IE63931B1 - Drilling fluids - Google Patents

Abstract

The invention describes the use of esters, which are fluid at room temperature and have flashpoints above 80 DEG C, selected from C1-15 monocarboxylic acids and/or mono or multifunctional alcohols as the oil phase or a component thereof in invert drilling muds which are suitable for the environmentally favourable extraction of petroleum or natural gas deposits and, in a closed oil phase, contain a dispersed aqueous phase together with emulsifiers, fillers, fluid loss additives and, if desired, other customary additives. In a further embodiment the invention relates to invert drilling muds of the aforementioned kind in which the oil phase contains esters of C1-15 monocarboxylic acids with mono and/or multifunctional alcohols mixed, if desired, with other components from the class of ecologically acceptable compounds.

Description

BACKGROUND OF THE INVENTION j) FTHTD CF THE INVENTION The invention relates to drilling fluids, and concerns in particular invert drilling muds for use in the drilling of petroleum and gas wells. ii) DESCRIPTION OF THE PRICK ART It is now common to drill a well (such as an oil well) using an oil-based drilling fluid of the so-called invert-emulsion mud type. This sort of drilling mud consists of a three-phase system of oil, water and finely particulate solids, and is a preparation of the water-in-oil (W/O) emulsion variety - that is, the aqueous phase is distributed as a heterogeneous fine dispersion in the continuous oil phase. A number of additives can be used to stabilize the system as a whole and to confer on it the desired application properties - particularly, emulsifiers or emulsifier systems, weighting agents, fluid-loss additives, alkali reserves, viscosity regulators and the like. Details of these may be ascertained iron the publication (by P.A. Boyd et al), New Base Oil Used in Low-Toxicity Oil Muds, Journal of Petroleum Technology, 1985, 137 to 142, and the publication (by R.B. Bennett), New Drilling Fluid Technology - Mineral Oil Mud, Journal of Petroleum Technology, 1984, 975 to 981 (and, of course, any of the literature cited in either of these).

Many of these earlier oil-based muds have been built around mineral (or diesel) oils, which have been found to cause serious - 2 equipment and environmental problems, and for seme time it has been recognised that organic oils, and specifically ester-based oils, could help to reduce the problems. For example, US Patent Specifications Nos. 4,374,737 and 4,481,121 disclose oil-based drilling fluids in which various non-polluting oils are to be used. Those mentioned as non-polluting oils of equal value are on the one hand mineral oil fractions not containing aromatic hydrocarbons, and on the other vegetable oils such as groundnut oil, soybean oil, linseed oil, com oil, rice oil or even oils of animal origin, such as whale oil. Without exception, these named ester oils of vegetable and animal origin are triglycerides of natural fatty acids; they are known to have a high environmental acceptability, and are in fact clearly superior, from the ecological viewpoint, when compared with hydrocarbon fractions even those free from aromatic hydrocarbons.

Interestingly enough, however, not one of the examples in the aforementioned US Patent Specifications actually describes the use of the identified natural ester oils in invert-drilling fluids; in every case, mineral oil fractions are used as the continuous oil phase. Oils of vegetable and/or animal origin are not considered for reasons of practicality. The rheological properties of such oil phases cannot be satisfactorily controlled over the wide temperature range the muds made therefrom will experience in use, from 0 to 5°C on the one hand up to 250°C on the other.

In addition to the rheological problems, there are other difficulties associated with the use of ester oils of the type in question; from a chemical viewpoint they do not behave in the same - 3 way as the mineral oil fractions based on pure hydrocarbons which were previously used. Specifically, ester oils are subject to partial hydrolysis, particularly in W/O invert drilling muds, with free carboxylic acids formed as a result. Our earlier German Patent Applications P 38 42 659.5 and ? 38 42 703.6 (D 8523 Verwendung ausgewahlter Esterole in Bohrspulungen (1) and also D 8524 Verwendung ausgewahlter Esterole in Bohrspulungen (II)) describe the problems caused thereby, and give suggestions for their solution.

The subject of these earlier Applications is the use of ester oils based on selected monocarboxylic acids (or mixtures thereof) and monofunctional alcohols with at least 2, and preferably with at least 4 carbon atcms. Ihe earlier Applications show that, with the esters and ester mixtures they disclose, monofunctional reactants can not only be given satisfactory rheological properties in fresh drilling fluid, but that by using selected kncwn alkali reserves (calcium hydroxide or lime and/or zinc oxide or comparable zinc compounds) it is possible to work with the drilling fluid and in this way to inhibit undesirable corrosion. Hcwever, in this case an additional restriction is advisable. If unwanted thickening of the oil-base invert-mud. system is to be prevented in practical use, the amount of alkali additive, and in particular the amount of lime, must be limited. The maximum amount satisfactory is about 2lb/bbl oil-base mud in the disclosure of the aforementioned earlier Applications (lb/bbl means pounds per barrel: this is the standard measurement used throughout the oil industry). - 4 BRIEF SUMMARY OF THE INVENTIVE CONCEPT The present invention suggests avoiding the problems described above by using a class of ester oils which, as a result of the limited ester hydrolysis which always occurs, forms carboxylic acids and carboxylic-acid salts that do not themselves give rise to difficulties. More specifically, the invention proposes the use of ester oils which are based on lower carboxylic acids having from 1 to 5 carbon atoms, and especially those esters based on acetic acid (the acetate salts forming during the partial hydrolysis of the ester oil do not have the emulsifying properties which could substantially disturb the W/O system). More generally, the invention suggests, as the oil phase (or as a component thereof) of an invert-drilling mud, the use of esters, fluid at room temperature and having flash points above 80°C, of c1_5~ monocarboxylic acids and mono- and/or polyfunctional alcohols. It is believed that these muds, which may contain in the continuous oil phase a dispersed aqueous phase together with emulsifiers, weighting agents, fluid-loss additives and various other conventional additives, will be suitable for an environmentfriendly development of petroleum or natural gas deposits.

In one aspect, therefore, the invention provides an invertdrilling fluid of the type described and containing in the continuous oil phase a dispersed aqueous phase together with any desired additives, wherein the oil phase contains esters of ^_5~ monocarboxylic acids with mono- and/or polyfunctional alcohols which are fluid at room temperature and have flash points above 80°C. - 5 DETAILED DESCRIPTION OF THE INVENTIVE CONCEPT Though notionally the carboxylic acids used to make the ester of the invention can be polycarboxylic acids, the most preferred esters are those derived from monocarboxylic acids, especially those having from 2 to 4 carbon atoms, with acetic acid (as already mentioned) being of particular importance.

The esters of the lower carboxylic acids suitable according to the invention can be divided into two sub-classes, those with monofunctional alcohols and those with polyfunctional alcohols. In the monofunctional alcohol class the alcohol preferably contains at least 6 carbon atoms, but advantageously has more i.e, at least 8 to 10 carbon atoms. In the polyfunctional alcohol class the alcohol is preferably a di- to tetra-hydric alcohol; lower alcohols of this type, especially those having from 2 to 6 carbon atoms, are particularly suitable. Typical examples of such polyhydric alcohols are glycol and/or the propanediols, with ethylene glycol, 1 ,2-propanediol and 1,3-propanediol being particularly important. In the case of esters with polyhydric alcohols, the completely esterified reaction products are preferred, even though partially esterified products can be employed (and particularly partial esters of the higher valency polyfunctional alcohols with the lower carboxylic acids mentioned).

When selecting the alcohol it is important to take account of the following additional considerations.

Firstly, as observed above, when the ester oil is used it is as a rule not possible to exclude partial saponification of the ester. - 6 Free alcohols form, in addition to the free carboxylic acids (or their salts with the alkali reserves). The alcohols should therefore be selected such that even after partial hydrolysis they are ensured operational conditions which are both ecologically and toxicologically harmless, with inhalation-toxicological considerations in particular being taken into account. The alcohols used should more especially possess such a low volatility that in the free state (under the conditions to be expected in practice), they do not result in any nuisance on the working platform.

Secondly, for ester oils based on the very short-chain monocarboxylic acids of the invention together with monofunctional alcohols, it is highly desirable from the outset to use comparatively long-chain monofunctional alcohols, so as to reduce sufficiently the volatility of the ester oil. The considerations discussed here are particularly important in cases where the ester oils of the invention are used in blends with other mixture components, in particular other carboxylic acid esters.

The alcohols, particularly the monofunctional alcohols, suitable for use to make the esters of the invention can be of natural or synthetic origin. They can be straight- or branched-chain, and olefin mono- or poly-unsaturated. The aliphatic (saturated) * alcohols preferably have a chain length of from 8 to 15 carbon atoms, while the mono- and poly-unsaturated alcohols (which can be obtained, for example, by the selective reduction of naturally occurring unsaturated fatty acids or fatty acid mixtures), can have up to 24 carbon atoms.

The Cj ^-carboxylic-acid esters used in the drilling mud of the invention most conveniently have solidification values (pour and setting point) belcw 0°C, preferably below -5°C, and particularly belcw -10°C. At the same time, especially for safety reasons, the flash points of these esters are advantageously as high as possible - most preferably the flash point is at least 90°C, and very desirably it is above 100°C.

The physical properties of the monocarboxylic acid esters used in the invention can be controlled by the selection of the alcohol components. The preferred esters (or mixtures thereof) are those that are fluid and pumpable even when cold (in the temperature range of 0 to 5°C). More specifically, these preferred esters, or their admixtures with ecologically-acceptable components from the class of so-called non-polluting oils, have in the temperature range of 0 to 5°C a Brookfield (RVT) viscosity of not more than 50 mPa.s, preferably not above 40 mPa.s. Very desirably the viscosity of the oil phase is at the most about 30 mPa.s.

The ester oils of the invention can form either the whole of the continuous oil phase of the W/O invert mud or only a part thereof, being one component of a mixture of components forming the oil phase. Practically any of the oil components previously known and/or described in the relevant area of application are suitable as the other oil components. Particularly suitable mixture components are discussed belcw.

The ester oils according to the invention are as a rule homogeneously miscible with the additional mixture components in any desired mixture ratio. It is useful, though, for at least 25% - 8 by weight, and particularly at least a third, of the oil phase to be in the form of the invention's C^^-ester oils. In the more important embodiments of the invention, these ester oils form the main part of the oil phase.

Mixture components in the oil phase Suitable oil components for admixture with the esters of the invention are the mineral oils currently used in drilling fluids, and preferably aliphatic and/or cycloaliphatic hydrocarbon fractions essentially free from aromatic hydrocarbons and with the required rheological properties. These materials are well known in the Art (as referred to above), and need no further comment here.

However, particularly important mixture components are other ecologically-acceptable ester oils as described, for example, in the aforementioned earlier Applications. The essential characteristics of these earlier esters (or ester mixtures) are new briefly summarized.

As the oil phase, in a first embodiment, there are used esters of monofunctional alcohols with from 2 to 12, particularly from 6 to 12, carbon atoms and aliphatic-unsaturated monocarboxylic acids with from 12 to 16 carbon atoms, which esters are fluid and pumpable in the temperature range of 0 to 5°C, or an admixture thereof with at most about the same amounts of other monocarboxylic acids. Ester oils are preferred which are at least about 60% by weight, based on the respective carboxylic acid mixture, esters of aliphatic ^2 .^-monocarboxylic acids, the - 9 remaining percentage being preferably based on smaller amounts of shorter-chain aliphatic and/or longer chain, in particular olefin mono- or poly-unsaturated, monocarboxylic acids. These esters preferably have at 0 to 5°C a Brookfield (RVT) viscosity of not more than 50 mPa.s, preferably not above 40 mPa.s and most especially of a maximum of 30 mPa.s. The esters used in the drilling mud have solidification values (pour and setting point) belcw -10°C, preferably belcw -15°C, and have at the same time flash points above 100°C, preferably above 150°C. The carboxylic acids present in the ester or ester mixture may be straightand/or branched-chain, and of vegetable and/or synthetic origin. They can be derived from corresponding triglycerides such as coconut oil, palm kernel oil and/or babassu oil. The alcohol radicals of the esters used are derived in particular from straight- and/or branched-chain saturated alcohols, preferably with from 6 to 10 carbon atoms. These alcohol components can also be of vegetable and/or animal origin, and can thus be obtained by reductive hydration of corresponding carboxylic acid esters.

A further class of particularly suitable ester oils is derived frcm olefin mono- and/or poly-unsaturated monocarboxylic acids having from 16 to 24 carbon atoms, or their admixtures with lower amounts of other, particularly saturated, monocarboxylic acids and monofunctional alcohols with preferably from 6 to 12 carbon atoms. These ester oils are also fluid and pumpable in the temperature range of 0 to 5°C. Particularly suitable are such esters based on (as to more than 70% by weight, preferably as to more than 80% by weight, and in particular as to more than 90% by weight) olefinunsaturated carboxylic acids having from 16 to 24 carbon atoms. - 10 Here, too, the solidification values (pour and setting point) lie below -10°C, preferably below -15°C, while the flash points lie above 100°C, and preferably above 160°C. In the temperature range of 0 to 5°C the esters used in the drilling mud have a Brookfield (RVT) viscosity of not more than 55 mPa.s, preferably not more than 45 mPa.s.

Two subclasses can be defined for the ester oils of the type in question. In the first, the unsaturated Cj 6_24-monocarboxylic acid radicals present in the ester are derived (as to not more than 35% by weight) frcm olefin di- and poly-unsaturated acids, with preferably at least about 60% by weight of the acid radicals being olefin mono-unsaturated. In the second embodiment the C1g_ 24-monocarboxylic acids present in the ester mixture are derived (as to at least 45% by weight, preferably as to at least 55% by weight) from olefin di- and/or poly-unsaturated acids. It is desirable if saturated carboxylic acids having from 16 to 18 carbon atoms do not amount to more than about 20% by weight of the ester mixture, and in particular not more than about 10% by weight. Preferably, saturated carboxylic acid esters, however, have lower numbers of carbon atoms in the acid radicals. The carboxylic acid radicals present can be of vegetable and/or animal origin. Vegetable starting materials are, for example, palm oil, groundnut oil, castor oil and in particular colza oil. Typical carboxylic acid starting materials of animal origin are mixtures of fish oils, such as herring oil.

A final group of suitable mixture components is the esters from monocarboxylic acids of synthetic and/or natural origin having from 6 to 11 carbon atoms and mono- and/or polyfunctional alcohols, as described in our Parallel Application ... (D8607 Ester von Carbonsauren mittlerer Kettenlange als Bestandteil der Olphase in Invert-Bohrspulschlammen) which are preferably also fluid and pumpable in the temperature range of 0 to 5 °C. For completion of the invention disclosure, reference is thus made in this regard to the above Parallel Application, the contents of which are hereby also made subject of the present disclosure.

Further mixture components of the invert drilling fluid These may be any of the constituents of mixtures for conditioning and for the practical uses of invert drilling muds that are currently used when mineral oils provide the continuous oil phase. In addition to the dispersed aqueous phase there may thus be present emulsifiers, weighting agents, fluid-loss additives, viscosifiers and alkali reserves.

A preferred embodiment of the invention also makes use of the further development of these ester oil-base invert drilling fluids which is the subject of the Applicant's earlier Application ... (D 8543 Olephile basische Aminverbindungen als Additiv in InvertBohrspulschlanmen).

The teaching of this Application is based on the concept of using a further additive in ester oil-based invert-drilling fluids, which helps to maintain the desired rheological properties in the drilling fluid even when, in use, increasingly large amounts of free carboxylic acids are formed by partial ester hydrolysis. It should be possible not only to trap these liberated carboxylic acids in a harmless form, but also to reform them, preferably into - 12 components having stabilizing or emulsifying properties for the whole system. According to this teaching, there are used as additives in the oil phase alkaline amine compounds of marked oleophilic nature and at best limited water solubility, which are capable of forming salts with carboxylic acids. These oleophilic amine compounds can at the same time act, at least in part, as alkali reserves in the invert drilling fluid (they can however also be used in combination with conventional alkali reserves, particularly lime). The use of oleophilic amine ccmpounds which are at least substantially free from aromatic constituents is preferred. In particular, there can be employed saturated, or optionally olefin unsaturated, aliphatic, cycloaliphatic and/or heterocyclic oleophilic basic amines containing one or more regroups capable of forming salts with carboxylic acids. In a preferred embodiment the water-solubility of these amines at room temperature is not greater than 5% by weight, and is usefully below 1% by weight.

Typical examples of such amine compounds are primary, secondary and/or tertiary amines, which are at least predominantly waterinsoluble and which can also to a limited extent be alkoxy la ted and/or substituted, particularly with hydroxyl groups. Further examples are the corresponding aminoamides and/or nitrogen heterocycles. For example, basic amine compounds having at least one long-chain hydrocarbon radical, preferably of from 8 to 36, particularly fron 10 to 24, carbon atoms, are suitable; these can be olefin mono- or poly-unsaturated. The oleophilic basic amine compounds can be added to the drilling fluid in amounts of up to about 10 lb/bbl, preferably in amounts up to about 5 lb/bbl and particularly in the range of about 0.1 to 2 lb/bbl.

It transpires that the use of such oleophilic basic amine compounds can effectively prevent thickening of the mud system. This can presumably can be attributed to a disturbance in the W/O invert system, and also to the format ion of free carboxylic acids by ester hydrolysis.

If there are used as mixture components esters of longer-chain carboxylic acids which on hydrolytic cleavage yield fatty acids or fatty-acid salts with a pronounced O/W-emulsifying effect, then in the method of the invention the measures described in detail in the aforementioned earlier German Patent Applications P 38 42 659.5 and P 38 42 703.6 regarding the alkali reserves should also be taken into consideration.

In a preferred embodiment of the use according to the invention, and when ester mixtures of the type just mentioned are used, care should be taken not to employ significant amounts of strongly hydrophilic inorganic and/or organic bases in the oil-based mud. In particular, there should not be used alkali hydroxides or strongly hydrophilic amines such as diethanolamine and/or triethanolamine. Lime can however be used effectively as an alkali reserve, in vhich case it is advantageous to limit the amount of lime to about 2 lb/bbl. Indeed it may be preferred to work with a drilling-mud lime content slightly belcw even this for exanple, from about 1 to 1.8 lb/bbl (lime/drilling fluid). Other known alkali reserves can be used in addition to, or in place of, the lime. The less basic metal oxides, such as zinc oxide, are particularly mentioned. Even when these so called - 14 acid traps are used, care should still be taken to ensure that the amounts used are not too large, so as to prevent undesired premature ageing of the drilling fluid, which causes increased viscosity and hence inferior rheological properties. The special features discussed here of the process according to the invention prevent, or at least restrict, the formation of undesirable amounts of highly active O/W-emulsifiers, so that the good rheological properties are maintained in use over a reasonable period of time, even when there is thermal ageing.

As mentioned hereinbefore, invert-drilling muds of the type being considered usually contain within the oil phase a finely dispersed aqueous phase. This may be present in amounts of from 5 to 45% by weight, and preferably from 5 to 25% by weight. A dispersed aqueous phase from 10 to 25% by weight is particularly useful.

Preferred invert drilling muds according to the invention have plastic viscosity (PV) values of from 10 to 60 mPa.s, and preferably frcm 15 to 40 mPa.s. Their yield point (YP) at 50°C is preferably in the range from 5 to 40 lb/100 ft^, and more preferably from 10 to 25 lb/100 ft^. Further details of the conventional composition of the invert drilling fluids described, and of the procedures for measurement of these rheological parameters, are given in those Prior Art Specifications cited above and are also described fully in the handbook (freely accessible to interested experts) Manual of Drilling Fluids Technology by NL-Baroid Co., London, GB, particularly in the chapters Mud Testing - Tools and Techniques and Oil Mud Technology. - 15 The emulsifiers which can be used in practice are systems which are suitable for the formation of the required W/O emulsions and, in particular, selected oleophilic fatty acid salts, for example, those based on amidoamine ccmpounds. Specific Examples of these are described in the already cited US Patent Specification No. 4,374,737, and the literature cited therein. A particularly suitable type of emulsifier is the product sold by NL-Baroid Co. under the brand name EZ-mul. These emulsifiers are sold ccnmercially as highly concentrated active-substance preparations and are conveniently used in amounts of from 2.5 to 5% by weight, and particularly from 3 to 4% by weight, based on the total ester oil phase.

The preferred fluid loss additive, for forming a dense coating on the bore-hole walls of a largely liquid-impermeable film, is hydrophobized lignite. Suitable quantities are, for example, from 15 to 20 lb/bbl, or from 5 to 7% by weight, based on the total ester oil phase.

The viscosifier conveniently used in drilling fluids of the type in question is a cation-modified finely particulate bentonite, used in amounts of from 8 to 10 lb/bbl or frcm about 2 to 4% by weight, based on the total ester oil phase. The weighting material conventionally used to establish the necessary pressure compensation is barite, the amounts added being varied according to the drilling conditions anticipated in each particular case. By adding barite it is possible, for example, to raise the specific weight of the drilling fluid up to 2.5, although a value in the range from 1.3 to 1.6 is preferred. - 16 The dispersed aqueous phase in these invert drilling fluids is loaded with soluble salts - generally calcium chloride and/or potassium chloride. Saturation (at room temperature) of the aqueous phase with the salt is preferred.

The aforementioned emulsifiers or emulsifier systems can also if desired be used to improve the oil wettability of the inorganic weighting materials. In addition to the aminoamides already mentioned, further suitable compounds are alkylbenzene sulfonates and imidazoline compounds. Additional information regarding the relevant Prior Art can be found in the following published Patent Specifications: GB 2 158 437, EP 229 912 and DE 32 47 123.

The drilling fluids of the invention using ester oils of the type described are distinguished, in addition to the advantages already described, by a notably improved lubricity. This is particularly important when (in very deep wells, for example) the path of the drill rod, and therefore the borehole, deviates from the vertical. The rotating drill rod then comes into contact with the borehole wall and when operating buries itself into it. Ester oils of the type used as the oil phase according to the invention have a notably better lubricity than the mineral oils previously used.

The invention discloses new drilling fluids based on ester oils, and invert drilling muds built up thereon, which are distinguished by high ecological acceptability and at the same time good keeping and application properties. An important area of utilisation of the new drilling fluids is in off-shore wells for the development of petroleum and/or natural gas deposits, the aim of the invention being particularly to make available technically usable drilling - 17 fluids with high ecological acceptability. Ihe use of the new drilling fluids has especial significance in the marine environment, but is not limited thereto. They can be put to quite general use even in land-based drilling - for example, in geothermal wells, water boreholes, in the drilling of geoscientific bores, and in drilling for the mining industry. Here too it is essentially true that associated ecotoxic problems are substantially simplified by the ester-based drilling oil fluids selected according to the invention. - 18 DETATT.m DESCRIPTION OF SPECIFIC EMBODIMENTS Examples In each of the Examples, a W/O invert drilling fluid is prepared in a known manner, the ester oil phase being varied in each case. The viscosities of the unaged and then the aged material are determined.

The viscosity is measured at 50°C in a Fann-35-viscosimeter supplied by NL Baroid Co. The plastic viscosity (PV), yield point (YP) and the gel strengths (lb/100 ft^) are determined first after 10 seconds and then after 10 minutes.

Ageing is carried out by treatment in an autoclave - in the roller-oven - for 16 hours at 125°C.

The results for all the Examples are presented in the Table following Example 11. - 19 Examples 1 and 2 In Examples 1 and 2, an invert drilling fluid is prepared using the following basic formulation: 230 ml ester oil ml water g organophilic bentonite (Geltone II of NL Baroid Co.) g organophilic lignite (Duratone of NL Baroid Co.) x g lime (x = 1 or 2; see belcw) g W/O emulsifier (EZ-mul NT of NL Baroid Co.) 346 g barite 9.2 g CaCl2 x 2 I^O In this formulation about 1.35 g of lime corresponds to 2 lb/bbl.

Isotridecyl acetate is used as the ester oil. This has a viscosity at 20°C of 5 mPa.s, and at 50°C of 2.1 mPa.s. Its setting point is below -10°C.

In Example 1 the amount of lime used in the basic formulation is 2 g, in Example 2 this amount is reduced to 1 g.

Ihe basic formulation in Examples 1 and 2 has a value of 90/10 for the oil phase/water weight ratio. In further tests the ester oil/water ratio is changed to 80/20.

Examples 3 and 4 In Example 3, an invert drilling fluid is prepared using ester oil based on isotridecyl acetate, according to the following basic formulation: 210 r nl ester oil 48.2 g water 6 g organophilic bentonite (Cmnigel) 13 g organophilic lignite (Duratone of NL Baroid Co.) 2 g lime 8 g W/O-emulsifier (EZ-mul NT of NL Baroid Co.) 270 g barite 20 g CaCl2 x 2 H2O In Example 4, 2 g of a strongly oleophilic amine (Applicant’s commercial product Araphen G2D - the reaction product of an epoxidized Cj 2/i 4-alpha-olefin and diethanolamine) is added to the basic formulation given above for Example 3.

Example 5 In this Example, the ester-mixture from acetic acid and a Cg_-|Q_ alcohol cut (Applicant's commercial product Lorol technisch) prepared by the reduction of the corresponding pre-fatty-acid cut of natural origin, is used as the ester oil. The basic formulation for the ester mud corresponds to the formulation given for Example 2.

The viscosity data are determined and the ageing is carried out as indicated in the previous Examples.

Examples 6 to 8 In parallel formulations, three drilling fluids based on isotridecyl acetate are produced according to the basic formulation in Examples 1 and 2 (oil phase/water = 90/10). As in the preceding Examples, their rheological data was determined imnediately after preparation and after ageing in the roller oven at 125°C for a period of 16 hours.

In Example 6 no lime is added, in Example 7, 2 g of lime is used, while in Example 8, 2 g of lime is used together with 1 g of the strongly oleophilic amine Araphen G2D.

Examples 9 to 11 In a further comparative series of tests, drilling fluids based on isotridecyl acetate are prepared using the basic formulation of Examples 6 to 8, but with the addition of: in Example 9, 1 g of lime; in Example 10, 2 g of lime (as in Example 7); in Example 11, 2 g of lime + 1 g of Araphen G2D (as in Example 8).

In these Examples the muds are, however, aged in the roller oven at 125°C for a period of 72 hours.

The results obtained in each of the Examples are collected in the table belew. co in TABLE VO cn CN <0 1 vo N* vo o 1 1 cn τ- 3 1 1 σ» Γ- Ο 1 1 cn (0 1 1 n* ΙΟ o 1 1 cn *" 3 1 1 00 io VO o 1 1 cn r— <0 1 1 1 Γ- VO Γ- o 1 1 η τ— 3 1 1 o in Ι'— 1 1 i <0 1 1 1 m 00 Γ— σν 1 1 CN 3 1 1 in CN 00 1 1 I CN *" (0 1 1 σν r— 00 CN 1 1 CN *" *_ 3 1 1 O cn oo O 1 1 I cn (0 1 1 1 o cn r- 00 1 1 cn 3 1 1 00 m σν o 1 1 CN .- r. 10 1 1 σν o σν N· 1 1 CN CN 3 1 1 00 Γ— σν N* 1 1 CN T— CN CO 1 1 N· CN cn in 1 1 cn cn 3 1 1 vo Ν' r— 1 1 1 cn cn *" CO 1 1 vo cn in 1 1 cn m CN cn 3 1 1 T CN in Γ— 1 1 1 cn in CN cn (0 1 1 1 in CN in Γ- 1 1 CN τ- 3 1 1 N* η· in ΟΟ 1 1 1 CN (0 1 1 1 cn cn γ- σν 1 1 cn 3 1 1 ιο σν 1 1 cn V— CN 4J MU O O M & 8~.3 cn jj +3 >|f .. *3 85 4J Ό 01 OJ ε mA fl 1) H o o Α Ή CD r— a. >, cn

Claims (25)

1. Use of esters, which are fluid at room temperature and have flash points above 80°C, from C^-monocarboxylic acids and mono- and/or polyfunctional alcohols as the oil phase, or a component of the oil phase of invert drilling fluids, which are suitable for the environment-friendly development of petroleum and natural gas deposits and contain, in a continuous oil phase, a dispersed aqueous phase together with emulsifiers, weighting agents, fluid-loss additives and preferably further conventional additives.

2. Use according to Claim 1, characterized in that esters or ester mixtures are used which are fluid and pumpable even in the temperature range of 0 to 5°C.

3. Use according to Claims 1 and 2, characterized in that Cj_^-monocarboxylic acid esters or their admixtures with ecologically acceptable components (non-polluting oils) are used as the oil phase, which in the temperature range of 0 to 5°C have a Brookfield (RVT) viscosity of not above 50 mPas, preferably not above 40 mPas and most preferably about 30 mPas.

4. Use according to Claims 1 to 3, characterized in that the C^-carboxylic acid esters used in the drilling mud have solidification values (pour and setting point) below 0°C, preferably below -5°C and in particular below -10°C and at the same time flash points not below 90° C, preferably about 100°C.

5. Use according to Claims 1 to 3, characterized in that Cj ^-carboxylic acid esters are used from monofunctional alcohols with at least 6 carbon atoms, perferably with at least 8 carbon atoms and/or esters of these acids with di- to tetrahydric alcohols with preferably 2 to 6 carbon atoms.

6. Use according to Claims 1 to 5, characterized in that polyhydric alcohols such as glycol and/or a propanediol can be used as the esters. - 24

7. Use according to Claims 1 to 6, characterized in that esters are used of monocarboxylic acids with 2 to 4 carbon atoms, particularly acetic-acid esters.

8. Use according to Claims 1 to 7, characterized in that in mixtures with other ester oils, the ester-base admixtures are used which even after a partial hydrolysis under working conditions are harmless ecologically and toxicologically - particularly inhalation-toxicologically harmless.

9. Use according to Claims 1 to 8, characterized in that esters are used from monofunctional alcohols of natural and/or synthetic origin, the chain-length of which, in the presence of predominantly aliphatic saturated alcohols, can be from 8 to 15 carbon atoms, in the case of olefin mono- and/or poly-unsaturated alcohols, however, can also be of higher carbon numbers, for example, up to about 24 carbon atoms.

10. Use according to Claims 1 to 9, characterized in that as the ester-base mixture components in the continuous oil phase, ester oils of monofunctional alcohols with 2 to 12, preferably with 6 to 10 carbon atoms and olefin mono- and/or poly-unsaturated monocarboxylic acids with 16 to 24 carbon atoms are present, which themselves preferably already have solidification values (pour and setting point) below 10°C, preferably below -15°C and at the same time flash points above 100°C.

11. Use according to Claim 10, characterized in that together with the esters of the lower carboxylic acids, as the mixture components olefin-unsaturated carboxylic acid esters are used, which are derived to more than 70% by weight, preferably more than 80% by weight and in particular more than 90% by weight of olefin-unsaturated carboxylic acids with from 16 to 24 carbon atoms and at the same time, particularly in the temperature range of 0 to 5°C, have a Brookfield (RVT) viscosity of not more than 55 mPas, preferably of not more than 45 mPas. - 25

12. Use according to Claims 10 and 11, characterized in that the esters used as mixture components, from unsaturated monocarboxylic acids are derived to not more than 35% by weight from olefin di- and poly-unsaturated acids, which are at least about 60% by weight olefin mono-unsaturated and/or to more than 45% by weight, preferably more than 55% by weight, from olefin di- and/or poly-unsaturated acids.

13. Use according to Claims 1 to 9, characterized in that, as the mixture components, esters of aliphatic saturated monocarboxylic acids with 6 to 16 carbon atoms are used, which are esterified with monoand/or polyhydric alcohols.

14. Use according to Claims 1 to 13, characterized in that carboxylic-acid esters or ester mixtures are used in invert drilling mud together with alkali reserves, with lime being a particularly preferred alkali reserve.

15. Use according to Claims 1 to 14, characterized in that the esters or ester mixtures are used in the invert drilling fluids together with amine compounds of pronounced oleophilic nature and at most limited water solubility which are capable of forming salts with free carboxylic acids.

16. Use according to Claims 1 to 15, characterized in that esters are used in the drilling fluids which contain together with the continuous ester-base oil phase the finely-dispersed aqueous phase in quantities of about 5 to 45 % by weight, preferably in amounts of about 5 to 25% by weight.

17. Invert drilling fluids, which are suitable for environmentfriendly development of petroleum or natural gas deposits and contain in a continuous oil phase a dispersed aqueous phase together with emulsifiers, weighting agents, fluid-loss additives and preferably further conventional additives, characterized in that the oil phase contains esters, fluid at room temperature and having flash points above 80°C, from C^-monocarboxyl ic acids with mono- and/or polyfunctional alcohols, preferably in admixture with other components from the class of ecologically acceptable compounds (non-polluting oils). - 26

18. Invert drilling fluid according to Claim 17, characterized in that esters of C2_ 4 -monocarboxy1ic acids, particularly acetic acid esters and monofunctional alcohols with at least 8 carbon atoms and/or corresponding esters with in particular lower di- to tetrahydric alcohols present in the oil phase.

19. Invert drilling fluid according to Claims 17 and 18, characterized in that the ester oils of the C^ ^-carboxylic acids constitute at least about 25% by weight, preferably at least about a third and particularly the main part of the oil phase.

20. Invert drilling fluid according to Claims 17 to 19, characterized in that the oil-base mud contains an alkali reserve in which there are preferably lime and/or other comparable metal oxides, such as zinc oxide and/or basic amine compounds which are capable of forming salts with carboxylic acids and are of pronounced oleophilic nature and at most limited water-solubility, and in particular without any considerable amounts of strongly hydrophilic bases, such as alkali hydroxides, or strongly hydrophilic amines, such as diethanolamine in the drilling fluid.

21. Invert drilling fluid according to Claims 17 to 20, characterized in that they have a plastic viscosity (PV) from about 10 to 60 mPas and a yield point (YP) from about 5 to 40 lb/lOOft - each determined at 50°C.

22. Invert drilling fluid according to Claims 17 to 21, characterized in that their dispersed water part constitutes about 5 to 45% by weight, perferably about 10 to 25% by weight and contains in particular salts such as CaC^ and/or KC1 in solution.

23. Invert drilling fluid according to Claims 17 to 22, characterized in that the oil phase of the invert mud in the temperature range of 0 to 5°C has a Brookfield (RVT) viscosity below 50 mPas, preferably not above 40 mPas.

24. Use as claimed in Claim 1 substantially as described herein with reference to the Examples. - 27

25. Invert drilling fluid as claimed in Claim 17 substantially as described herein with reference to the Examples.