The present invention concerns water-soluble graft copolymer of a polyalkylene glycol and a water-soluble ethylenically unsaturated monomer. These polymers are useful for inhibiting swelling and/or disintegration of clay and/or shale in subterranean formations or in the walls of well bores. The polymers may also be useful as flocculants in various solids/liquids separation processes.

The preparation of graft polymers in general is well-documented in the prior art. Numerous methods are given in the literature for preparing a multitude of different types of graft polymers, covering a variety of different chemical structures and physical forms. Typically graft polymers described in the literature are used for a variety of applications. In general the preparation of a specific graft polymer, having particular properties designed for a particular application, is dependent upon the choice of starting materials and the process conditions.

An example of the preparation of graft polymers includes GB 922457, which reveals a process for making graft copolymers by dissolving a polyalkylene glycol in at least one monomer, such as vinyl esters and esters of acrylic or methacrylic acid, either in the presence or the absence of a solvent. The process employs a free radical polymerisation catalyst under the action of actinic light. Dibenzoyl peroxide is proposed as an initiator, which can decompose thermally or by ultraviolet light. This process would involve a type I photo initiation.

US 4846994 and US 4846995 each propose the use of graft polymers prepared according to GB 922457 as greyness inhibitors in the wash and after treatment of textiles. US 5635554 describes low viscosity formulations containing graft polymers made in the same way for use as viscosity reducing additives.

In PCT/EP 04/005657 (Attorney's docket 22346), which was unpublished at the date of filing of the present application, describes graft polymeric surfactants formed from ethylenically unsaturated monomer and a polyethyleneglycol substrate polymer using a Type Il photoinitiator are described. The polymers are of relatively low molecular weight, having a weight average molecular weight of below 100,000. No description of polymers suitable for shale or clay stabilisation is given.

US 4111769 and an article entitled, "Ultraviolet cured pressure sensitive adhesives", Kenneth C Stueben, Union Carbide Corporation, Polymer Science and Technology, 1984 (29) 319-350, describes photo cure of mono- and multifunctional acrylate-poly ethers-benzophenone blends. Grafting is effected by ultraviolet radiation. The reference suggests that carbamyloxy alkyl acrylates can be grafted onto polyethylene oxides of molecular weight 1700 to 90,000 preferably 2500 to 21 ,000. The graft polymer thus formed would tend to have a high molecular weight in order to function as a pressure sensitive adhesive and the polymers described would be water insoluble.

GB 1550292 describes thermoformable water-soluble photopolymer compositions that contain copolymers of ethylene oxide, ethylenically unsaturated monomers and photoinitiators. These compositions are irradiated using actinic light and converted to rigid, insoluble, tough structures. Thus the graft polymers formed are in fact water insoluble. Consequently there is no teaching of how to make water-soluble graft polymers.

GB 903619 describes photopolymerisable compositions containing polyethylene oxides and ethylenically unsaturated compounds with a small amount of polymerisation initiator activated by actinic light. Photo polymerisation results in solid articles that are water insoluble.

GB 1439132 discloses a method for the production of a hydrophilic grafted polymer product. Gamma radiation is used to generate radicals along a hydrophobic polymer backbone from which hydrophilic monomer will polymerise. The process does not use a chemical polymerisation initiator.

GB 1032505 also reveals preparing graft copolymers using high energy radiation or by chemical free radical generating catalysts.

To our knowledge graft polymers of polyalkylene glycol with water-soluble monomers prepared using Type Il photo initiators suitable for inhibiting swelling and/or disintegration of clay and/or shale in subterranean formations or in the walls of well bores have never been disclosed.

It is known that when aqueous based fluids are used in drilling, particularly in a formation formed from the minerals known as shales that significant problems can result from the interaction of water with the shale. Water can become absorbed into the shale that swells or weakens thus disrupting its internal structure. This can lead to contraction of the wellbore and softening and disintegration of the wall of the well shaft.

The use of oil-based drilling fluids would alleviate these problems but they are expensive and are also thought of as environmentally undesirable. Therefore methods have been sought for the inhibition of shale disintegration (shale inhibition) when using aqueous drilling fluids. Similar problems occur with swelling and disintegration of clay materials within oil- and gas-bearing reservoirs on contact with aqueous reservoir fluids. Such swelling tends to lead to permeability problems with these reservoirs. Therefore it is also desirable to provide methods of inhibiting disintegration of clay ('clay inhibition) in such environments.

Various polymeric materials are known for incorporation into drilling fluids as

shale and clay inhibitors. High molecular weight (5 to 15 million) polyacrylamides and acrylamide/acrylate copolymers (anionic polyacrylamides) are known for this purpose. They are believed to work by absorbing onto the shale, coating it and preventing penetration by water. However, it is common to incorporate bentonite as a component of drilling fluids as a viscosifier.

Polyacrylamides, in particular anionic polyacrylamides, tend to absorb onto the surface of bentonite in the drilling fluid and portions of the polymer dose are lost.

It is also known to incorporate polyglycols into drilling fluids as inhibitors of shale disintegration. These act by penetrating the shale and aiding in retaining its internal structure. They are also believed to cause some dehydration of the shale. Polyglycols are generally accepted as the industry standard shale inhibitors. The use of water-based drilling fluids containing potassium salts and polyalkylene glycols for shale inhibition is described in EP-A-495579 and Special Publication - Royal Society of Chemistry (1998), 211 (Chemicals in the Oil Industry), 58 - 70). This is also believed to work by absorbing onto the shale or clay, coating it and preventing penetration by water.

US-A-4 ,440,649 suggests the use of a vinyl amide-vinyl sulphonate terpolymer with acrylamide for the prevention of disintegration of clay-containing materials. The terpolymer suggested is described in U.S. Pat. No. 4,309,523. All of the exemplified polymers contain 2-acrylamide-2-methyl-propane-3-sulphonic acid (AMPS). Amounts of AMPS are often very high, for instance at least 50 wt %, often at least 65 wt %. The vinyl amide used is N-vinyl-N-methyl-acetamide, vinyl acetamide or vinyl formamide. These monomers are generally present in minor amounts in the exemplified polymers, in particular never more than 50 wt % of the polymer. When such monomers are present in amounts of 50% it is always in combination with significant amounts of AMPS (for instance at least 35 wt %). US-A-4, 536, 297 also suggests the use of a vinyl amide-vinyl sulphonate terpolymer for prevention of disintegration of clay-containing materials. This terpolymer is described in DE-A-3, 144,770. Again, the

exemplified polymers contain significant amounts of anionic monomer, in this case sodium styrene sulphonate. In the terpolymers described the sulphonate is often present in an amount of at least 50 wt %. Amide monomers such as N- vinyl-N-methyl acetamide, N-vinyl formamide are also used. Generally however these are used in minor amounts, in particular in the terpolymers described, in which they are always used in amounts of less than 50 wt %. These predominantly anionic polymers can suffer from similar problems as those seen with anionic polyacrylamides.

It is also known to use rather low molecular weight highly cationic polymers, such as diallyl dimethyl ammonium chloride (DADMAC) as shale-inhibiting components of drilling fluids. These act to inhibit disintegration of shale by penetrating the shale and acting to increase its internal strength and reduce swelling on contact with water. Unfortunately, these cationic polymers have a tendency to absorb onto solid surfaces other than the shale with the result that a portion of the dose is lost and the use of such polymers is inefficient

GB-A-2267921 describes an aqueous based drilling fluid comprising polyvinylpyrrolidone (PVP) as a shale inhibitor. This is the only material mentioned as shale inhibitor. It is stated that the PVP polymer may have a molecular weight from 5,000 upwards, but that it is preferably greater than one million. The examples show that high molecular weight is clearly preferred. It appears that the PVP is acting as a coating polymer to prevent penetration of water into the shale.

WO96/04349 mentions the possibility of including dissolved molecular solutes. These may be polymers. No specific polymers are suggested. WO96/03474 suggests a particular composition which includes a specific surfactant together with a water soluble polymer such as PVP, polyvinyl alcohol, polysaccharide or partially hydrolysed (i.e. anionic) polyacrylamide

US-A-6,020,289 describes low molecular weight polymers of monomers selected from dialkyl (meth)acrylamides, N-vinyl formamide, N-vinyl acetamide and diacetone acrylamide in a drilling fluid for inhibiting shale disintegration during the drilling of a wellbore in shale-containing rock.

An article by Li-Ming Zhang et al., Polymer International 48: 921-926 [1999] describes modified cellulosic polymers with amphoteric character prepared by grafting 2-dimethyl amino ethyl methacrylate and 4-vinyl benzene sulfonic acid sodium salt onto sodium carboxy methyl cellulose useful as drilling fluid additives in oilfields in order to achieve shale inhibition, filtration control and viscosity enhancement.

An article by Li-Ming Zhang et al., Journal of Applied Polymer Science, vols. 74, 3088-3093 [1999] discloses water soluble cationic graft polymers of hydroxy ethyl cellulose with vinyl monomers dimethyldiallyl ammonium chloride and acrylamide for inhibiting dehydration of water sensitive clay in oilfields.

It is an objective of the present invention to provide an additive which can be included in an aqueous drilling fluid or other fluid injected into aqueous a subterranean formation that will prevent the swelling and/or disintegration of shale and/or clay. It is a further objective to provide an additive which is more effective than conventional clay or shale stabilizers.

In achieving this objective a new polymer has been developed.

Thus in accordance with the present invention we provide a water-soluble graft copolymer of a polyalkylene glycol and a water-soluble ethylenically unsaturated monomer said graft polymer having a weight average molecular weight of above 100,000, wherein the graft polymer is obtainable by the reaction of the polyalkylene glycol with the water-soluble ethylenically unsaturated monomer in which the reaction

is conducted in the presence of a type Il photo initiator and by the action of actinic radiation.

The action of the actinic radiation upon the photo initiator induces photo- initiation. In principle there are two types of photoinitiation mechanisms according to the process by which the initiating radicals are formed. Compounds undergoing homolytic cleavage are termed type I photoinitiators, which is not the case in the present invention, and compounds that interact with a second molecule (known as co-initiators) as in the present invention, are known as type Il photo initiators. The reaction pathways available for Type Il photoinitiators are via hydrogen abstraction or electron transfer (followed by proton transfer) mechanisms, but under certain conditions both mechanisms may be involved.

These type Il photoinitiations thus require co-initiators (usually hydrogen donating compounds typified by amines, alcohols, thiols or ethers) generating the radicals that trigger polymerisation and thus this type of initiation has the potential to incorporate hydrogen donating compounds into polymers (i.e. photografted polymers). However, photo initiated graft polymerisation using type Il initiators has previously only been used to prepare hard resinous solids or adhesives.

Generally in the preparation of water-soluble graft polymers it can be difficult to control the water-solubility and the molecular weight, in particular the molecular weight of the pendant graft polymer chains. Furthermore, the overall structure of the graft polymer is critical in order to provide the right properties.

Surprisingly, we have been able to provide a graft polymer, which is suitable as a clay and/or shale inhibitor or flocculant, using a photo initiated graft polymerisation process employing type Il photo initiators. Thus the process not only has the advantage in terms of convenience, but also can be controlled easily to provide a graft polymer with the right properties for a given application. The graft polymers of the present invention have a unique molecular structure

and in particular comprise polymer chains, formed from the chosen monomer, grafted directly onto the substrate by covalent bonding at a position on the substrate previously occupied by hydrogen atoms.

The graft polymer may have a molecular weight of several hundred thousand up to 50 million or more. For some applications, for example when used as flocculants it may be desirable for the graft polymer to have a molecular weight of at least 500,000 and up to 20 million or more. Molecular weight of between 3 or 4 million up to 15 million may be particularly preferred. When used as a clay or shale stabilizer it may be desirable to employ graft polymers of molecular weights between 120,000 and one or two million.

The polyalkylene glycol may be unsubstituted or substituted for instance a dialkyl end caped polyalkylene glycol. Typically, it may be one of a number of polyethylene glycols or polypropylene glycols that preferably it is a polyethylene glycol which is desirably unsubstituted.

The polyalkylene glycol will usually have a weight average molecular weight of up to 10,000, typically between 200 and 10,000. Preferably it is in the range of 1000 to 3000 and more preferably around 2000. A particularly preferred polyalkylene glycol is PEG 2000 (polyethylene glycol with a molecular weight of 2000).

The water-soluble ethylenically unsaturated monomer that is grafted onto the polyalkylene glycol substrate can be any monomer that readily undergoes direct reaction with the activated sites on the substrate. Typically such activated sites would include positions on the polyalkylene glycol where a type Il photo initiator has generated a radical. In general the monomer molecule will tend to react through the double bond and become covalently bonded directly to the polyalkylene glycol. The monomer unit can then carry a radical onto which a further monomer molecule will react through the double bond and this process

will continue to form a grafted polymer. It may also be possible for further polymer chains to develop from a grafted polymer chain rather than directly from the polyalkylene glycol. Such a process may be termed secondary grafting.

The water-soluble ethylenically unsaturated monomer desirably has a solubility in water of at least 5g monomer per 100 mis of water at 25°C. The monomer may be potentially water-soluble such that it can be modified, for instance after polymerization, to provide a monomer unit that would have been soluble in water, for instance having the above defined solubility.

Typical water-soluble monomers that may be used in the invention include water-soluble or potentially water-soluble monomers are selected from the group consisting of acrylamides (e.g. acrylamide and methacrylamide), N- alkylacrylamides, hydroxy alkyl (meth) acrylates (e.g. hydroxyethyl acrylate), N- vinylpyrrolidone, vinyl acetate, vinyl acetamide, acrylic acid (or salts thereof), methacrylic acid (or salts thereof), maleic acid (or salts thereof), maleic anhydride, itaconic acid (or salts thereof), crotonic acid (or salts), 2- acrylamido- 2-methyl propane sulfonic acid (or salts thereof), (meth) allyl sulfonic acid (or salts thereof), vinyl sulfonic acid (or salts thereof), dialkyl amino alkyl (meth) acrylates or quaternary ammonium or acid addition salts thereof, dialkyl amino alkyl (meth) acrylamides or quaternary ammonium and acid addition salts thereof and diallyl dialkyl ammonium halide (e.g. diallyl dimethyl ammonium chloride).

Preferred cationic monomers include the methyl chloride quaternary ammonium salts of dimethylamino ethyl acrylate and dimethyl aminoethyl methacrylate. Other ethylenically unsaturated monomers may also be included with the water soluble monomer such as, styrenes, C1-30 alkyl (meth) acrylates, (meth) acrylonitrile and halogenated vinylic monomers, such as vinylidene chloride or vinyl chloride. If such other monomers are included, they tend to be included in small amounts based on total weight of definitely unsaturated monomer, for

instance below 20% by weight and typically been a 10% by weight. Preferably the graft polymer is formed using definitely a saturated monomer or monomer blend consisting essentially of water-soluble monomer or potentially water- soluble monomer.

The graft polymer may be nonionic and in this case would be made by grafting nonionic monomers onto the polyalkylene glycol. Typically the nonionic monomers may be one or more of acrylamides (e.g. acrylamide and methacrylamide), N-alkylacrylamides, hydroxy alkyl (meth) acrylates (e.g. hydroxyethyl acrylate), N-vinylpyrrolidone, vinyl acetate, vinyl acetamide etc.

The graft polymer may be anionic and as that may be formed by grafting any anionic monomers onto the polyalkylene glycol substrate. The anionic monomers usually carry an acid group such as carboxylate, sulfonate or sulfate etc. Preferred anionic monomers include acrylic acid (or salts thereof), methacrylic acid (or salts thereof), maleic acid (or salts thereof, itaconic acid (or salts thereof), crotonic acid (or salts), 2- acrylamido-2-methyl propane sulfonic acid (or salts thereof), (meth) allyl sulfonic acid (or salts thereof), vinyl sulfonic acid (or salts thereof). The anionic monomer may be potentially anionic for example ) maleic anhydride or any other anhydride monomer which can be hydrolysed after polymerisation to for instance yield the corresponding carboxylic acid. The anionic monomer may be a blend of anionic monomers or a blend of at least one anionic monomer with one or more nonionic monomers such as those given above, for instance acrylamide.

Particularly suitable polymers for the application of clay or shale stabilisation can be prepared using water-soluble ethylenically unsaturated monomers which are cationic or potentially cationic. By potentially cationic we include groups that are able to subsequently exhibit a cationic charge, for instance following a chemical reaction, such as quaternisation of a tertiary amine or acidification of a primary or secondary amine. Preferably, the water-soluble ethylenically

unsaturated monomer is selected from the group consisting of dialkyl amino alkyl (meth) acrylates or quaternary ammonium or acid addition salts thereof, dialkyl amino alkyl (meth) acrylamides or quaternary ammonium and acid addition salts thereof, diallyl dialkyl ammonium halide. Dialkyl amino alkyl (meth) acrylates or acrylamides may be rendered cationic by reducing the pH to below 4 or 5 with for instance sulphuric acid or hydrochloric acid or preferably by quaternising using an alkyl halide such as methyl chloride or an alkyl sulphate such as dimethyl sulphate. A more preferred class of water-soluble monomers include (meth)acryloyloxy alkyl trialkyl ammonium compounds, normally obtained by the quaternisation of dialkyl amino alkyl acrylates or methacrylates. Preferably the (meth)acryloyloxy alkyl trialkyl ammonium compound are as defined by formula (I)

R O R ₁ I Il I

CH ₂ = C — C — O — A — N ⁺ — R ₂ (I)

X ^" R ₃

in which R is -H or CH ₃ ; Ri , R ₂ , R ₃ are each independently C 1 to 4 alkyl; A is an alkylene group; and X ^" is an anion. A particularly preferred water-soluble ethylenically unsaturated monomer is acryloyloxy ethyl trimethyl ammonium chloride.

When the graft polymer is cationic it may be formed by grafting onto the polyalkylene glycol water-soluble monomer comprising at least one cationic monomer. It may be desirable to used two or more cationic monomers or a blend of at least one cationic monomer with a nonionic monomer such as acrylamide or methacrylamide or other nonionic monomers identified above.

The weight ratio of polyalkylene glycol substrate to grafted moiety (i.e. portion formed from the ethylenically unsaturated monomer) is desirably in the range of

99:1 to 1 :99. Preferably the ratio would be in the range 50:1 - 1 :50. More preferably still the ratio should be between 20:1 - 1:20, especially between 10: 1 and 1 : 10 and in particular around 1:1.

The type Il photo initiator may be any substance which is capable of a photoreaction with a so-called co initiator or substrate to form a radical when exposed to a suitable actinic radiation. Preferably, the photo initiator may be any one of benzophenone, diaryl ketones, xanthones, thioxanthones, acridones, anthraquinones, diketones, ketocoumarines or imides. More preferably, the photo initiator is selected from the group consisting of ammoniumalkyl derivatives of benzophenones, sulfonylalkyl derivatives of benzophenones, ammoniumalkyl derivatives of anthraquinones, sulfonylalkyl derivatives of anthraquinones and thioxanthones.

It is further possible to use type Il photoinitiators substituted by co-polymerisable groups that are co-polymerised with the growing side chain, or type Il photoinitiators that are bound to a polymer backbone. It is in addition possible to use blends of one or more of the previously mentioned type Il photoinitiators.

Actinic radiation includes any electromagnetic radiation capable of initiating photochemical reactions. The choice of actinic radiation will depend upon the particular initiator used and will also depend to some extent on the reactants and if used the solvent. Desirably the actinic radiation includes electromagnetic radiation selected from the group consisting of ultraviolet light, infrared light, and visible light.

In accordance with the invention we also provide a method of producing a water-soluble graft copolymer of a polyalkylene glycol and a water-soluble ethylenically unsaturated monomer said graft polymer having a weight average molecular weight of above 100,000,

comprising contacting the polyalkylene glycol with water-soluble ethylenically unsaturated monomer and a type Il photo initiator to form a reaction mixture and wherein the reaction mixture is subjected to actinic radiation to induce grafting of the water-soluble ethylenically unsaturated monomer onto the polyalkylene glycol and photo polymerisation to form the graft copolymer.

Preferably, the method employs any of the aforementioned features relating to the graft polymer.

The ratio of substrate to ethylenically unsaturated monomer will be appropriate to provide the desired ratio of substrate component to grafted polymer chains as described above.

The amount of type Il photo initiator will depend upon many factors, including choice of photo initiator, substrate, monomer and solvent (if used). Typically the photo initiator may be used in amount of 0.005 - 30% w/w upon polyalkylene glycol substrate. Preferably this will be within the range of 0.01 - 10 % and more preferably 0.1-5%. Particularly suitable polymers may be prepared using between 0.5 and 3.5%, especially between 1 and 3%.

It is particularly preferable to use ultraviolet light as the actinic radiation. The UV light source may include low, medium or high-pressure UV lamps, metal halide lamps, microwave-stimulated metal vapor lamps, carbon arc lamps, xenon arc lamps, excimer lamps, superactinic fluorescent tubes, fluorescent lamps or light emitting diodes, and the UV spectral output should ideally match the UV absorbance of the chosen photoinitiator.

A suitable UV light source for a typical photoinitiator such as benzophenone can be a medium pressure mercury UV lamp. Desirably, the UV light should have a wavelength in the range of 200 - 500 nm and a peak power density of at least 0.1 mW/ cm ² and normally at least 0.5 mW/ cm ² . Usually the peak power

density will be in the range of 1 mW/cm ² to 200W/cm ² , and typically 1.5 mW/ cm ² to 100 mW/ cm ² . A particularly preferred irradiation employs UV light at a wavelength between 360 and 370 nm and an intensity between 20 and 60 mW/cm ² , more particularly between 30 and 50 mW/cm ² .

The exposure length of the UV irradiation can be as short as a fraction of a second to several hours. Typically, the irradiation will be for a duration of up to 300 minutes. Preferably the actinic radiation is applied for a period of less than 60 or 70 minutes. The irradiation may be from as little as a few seconds, usually one or more minutes. In some cases it may be desirable to irradiate the reaction mixture for between 45 and 70 minutes. In other cases this can be within the range of 1 to 35 or 45 minutes.

The UV light source can be applied to the reactants internally or externally provided there is no barrier to the specific wavelength of UV light that is required by the photoinitiator to function.

The reactant mixture can be introduced into the reactor vessel separately, together as a mixture, or passed through an irradiating chamber in a continuous fashion, or can be recycled with similar or different monomer/initiators mixtures.

The reactants can be degassed in order to remove unwanted oxygen from the reaction medium. Degassing is typically carried out by passing an inert gas such as nitrogen to the liquid reaction medium for sufficient time and after sufficient rate to remove dissolved and entrained oxygen or by using a vacuum technique (3 or 4 freeze-pump thaw cycles) at <10 ^'4 Torr.

Preferably, the reaction mixture is dissolved or dispersed in a liquid medium. In one aspect the reaction mixture is dispersed in the liquid medium to form a suspension or alternatively may be emulsified in the liquid medium to form an emulsion, for example according to a process defined by EP-A-150933, EP-A- 102760 or EP-A-126528. Preferably though the reaction mixture is dissolved in

the liquid medium. The liquid medium can for instance be one of the range of solvents suitable for carrying out photo polymerisation reactions and desirably will be selected from the group consisting of methanol, toluene, cyclohexane, acetonitrile, dimethylformamide and water etc. Preferably, the solvents should not participate as hydrogen donors in the photo initiation step.

Therefore in one preferred form of the method of preparing the polymeric product, the polyalkylene glycol substrate, ethylenically unsaturated monomer and type Il photo initiator are combined together in a suitable solvent to form a reaction mixture. All of the components may be dissolved in the solvent or one or more of the components may be dispersed throughout the solvent, provided that this does not adversely affect the reaction. The reaction mixture is then irradiated using UV light to initiate the reaction. The solvent used can be present in an amount of 10 -90% of the reaction mixture. The photopolymerisation reaction can be carried out at a range of different temperatures, isothermally or adibatically. Typical temperature ranges include 10 - 100 ⁰ C.

More preferably, the liquid medium is a polar solvent, preferably water, and the type Il photo initiator is soluble in said polar solvent.

If the photoreaction is performed in water or a polar solvent, the use of water- soluble type Il photoinitiators, such as the salts of ammoniumalkyl or sulfonylalkyl derivatives of benzophenones, anthraquinones or thioxanthones is preferred.

The polymerisation may be carried out in an aqueous medium as a pH of between 2 and 10. Advantageously, we find that the polymerisation may be carried out at essentially relatively neutral pH, for instance between pH 6 and 8.

The graft polymer of the present invention may be used for a variety of applications, including flocculants for the separation of solids from suspensions, the polymer. It may be used as a flocculant in the treatment of mineral suspensions such as red mud or coal tailings. It may also be used as a dewatering aid for the treatment of sewage sludges are as a retention/dewatering aid in papermaking. However, it is particularly suitable as a clay or shale inhibitor. Thus according to a further aspect of the invention we provide a method of preventing the disintegration and/or dispersion of clay and/or shale in a subterranean formation or a well bore by bringing into contact with the clay or shale a polymeric material which is a water soluble graft copolymer of a polyalkylene glycol and a water-soluble ethylenically unsaturated monomer said graft polymer having a weight average molecular weight of above

100,000, wherein the graft polymer is obtainable by the reaction of the polyalkylene glycol with the water-soluble ethylenically unsaturated monomer in which the reaction is conducted in the presence of a type Il photo initiator and by the action of actinic radiation.

The graft polymer may contain any of the more specifically defined features defined above.

The graft polymer is preferably introduced into the well bore or the subterranean formation in an aqueous fluid. In the treatment of a well bore to inhibit clay and/or shale the graft polymer may be dissolved or dispersed in an aqueous drilling fluid. Alternatively, in the treatment of a subterranean formation in order to inhibit clay and/or shale the polymer may be introduced into either a production well or an injection well whichever is the most appropriate for the desired treatment.

Methods of inhibiting clay and/or shale are given in the aforementioned prior art and also the UK patent application filed on the equivalent date under the attorney docket number (OS/3-22368/P1).

The following examples illustrate the invention.

Examples

General Preparation of Graft Copolymers

With (or without stirring) a mixture of the hydrogen donating substrate, monomer, photoinitiator, and cosolvent (if required) in a suitable reactor, is irradiated with UV light for a period of time until all or most of the monomer has been consumed. Cosolvent if used is removed from the crude product mixture, which affords the product.

Synthesis of Graft Copolymers

Example 1

Preparation of a 1 :1 w/w Polyethyleneglycol - \2-

(acryloyloxy)ethylltrimethylammonium chloride graft polymer.

(4-Benzoylbenzyl)trimethylammonium chloride (0.06 parts), 3.16 parts of polyethyleneglycol (Mwt 2000), 3.64 parts of a 80% aqueous solution of [2- (acryloyloxy)ethyl]trimethylammonium chloride and 5.39 parts of water were placed in a glass petri dish (11 cm diameter and 2 cm deep). The petri dish containing the mixture was placed at a distance of 12 cm under a medium pressure Hg Black Ray UV lamp 360-370 nm, 40mW/cm ² . After 60 minutes the sample had completely gelled to form a polymeric film.

Example 2 Preparation of a 1:1.9 w/w Polypropyleneglycol (Average M ₀ ca. 2000)- Polvvinylpyrrolidone graft polymer.

Benzophenone (0.10 parts), 4.01 parts polypropyleneglycol (average M _n ca.

2000), and 7.55 parts of 1-vinyl-2-pyrrolidinone were placed in a glass petri dish (11 cm diameter and 2 cm deep). The petri dish containing the mixture was placed at a distance of 12 cm under a medium pressure Hg Black Ray UV lamp

360-370 nm, 40mW/cm ² . After 60 minutes the sample had completely gelled to form a hard polymeric film.

Example 3 Preparation of a larger sample of a 1 :1 w/w Polyethyleneglycol - \2-

(acryloyloxy)ethylithmethylammonium chloride quaternarised graft polymer.

(4-Benzoylbenzyl)trimethylammonium chloride (0.46 parts), 25.85 parts of polyethyleneglycol (Mwt 2000), 29.67 parts of a 80% aqueous solution of [2- (acryloyloxy)ethyl]trimethylammonium chloride and 44.00 parts of water were placed in a glass petri dish (11 cm diameter and 2 cm deep). The petri dish containing the mixture was placed at a distance of 12 cm under a medium pressure Hg Black Ray UV lamp 360-370 nm, 40mW/cm ² . After 60 minutes the sample had completely gelled to form a polymeric film.

Analysis of Products from Examples 1 and 3

The samples from examples 1 and 3 are analysed by size exclusion chromatography (SEC) using TSK PWXL columns connected in series (G6000 and G3000 and guard or equivalents). The mobile phase is 0.2M sodium chloride with a 0.01 M dipotassium hydrogen phosphate in purified water that is pumped through the system a nominal flow rate of 0.5 ml/minute. Sample detection is by differential refractive index and a series of polyethylene oxide and polyethylene glycol standards used in the calibration.

Example 1 and Example 3

The molecular weights as determined by GPC are not absolute but relative to the conditions used with a PEG/PEO calibration.