocol (Binders for Paints and Varnishes - Gel Permeation Chromatography (GPC) - Part 1 : Tetrahydrofuran (THF) as eluent).

As evident from the formula above, the surfactant of formula (II) is a non-ionic surfactant.

As evident from the formula above, the surfactant of formula (I) is non-ionic or anionic.

When the surfactant of formula (I) is non-ionic -Z is: CH₃, C₂H₅, C₃H₇ or C₄H₉; when it is anionic Z is H.

In the present description, since the ratios between the two surfactants are always indicated with respect to a total of 100, the terms weight ratio and weight percentage ratio are synonymous expressions.

Preferably, according to the present invention, X is 6, 8, 10 or 12, even more preferably X is 8.

Preferably, according to the present invention, n in the surfactant of formula (I) is from 3 to 7.

When the surfactant of formula (I) is a salt, said salt will preferably be an alkali metal salt or an organic salt. In particular, therefore, Z can be Na, K, Mg, NH4⁺’ amino group, preferably, Z is H, Na or K.

According to the invention, the surfactant salt of formula (I) can be a salt of organic or inorganic bases. Inorganic bases suitable for the formation of salts of the surfactant of formula (I) of the present invention include NH4⁺ and metal cations. A non-limiting example of suitable alkali metals is represented by K, Mg and Na.

Organic bases suitable for the formation of salts of the surfactant of formula (I) of the present invention include amines and amine derivatives.

In particular, therefore, Z can be Na, K, Mg, NH₄ ⁺' amino group, preferably, Z is H, Na or K. In a preferred embodiment of the invention, said surfactant or a salt thereof having formula (I) is ethoxylated carboxymethylated octan-1-ol and is 3 or 7; even more preferably n is 3.

In a further preferred embodiment of the invention, said surfactant salt having formula (I) is the sodium or potassium salt of ethoxylated carboxymethylated octan-1-ol.

Preferably, according to the present invention, in the surfactant of formula (II) having a molecular weight lower than 1000Da, n is 8, 10, 12, 14, 16, 18 and even more preferably n is 8.

As mentioned above, the two surfactants present in the mixture of the invention must have a well-defined reciprocal weight ratio in order to provide the desired technical effect. This weight ratio is between about 70% and 99% w/w of surfactant of formula (I), and about 30% and 1% w/w of said surfactant of formula (II) having a molecular weight lower than 1000Da, therefore a weight ratio of about 70:30 to about 99:1.

In some embodiments, said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da, are in a weight ratio ranging from 80:20 to 9.5:2.5 or from 80:20 to 95:5; or from 90:10 to 97.5:2.5 or from 90:10 to 95:5.

In a preferred embodiment said ratio is 95:5.

Therefore, a further object of the present invention is also a foaming agent comprising the mixture as defined in the present description and one or more solvents and/or additives.

According to the invention, said one or more solvents present in the aforementioned mixture can be water, alcohols, glycols, glycol ethers, or mixtures thereof, more preferably water and glycol ethers.

In one embodiment, said one or more additives may be selected trabiocides, demulsifiers, dispersants, scale inhibitors, corrosion inhibitors, sequestering agents, chelators or combinations thereof. The expert in the field will be able to select the most suitable additives among those commonly used in the sector.

According to the present invention, non-limiting examples of bioacids include quaternary ammonium salts, aldehydes, Tetrakis (hydroxymethyl) phosphonium sulfate (THPS); limiting examples of demulsifiers include alkoxylated resins, oxyethylene /propylene oxide polymers; non-limiting examples of scale inhibitors include phosphonates and polycarboxylates; non-limiting examples of corrosion inhibitors include imidazolines and fatty amines; non-limiting examples of sequestering agents include ethylenediaminetetraacetic acid, nitrilotriacetic acid, and tetrasodium glutamate di acetate.

In particular, corrosion inhibitors and scale inhibitors chosen between phosphonobutanetricarboxylic acid (PBTCA) and sodium hydroxide are excluded from the mixture of the invention.

According to a further embodiment, the mixture does not include scale inhibitors and/or corrosion inhibitors.

Depending on the solvents and/or additives used, the foaming agent of the invention can be in solid, liquid, gel, powder, granulate, paste, emulsion form.

The foaming agent disclosed in the present description is characterized by high biocompatibility and high foam generation and stability capabilities, characterized by the "Foam formation time" parameters (ability to generate a certain volume of foam in a given interval of time) and “Half-life of the foam time” (ability of the foam to resist beyond 50% of its volume without collapsing), and reported in Table 3. Furthermore, the foaming agent of the invention has the peculiarity of being usable in systems wherein requires high thermal stability, since it maintains its performance unchanged in terms of "Foam formation time" and "Foam half-life time" even when said mixture is exposed to a temperature of 130°C for more than 1 week.

Additionally, the foaming agent of the present invention has the ability to generate foam in gas wells where the hydrostatic column of liquid that has accumulated over time (whether composed of water alone, hydrocarbon alone, or a mixture of the two in any ratio) limits or completely blocks the production of gas towards the surface.

In a preferred embodiment, the foaming agent of the present invention is characterized by not comprising one or more of: sodium gluconate, EDTA-4Na chelate, hydroxyethylene diphosphonic acid (HEDB) chelate, corrosion inhibitors and scale inhibitors selected from phosphonobutanetricarboxylic acid (PBTCA) and sodium hydroxide.

Below are some examples of formulations of the foaming agents of the present invention.

Formulation example1:

In the formulation example reported above, the mixture of surfactants of formula (I) and (II) can be in any of the embodiments described in the present invention, i.e. their ratio must be within the ranges as described herein. Point examples are provided below but the invention is not limited to these point examples and covers any intermediate value between the extremes given in examples a to d below.

Formulation example 1a said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 70:30 to 99:1

Formulation example 1b said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 80:20 to 97.5:2.5;

Formulation example 1c said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio from 90:10 to 97.5:2.5

Formulation example 1d said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 92.5:7.5 to 97.5:2,5._Formulation example 1 and said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 70:30.

Formulation example 1f said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 99:1. Example of formulation 1g said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 80:20.

Example of formulation 1h said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000 Da are, respectively, in a weight ratio of 97.5:2.5;

Formulation example 1i said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 90:10.

Formulation example 1j said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 92.5:7.5.

Formulation example 2:

Formulation example 2a said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 70:30 to 99:1

Formulation example 2b said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 80:20 to 97.5:2.5;

Example of formulation 2c said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio from 90:10 to 97.5:2.5 Example of formulation 2d said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio from 92.5:7.5 to 97.5:2,5.

Formulation example 2 and said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 70:30.

Formulation example 2f said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 99:1.

Example of formulation 2g said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 80:20.

Formulation example 2h said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 97.5:2.5.

Formulation example 2 said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 90:10.

Formulation example 2j said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 92.5:7.5.

Formulation example 3:

In the formulation example reported above, the mixture of surfactants of formula (I) and

(II) can be in any of the embodiments described in the present invention, i.e. their ratio must be within the ranges as described herein. Point examples are provided below but the invention is not limited to these point examples and covers any intermediate value between the extremes given in examples a to d below. Example of formulation 3a said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 70:30 to 99:1

Formulation example 3b said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 80:20 to 97.5:2.5;

Example of formulation 3c said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio from 90:10 to 97.5:2.5

Example of formulation 3d said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio from 92.5:7.5 to 97.5:2,5.

Formulation example 3 and said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 70:30.

Formulation example 3f said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 99:1.

Example of formulation 3g said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 80:20.

Formulation example 3h said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 97.5:2.5.

Formulation example 3i said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 90:10.

Formulation example 3j said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 92.5:7.5.

Object of the present invention is also the use of a mixture according to any of the embodiments of the present invention, or of a foaming agent according to any of the embodiments of the present invention, in a method for the removal of the hydrostatic column of liquid accumulated in a well for gas extraction.

The invention also concerns a process for the removal of the hydrostatic column of liquid accumulated in a well for the extraction of gas or in the transport pipelines of said well, said process comprising one or more steps for introducing the foaming agent according to the present disclosure, wherein said foaming agent is batched or in continuous injected into said well to develop foam in the pipelines of said well.

In a preferred embodiment said well comprises a degassing separator.

In the process of throwing solid soap (soap sticks) it is impossible to precisely calculate a concentration of use of the foaming agent, as it is almost never possible to determine the quantity of liquids accumulated at the bottom of the well and furthermore, being rapid release, the concentration real is also dependent on the amount of soap actually dissolved. The dosages are calculated based on the engineering estimates of well construction, the amounts used usually range from a few kg to a few tens of kg.

In batch treatments in the annulus, concentrated solutions of foaming agents are pumped, with the aim of reaching the concentration functional to the development of foam as effectively as possible. The dosages used for the purpose of the present invention are between 4,000 and 10,000 ppm referring to the total volume of liquid to be treated. The expert in the sector is able to make an estimate of the quantity of liquid present in the well, therefore as "quantity of liquid to be treated” obviously means the estimated quantity of liquid present in the well. The surfactant solutions used, being generally between 30 and 70% as the sum of the total surfactants, are used in the present invention with a typical dosage of the active mixture around 1,000 - 7,000 ppm.

This treatment can be carried out whenever necessary.

In the continuous downhole injection technique (i.e. at the bottom of the well), through a capillary string consisting of a small diameter tube inserted inside the well production tube, the additives are more limited but the very long additive times allow the accumulation of large amounts of foaming agent. The additions are made based on the flow rates of the pumps available (of the order of 5 - 10 liters/h) and the correctness of the dosages can be verified by the increase in the production pressure of the well: the dosages, calculated as a ratio of liters added to the amounts of liquids produced, are for the purpose of the present invention of the order of 5 - 20 ppm of solution (2 - 10 ppm of total surfactant). Thus, according to different embodiments of the process, the invention concerns a process for the removal of a hydrostatic column of liquid accumulated in a well for gas extraction or in the transport pipelines of said well, wherein said foaming agent, is introduced in batches into said well, in an amount of 4000 to 7000 ppm of foaming agent per volume of total liquid to be treated, or in quantities of total surfactants of 1000 to 7000 ppm, or, alternatively, wherein said foaming agent, is in continuous injected into said well, with a dosage of 5 to 20 ppm of foaming agent per volume of total liquid to be treated.

In continuous treatment, the expert in the field will carry out the treatment as indicated above by calculating the total volume to be treated, initially on the estimate of the amount of liquid present in the well, subsequently adjusting the calculation, and therefore the dosage to be used, also taking into account the quantity of liquid produced (leaked) from the well.

In any point of this description and the claims the term "comprising" can be replaced by the term "consisting of' or "consisting of".

EXAMPLES

The average molecular weight of all tested samples was measured by gel permeation chromatography, preferably by ASTM D6474 (Standard Test Method for Determining Molecular Weight Distribution and Molecular Weight Averages of Polyolefins by Gel Permeation Chromatography high temperature), ASTM D5296 (Standard Test Method for Molecular Weight Averages and Molecular Weight Distribution of Polystyrene by High Performance Size Exclusion Chromatography) or the ISO 13885-1 protocol (Binders for Paints and Varnishes - Chromatography at gel permeation (GPC) - Part 1 : Tetrahydrofuran (THF) as eluent).

The evaluation tests most used for the efficiency of foaming agents classify the product according to its ability to generate a certain foam volume in a given time interval (Foam formation time), and the ability of the foam to resist without collapsing more than 50% of its volume (Foam half-life).

Laboratory tests are conducted to verify the response of the foaming product in plant conditions but, as these are sometimes prohibitive for the equipment to be adopted, we refer to standard procedures shared with O&G operators, such as the one shown below, in accordance with ASTM D892.

Foaming agent preparation procedure The preparation of the foaming agent used in the experiments reported below was carried out by dissolving the two surfactants of formula I and II indicated in the tables below, in the appropriate solvents and, in the case of the surfactant of formula I reported in the tables, salification and neutralization was carried out until neutral pH.

A solution of surfactant of formula I in water/glycol or water/glycol ether solvent was then prepared and added to a caustic solution (KOH 50%) until complete neutralization; to this solution a quantity of an aqueous solution of the surfactant of formula II was added.

As an example, the concentrations of the final mixture relating to the ratio 95:5 Surfactant I: Surfactant II are reported

50% surfactant formula I

2.5% surfactant formula II

- KOH 7.5 %

Glycol ether 24.5%

Water 15.5

The final solution has a pH value of 7.0 +/- 1.0

200 ml of test liquids were transferred into a 1000 ml graduated cylinder (h = +/- 450 mm, 0 = 60 mm) and heated to 90°C. This includes at least 10ml of hydrocarbon condensate (but may change if specific to well testing). The foam product is added after the fluids are warmed up and just before the tests begin shake briefly to mix and ensure that all the foam product is in the test fluids.

The efficiency comparison tests were carried out by keeping the total concentration of the two surfactants fixed in the solution with which the additions were made, varying the ratio between them case by case. The pH of the solutions was adjusted up to the neutralization value by modulating the amount of KOH necessary from time to time.

The standard tests were performed with two levels of product dosage, intended as a final formulation containing the two surfactants at a fixed concentration. The dosages were: 1000 ppmv for the tests with water alone, 10,000 ppmv if 5% hydrocarbon was present (hydrocarbons strongly depress the effectiveness of foaming agents).

A P2 sintered glass nitrogen diffuser (pore size = 40 -100 mm), with a flow rate of 50 L/hour, is inserted into the graduated cylinder. The height reached in the column after 2 minutes of bubbling or the time taken to fill the column to the 1000 ml mark is noted, referred to as the “foaming time”. Then the gas flow is removed and the time it takes for the foam column to collapse by 50% is noted ((1000-200): 2 = 600ml marker considering the liquid volume of 200ml), this is noted as “ foam half-life”. Possibly, after complete collapse, observations regarding the foam-water-condensate mixture can be noted regarding emulsions, solids and water/condensate appearance.

Since it is not possible to simulate dosages over time or in continuous in the laboratory, the indicated dosage is applied in shock, in a single addition carried out on 200 ml of test fluids.

As shown in the following table, the performance indicators are divided into: Poor, Moderate and Good.

Times are indicated in seconds (s).

As is easy to imagine, the best product is the one classified as "Good" both in terms of foam generation time and blast chilling time. For each individual product, these tests are repeated on the fresh chemical product and after thermal aging, for example at 130°C for 1 week. The results of the tests above for times greater than 120” (in the case of Foaming Time) are not monitored and therefore the limit value is reported.

Different test liquids were tested resulting from different types of water reported in the table below or from the possible water/ hydrocarbon combinations given by 3 types of water (low, medium and high salinity) and 2 of hydrocarbon (petroleum spirit and low aromatic white spirit) were in order to reproduce real application scenarios which see the alternation of different types of fluids in gas wells.

Types of water:

• Phases Water with different salinity

The pH was 4.5 for each Water phase indicated in the table above.

Types of hydrocarbon:

• Hydrocarbon phases with different characteristics

LAB TEST

Taking into account the class of non-ionic surfactants, as alkyl glucoside derivatives (including formula II surfactants), which potentially represents the most suitable class for this type of applications given the high eco-compatibility and thermal stability, we report Below are the results of the performance tests of two types as examples.

The tests in the following table are conducted with the Medium Salinity Water phase and with 5% LAWS as hydrocarbon.

In light of the table above, a non-ionic surfactant product that reflects the requirements of eco-compatibility and thermal stability does not always perform well in the test conditions, and is therefore not chosen in field applications.

Always analyzing the same type of surfactants, considering for example the esters of ethoxylated and methylated fatty acids (which include the formula I surfactants), the latter are excellent foaming agents and have been the subject of laboratory tests.

Below are the results using the fresh and thermally aged product at 130°C for 1 week, in the presence of only medium salinity water.

Furthermore, given that usually in gas well systems there is always present, in addition to the formation water, also a certain presence of light hydrocarbon (also called "condensate"), the same surfactant was tested in the presence of a certain percentage of condensate.

Below are the results obtained considering 5% of LAWS hydrocarbon together with medium salinity production water.

In light of these results, this class of compounds also cannot be used in applications where the product must guarantee high performance in the presence of condensate and when subjected to thermal stress.

During laboratory tests, the study of the combination of the products reported above meant that completely unexpected and more performing results were surprisingly obtained than the substances taken individually. However, it has emerged that the combination must be subject to a certain relative ratio between the substances which cannot be exceeded otherwise the performance becomes poor.

In fact, if looking at the table below, it can be seen how the ratio between the two components has an optimal value beyond which, towards one substance or another, the effects are worsening.

Below are the general results of the efficiency tests considering medium salinity water with the presence of 5% LAWS hydrocarbon.

Surprisingly, the authors of the invention verified that the same performances are maintained even after thermal aging of the mixtures in the same ratios, at 130°C for at least 1 week.

Therefore, the synergistic effect between the active ingredients is of an exclusive nature as the properties of the mixture are not the sum of the individual substances, but in a given ratio they have a chemical interaction such that the lamellae of foam formed by the ester of methylated ethoxylated fatty acid, which would collapse given the presence of hydrocarbon, are stabilized by the alkyl glucoside which therefore manages to give body and structure to the foam.

Below are the results of the foam formation capacity tests in test liquids prepared considering the types of fluids reported above, testing as an example the products in the following ratios of the individual substances, to emphasize the synergy between the active ingredients, thus named:

The performance results are reported by dividing them by water salinity, considering an exemplary dosage of 10,000 ppm of product for each single test.

Performance with low salinity water and 5% hydrocarbon

Performance with medium salinity water and 5% hydrocarbon

Performance with high salinity water and 5% hydrocarbon

The results reported above demonstrate that the components in play have a synergistic effect that performs its optimal function around a particular ratio, i.e. 95:5. In fact, for example, by taking the ratio to extremes in the opposite way, as done for "Product 4", the ability to generate foam collapses to insufficient values.

Since the medium salinity tests are the most representative of possible application scenarios, they were repeated using different surfactants with formula (I) and (II) compared to those used in the examples above.

Taking the 95:5 weight percentage ratio as a reference, the following products were tested by varying the chemicals involved. In one or both compounds the n value was varied.

Below are the foaming tests carried out on medium salinity water with 5% hydrocarbon.

Performance with medium salinity water and 5% hydrocarbon

The results reported above demonstrate that different surfactants having formula (I) and (II) and their different combinations, mixed according to the claimed weight percentages, maintain the synergistic effect reported in this description and always manage to obtain a rating between Good and Moderate, therefore considered satisfactory for the solution of the technical problem.

Claims

1. A mixture comprising a combination of two surfactants, wherein said surfactants are:

- A surfactant having formuia (I),

wherein:

- X is an integer from 6 to 12;

-Y is an integer from 1 to 4;

-Z is H, CH₃. C₂H₅, C₃H₇or C₄H₉;

-n is a number ranging from 2,5 to 10 or a salt thereof; a surfactant having formula (II) and a molecular weight lower than 1000Da

wherein: n is an integer from 6 to 18, m is an integer from 1 to 3. wherein said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio ranging from 70:30 to 99:1.

2. The mixture according to claim 1, wherein, in said surfactant of formula (I) X is 6, 8, 10 or 12, preferably 8.

3. The mixture according to claim 1 or 2, wherein, in said surfactant of formula (I) n is from 3 to 7.

4. The mixture according to any one of claims 1 to 3 wherein in said surfactant of formula (I) Z is Na, K, Mg, NH ₄ ⁺.

5. The mixture according to any one of claims 1 to 4 wherein said surfactant of formula (I) is carboxymethyiated ethoxylated octan-1-ol n being 3 or 7, or a sodium or potassium salt of ethoxylated carboxymethylated octan-1-ol.

6. The mixture according to any one of claims 1 to 5 wherein in said surfactant of formula (II) having a molecular weight less than 1000Da n is 8, 10 or 12.

7. The mixture according to any one of claims 1 to 6 wherein in said surfactant of formula (II) having a molecular weight of less than 1000Da m is 1.

8. The mixture according to any of claims 1 to 7, wherein said surfactant of formula (I), and said surfactant of formula (II) having a molecular weight lower than 1000Da are, respectively, in a weight ratio of 70:30 to 99:1 or from 80:20 to 97,5:2,5; or from 90:10 to 97,5:2,5 or from 92,5:7,5 to 97,5:2,5.

9. A foaming agent comprising the mixture according to any one of claims 1 to 8 and one or more solvents and/or additives.

10. The foaming agent according to claim 9 wherein said one or more additives are selected from biocides, demulsifiers, dispersants, scale inhibitors, corrosion inhibitors, sequestrants, chelators or combinations thereof.

11. The foaming agent according to claim 10, wherein said solvents are water, alcohols, glycols, glycol ethers, or mixtures thereof.

12. The foaming agent according to any of claims 9 to 11, in solid, liquid, gel, powder, granulate, paste, emulsion form.

13. Use of a foaming agent as defined in any of claims 9 to 12 for the removal of a hydrostatic column of liquid accumulated in a gas extraction well.

14. A process for the removal of a hydrostatic column of liquid accumulated in a gas extraction well or in the transport pipelines of said well, said process comprising one or more steps for introducing the foaming agent as defined in any of claims 9 to 11 in said well and/or in said transport pipelines wherein said foaming agent is introduced in batches, or in continuous, or by throwing foaming agent in solid form into said well, so as to obtain the development of foam in said well and/or in its pipelines.

15. The process according to claim 14 wherein said foaming agent is introduced in batches into said well, in an amount of from 4000 to 7000 ppm of foaming agent per volume of total liquid to be treated or in amounts of total surfactants from 1000 to 7000 ppm.

16. The process according to claim 14 wherein said foaming agent is introduced in continuous into said well, with a dosage of 5 to 20 ppm of foaming agent per volume of total liquid treated.