The present invention relates to the use of a chemically modified polysaccharide-protein blend as an additive for drilling muds.

Deep wells always require an appropriate drilling mud. These drilling muds can be classified by the nature of the liquid phase (water, oil), by the nature of the solids present in the mud (clay muds, solids-free muds) or by the density, where a distinction is in turn made between unweighted muds and weighted muds. Drilling muds serve essentially to support the well and to discharge the drilled earth material (well cuttings), they remove the heat of friction which arises in the drill bit, and they reduce the frictional resistance to the drill bit and rotating drill rods and damp the vibrations thereof.

Muds having water as the liquid phase are referred to as water-based muds. Frequently, bentonite-water mixtures are used, which are processed to give a suspension by means of high-speed special mixers. For precise control of the rheological properties, assistants, usually polymers, are also added to the suspension. It is important for the rheological characteristics of drilling mud suspensions and solutions that the addition of clay particles and/or polymeric additives produces a plastic viscosity as far as possible in the mud. This is because, when mud circulation commences, the contact sites between the bentonite particles are broken and/or superstructures in the dissolved polymers are destroyed and broken up, such that the higher the external pumping force and hence the flow rate, the thinner the mud becomes. In other words, the muds lose viscosity with increasing shear rate, which is also referred to as pseudoplastic characteristics.

Polymers which exhibit such rheological characteristics are, for example, hydrogels. The aqueous solutions thereof feature high storage moduli (C) and loss moduli (G"). The elastic (C) and friction-afflicted components (G") are reflected therein, the effect of which has a crucial influence on the quality of the drilling mud solution. In other words, only through the polymeric additives is the mud capable of transporting the well cuttings from the base upward, of keeping them suspended when the mud pumps are shutdown, of protecting the walls by formation of a filtercake, of providing a positive pressure against the pressures of the liquids and gases in the formation, and of cooling and lubricating the bit.

As already mentioned, the polymeric additives used in the drilling mud have to fulfil a multitude of functions. One of these functions is fluid-loss control. In simplified terms, this involves keeping the water in the drilling mud. Since the drilling mud, in the course of circulation thereof in the well, is frequently in contact with porous rock formations which can withdraw water from the drilling mud, the addition of fluid-loss additives is essential. These fluid-loss additives form a filtercake at the well wall and thus prevent the flow of water out of the drilling mud into the formation. The fluid-loss additives used according to the prior art are, for example, starch and starch derivatives such as hydroxypropyl starch or else polyanionic cellulose. At higher temperatures, synthetic polymers are employed. Mention should be made here by way of example of Polyd rill, an anionic condensate from BASF Construction Polymers GmbH, and AMPS®-based copolymers, as described, for example, in EP 1358233 A2 and the documents cited therein.

Aside from the polysaccharides already mentioned, no further suitable compounds based on renewable raw materials have become known to date.

The inventors have therefore addressed the problem of developing alternative compounds based on renewable raw materials, which should if at all possible lead to an improvement in performance.

This problem has been solved by the features of the independent claim. The dependent claims indicate advantageous embodiments.

PCT/EP2013/065441 of 22.07.2013, with priority of 20.07.2012, which was yet to be published at the priority date of the present application, disclosed a chemically derivatized polysaccharide-protein blend (PPB), comprising partially water-swellable polysaccharides and proteins, wherein the polysaccharides and proteins have each been at least partially chemically covalently modified by a) at least one noncrosslinking denvatization; and b) at least one crosslinking denvatization, wherein the polysaccharides and proteins have been at least partially chemically covalently crosslinked with one another, characterized in that the chemically derivatized polysaccharide-protein blend in aqueous medium forms a hydrogel.

In addition, PCT/EP2013/065441 describes the use of the chemically modified PPB only as an additive for dry mortar applications. There was no mention here of the use of the chemically modified PPB as an additive for drilling muds.

It has now been found that, surprisingly, this chemically modified PPB can likewise be used as an additive for drilling muds, especially as a fluid-loss additive and rheological additive.

The present invention accordingly provides for the use of a chemically derivatized polysaccharide-protein blend comprising partially water-swellable polysaccharides and proteins, wherein the polysaccharides and proteins have each been at least partially chemically covalently modified by a) at least one noncrosslinking denvatization; and b) at least one crosslinking denvatization, wherein the polysaccharides and proteins have been at least partially chemically covalently crosslinked with one another, and wherein the chemically derivatized polysaccharide-protein blend in aqueous medium forms a hydrogel, as an additive for drilling muds.

The PPB hydrogel used is characterized by a high water binding potential and is thus ideally suitable as a fluid-loss additive.

The word "gel" derives from the term gelatine (lat. gelatum: frozen). In colloid chemistry, this is understood to mean a dimensionally stable, deformable, liquid-rich disperse system composed of at least two components, usually consisting of a solid, colloidally distributed substance and a liquid as a dispersant.

The three-dimensional network of a gel forms through crosslinks between the individual polymer chains. These node points are either chemical (covalent) or physical in nature. Physical interactions may be ionic (coulombic), nonionic (hydrogen bonds) or micellar in nature (van der Waals forces). If the dispersant consists of water, reference is made to hydrogels. They are based on hydrophilic but water-insoluble polymers. These polymers swell in water with retention of shape up to an equilibrium volume.

Whether a gel is present can be determined by means of dynamic rheology, in which the storage modulus G' and loss modulus G" are determined as a function of frequency. On the basis of the profile of these characteristics, a conclusion can be drawn about the structure present, viscoelastic solution or gel. According to the definition of a gel, the storage modulus G' is above the loss modulus G" and is virtually independent of the measurement frequency over at least one decade.

The noncrosslinking derivatization of the partially water-swellable polysaccharides and proteins achieves destructuring of superstructures. For example, the destructuring suppresses recrystallization of the originally partially water-swellable polysaccharides. Firstly, this gives rise to an increased swellability and solubility of the derivatized polysaccharides, which can be manifested in cold-water swellability. Secondly, the breakup of the superstructures enables homogeneous derivatization along the

polysaccharide chain, which is the reason for the ability of partially water-swellable polysaccharides to form hydrogel when there is appropriate crosslinking between glucan chains of the polysaccharides or between polysaccharide and protein.

The noncrosslinking derivatization of proteins can also cause irreversible denaturing of the proteins. Denatured proteins assume a "random coil" structure which enables

derivatization of the protein along the polypeptide chain, i.e. derivatization at sites inaccessible in the native protein state. This gives rise to the possibility of influencing the solubility properties of the proteins in a controlled manner.

The crosslinking derivatization of the polysaccharides and proteins produces the hydrogel character thereof, which is reflected in a plastic viscosity. The higher the difference between storage modulus (C) and loss modulus (G"), the more marked are the hydrogel properties of the crosslinking product. The viscosities of the samples used in the examples and the viscoelastic properties thereof in aqueous solution (hydrogel character) are shown in the appended drawings. An explanation of the drawings can be found immediately before the experimental section of this specification.

The term "viscoelasticity" originates from the conventional theory of elasticity, which describes mechanical properties of a perfectly elastic solid. Depending on the structure of a solid, of a melt, of a gel or of a dispersion, there are deviations from purely elastic characteristics; viscous and elastic components are present alongside one another. These properties are referred to as viscoelastic.

It has now been found that these viscoelastic properties of the inventive chemically derivatized PPB are of crucial significance in order to display its positive effect as a fluid- loss additive in drilling muds. In the experimental section of this patent application, this is demonstrated by a controlled fractionation of the PPB hydrogels into a fraction A having a very high plastic viscosity, i.e. consisting predominantly of the crosslinked constituents of the PPB, and a fraction B having very substantially no hydrogel character, i.e. consisting predominantly of polymer constituents of the PPB dissolved in disperse form in the aqueous medium and generating barely any intrinsic viscosity.

The chemically derivatized polysaccharide-protein blend additionally has, over the entire pH range of 1 -14, the property of binding and/or immobilizing water.

In a preferred embodiment of the invention, the inventive polysaccharide-protein blend, based on the nonderivatized, anhydrous state thereof, comprises

20-99% by weight, preferably 55-96% by weight, more preferably 70-85% by weight, of polysaccharides and/or

1 -80% by weight, preferably 4-45% by weight, more preferably 15-30% by weight, of proteins.

A content of polysaccharide and/or protein within this range has been found to be particularly advantageous with regard to hydrogel formation and the production costs of the PPB.

In a preferred embodiment of the invention, the soluble polysaccharides in the inventive PPB have a mean molar mass of 10 ⁶ to 10 ⁷ g/mol. This figure is based on the molar mass of an average polysaccharide in the PPB, which is not caused by the chemically covalent derivatization but is founded solely in the mass of the polysaccharide without chemical derivatization. It is advantageous here that the PPB has essentially the natural crosslinking of the polysaccharide monomers via a glycosidic bond. It has been found that a mean molar mass of the polysaccharides in the region of 10 ⁶ to 10 ⁷ g/mol has an advantageous effect on the hydrogel formation of the PPB.

The partially water-swellable polysaccharides and proteins may comprise or essentially consist of vegetable or animal proteins and/or polysaccharides. Preference is given in this context to polysaccharides and/or proteins from cereals, pseudocereals, vegetable tubers, vegetable rhizomes and/or leguminous fruits. Preferred cereals are wheat, spelt, rye, oats, barley, millet/sorghum, triticale, maize and rice. Preferred pseudocereals are buckwheat, amaranth, quinoa and hemp. Preferred vegetable tubers are potato, sweet potato (batata) and manioc (tapioca). Preferred vegetable rhizomes are taro and arrowroot, and preferred legumes are beans, peas, lentils and chestnuts. In addition, it is possible to use vegetable marrow, preferably sago palm marrow. Particular preference is given to polysaccharides and/or proteins from rye, especially in the form of rye flours. The advantage of polysaccharides and/or proteins from a vegetable source is that renewable raw materials can be used as the crude product or reactant for the preparation of the inventive PPB. This constitutes an enormous economical and ecological advantage.

The polysaccharides and proteins of the inventive PPB may have at least one

noncrosslinking derivatization, but also a plurality of such derivatizations, preferably selected from the group consisting of neutral, hydrophobic and cationic substituents.

In a preferred configuration, the polysaccharides and proteins in the PPB have a hydroxyalkylation, preferably a hydroxyalkylation by a hydroxylating agent selected from the group of the oxiranes, more preferably selected from the group consisting of alkylene oxides having straight-chain or branched Ci-is-alkyl groups, especially ethylene oxide and/or propylene oxide.

In addition, the inventive PPB may have a functionalization with chemical compounds from the group consisting of quaternary ammonium salts and organic chlorine

compounds, preferably 3-chloro-2-hydroxypropyltrimethylammonium chloride and/or 3-chloro-2-hydroxypropylalkyldimethylammonium chloride. Particular preference is given to alkylation with trialkylammonioethyl chloride and/or trialkylammonium glycide. The alkyl group may be the same or different in each case and/or comprise or consist of at least one straight-chain or branched Ci-Cis-alkyl group.

The polysaccharides and proteins in the inventive PPB may be modified with an amount of 0.001 -2.0 mol, preferably 0.01 -0.5 mol, more preferably 0.1 -0.4 mol, of noncrosslinking derivatizing reagent per mole of anhydroglucose unit of the polysaccharides. In this context, the polysaccharides and/or proteins of the PPB, in relation to the noncrosslinking derivatization, may have a degree of substitution (DS) of 0.001 -1 .0, preferably 0.01 -0.5, more preferably 0.1 -0.4.

The polysaccharides and proteins preferably have noncrosslinking substitution in such a way that the polysaccharides after the derivatization cannot form a compact structure and/or the proteins are in denatured form. In this respect, a degree of substitution of≥ 0.1 is particularly advantageous in relation to the polysaccharides in order to prevent the recrystallization of the modified polysaccharides.

With regard to the chemically covalent crosslinking, the polysaccharides and proteins in the PPB may be modified with an amount of 0.001-1 .0 mol, preferably 0.01 -0.5 mol, more preferably 0.05-0.2 mol, of crosslinking derivatizing reagent per mole of anhydroglucose unit of the polysaccharides. In this regard, a degree of crosslinking of≥ 0.05 mol of crosslinking derivatizing reagent per mole of anhydroglucose unit of the polysaccharides is particularly advantageous for a higher adhesive effect of the PPB.

The polysaccharides and proteins in the inventive PPB are preferably crosslinked by means of a derivatizing reagent selected from the group consisting of a) epihalohydrin, diglycidyl ethers and (poly)alkylene glycol diglycidyl ethers,

preferably polyalkylene glycol diglycidyl ethers having 1 -100 ethylene glycol units; b) phosphoric acid and phosphoric acid derivatives, preferably phosphoric

anhydrides, phosphoryl chlorides and/or phosphoric esters;

c) bi- or oligofunctional organic alkyl and aryl compounds, preferably carboxylic acids and/or carboxylic esters;

d) aldehydes, preferably formaldehyde, glutaraldehyde and/or glyoxal;

e) grafting reagents, preferably acrylic acid compounds, substituted acrylates, vinyl- containing compounds and/or aldehyde-amide condensates; and

f) halides, preferably epoxy halides, aliphatic dihalides, halogenated polyethylene glycol and/or diglycol dichloride.

In the inventive PPB, only a portion of the proteins and polysaccharides may be chemically covalently crosslinked at least in some regions. Preferably, this crosslinking is implemented via hydroxyl, amino and/or sulphhydryl groups on the proteins and/or polysaccharides. In this regard, at least some of the proteins and/or polysaccharides may be chemically covalently crosslinked at least in some regions exclusively via functional groups which are present on the polysaccharides and/or proteins or have been introduced because of the noncrosslinking derivatization.

According to the invention, the PPB in the alkaline medium may have a soluble component of 0-30%. A preferred embodiment of the invention relates to the use of the chemically derivatized PPB as a fluid-loss additive or as a rheology-modifying additive for water-based drilling muds. It is possible to use further additives which are suitable for water-based drilling muds and are known per se in the prior art together with the inventive additive. Said chemically derivatized PPB is preferably used in the development, completion and exploitation of underground mineral oil and natural gas deposits, and in deep wells.

In principle, on the basis of the performance tests which follow, it has been shown that the PPB chemically modified in accordance with the invention is suitable as an additive in drilling muds. In a fluid-loss test, a considerable difference in action is found between the two fractions A and B (compared to the reference Polydrill® from BASF SE), which is attributable to the presence of a hydrogel character in the chemically modified PPB. In other words, from a performance point of view, the hydrogel character of the additive is of essential significance when additives are used for drilling muds. Accordingly, sample 1 and sample 5 (fraction B), which have (almost) no chemical crosslinking and thus do not have any pseudoplastic viscosity, are found to be ineffective additives, while sample 4 (fraction A), which exhibits high viscoelastic characteristics through the crosslinking, is found to be an extremely effective additive (Table 2). The usability of the chemically modified PPB in drilling muds is additionally reinforced by rheological tests of drilling muds according to API - Recommended Practice For Field Testing Of Water-Based Drilling Fluids 13 B-1 . The rheological data in Example 3 show that the inventive additive "fraction A" (sample 4) in all four different drilling muds has much higher viscosities at low shear rates. This is further illustrated by the yield point (YP)- A high yield point or a high viscosity at low shear rates is very advantageous for the function of a drilling mud, since this gives a positive statement about the load-bearing capacity of the drilling mud at rest. During the drilling operation, the drilling mud is usually in flux. However, during the drilling, it is necessary to stop the drilling operation time and again, in order, for example, to change the drill bit or to extend the drill rods. During these phases, the drilling mud is then at rest. However, in these rest phases too, it is very important that the drilling mud fulfils its function and keeps the well cuttings suspended. Subsidence of the well cuttings would lead to blockage and result in damage to the drill bit and rods when the drilling operation is restarted. In addition, the inventive additive achieves better control of the liquid loss (see Example 2 and Example 3 with regard to a CaC -containing drilling mud).

With reference to the examples which follow and with regard to the appended drawings, the subject-matter of the invention is now to be illustrated in detail, without any intention of restricting it to the specific embodiments described here. The drawings show:

Fig. 1 A) the viscosity profile of sample 2 as a function of shear rate,

Fig. 1 B) the profile of G' and G" for sample 2 as a function of frequency,

Fig. 2 A) the viscosity profile of samples 4 and 5 as a function of shear rate,

Fig. 2 B) the profile of G' and G" for sample 4 as a function of frequency.

EXAMPLES Example 1 : Composition of chemically modified PPB

PPB raw materials:

Various sources for polysaccharide-protein blends which were employed as reactants for production of the inventive PPB are given hereinafter. The sum of the constituents does not always add up to 100% by weight, since fats, sugars and the non-starch

polysaccharides have not been determined, for example rye flour type 997 (industrial specimen from Kampffmeyer Muhlen GmbH from roll milling) with the following

composition: starch 74.0 to 76.0%; protein 7.5 to 8.5%; minerals 0.9 to 1 .0% and pentosans 4.8 to 5.1 %. Further PPBs were obtained in the form of wheat and barley flours. According to the manner of pretreatment (e.g. milling, sifting, fractionating, etc.), it was additionally possible to influence or vary the ratio of polysaccharide and protein: starch 55.0 to 86.0%; protein 4.5 to 15.0%; minerals 0.4 to 1.9%; and pentosans 1 .0 to 5.1 %. Preparation of chemically modified PPB:

First of all, 1065 g of water were initially charged in a reactor and 9.34 g of CaO were added while stirring. Subsequently, 335 g of rye flour were added at room temperature while stirring, and the mixture was stirred for 2 h. After this treatment, the rye flour was partially dissolved and fully swollen. After dispersion of the alkaline suspension, 107.5 g of epoxypropane (propylene oxide) were added as a non crosslinking derivatizing reagent. The mixture was stirred at 35°C for 24 hours. Thereafter, 1 .712 g of epichlorohydrin ("ECH") as a crosslinking derivatizing reagent were added and the mixture was stirred at 35°C for 24 hours. Finally, the product was optionally neutralized with 0.5 N H2SO4, dried and ground. The product obtained was a chemically derivatized polysaccharide-protein blend (PPB) which formed a hydrogel in aqueous medium. The molar degree of etherification (MS) of the product was about 0.5 and the degree of substitution (DS) about 0.23.

Fractionation of chemically modified PPB

The fractionation of the PPB into a water-insoluble fraction and a water-soluble fraction was effected by the following method. For this purpose, it was admixed with about 5% by weight of water, and 40% by weight of ethanol was added. Subsequently, the dispersion formed was centrifuged at 38 600 g for 1.5 hours. The sediment ("fraction A") was a pure PPB hydrogel. For drying, the sediment was dewatered with acetone, filtered off by means of a suction filter, dried at 50°C under reduced pressure and then ground. This gave a dry PPB, which was very clean and formed a hydrogel in aqueous medium. The chemically modified PPBs prepared and performance-tested have the raw material sources and compositions reproduced in Table 1 below (the figures are in % by weight):

Table 1

¹⁾ 1.0 molar equivalent of propylene oxide/anhydroglucose unit (162.9 g/mol), catalyst: CaO ¾ 0.01 molar equivalent of the epichlorohydrin/anhydroglucose unit crosslinking agent 3 ⁾ Neutralization of the catalyst with 0.5 N H2SO4

4 ⁾ MS(HP) = molar substitution by hydroxypropyl ether (determined via NMR spectroscopy)

5) Constitution: 0.9-1.0% minerals, 8.0-9.0% protein, 74.0-75.0% starch, 4.5-5.0% pentosane

6) Constitution: 0.4-0.5% minerals, 7.0-8.0% protein, 85.0-86.0% starch, 1.5-2.0% pentosane

⁷⁾ Constitution: 1.5-1.6% minerals, 9.0-10.0% protein, 65.0-66.0% starch, 7.0-8.0% pentosane

⁸⁾ Fraction A (water-insoluble fractions of sample 3): mostly crosslinked with ECH

9 ⁾ Fraction B (water-soluble fractions of sample 3): mostly not crosslinked

Example 2: Fluid-loss test

In a drilling mud composed of 350 g of Tixoton® suspension (bentonite, 4% by weight in H ₂ 0, Sud-Chemie AG), 1 18 g of NaCI and 2.0 ml of a defoaming agent (Antifoam 422) the samples according to Example 1 were added: 10.5 g of each sample 1 , 4, 5 and reference (Polydrill®, a salt insensitive, rheology neutral fluid-loss additive of BASF SE) as well as 21.0 g of each sample 2, 2a and 2b. The fluid loss was determined according to "API Recommended Practice 13B". The ageing in a roller oven was affected at 121 °C. The results are reproduced in Table 2.

Table 2

The example shows that a much smaller fluid loss is achieved when samples have shown significant hydrogel characteristics. In principle, improved fluid loss behavior is achieved compared to the commercial fluid-loss additive Polydrill®.

Example 2: Fluid-loss and rheology test According to "API Recommended Practice 13B", in a drilling mud composed of 420 ml of H ₂ 0, 18 g of Cebogel® (bentonite, Cebo Holland B.V.), 10 g of Antisol ® FL 10 (polyanio- nic cellulose from DOW Chemicals) or 10 g of the sample No. 4 (fraction A) according to Example 1 , and 24 g of Ba2S0 ₄ and further additives according to Table 3, the fluid loss and rheology were determined. The ageing was effected at 121 °C over 16 h. The results are reproduced in Table 3 below. Table 3

PV: "Plastic Viscosity", calc. from the difference of the values at 600 and 300 min ¹ in [lbs/100 ft ² ] YP: "Yield Point", calculated from the difference between the value at 300 min ¹ and PV [lbs/100 ft ² ] Gels: "Gel strength", value at 3 min ¹ after 10 s / value at 3 min ¹ after 10 min [lbs/100 ft ² ]

FL: "Fluid Loss", according to API

The example shows that inventive PPB having pronounced hydrogel character is at least on a par with Antisol ® FL 10 in tap water, saltwater and seawater, but is far superior in the CaC -containing drilling mud.