WO2016156559A1

WO2016156559A1 - Clay stabilizing compositions and use of said compositions for stabilizing water sensitive formations

Info

Publication number: WO2016156559A1
Application number: PCT/EP2016/057191
Authority: WO
Inventors: Robin MATTON; Kristof Moonen; Peter Roose
Original assignee: Taminco BV
Current assignee: Taminco BV
Priority date: 2015-04-01
Filing date: 2016-04-01
Publication date: 2016-10-06
Anticipated expiration: 2017-10-01

Abstract

The present invention provides a clay stabilizing composition comprising a compound according to formula (I) and water, whereby R₁, R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R₁, R₂, R₃, R₄ is alkyl; whereby R₅, R₆, R₇ are independently selected from H, alkyl; and whereby X" comprises an anion. In addition, the present invention provides a method for controlling clay stability properties by contacting a clay stabilizing composition comprising a compound according to formula (I) and water with at least a part of a wellbore.

Description

CLAY STABI LI Zl NG COMPOSI Tl ONS AND USE OF SAI D COMPOSI Tl ONS FOR STABI LI Zl NG WATER SENSI Tl VE FORMATI ONS

TECHNICAL FIELD

This invention concerns the use of certain amines as a means of controlling clay stability, e.g. in water based drilling fluids, completion fluids, workover fluids or stimulation fluids. More specifically, it relates to the use of derivatives of choline salts as clay swelling inhibitors and/or stimulation agents.

INTRODUCTION

Drilling fluids are used to facilitate the drilling of oil and gas wells. During drilling, the drilling fluid (often called "drilling mud" or simply "mud") is pumped down the hollow drill string, discharged through nozzles in the drill bit and returned to the surface via the annular space between the drill pipe and the surrounding formation. The drilling fluid is required to perform a number of functions to ensure that a well is drilled with few problems and at an acceptable cost. These functions include:

- cooling and lubricating the drill bit,

- lubricating the drill pipe,

- removing rock cuttings that are generated by the drill bit and transporting them from the well,

- suspending cuttings and other solid materials when mud circulation is stopped, - exerting sufficient hydrostatic pressure on the formation to prevent the rock from collapsing and to prevent formation fluids contained in the rock from entering the wellbore,

- formation of a low permeability filter cake that protects the formations from the ingress of whole drilling fluid or drilling fluid filtrate and,

- ensuring that any reaction between the drilling fluid and swelling clay minerals that are present in some formations is kept to a level that does not compromise wellbore stability.

Such drilling fluids generally comprise a carrier fluid, a weighting/densifiying agent and chemical additives. The carrier fluid can be water, oil, air, foam or a water mist. The most common types of drilling fluids comprise water or oil as the carrier fluid. Water based muds are often abbreviated to WBM. When considering amine-based shale inhibitors, several classes of molecules have been used in WBM. A useful reference is a paper published through the Society of Petroleum Engineers (SPE) by A. D. Patel: SPE 121737 "Design and Development of Quaternary Amine Compounds: Shale Inhibition With Improved Environmental Profile." While this list of molecules is not exhaustive, it gives an indication of the diversity of amine chemistry that has been proposed for the purpose of providing shale inhibition in WBM.

Such inhibitors are known from the state of the art. For example, US 5,380,706 describes improved well drilling fluids and methods which prevent damage to water sensitive formations while drilling. The drilling fluids include a formation stabilizing compound which contains an organic quaternary ammonium cation and an inorganic, organic or combination anion. The formation stabilizing compounds in the drilling fluids reported in US 5,380,706 are comprised in the solutions in an amount of 0.1 to 0.5 wt.%.

The application of choline compounds is also known, e.g. from US 2012/118645. In such technologies, clay is stabilized in methods for drilling of wells and other formation treatment for hydrocarbon production by the addition to the drilling or other fluid of a choline compound together with a formation control additive.

While some of these materials are good shale inhibitors, they may fail in terms of commercial viability or because they do not satisfy health, safety and environmental (HSE) criteria. Others may be acceptable in HSE terms but may not be effective shale inhibitors, or may be incompatible with other commonly used mud additives. Still other inhibitors provide acceptable stabilizing activity but do not maintain high performance of the drilling fluid over multiple runs. Very few of these amines satisfy all the requirements necessary to provide a practical inhibitive WBM.

Hydraulic fracturing is performed by injecting high pressure fluids, also known as stimulation fluids and typically comprised of 99 wt.% or more of water and sand and less than 1 wt.% of additives, into the wellbore and into the perforation tunnels to cause the rock formation to fracture. This can either be done by injecting hydraulic fluid from surface, a process called hydraulic fracturing or using an explosive to generate a high speed gas flow, a process called propellant stimulation. Additives are comprised in the stimulation fluids to manage the properties of the formation, i.e. stability of the formation. Such drilling or hydraulic fracturing fluids are reused at the site. It is commonly experienced that a certain 'exhaustion' of the fluid occurs, requiring On site' adjustment of the formulation of the fluid to maintain excellent stabilizing potential. One object of the invention is to provide a drilling or hydraulic fracturing fluid which is able to maintain a high and stable stabilizing activity over a prolonged processing period.

Another object of the present invention is to provide aqueous compositions for use as water based drilling fluids, comprising one or more clay stability control agents which exhibit excellent shale inhibiting properties and comply with health, safety and environmental criteria. In addition, it is an object of the invention to provide aqueous hydraulic fracturing fluids, completion fluids and workover fluids where there is a need to control subterranean formations containing swelling clays.

Also, the invention aims to provide solutions to improve wellbore stability, avoid deterioration of drilling fluid properties and avoid interruptions of the drilling process, all of which can add to the cost and duration of the drilling process. SUMMARY OF THE I NVENTI ON

The current invention provides in a solution for at least one of the above mentioned problems by providing clay stabilizing compositions and use of said compositions for stabilizing water sensitive formations, as described in claims 1 and 15.

In a first aspect, the present invention provides a clay stabilizing composition comprising a compound according to formula (I) and water, formula (I)

whereby R_1: R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R R₂, R₃, R₄ is alkyl; whereby R₅, R₆, R7 are independently selected from H, alkyl; and whereby X^" comprises an anion.

The inventors have discovered that by providing a drilling fluid comprising selected salts according to formula (I), the shale inhibiting performance of the cation can be significantly increased compared to the performance seen with a simple choline cation, while maintaining the HSE acceptability, low human toxicity, compatibility with common water based mud additives and cost-effectiveness. Clays are better and more rapidly stabilized when contacted with compositions according to the invention.

In a second aspect, the present invention provides a method for controlling clay stability properties by contacting a clay stabilizing composition comprising a compound according to formula (I) and water with at least a part of a wellbore, formula (I)

whereby R_1: R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R_1: R₂, R₃, R₄ is alkyl; whereby R₅, R₆, R7 are independently selected from H, alkyl; and whereby X^" comprises an anion.

This is of interest because clay stability properties are thereby improved during, for example, drilling operations. Improved clay stability in turn offers better process stability during the drilling operation.

In a third aspect, the present invention provides a use of a clay stabilizing composition according to the first aspect of the invention for treating a water sensitive formation.

DESCRIPTION OF THE FIGURES

By means of further guidance, figures are included to better appreciate the teaching of the present invention. Said figures are intended to assist the description of the invention and are nowhere intended as a limitation of the presently disclosed invention.

Figure 1 shows the stabilizing potential of a clay stabilizing fluid comprising 3.0 wt.% choline chloride, methyl choline chloride and ethyl choline chloride, respectively, wherein the stabilizing potential of the fluid in a subsequent run (reuse) is expressed as a percentage of the clay stabilizing potential of the freshly formulated clay stabilizing fluid. In each subsequent run, the fluid was separated from the clay and exposed to fresh clay cuttings. DETAI LED DESCRI PTI ON OF THE I NVENTI ON

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

As used herein, the following terms have the following meanings:

"A", "an", and "the" as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more than one compartment. "About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + /-20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-1% or less, and still more preferably +/-0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

"Comprise," "comprising," and "comprises" and "comprised of" as used herein are synonymous with "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open-ended terms that specifies the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, element, members, steps, known in the art or disclosed therein. The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints. All percentages are to be understood as percentage by weight and are abbreviated as "%wt.", unless otherwise defined or unless a different meaning is obvious to the person skilled in the art from its use and in the context wherein it is used.

The current invention provides in a solution for at least one of the above mentioned problems by providing a clay stabilizing composition, as described in claim 1. The term "clay stabilizing composition" is to be understood as comprising the terms "drilling fluid," "completion fluid," "workover fluid," "stimulation fluid," "hydraulic fracturing fluid" and refers to an aqueous composition comprising a clay stabilizing compound.

The term "drilling fluid" is to be understood as synonymous to the terms "completion fluid" and "workover fluid," and refers to an aqueous clay stabilizing composition comprising at least one clay stabilizing compound and one or more drilling fluid additives, such as but not limited to, osmotic agents, density control agents, viscosity control agents, dispersants, fluid loss control agents, pH control agents, bactericides, lubricants, stabilizers and corrosion control agents.

The term "hydraulic fracturing fluid" is to be understood as synonymous to the term "stimulation fluid" and refers to a composition comprised of 99 wt.% or more of water and sand and less than 1 wt.% of stimulation additives, such as but not limited to, alcohols (i.e. ethylene glycol, isopropanol) , acids (i.e. citric acid), osmotic agents (salts, i.e. sodium chloride, potassium chloride), viscosity control agents, thickening agents (i.e. guar gum), lubricants, fluid loss control agents, deoxygenating agents (i.e. ammonium bisulfite), proppants, bactericides (i.e. glutaraldehyde), stabilizers and corrosion inhibiting agents (i.e. N,N- dimethylformam ide) .

The term "clay stabilizing compound" is to be understood as synonymous to the terms "shale inhibitor", "clay swelling inhibitor", "shale control agent", "inhibition agent", "clay stabilizer", and refers to a compound suitable for controlling swelling properties of clay or more generally of clay containing formations, such as clay- rich rock formations or shales. In the context of the present invention, the term " alky I choline homologue" refers to a compound according to formula (I), formula (I)

whereby R_1: R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R_1: R₂, R₃, R₄ is alkyl;

whereby R₅, R₆, R₇ are independently selected from H, alkyl; and whereby X^" comprises an anion.

More preferably, the term " alky I choline homologue" refers to a compound according to formula (I),

whereby is methyl or ethyl and R₂, R₃, R₄ are H or methyl;

whereby R₅, R₆, R7 are methyl or ethyl; and

whereby X^" comprises an anion.

Most preferably, the term " alky I choline homologue" refers to a methyl choline salt according to formula (I) ,

whereby is methyl and R₂, R₃, R₄ are H;

whereby R₅, R₆, R₇ are methyl; and

whereby X^" comprises an anion. The term " alky I choline salt" refers to 2-hydroxy-/V,/V,/V-trimethylalkan-1 -aminium salts, whereby the carbon main chain comprises at least three carbon atoms, and preferably comprises three, four, five or six carbon atoms.

The term "water" refers to fresh water, seawater, brine or saturated sodium chloride. Said brine can comprise various types of brine selected from the group comprising seawater, potassium chloride, sodium chloride, sodium formate, calcium chloride, potassium formate, sodium bromide, calcium bromide, zinc bromide and caesium formate.

whereby R_1: R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R R₂, R₃, R₄ is alkyl; whereby R₅, R₆, R7 are independently selected from H, alkyl; and whereby X^" comprises an anion. More preferably, at least one of Ri, R₂, R₃, R₄ is alkyl and at least two of, and preferably three of, R_1: R₂, R₃, R₄ is hydrogen. Preferably, said alkyl is methyl or ethyl, most preferably ethyl.

The inventors have discovered that by providing a clay stabilizing composition comprising selected salts according to formula (I), the shale inhibiting performance of the cation can be significantly increased compared to the performance seen with a simple choline cation, while maintaining the HSE acceptability, low human toxicity, compatibility with common water based mud additives and cost-effectiveness. Also, the inventors have found that such clay stabilizing compositions maintain good stabilizing properties even when exposed to fresh amounts of clay over a prolonged period.

This is advantageous, because said composition results in a rapid and significant enhancement of the stability of a clay with which it is contacted and consequently promotes improved wellbore stability during the drilling, completion or workover operation and process stability and/or during stimulation of the wellbore, without compromising health, safety or environment.

In one embodiment, said clay stabilizing composition according to the first aspect of the invention comprises a drilling fluid comprising a compound according to formula (I) and water, whereby said compound according to formula (I) is comprised in said composition in an amount of at least 0.1 wt.%, relative to the total weight of said clay stabilizing composition, preferably at least 0.5 wt.%, more preferably at least 0.6 wt.%, 0.7 wt.%, 0.8 wt.% or 0.9 wt.%, and most preferably at least 1.0 wt.%.

It was found said clay stabilizing compositions comprising a compound according to formula (I) in an amount of 0.1 wt.% to 1.0 wt.% provide clay stabilizing properties and can be usefully employed as clay stabilizing compounds within the meaning of the current invention, albeit with lower efficiency compared to similar compositions with higher concentrations of alkyl choline compound. Therefore, concentrations of at least 1 wt.% are preferred. Significantly enhanced stabilizing capacity was observed for clay stabilizing compositions with 1.00 wt.% of alkyl choline homologue, and more so with 1.20 wt.%, 1.40 wt.%, 1.60 wt.%, 1.80 wt.%, 2.00 wt.%, 2.20 wt.%, 2.40 wt.%, 2.60 wt.%, 2.80 wt.% and 3.00 wt.% of alkyl choline homologue, respectively, or any values there in between. Thus, satisfactory stabilization properties were obtained with clay stabilizing compositions comprising at least 1 wt.% alkyl choline homologue in water, relative to the total weight of said clay stabilizing composition.

In a second embodiment, said clay stabilizing composition according to the first aspect of the invention comprises a stimulation fluid, also known as a hydraulic tracking fluid, comprising a compound according to formula (I) and water, whereby said compound according to formula (I) is comprised in said composition in an amount of at least 0.01 wt.%, relative to the total weight of said clay stabilizing composition, preferably at least 0.05 wt.%, more preferably at least 0.06 wt.%, 0.07 wt.%, 0.08 wt.% or 0.09 wt.%, and most preferably at least 0.10 wt.%.

It was found that said stimulation fluids comprising a compound according to formula (I) in an amount of at least 0.01 wt.%, relative to the total weight of said clay stabilizing composition, provide beneficial stimulation properties. Concentrations of at least 0.10 wt.% are preferred. Enhanced stimulation capacity was observed for clay stabilizing compositions with 0.10 wt.% of alkyl choline homologue, and more so with 0.15 wt.%, 0.20 wt.%, 0.25 wt.%, 0.30 wt.%, 0.35 wt.%, 0.40 wt.%, 0.45 wt.%, 0.50 wt.%, 0.55 wt.% and 0.60 wt.% of alkyl choline homologue, respectively, or any values there in between.

In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said alkyl is selected from the group consisting of methyl, ethyl, propyl and butyl, and more preferably selected from the group consisting of methyl and ethyl.

It was found that choline derivatives comprising an alkyl group exhibit better clay stabilizing properties compared to analogous choline compounds without said alkyl group. Although various alkyl groups are suitable, methyl, ethyl, propyl and butyl groups provide excellent stabilizing properties while the alkyl choline homologue is easily obtainable from reaction of the corresponding epoxide with the acidic form of trialkylamine.

In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said alkyl choline homologue comprises methyl choline salt. Methyl choline salts are easily obtainable by reacting trimethylamine with an acid, e.g. hydrochloric acid or water, and reaction with propylene oxide. Alternatively, trimethylamine is reacted with propylene oxide and subsequently reacted with an acid, such as i.e. hydrochloric acid or water. As such, atom-efficient routes are available to obtain highly active clay stabilizer compounds. In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said alkyl comprises a linear alkyl. In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said alkyl choline homologue comprises an anion selected from the group comprising halides, bicarbonate, carboxylates, nitrite, nitrate, sulfite, sulfate, phosphite, phosphate.

Suitable halide anions comprise fluoride, chloride, bromide and iodide. Suitable carboxylate anions comprise formate, acetate, hydroxyacetate, lactate, citrate and benzoate. Alternatively, hydroxide can beneficially be used as the anion. Other inorganic, organic or combination anions can be utilized so long as they are compatible with the various components of the clay stabilizing composition, the drilling fluid, and with the subterranean formations to be contacted therewith. With respect to inorganic anions, use of chloride is preferred, or when its application cannot be tolerated, use of nitrate is preferred. In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said clay stabilizing composition comprises a drilling fluid and whereby said alkyl choline homologue is comprised in an amount of 1 wt.% to 5 wt.%, relative to the total weight of said clay stabilizing composition.

It has been shown that drilling fluids comprising at least 1 wt.% of said alkyl choline homologue, relative to the total weight of said clay stabilizing composition, show significantly enhanced clay stabilizing activity. Higher amounts of alkyl choline homologue prove to further enhance the clay stabilizing properties of the composition. As such, compositions comprising 50 wt.%, 40 wt.%, 30 wt.%, 20 wt.%, 15 wt.%, 10 wt.% or 5 wt.%, relative to the total weight of said clay stabilizing composition, can usefully be employed as clay stabilizing compositions. However, for reasons of economy, concentrations of said alkyl choline homologue in said clay stabilizing composition are preferably below 15 wt.%, and more preferably below 10 wt.%, and even more preferably below 5 wt.%, relative to the total weight of said clay stabilizing composition. In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said clay stabilizing composition comprises a drilling fluid and whereby said alkyl choline homologue is comprised in an amount of 1.5 wt.% to 3.0 wt.%, relative to the total weight of said clay stabilizing composition.

With regard to the optimal use of alkyl choline homologue in a drilling fluid, concentrations of 1.50 wt.% of alkyl choline homologue, and more so of 1.60 wt.%, 1.80 wt.%, 2.00 wt.%, 2.20 wt.%, 2.40 wt.%, 2.60 wt.%, 2.80 wt.% and 3.00 wt.% of said alkyl choline homologue, relative to the total weight of said clay stabilizing composition, are preferred due to enhanced clay stabilizing activity. Higher amounts of alkyl choline homologue, such as 2.5 wt.%, 3.5 wt.%, 4.0 wt.%, 4.5 wt.%, 5.0 wt.%, prove to further enhance the clay stabilizing properties of the composition. For reasons of economy, concentrations of said alkyl choline homologue in said clay stabilizing composition are preferably below 3.0 wt.%, more preferably below 2.5 wt.% and more preferably below 2.0 wt.%, relative to the total weight of said clay stabilizing composition.

In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said composition comprises a drilling fluid and whereby said composition comprises a pH between 7 and 13, and more preferably between 8 and 12. Said pH can be obtained by adding a pH control agent such as bases to said composition. E.g., sodium or potassium hydroxides can be added in measured amounts to obtain a composition with pH between 7 and 13. Said basicity is required to obtain a composition suitable for operation within the operational window of the drilling activities. Preferably, a buffer composition with stable pH window between 7 and 13 is used. Suitable buffers are, but not limited, carbonate buffers, ammonium buffers, borate buffers and phosphate buffers.

In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, whereby said composition comprises a drilling fluid and whereby said compositions comprises a pH between 9 and 11, and more preferably equal to about 10. Accordingly, an optimal basicity for the clay stabilizing composition is obtained. Said basicity may be obtained by mixing bases such as hydroxides with said clay stabilizing composition, or by use of buffers. In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, further comprising a viscosity control agent. Preferably, said viscosity control agents are selected from the group comprising bentonite (or other clays), biopolymers, carboxymethyl cellulose, polyanionic cellulose, guar gum (polysaccharide) and synthetic polymers. Bentonite or other clays are also employed as fluid loss control agent. Biopolymers, starch, carboxymethyl cellulose and polyanionic cellulose may be used for fluid loss control. Biopolymers and polyanionic cellulose may be used for fluid friction reduction.

In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, further comprising one or more drilling fluid additives, such as but not limited to, osmotic agents, density control agents, dispersants, fluid loss control agents and pH control agents.

Preferably, said osmotic agents are selected from the group comprising CaCI₂, KCI, ZnBr₂/CaBr₂ and formates. CaCI₂ can be employed for well control and formation stability. KCI can be employed for formation stability. ZnBr₂/CaBr₂ is generally employed as additive to the completion fluid. Formates are employed during drilling and completion operations.

Preferably, said density control agents are selected from the group comprising barite (barium sulphate), calcium carbonate, iron carbonate, hematite and ilmenite. Calcium carbonate can also be employed as a bridging or plugging agent.

Preferably, said dispersants are selected from the group comprising modified polyacrylates, lignosulphonates and tannins.

Preferably, said fluid loss control agents are selected from the group comprising synthetic polymers, carboxymethyl cellulose, polyanionic cellulose, starches such as pregelatonized corn starch, potato starch, carboxymethyl starch and mixtures thereof, bentonite, modified lignites, asphalt, resins or gilsonite. Synthetic polymers, carboxymethyl cellulose and polyanionic cellulose can also be employed as a viscosity control agent. Carboxymethyl cellulose and polyanionic cellulose may also be employed for hole cleaning. Polyanionic cellulose and resins may also be employed for shale stabilization. Preferably, said pH control agents are selected from the group comprising NaOH/KOH, Ca(OH)₂, citric acid and NaHC0₃. NaHC0₃ can also be employed for sequestering calcium ions. In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, further comprising one or more drilling fluid additives, such as bactericides, lubricants, stabilizers and corrosion control agents. Said bactericides are employed to control or prevent bacterial development. Lubricants are employed for both enhancing the lubricity of metal-metal and metal-formation contact. Polymer stabilizers are employed for stabilization of polymer compounds towards extremely high temperatures, salts and specific chemicals concentrations and bacteria. Corrosion control agents such as oxygen scavengers or filming agents are used for various specific working conditions.

In a preferred embodiment, the present invention provides a clay stabilizing composition according to the first aspect of the invention, further comprising a composition stabilizer. The clay stabilizing solution may itself be stabilized using any suitable stabilizers known in the art, for example, for the purpose of preventing colour formation and preserving the overall quality of the product. As used herein, the terms "composition stabilizer" is intended to encompass a choline solution according to the invention that undergoes minimal or no degradation reactions that would otherwise deteriorate the quality of the choline solution according to the invention. In other words, there is reduced or no development of heavy/dark colour, formation of precipitates, volatility, a strong smell, etc. Instead, the stabilized choline solution according to the invention may maintain a clear or slightly off-colour (e.g., APHA of less than 500, as determined by ASTM D1209) appearance for an extended period of time (e.g., at least one week, more preferably at least one month, most at least three months) at room temperature (e.g., about 20 to 25°C) under standard conditions. Any suitable stabilizer may be used, including but are not limited to, dithionite salts (e.g., an alkali metal dithionite), amines (e.g., dialkylhydroxylamines), sulfites, hydroquinones, hydrides, carboxylic acids, piperazines, etc. For example, the stabilizer may comprise sodium dithionite, Ν,Ν-diethylhydroxylamine, ethylenediaminetetraacetic acid (EDTA), methoxyhydroquinone (MEHQ), tetramethylpiperazine-N-oxide (TEMPO), diethylenetriamine (DETA), benzaldehyde, sodium sulfite, boric acid, tetraethylenetriamine (TETA), sodium borohydride, butylated hydroxyanisole, sodium metabisulfite, ascorbic acid, thiourea, and mixtures thereof. The stabilizer may be added in any suitable form, e.g., powder, aqueous solution, emulsion, or in any form convenient for solubilizing or suspending said stabilizer in an aqueous solution.

In addition to the shale inhibitor component in said clay stabilizing composition according to the first aspect of the invention, said clay stabilizing composition may further comprise at least one shale inhibitor known in the state of the art, such as but not limited to, salts (e.g. KCI), glycols and/or polyglycols, silicate, gypsum, (partially hydrolysed) polyacrylam ides, modified PAC and others. Salts are known to act as shale control and stability agents. Polyacrylamides and modified PAC further assist filter cake formation.

whereby R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R_1: R₂, R₃, R₄ is alkyl; whereby R₅, R₆, R₇ are independently selected from H, alkyl; and whereby X^" comprises an anion. More preferably, at least one of R R₂, R₃, R₄ is alkyl and at least two of, and preferably three of, R_1: R₂, R₃, R₄ is hydrogen. Preferably, said alkyl is methyl or ethyl, most preferably ethyl.

This is of interest because said composition provides no or low health, safety or environmentally hazardous effects, while stability of clay, and thus of the drilled formation, are improved during e.g. drilling operations. Improved clay stability in turn offers better process stability during the drilling operation.

In one embodiment, the invention provides a method according to the second aspect of the invention, whereby said method for controlling clay stability properties by drilling into or through a formation by drilling into or through a formation, thereby creating a well and contacting at least a part of the wellbore with a clay stabilizing composition according to the first aspect of the invention, i.e. a drilling fluid, comprising a compound according to formula (I) and water. Preferably, said compound according to formula (I) is comprised in said composition in an amount of at least 0.1 wt.%, relative to the total weight of said clay stabilizing composition, preferably at least 0.5 wt.%, more preferably at least 0.6 wt.%, 0.7 wt.%, 0.8 wt.% or 0.9 wt.%, and most preferably at least 1.0 wt.%. Significantly enhanced stabilizing capacity was observed for clay stabilizing compositions with 1.00 wt.% of alkyl choline homologue, and more so with 1.20 wt.%, 1.40 wt.%, 1.60 wt.%, 1.80 wt.%, 2.00 wt.%, 2.20 wt.%, 2.40 wt.%, 2.60 wt.%, 2.80 wt.% and 3.00 wt.% of alkyl choline homologue, respectively, or any values there in between. Wellbore drilling can be advantageously performed using a stabilizing composition comprising more than 0.60 wt.%, more than 0.70 wt.%, more than 0.80 wt.% or more than 0.90 wt.% alkyl choline homologue, relative to the total weight of said clay stabilizing composition, but is preferably performed using more than 1.0 wt.% alkyl choline homologue in said clay stabilizing composition and more preferably more than 1.00 wt.% of alkyl choline homologue, and more so with 1.20 wt.%, 1.40 wt.%, 1.60 wt.%, 1.80 wt.%, 2.00 wt.%, 2.20 wt.%, 2.40 wt.%, 2.60 wt.%, 2.80 wt.% and 3.00 wt.% of alkyl choline homologue, respectively, or any values there in between. Using higher amounts of alkyl choline homologue provides better clay stabilizing properties. Even higher amounts are allowable, although less desirable for reasons of economy of materials. More specifically, said clay stabilizing composition preferably comprises less than 50 wt.% alkyl choline homologue, and more preferably less than 20 wt.% alkyl choline homologue, and even more preferably less than 15 wt.% alkyl choline homologue, relative to the total weight of said clay stabilizing composition.

In a preferred embodiment, the present invention provides a method according to the second aspect of the invention, whereby said alkyl choline homologue is comprised in said composition in an amount of between 1 wt.% and 5 wt.%, relative to the total weight of said clay stabilizing composition. More preferably, said alkyl choline homologue is comprised in said composition in an amount of 1.50 wt.% of alkyl choline homologue, and more so of 1.60 wt.%, 1.80 wt.%, 2.00 wt.%, 2.20 wt.%, 2.40 wt.%, 2.60 wt.%, 2.80 wt.% and 3.00 wt.% of said alkyl choline homologue, relative to the total weight of said clay stabilizing composition, or any value there in between. In a second embodiment, the invention provides a method according to the second aspect of the invention, whereby said method for controlling clay stability properties by contacting a clay stabilizing composition, i.e. a hydraulic tracking fluid, also known as a stimulation fluid, comprising a compound according to formula (I) and water with at least a part of a wellbore, whereby said composition comprises a compound according to formula (I) and water, whereby said compound according to formula (I) is comprised in said composition in an amount of at least 0.01 wt.%, relative to the total weight of said clay stabilizing composition, preferably at least 0.05 wt.%, more preferably at least 0.06 wt.%, 0.07 wt.%, 0.08 wt.% or 0.09 wt.%, and most preferably at least 0.10 wt.%.

It was found that said stimulation fluids comprising a compound according to formula (I) in an amount of at least 0.01 wt.%, relative to the total weight of said clay stabilizing composition, provide beneficial stimulation properties. Concentrations of at least 0.10 wt.% are preferred. Significantly enhanced stimulation capacity was observed for clay stabilizing compositions with 0.10 wt.% of alkyl choline homologue, and more so with 0.15 wt.%, 0.20 wt.%, 0.25 wt.%, 0.30 wt.%, 0.35 wt.%, 0.40 wt.%, 0.45 wt.%, 0.50 wt.%, 0.55 wt.% and 0.60 wt.% of alkyl choline homologue, respectively, or any values there in between.

In a preferred embodiment, the present invention provides a method according to the second aspect of the invention, whereby a base is added to a composition comprising an alkyl choline homologue in order to obtain a solution with pH of between 7 and 13, more preferably between 8 and 12, even more preferably between 9 and 11 , and most preferably of around 10.

Preferably, said solution is further supplemented with drilling fluid additives, such as, but not limited to, osmotic agents, density control agents, dispersants, fluid loss control agents, viscosity modifying agents, bactericides and pH control agents, such as buffers.

In a preferred embodiment, the present invention provides a method according to the second aspect of the invention, whereby water is added to an alkyl choline homologue to obtain a clay stabilizing composition according to the first aspect of the invention.

This is advantageous during transport and distribution of said alkyl choline compound. Accordingly, an alkyl choline homologue or a highly concentrated solution of alkyl choline homologue can be provided at the location of the drilling operations and be mixed with or diluted with water, or a water based solution, to provide an aqueous solution with clay stabilizing properties for use in said drilling operation.

In one embodiment, the present invention provides a use of a clay stabilizing composition as a drilling fluid, a completion fluid and/or a workover fluid, comprising a compound according to formula (I) and water, formula (I)

whereby R_1: R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R_1: R₂, R₃, R₄ is alkyl; whereby R₅, R₆, R₇ are independently selected from H, alkyl; and whereby X^" comprises an anion. More preferably, at least one of R R₂, R₃, R₄ is alkyl and at least two of, and preferably three of, R_1: R₂, R₃, R₄ is hydrogen. Preferably, said alkyl is methyl or ethyl, most preferably ethyl.

In such fluids, the amount of said compound according to formula (I) is typically more than 1.00 wt.%, relative to the total weight of said composition, and more preferably equal to 1.60 wt.%, 1.80 wt.%, 2.00 wt.%, 2.20 wt.%, 2.40 wt.%, 2.60 wt.%, 2.80 wt.% or 3.00 wt.%, or any value there in between.

The invention is furthermore applicable to aqueous hydraulic fracturing fluids, where there is a need to control subterranean formations containing swelling clays. Many clay-rich rocks encountered during drilling are termed shales; many of these shales contain swelling clays which, if not controlled by certain additives in the drilling fluid, can result in wellbore instability, a deterioration of drilling fluid properties and, possibly, an interruption of the drilling process - all of which can add to the cost and duration of processing.

In a second embodiment, the present invention provides a use of a clay stabilizing composition as a stimulation fluid, also known as a hydraulic fracturing fluid, comprising a compound according to formula (I) and water, formula (I)

whereby R₂, R₃, R₄ are independently selected from H, alkyl, and whereby at least one of R_1: R₂, R₃, R₄ is alkyl; whereby R₅, R₆, R7 are independently selected from H, alkyl; and whereby X^" comprises an anion. More preferably, at least one of Ri, R₂, R₃, R4 is alkyl and at least two of, and preferably three of, R_1: R₂, R₃, R₄ is hydrogen. Preferably, said alkyl is methyl or ethyl, most preferably ethyl.

In such fluids, the amount of said compound is typically less than 0.50 wt.%, and more preferably between 0.01 and 0.40 wt.%. More preferably, said compound is comprised in an amount of between 0.10 and 0.30 wt.%, and most preferably equal to 0.10 wt.%, 0.12 wt.%, 0.14 wt.%, 0.16 wt.%, 0.18 wt.%, 0.20 wt.%, 0.22 wt.%, 0.24 wt.%, 0.26 wt.%, 0.28 wt.%, 0.30 wt.%, or any value there in between.

EXAMPLES

In the following examples are intended to further clarify the present invention, and are nowhere intended to limit the scope of the present invention.

A stabilizer composition is prepared comprising 1.5 wt.% of methyl choline chloride in water using KOH to adjust the composition to pH 10. Said composition is applied in tests for assessing the stabilizing properties of said stabilizer composition. Testing was performed using London Clay as a reference clay. Prior to testing, the London Clay was sieved to obtain a fraction of clay of 2 to 4 mm.

Subsequently, tests were carried out according to ISO 10416:2008(E) Section 23 Shale Particle Disintegration test. 10 g of clay was added to a 100 mL of the stabilizer composition and mixed for 4 hours at room temperature. Results of the test are given in Table 1 as Example 1. Other stabilizer compositions were prepared according to the preparation procedure of Example 1 with compositions as described in Table 1 as Examples 2 to 6 and Comparative Examples 1 to 5. Table 1 also reports the results of the testing procedure performed with said stabilizer compositions. Table 1. Test results of various stabilizer compositions according to Examples 1 to 6 and Comparative Examples 1 to 5.

^* "1" being hardest, "4" being softest. Hardness of the clay after testing was determined qualitatively by according a value of 1 to 4, whereby the value "1" describes the residue as being hardest and the value "4" describes the residue as being softest. The mass residue was determined by determining the mass of clay before and after testing, whereby the mass of clay after testing is expressed as a fraction of the mass of clay before testing, expressed in percent.

The results in Table 1 show that excellent hardness is obtained for stabilizer compositions comprising 1.5 to 8.0 wt.% of methyl choline chloride. Similarly, high mass residue (> 95%) is obtained for said stabilizer compositions (Examples 1 to 5). A minor reduction of mass corresponds to little or no material entrainment with the drilling fluid during operation. Such entrainment results in deterioration of the drilling fluid quality and may require an additional separation step in the drilling fluid circuit to separate any solid entrainment material from the drilling fluid.

Also, Example 6 illustrates that high stabilizing activity is obtained for ethyl choline chloride, as can be derived from the excellent hardness and high mass residue upon testing. Within the margin of error, methyl choline chloride and ethyl choline chloride perform equally well in the above experiments. In contrast, application of a stabilizer composition comprising merely 0.75 wt.% of methyl choline chloride results in a strongly reduced hardness and a distinct reduction of mass residue (Comparative Example 1, hardness 3, mass residue 53%). These results show that in order to obtain satisfactory stabilizing properties, the amount of stabilizer in the composition preferably exceeds 0.75 wt.%.

Further experiments were aimed to compare performance of methyl choline chloride compared to a known clay stabilizer, i.e. choline chloride (Comparative Examples 2 to 5). Results show that better hardness was obtained for methyl and ethyl choline chloride stabilizers in addition to a better performance as expressed by mass residue after testing.

In further experiments, the performance of the clay stabilizer compositions was tested over several runs. When employed for drilling operations, the drilling fluid is typically recycled and applied again to the clay. In order to allow a stable drilling operation, the clay stabilizing potential of the fluid must stay high and constant over a prolonged period, which is simulated in the lab experiment by separating the fluid after exposure to clay and use the recovered fluid again with fresh clay cuttings. Choline chloride, methyl choline chloride and ethyl choline chloride were formulated in a drilling fluid in an amount of 3 wt.%. The clay stabilizing activity of the thus obtained drilling fluids over multiple cycles was assessed according to ISO 10416:2008(E) Section 23 Shale Particle Disintegration test. The stabilizing activity in further runs relative to the stabilizing activity of freshly formulated drilling fluid is depicted in Figure 1. The results clearly show that alkylated choline chloride as stabilizer allows for maintaining a high and constant stabilizing activity after 4 and 5 runs, while the activity of choline chloride strongly decreases already in the second run. Thus, the newly developed stabilizing solutions perform consistently during prolonged periods of processing at a drilling site within stable operating parameters, where it is constantly in contact with fresh cuttings, without the need for adjusting the formulation. Further, the results showed that ethyl choline chloride yields a higher stabilizing activity compared to methyl choline chloride, and that ethyl choline chloride allowed to maintain the stabilizing activity of the drilling fluid better over multiple runs (4 or 5 runs) compared to methyl choline chloride.

In conclusion, the results show that clay stabilizer compositions according to the present invention exhibit enhanced stabilizing properties as determined by hardness and mass residue, compared to compositions according to the state of the art. Furthermore, clay stabilizer compositions according to the invention provide an excellent performance, also when the stabilizer compositions are recycled and used again in a next run. Accordingly, the stabilizer compositions provide a stable performance of the fluid during drilling operations.

Claims

CLAI MS

Clay stabilizing composition comprising a compound according to formula (I) and water, formula (I)

whereby R₅, R₆, R₇ are independently selected from H, alkyl; and

whereby X^" comprises an anion. 2. Clay stabilizing composition according to claim 1, whereby said compound according to formula (I) is comprised in said composition in an amount of at least 1 wt.%, relative to the total weight of said clay stabilizing composition. 3. Clay stabilizing composition according to claim 1 or 2, whereby is selected from the group consisting of methyl, ethyl, propyl and butyl.

Clay stabilizing composition according to any of claims 1 to 3, whereby R₅, R₆, R₇ are independently selected from the group consisting of methyl, ethyl, propyl and butyl.

Clay stabilizing composition according to any of claims 1 to 4, whereby said compound according to formula (I) comprises methyl choline salt.

6. Clay stabilizing composition according to any of claims 1 to 5, whereby said alkyl choline homologue comprises an anion selected from the group comprising halides, bicarbonate, carboxylates, nitrite, nitrate, sulfite, sulfate, phosphite, phosphate.

7. Clay stabilizing composition according to any of claims 1 to 5, whereby said alkyl choline homologue is comprised in an amount of 1 wt.% to 5 wt.%, relative to the total weight of said clay stabilizing composition.

8. Clay stabilizing composition according to claim 7, whereby said alkyl choline homologue is comprised in an amount of 1.5 wt.% to 3.0 wt.%, relative to the total weight of said clay stabilizing composition.

9. Clay stabilizing composition according to any of claims 1 to 8, whereby said composition comprises a drilling fluid and whereby said compositions comprises a pH between 7 and 13.

10. Clay stabilizing composition according to any of claims 1 to 9, further comprising a viscosity control agent.

11. Method for controlling clay stability properties by contacting a clay stabilizing composition comprising a compound according to formula (I) and water with at least a part of a wellbore, formula (I)

whereby R₅, R₆, R₇ are independently selected from H, alkyl; and

whereby X^" comprises an anion.

12. Method according to claim 11, whereby said clay stabilizing composition is obtained by mixing said compound according to formula (I) in an amount of at least 1 wt.%, relative to the total weight of said clay stabilizing composition.

13. Method according to claim 11 or 12, whereby a base is added to a composition comprising said compound according to formula (I) in order to obtain a solution with pH of between 7 and 13.

14. Method according to any of claims 11 to 13, whereby water is added to said compound according to formula (I) to obtain a clay stabilizing composition according to any of claims 1 to 10.

15. Use of a clay stabilizing composition according to any of claims 1 to 10 for treating a water sensitive formation.