FIELD OF THE INVENTION

The present invention relates to a method for inhibiting shale hydration in the treatment of subterranean formations.

In another aspect, the invention relates to shaped solid shale inhibitors comprising a carboxymethyl cellulose and at least one shale inhibiting agent.

BACKGROUND OF THE ART

In the rotary drilling of wells a drilling fluid circulates throughout the underground well to carry the cuttings from the bit and to transport these cuttings to the surface. Contemporaneously, the drilling fluid cools and cleans the drill bit, it reduces the friction between the drill string and the drilled hole, and stabilizes the uncased sections of the well.

Usually the drilling fluids also form a low permeability filter cake in order to seal any permeability associated with the surrounding geological formations.

The drilling fluids may be classified according to their fluid base: oil based fluids which contain solid particles suspended in an oil continuous phase and, possibly, water or brine emulsified with the oil. Alternatively, water base fluids contain solid particles suspended in water or brine. Various other components may be added, deliberately or otherwise, to water based drilling fluids: a) organic or inorganic colloids, such as clays, used to impart viscosity and filtration properties; b) soluble salts or insoluble inorganic minerals used to increase the fluid density; c) other optional components may be added to impart desirable properties, such as dispersants, lubricants, corrosion inhibitors, defoamers or surfactants; d) formation solids which may disperse into the fluid during the drilling operations.

Formation solids that become dispersed in a drilling fluid include cuttings from drilling and soil and solids from the surrounding unstable formation. When the formation yields solids which can swell, hereinafter defined shale, this can potentially compromise drilling time and increase costs. Shales are mineralogically classified as layered aluminum silica because l the dominant structure consists of layers formed by sheets of silica and alumina, that can have exposed surface hydroxyls. Multivalent atoms may create a negative potential at the shale surface and, in this case, cations can be adsorbed onto the surface. These cations may be exchangeable. Substitutions within the shale structure and the presence of exchangeable cations affect the tendency of the shale to swell in water.

There are different types of swelling. For example surface hydration gives swelling with water molecules adsorbed on clay surfaces. All types of shale can swell in this manner.

Another type of swelling is called osmotic swelling, when the interlayer ion concentration leaches water between the shale unit layers, swelling the shale. Only some clays can undergo osmotic swelling. The clays that don't give this inter-layers swelling with an increasing in volume, tend to disperse in water.

All types of shale swelling can cause a series of problems, for example increasing drag between the drill string and the sides of the borehole, loss of fluid circulation and sticking onto the drill string and bit.

This is why the development of effective shale swelling inhibitors is important to the oil and gas industry. The present invention works towards a solution to these difficulties. Many shale inhibitors are known, including the use of inorganic salts such as potassium chloride, which effectively inhibit shale swelling and which are well known to those skilled in the art. Several patents have been filed which describe techniques or products which can be used to inhibit shale swelling. Without completely summarizing the patent literature, and by way of example, we can cite inhibitor compositions based on: a) inorganic phosphates, described in US 4,605,068 ; b) polyalkoxy diamines and their salts, in US 6,484,821, US 6,609,578, US 6,247,543 and US 2003/0106718; c) choline derivatives in US 5,908,814; d) oligomethylene diamines and their salts, in US 5,771,971 and US 2002/0155956; e) bis-hexamethylene-triamine and salts thereof, in WO 2011/083182; f) reaction product of an epoxy resin with at least one primary or secondary aliphatic or cycloaliphatic amine, in US2008/0275939; and g) polymeric heterocyclic nitrogen-containing compound, in WO 2004/090067.

In particular, WO 2006/ 013595 describes solid shale inhibitor in the form of powder consisting of 80 to 99.5 parts by weight (pbw) of carboxymethyl cellulose having DS from 0.8 to 1.3 with 0.5 to 20 pbw of an organic amine. The shale inhibitor is obtained by high shear mixing of the two components.

However the process described in WO 2006/013595 for the preparation of the solid shale inhibitors cannot manage high amounts of water, in particular above about 15 pbw, for this reason the amount of amine, which are provided as water solutions, must be limited below certain levels. For example, in WO 2006/013595, only a solid shale inhibitor containing max. 7 pbw of amine is exemplified.

In addition, the shale inhibitors described in WO 2006/013595 have shown problems of migration of the amines from the internal surface of the packaging towards the external surface, especially for products with concentration of amines higher than 10 wt%. Since these amines are toxic chemicals, these problems can cause environmental and health concern.

Another problem regards the handling of the inhibitors. Also if dried, at concentration of amines higher than 10 wt%, the inhibitors of WO 2006/013595 looks like sticky pastes and have a really inadequate pourability/dosability. This can create difficulties for their handling in oil plants and longer total process time.

Moreover handling of such powders and dust generation during processing create environmental and health problems that must be dealt with by the manufacturer and the final user.

Furthermore compositions containing CMC in form of powders are difficult to dissolve in complex and thick treatment fluids and, if not stirred for enough time and/or with a high shear mixer, they can create lumps or aggregates in the fluid. After preparation, the fluids must be sieved to eliminate impurities and aggregates, with a consequent loss of active material.

A typical solution to these problems commonly used in many fields is to granulate the powdery compounds or compositions. Unfortunately the granules obtained during the granulation process are different in their forms and dimensions, thus making it necessary to sieve the granulated material, for the purpose of selecting the granules presenting dimensions above a minimum value. Moreover granulation does not eliminate dust. In fact, a percentage of this dust, even if small, remains embedded in between the granules and tends to spread around.

It has been now found that compositions comprising a carboxymethyl cellulose and high amounts of shale inhibitor(s) can be prepared in form of shaped solids.

The composition and dimensions of the shaped solid shale inhibitors can be easily controlled in order to avoid hazards and to optimize on-field processing, handling/shipping, dosing, etc. In particular the shaped solid shale inhibitors have revealed to be less prone to problem of migration of the amines into the packaging.

At the same time these shaped solids are really compact, do not produce dust when handled and have a better dispersibility than the powders, which reduces significantly the formation of lumps in the treatment fluids. As far as the Applicant knows, shaped solid shale inhibitors comprising a mixture of a carboxymethyl cellulose and at least one shale inhibiting agent and their use for the preparation of treatment fluids have not been described in the previous literature.

As used herein, the term "shale" is defined to mean any subterranean material, that may "swell" or increase in volume or disperse, when exposed to water.

By "shaped solid" is meant a body in solid form which retains its shape after manufacture and during transport and storage, including, but not limited to, pellets, tablets, pearls, flakes, briquettes, or bars.

In the present text, the expression "carboxymethyl cellulose" (CMC) means both technical or purified carboxymethyl cellulose, having a percentage of active substance comprised between 50 and 99.5 % by weight on dry matter, preferably from 55 to 98.5 %; the remaining part being mainly glycolate and other organic/inorganic salts deriving from its preparation.

The expression "degree of substitution" (DS) means the average number of carboxymethyl groups for each anhydroglucosidic unit of the cellulose and can be determined, for example, according to the standard method ASTM D1439 or by H-NMR .

DESCRIPTION OF THE INVENTION

It is therefore a fundamental object of the present invention shaped solid shale inhibitors comprising from 55 to 90 % by weight (wt%) as dry matter of a carboxymethyl cellulose (CMC) and from 10 to 45 % by weight as dry matter of at least one shale inhibiting agent.

In another aspect the present invention is a method for inhibiting shale during the treatment of subterranean formations comprising the step of:

A) providing a shaped solid shale inhibitor comprising from 55 to 90 % by weight as dry matter of a carboxymethyl cellulose (CMC) and from 10 to 45 % by weight as dry matter of at least one shale inhibiting agent;

B) dissolving said shaped solid shale inhibitor into a treatment fluid in an amount comprised between 0.5 and 6 wt% of the fluid;

C) introducing the treatment fluid to the wellbore at a pressure sufficient to treat the subterranean formation.

DESCRIPTION OF THE DRAWINGS

Fig. 1: Spectra of the internal paper sheet of the packaging specimen in contact with the shale inhibitor of Example 12 (comparative).

Fig. 2: Spectra of the polyethylene sheet of the packaging specimen in contact with the shale inhibitor of Example 12 (comparative).

Fig. 3: Spectra of the internal paper sheet of the packaging specimen in contact with the shale inhibitor of Example 9.

Fig. 4: Spectra of the polyethylene sheet of the packaging specimen in contact with the shale inhibitor of Example 9.

DETAILED DESCRIPTION OF THE INVENTION

Preferably, said shaped solid shale inhibitors comprise from 60 to 80 %, more preferably from 63 to 78 %, by weight as dry matter of CMC and from 20 to 40 %, more preferably from 22 to 37 %, by weight as dry matter of at least one shale inhibiting agent.

The carboxymethyl cellulose suitable for the realization of the present invention can be chosen among those commonly used in the field and known to those expert in the art. The preferred CMC has a degree of substitution comprised between 0.5 and 1.5, more preferably between 0.6 and 1.2, most preferably from 0.7 to 1.1. Both low and high viscosity CMC are suitable for the realization of the present invention. They can have a Brookfield LVT® viscosity, at 4 wt% in water, 60 rpm and 20 °C, comprised between 2 and 10,000 mPa*s, preferably between 10 and 5,000 mPa*s or a Brookfield LVT® viscosity at 1% in water, 30 rpm and 20 °C, comprised between 100 and 10,000 mPa*s. Preferably the CMC of the invention is a low viscosity CMC.

Usually, the carboxymethyl cellulose of the invention is salified with alkali metal ions, such as sodium or potassium, ammonium or quaternary ammonium salts. Preferably, the carboxymethyl cellulose of the invention is a potassium CMC (K-CMC).

Advantageously, the carboxymethyl cellulose is a technical grade polyanionic cellulose (PAC) having a percentage of active substance of from 55 to75 wt% as dry matter.

PACs are carboxymethyl celluloses well known in the oil industry and considered to be premium products because they typically have a high degree of carboxymethyl substitution and a more homogeneous anionic distribution along the polysaccharide chain.

Any shale inhibiting agent commonly used in the field can be utilized for the preparation of the shaped solid shale inhibitors of the inventions. Examples are those described in the literature reported above, potassium salts, inorganic and organic phosphates; silicates; polyalkoxy diamines and their salts, for example those sold with the commercial name of Jeffamine®; choline derivatives; diamines, triamines, polyamines and their salts; high boiling by-products of hexamethylenediamine purification and their salts; partially hydrolyzed (meth)acrylamide copolymers (PHPA) and their cationic derivatives; dialkyl aminoalkyl (meth)acrylate/ (meth)acrylamide copolymers; quaternary ammonium compounds; cationic polyvinyl alcohols; and mixtures thereof.

Examples of diamines are diamines with a saturated C ₂ -C ₈ alkyl chain, such as 1 ,6-hexamethylene diamine, 1,2-ethylene diamine, 1 ,3-propylene diamine, 1,4-butane diamine, 1,5-pentane diamine, 1 ,2-cyclohexane diamine and mixtures thereof.

Examples of triamines and polyamines are diethylene triamine, bis- hexamethylene-triamine, triethylene tetramine and tetraethylene pentamine, higher amines, and mixtures thereof.

Examples of polyalkoxy diamines are those represented by the general formula I :

in which x has a value from 1 to 25 and R and Ri are, independently one of the other, alkylene groups having from 1 to 6 carbon atoms.

The amine salts useful for the realization of the invention are of the inorganic or of the organic kind, the preferred salts being salts formed with hydrochloric acid, phosphoric acid, formic acid, acetic acid, lactic acid, adipic acid, citric acid, etc., more preferably with acetic acid. Preferably all the amine groups of the amines are salified.

Advantageously, the shale inhibiting agent of the invention is a high boiling by-product of hexamethylenediamine purification (product that is commercially known as HMDA bottoms) or a salt thereof. These products, described in WO 2011/083182, typically comprise variable amounts of bis- h exam ethylene- triamine.

The typical contents of amines of HMDA bottoms is the following (as wt%):

Bis-hexamethylene-triam ine 20-50

Hexamethylendiam ine 20-70

1 ,2-Cyclohexanediamine 0-30

Higher amines 0-20

Preferred shale inhibiting agents are diamines, triam ines,polyam ines, polyalkoxy diamine represented by the general formula I, their salts, and m ixture thereof. Other ingredients that can be advantageously added to the said shaped solid shale inhibitors of the invention are fillers; disintegrating agents such as polyvinylpyrrolidones, dextrans, maltodextrins, m icrocrystalline cellulose, cross-carmellose and starches or mixtures of carboxylic acids, for example citric or tartaric acid, and water soluble carbonates or bicarbonates, i.e. sodium carbonate; plasticizers such as ethyl cellulose and polyethylene glycol.

The method of preparation of a shaped solid shale inhibitor of the invention comprises the following phases:

I. mixing a carboxymethyl cellulose, at least one shale inhibiting agent and, optionally, water, in the appropriate amounts to form a m ixture;

II. exerting sufficient pressure on the mixture to form a shaped solid shale inhibitor;

III. optionally, further comminuting the shaped solid body to form a comminuted shaped solid shale inhibitor.

The mixing step (phase I) is performed by conventional means in a manner sufficient to preferably provide a uniform mixture of the starting materials typically under atmospheric pressure and ambient temperature. The optional water addition to the mixture is only important in that it should be high enough to allow the intimate and uniform mixing of the different components and should give a good plasticity to the mixture. Conversely, the water content of the mixture should not be so high that it does not maintain its shape after it is compressed. Generally, the water content of the mixture is from 5.0 to 50 % by weight.

In a preferred embodiment a wet CMC, i.e. a CMC comprising from 20 to 45 % by weight of water, is combined with the shale inhibiting agent. The thus prepared mixture is shaped into a solid body (phase II) by processes such as dry pressing or extrusion, preferably by extrusion.

In shaping by dry pressing, the pressure for forming a solid body is typically in a range from about 40 to 140 MPa, and the temperature is typically ambient.

In shaping by extrusion, the mixture, preferably hydrated, is knead in a typical kneader of appropriate size and then extruded. Usually the mixture is heated to or maintained at a temperature in the range from about 20 to about 100 °C. The optimum temperature for extrusion will vary somewhat dependent upon the components of the mixture, but the optimum temperature can readily be determined empirically. The temperature of the mixture may vary depending upon where it is in the extruder, but generally a uniform temperature profile is preferred. The temperature referred to herein is the mixture temperature in the extruder just before it passes through the die. High temperatures which can cause decomposition should be avoided.

The mixture is extruded through a die, preferably a multi-hole die. In general, the shape and size of the orifices fix the cross-sectional shape and size of the extrudate. Although any shape of orifice may be used, i.e. circle, triangle, square, rectangle and star, it is preferred that the extrusion of the mixture is through equiaxial orifices. Equiaxial orifices are orifices that have approximately equal dimensions in all directions. The cross-sectional area of the orifices should be small enough so that the extruded mixture fibers line up parallel to each other in a tightly formed filaments (strands). On the other hand, the cross-sectional area of the orifice should not be so small that an excessive amount of energy must be exerted to press the mixture through the orifices. Generally, the orifices are of dimensions ranging from 1.0 to 6.0 mm, preferably from 2.0 to 3.5 mm.

The extrusion can be done with any device that applies sufficient pressure to push the mixture through the extrusion orifices at a temperature not too high. For example, a pump-type extruder, such as a positive displacement piston or a gear pump, can be used. Another example of suitable extrusion equipment is a screw-type extruder which advances the mixture by means of a screw rotating inside a cylinder. A twin screw extruder in co-rotating or counter-rotating mode, intermeshing or non- intermeshing may be utilized in the processes of the invention, but equally a single screw extruder or a multi screw extruder may also be suitable providing always that mixing can be achieved. Usually the extrusion process is carried out at pressures well above atmospheric pressure, preferably the extrusion is carried out at pressures of from about 2 to about 16 MPa.

The inhibitor is a firm material appearing uniform in texture and color. Generally, the extruded inhibitor of the invention is in the form of long, narrow filaments. The filaments have a uniform cross-sectional area that is approximately the same as the extrusion orifices described above.

Typically, the extruded inhibitor has a residual moisture content ranging from 5.0 to 50 % by weight, preferably from 15 to 30 % by weight.

The shaped bodies obtained from phase II, such as extruded filaments, can be further comminuted in order to reduce/optimize their dimensions (phase III).

The comminuting can be accomplished by using standard equipment known in the art. Typical comminuting devices are air-swept impact mills, ball mills, hammer mills, and disk mills. This is preferably done in an air- swept impact mill because the other mills, i.e. ball mills, have a tendency to overmill the product into fine particles that are dusty. In addition, an air-swept impact mill will dry the extruded material, if necessary, by blowing hot air across the mill.

Another method for comminuting the shaped bodies is to cut it with a die- faced cutter. A die-face cutter operates by moving a blade across a stationary die or by moving a die across the stationary blade. Thus, the shale inhibitor is cut as it come out through the plurality of orifices in the die.

The size of the orifice fix two of the dimensions of the product. Therefore, it is only necessary to cut the filaments to shorten the length. Typically, the extruded inhibitor is cut to a length/diameter ratio of from 0.2 to 3, preferably to a length/diameter ratio of from 1 to 2.

It may be advantageous to dry the shaped solid shale inhibitors obtained from the described processes. The drying of the these materials can be accomplished with standard drying equipment and methods known in the art. Typical driers include those commonly used in the art, for example belt driers and fluid bed driers. Typically the shaped solid shale inhibitors have a residual moisture content generally ranging from 5.0 to 15 % by weight.

The disclosed shaped solid shale inhibitors can be utilized for inhibiting shale hydration during the treatment of subterranean formations according to the method of the invention.

The shaped solid shale inhibitors are dissolved in a treatment fluid in an amount comprised between 0.5 to 6.0 wt%, preferably between 2.0 and 5.0 wt%.

Usually, the treatment fluid contains an aqueous based continuous phase and the normally used additives, well known by those skilled in the art, such as weighting materials, viscosifying agents, dispersants, lubricants, corrosion inhibitors, defoamers and surfactants; the order in which the additives and the shale inhibitors of the invention are added into the fluid is not critical. Useful weighting materials may be selected from: barite, hematite, iron oxide, calcium carbonate, magnesium carbonate, magnesium organic and inorganic salts, calcium chloride, calcium bromide, magnesium chloride, zinc halides, alkali metal formates, alkali metal nitrates, and combinations thereof.

The aqueous based continuous phase may be selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof.

The treatment fluids of the present invention are suitable for use in any treatment of subterranean formations wherein shale inhibitors can be necessary. As used herein, the term "treatment," or "treating," refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The fluids disclosed herein are especially useful in the drilling, completion and working-over of subterranean oil and gas wells and also in stimulation operations (such as fracturing), gravel pack, cementing, maintenance, reactivation, etc.

The following examples are included to demonstrate the preferred embodiments of the invention.

EXAMPLES

In the Examples the following materials were used : K-CMC: potassium CMC, active content 57 wt% ; DS 0.80; Brookfield® LVT viscosity 400 mPa*s, 4 wt% water solution at 25 °C and 60 rpm; NA-CMC: sodium CMC; active >97 wt% ; DS 0.80; Brookfield LVT® viscosity 80 mPa*s, 4 wt% water solution at 25 °C and 60 rpm;

HMDA-AC: hexamethylene diamine bottoms acetate water sol.; active 70 wt% ; pH about 6 (5 wt% water solution);

TETA 6 PO ACETATE: propoxylated triethylentetramine acetate water sol.; active 70 wt%; pH about 5.5 (5 wt% water solution);

Q MAX DRILL®: amine based shale inhibiting agent, supplied by Qmax Solutions;

KLA-STOP®: polyether amine shale inhibiting agent, supplied by Ml SWACO;

KLA-CURE: amine based shale inhibiting agent, supplied by Ml SWACO; MAX-GUARD®: amine based shale inhibiting agent, supplied by Baker Hughes;

NA-CMC1 : sodium CMC, active 65 wt% ; DS 0.85; Brookfield LVT® viscosity 1000 mPa*s, 4% water solution at 25°C and 60 rpm;

JEFFAMINE® D230: polyoxyalkylene diamine, supplied by Huntsman Corporation;

XG: drilling grade Xanthan Gum; Brookfield LVT® viscosity 1400 mPa*s, 1% in 10 g/l KCI water solution at 20 °C and 60 rpm;

CaCO ₃ V/60: calcium carbonate, active > 99wt% ;

Examples 1-7

Appropriate amount of the ingredients reported in Table 1 were homogenized in a mixer, using a "K" shaped stirrer.

In Examples 1, 2, 4 and 7 pre-moisturized K-CMC, with a moisture content of 25 wt%, was used for the preparation of the solid shaped shale inhibitor and no further water was added to the mixture.

In Examples 5 and 6 dried K-CMC, with a moisture content of 5 wt%, was used for the preparation of the solid shaped shale inhibitor and no further water was added to the mixture.

In Example 3 dried NA-CMC, with a moisture content of 5 wt%, was used for the mixture and 14% by weight of dem ineralized water was added to the mixture.

The mixtures of Examples 1-7 were fed into a laboratory Bausano TR80® extruder equipped with 2 counter rotating screws, a multi-hole die with holes with a diameter of 2.5 mm and a die-faced cutter.

The speed of the screws and the cutter was adjusted to produce about 50-80 g/min of pellets about 2.5 mm large and 2.6 mm long. The internal temperature and pressure during extrusion were around 60-70 °C and 13 MPa respectively.

The extruded pellets were dried on fluid bed at 80 °C to obtain a residual moisture in the range from 7 to 12 wt%.

The final composition (% wt as dry matter) of the shaped solid shale inhibitors are described in Table 1.

Table 1

Examples 8 (Comparative)

The shaped solid shale inhibitor were compared with shale inhibitor of the prior art prepared by simply mixing 36 g of a 50 wt% water solution of JEFFAMINE® D230 and 100 g of CEPAC A1 L (15 and 85 wt% as dry matter, respectively).

Pourability Test

The pourability of the shaped solid shale inhibitors of Examples 1, 3, 7 and of the comparative Example 8 were evaluated following the procedure described in the standard method ASTM 1895-96(10) with some modification. The funnel described in the Test Method B with 500 g of each sample was used.

The results are reported in Table 2.

Table 2

^* Comparative

N.D. = Not Determinable

The pourability test demonstrates that the shale inhibitor of the prior art was not able to flow through the hole of the funnel, while the shaped solid shale inhibitors of the invention showed a good flowability, which eases the handling and the dosing of these products.

Performance Testing

The performances of the shaped solid shale inhibitors of the invention were evaluated with two different kind of shales, a Oxford clay and an Arne clay.

Each clay was dried at 70°C for 3 hours. The dried clays were then ground and sieved through both a 5 mesh (4 mm) sieve and a 10 mesh (2 mm sieve). The clay particles with a size below 4 mm but larger than 2 mm were used in this test.

Two different methods were used: Shale Particle Disintegration Test and Bulk Hardness Test.

Shale Particle Disintegration Test

The test was performed following the procedure described in the standard method ISO10416, section 22, with some modifications.

350 ml of typical drilling muds were prepared by means of an Hamilton Beach Mixer according to the formulations described in Table 3. Table 3

^* Comparative

All muds were adjusted to pH 9.0 by adding some drops of NaOH 20 wt% solution.

30.0 g of sized clay were added to each mud in a glass bottle which were subsequently closed and vigorously shacked to disperse the clay particles. The bottles were then placed in a pre-heated oven and hot-rolled at 80 °C for 16 hours. After the thermal treatment, each bottle was cooled to room temperature.

The treated muds were then poured onto two sieves: 10 mesh (2 mm) and 35 mesh (0.5 mm). The residual clays in the bottles were recovered by washing with a KCI solution (42.75 g/l).

The sieves were transferred in a bath containing tap water and quickly but gently submerged in order to rinse both the sieve and the clays.

The recovered clays were then placed in a pre-weighed dish and dried in oven at 105 °C to constant weight. After drying, the clays were cooled in a desiccator and weighed. The % recovery of the clays for each mud was calculated with following formula:

% recovery = (weight in grams of shale recovered)/ (100-w _h ) x 100 where w _h is the initial moisture content in % by weight of the sized clay. The initial moisture content of the clay was determined by weight loss at 105 °C.

The results (% recovery) with Oxford Clay and Arne Clay are reported in Table 4 and 5, respectively. The higher the % recovery, in particular on the 10 mesh sieve, the higher the performance of the shale inhibitors.

Table 4

Table 5

Bulk Hardness Test

This test was described by Patel, A., et al., in "Designing for the future— a review of the design, development and inhibitive water-based drilling fluid"; Drilling and Completion Fluids and Waste Management, Houston (TX), April 2-3, 2002. Some modifications were introduced.

350 ml of drilling muds were prepared by means of an Hamilton Beach mixer according to the formulations described in Table 3. All samples were adjusted to pH 9.0 by adding some drops of NaOH 20 wt% solution.

30.0 g of sized clay (Oxford Clay or Arne Clay) were added to each mud in a glass bottle which were subsequently closed and carefully shaked to disperse the clay particles. The bottles were then subjected to the same thermal treatment described in the previous test.

The treated muds were then poured onto a 10 mesh sieve. The residual clays in the bottles were recovered by washing with a KCI solution (42.75 g/i)- The sieves were transferred in a bath containing tap water and it is quickly but gently submerged in order to rinse the sieve and the shale. Using a torque wrench, the recovered clays were extruded through a perforated plate, measuring the torque required for each turn in compression. The torque is directly correlated to the hardness of the shale and, since the shale that interact with the fluid become softer, to the shale inhibitor efficiency. The average torque values relative to the 14th, 15th, 16th turn are reported in Table 6 . The higher the value the better the performance of the inhibitor.

Table 6

N.D. = Not Determined

The results reported in Tables 4-6 demonstrate that the shaped solid shale inhibitors show very good inhibition properties both with swellable (Oxford) shale and with dispersive (Arne) shale.

Migration Testing

For this test the shaped solid shale inhibitors of Examples 1 and 2 were used.

Moreover, other shale inhibitors were prepared: Examples 9, according to the invention, and comparative Examples 10-12, according to WO 2006/013595. The shale inhibitors were prepared with the ingredients reported in Table 7 and the procedure described for Example 1 (Example 9) and Example 8 (Examples 10-12). The moisture content of each inhibitor was brought in the range between 7 and 12 % by weight.

Table 7

* Comparative

Packaging specimens with a surface area of 24 cm ² (6x4 cm) were obtained from typical packaging for powder products (three layer paper bags: paper-polyethylene-paper).

The specimens were placed in a desiccator for 24 hours and weighed on an analytical balance, with an accuracy of 0.0001 g.

An amount of each solid shale inhibitors of the Examples equivalent to

5.00 g of dry product was inserted between two specimens creating a sort of sandwich (specimen-inhibitor-specimen). All sandwiches were stored in oven at 60 ⁰ C for 10 days.

During this period, a pressure of about 833.33 Kg/m ² (typical pressure that is exerted on the product in a pallet of 1000 Kg ) was applied on these "sandwiches" using a weight of 2 kg.

A "blank sandwich", without shale inhibitor, was subjected to the same treatment.

After 10 days, the "sandwiches" were removed from the oven and the solid shale inhibitors were carefully abraded from the specimens.

The specimens were again placed in a dessicator for 24 hours and weighed.

The weight difference between the packaging specimens before and after the thermal treatment are reported in Table 8. Table 8

^* Comparative

Each sheet of the packaging specimens on the upper part of the sandwich was analyzed by means of attenuated total reflectance FT- IR (FT-IR Spectrum ONE, Perkin Elmer, equipped with a ATR accessory with a Diamond/ZnSe contact crystal). The spectra were acquired pressing the paper or the polyethylene sheets on the crystal using the pressure arm of the accessory (about 140 pressure arbitrary unit).

The data of Table 8 demonstrate the heavy contamination of the packaging for the shale inhibitors of the prior art (Examples 10-12). This problem was less evident or totally absent for the shaped solid shale inhibitors of the invention (Examples 1, 2 and 9).

The spectra obtained from the specimens of Example 9 and 12 are shown in Fig. 1-4.

The comparison of the IR spectra of Fig. 1 and 2 also confirm that, with the shale inhibitors of the prior art, the amine migrate through the different sheets of the packaging. This does not happen with the shaped solid shale inhibitor of the invention (Fig 3-4), which show only a very slight contamination of the internal paper sheet.

The external paper sheet of the specimen in contact with the comparative shale inhibitors did not show any contamination after 10 day at 60 °C, but, given enough time, the amine would definitely migrate also to the outer sheet of the packaging. Certainly this is a hard problem since the industrial products can be stored for a much longer time possibly under high temperature conditions.