CA2089095A1

CA2089095A1 - Use of surface-active ester

Info

Publication number: CA2089095A1
Application number: CA002089095A
Authority: CA
Inventors: Heinz Mueller; Claus-Peter Herold; Frank Wangemann; Stephan Von Tapavicza
Original assignee: Individual
Current assignee: Henkel AG and Co KGaA
Priority date: 1990-08-06
Filing date: 1991-07-29
Publication date: 1992-02-07
Also published as: DK0542808T3; NO924548L; EP0542808A1; NO302127B1; NO924548D0; EP0542808B1; WO1992002595A1; MY107156A; DE59104166D1; MX9100504A; DE4024892A1

Abstract

Described is the use of surface-active salts of internally sulphonated esters, in which most of the sulphur is organically bound, made from at least once olefinically unsaturated carboxylic acids with at least 8 C-atoms and lower monohydric and/or polyhydric alcohols (ester sulphonate salts) as environmentally compatible emulsifiers of the water-in-oil type or oil-in-water type in fluid, pumpable bore-flushing agents or other drilling fluids which have, in addition to an aqueous phase, a closed or disperse oil phase and are suitable for the non-polluting exploitation of natural deposits of e.g. oil or gas. The invention also concerns in particular invert bore-flushing agents with a closed oil phase containing a disperse aqueous phase and which contain, in addition to emulsifiers, other usual additives such as thickeners, fluid-loss additives, filling agents, water-soluble salts and alkali reserves. The invert bore-flushing agents are characterized in that they contain, in addition to an environmentally compatible closed oil phase, surface-active ester sulphonate salts of the kind stated as the emulsifier or as a component of the emulsifier.

Description

2 ~ 9 r) D 9243 Mar. 04, 1991 USE OF SURFACE-ACTIV~ ESTER SU~FONATE S~LTS
IN WATER- AND OIL-BASED D~ILLING FrUIDS
AND OTHrR DRILL-HOLE TREATME~T AGENTS

The invention relates to the use of selected emulsifiers having an increased ecological compatibility for the production of fluid dispersed systems which are present either as W/O inverted emulsions comprising a continuous oil phase or as aqueous emulsions containing a dispersed oil phase and which are suitable for the technical application within the field of use of fluid drill-hole treatment agents. Referring to a character-istic example for agents of this kind, the invention is described hereinbelow by way of oil-based and water-based drilling fluids, respectively, and drilling muds formed therewith. Ho~lever, the field of application or the modification according to the invention of auxiliary liquids of the Xind involved here is not limited there-to, while it also includes in particular the areas of spotting fluids, spacers, auxiliary liguids for wor~over and stimulation and for fracturing.

It is one particular object of the invention to substantially in~luence the ecological compatibili~y of said auxiliary a~ents which are beinq worldwide used today by employing selected and, more specifically, .

7, ~3 `~ 3 3 D 9243 - 2 - Mar. 04, l991 ecologically acceptable types of e~ulsifiers. In its preferred embodiment the invention intends to use said biologically acceptable emulsifiers simultaneously in combination with oil phases having an increased environ-mental compatibility and especially a biological degrad-ability.

Re ~eneral prior art In the area of liquid sweeping systems for rock-drilling to bring-up the removed drill cuttings, the so-called inverted drilling muds are of excellent importance which, based on W/O e~.uls-ons, contain a dispersed aqueous phase in the continuous phase. The content of the dispersed aqueous phase usually is within the range of from about 5 to 50~ by weigh~.

However, also known are water-based drilling fluids comprising an emulsified dispersed oil phase (O/W type), the oil content of which may range f.om some percent to about 50% by weight. O/W emulsion fluids of this kind exhibit a number of considerable advantages over merely water-based fluid systems.

The stabilization of each of the selected dispers-ion forms requires the use of appropriate emulsifiers either of the W/O type (inverted fluids) or of the O/W
type (emulsion fluids), respectively. Hereto, reference is made to the pertinent literatur2, for example, G. R.
Gray, H. C. H. Darley, "Composition and Properties of Oil Well Drilling Fluids", 4th Edition, Gulf Pu~lishing Cp., Houston, London 1981, especially pages 51, 64 and 320 et seq..

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D 9243 - 3 - Mar. 04, 1991 Today the oil phases of drilling fluids of the type described here and comparably composed other drill-hole treat~ent agents in practice are almost exclusively formed by mineral oil fractions. This involves a con-siderable environmental pollution, if, for example, the drilling muds directly or via the drilled rock will infiltrate the environment. Mineral oils are only difficult to decompose and are virtually not anerobic-ally degradable at all and, thus, to ~e rated as long-term pollutants. ~evertheless, even i^ these oil phases as the main constituent or at le~st a substantial portion of the drilling fluid make a significant start-ing point for ecological consideraticrs, an equivalent attention will have to be paid also ~o the other com-ponents of such multi-component sys~ems. Here, the emulsifiers are of specific i~portance. Compounds of this type, in accordance with the intended use thereof, are highly active substances already at a low concen-tration which are ~nown to be capable of an intense interaction with ~he vegetable or ani~al organism.

Obiect of the invention It is the object of the present invention to sub-stantially improve the working agents of the described type based on continuous or disparsed oil phases in admixture with aqueous phases, in ap~reciation of the ecological compatability thereof, over the working agents of this kind as co~on to-day. More specific-ally, it is the object of the invention, for the field o~ use as involved here, to provide e~ulsifiers and/or emulsifier combinations which have been per se ~nown and have been described to be environmentally compatible to a high degree, while they have not been put into use in :. :
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D 9243 - 4 - Mar. 04, 1991 the field of use involved here. In the preferred embodiment of the invention, these environmentally compatible emulsifiers of the W/O type or of the O/W
type are to be employed in combination with oil/water phases, where the oil phases themselves have an in-creased ecological compatibility and, more specifically, are capable of being decomposed by natural degradation mechanisms doing little harm to the environment.

On how to attain the object of the invention The invention, in order to attain the first partial object thereof, provides the use of per se ~nown surface-active ester sulfonate salts as ecologically compatible or acceptable compounds which, depending on their constitution and kind of interaction with the surrounding system are to be classified as W/O emulsi-fiers or as O/W emulsifiers.

Thus, in a first embodiment, the invention relates to the use of surface-active salts of esters from mono-and/or polyolefinically unsaturated carboxylic aci s having at least 8 carbon atoms and lower mono- and/or polyhydric alcohols, which esters have been sulfonated in (an) inner position(s) and comprise sulfur that has been organically bonded to an at least predominant degree, (briefly: ester sulfonate salts) as ecologically compatible emulsifiers of the W/O type and/or o/W type in fluid and pumpable drilling fluids and other fluid drilling-hole treatment agen~s which comprise a con-tinuous or a dispersed oil phase toge~her with an aqueous phase and which are suitable for an environ-mentally acceptable exploitation of geological ~ resources, for example oil or natural gas deposits.
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2 0 ~ 5 D 9243 - 5 - Mar. 04, 1991 Of particular importance in this context are the corresponding inverted drilling fluids which in continuous oil phase contain a dispersed aqueous phase together with emulsifiers and further conventional auxiliary agents such as thickeners, fluid-loss additives, weighting agents, soluble salts and/or alkali reserve. In this embodiment according to the inventlon there is provided the use of selected surface-active ester sulfonate salts as emulsifier or at least as a component on an ecolcgically compatible emulsifier system.

Preferred is the use of emu!sifiers based on surface-active ester sulfonate salts in combination with environmentally compatible ester oils, oleophilic alcohols and/or corresponding ethers as continuous or dispersed oil phase. Here particular reference is to oe made to pertinent developments by applicant describir.g, in a greater number older patent applications, proposals for substituting the previously co~mon mineral oil fractions with ecologically compatible readily degradab-le oil phases. Thereby, various types of substituti-.g oils h~ve been presented which may also be used as mixtures. They include selected oleophilic monocarb-oxylic acid esters, selected polycarboxylic acid esters, at least largely water-insoluble alcohols which are fluid under the operation conditions, corresponding ethers and selected carbonic acid esters. In summary, reference is made here to the older applications P 38 42 659.5 (D 8523), P 38 42 703.6 (D 8524), P 39 07 391.2 (D 8506), P 39 07 392.0 (D 8607), p 39 03 785.1 (D 8543), P 39 03 784.3 (D 8549), P 39 11 238.1 (D 8511), P 39 11 299.3 ~D 8539), P 40 18 228.2 (D 9167) and P 40 19 266.0 (D 9185). All ... ~

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D 9243 - 6 - Mar. 04, 1991 of the older applications mentioned here relate to the field of oil-based drilling fluid systems, especially of the W/O inverted type. Water-based emulsion fluids using these oil phases of an increased degradability have been described in the older German applications P 39 15 876.4 (D 8704), P 39 15 875.6 tD 8705), P 39 16 550 7 (D 8714) and the applicatlons P 40 18 228.2 (D 9167) and P 40 19 266.0 (D 9185) as already mentioned.

The invention, in its most important embodiment, comprises the use, in combination, of the a_ove-described e~ulsifiers of the class of the surface-active ester sulfonate salts toyether with dispersed or con-tinuous oil phases of the type described last. ~he disclosure of said older applications is hereby expli-citly incorporated by reference.

Details of the teachinq accordinq to the invention before the backqround of a special technical knowled~e The sulfation of unsaturated ~arboxylic acids o~
natural or synthetic origin and of the esters thereof with mono- and/or polyfunctional alcohols has been Xnown for long. Here the term sulfation to be classified as a superordinate term, in its precise chemical definition, comprises two different possible subjects with respect to the reactions occurring or the reac~ion products being formed, both of which subjects may as well be simultaneously involved. The first of these subjects, in its chemical definition, is to be described 25 a sulfat~ formation ("sulfation" in a narrower sense) wherein sulfuric acid ester groups are formed which contain the sulfur bonded to carbon through an oxygen .

, D 9243 - 7 - Uar. 04, 1991 atom. Such sulfation products are formed, for example, by the addition of a sulfuric acid residue to the olefinic double bond of unsaturated carboxylic acid molecules or by esterification of free hydroxyl groups present on the carbon backbone.

To be distinguished therefrom is the sulfonation.
Typical for this reaction is the attachment of organic-ally bonded sulfur to the carbon backbone to for~ direct C-S bonds. The te~ching of the invention deals with emulsifiers of the described type which at least pre-dominantly are true sulfonates within the last-described .eaning, that is with directly organically bonded sulfur in the molecule thereof.

In spite of these clear differences in constitution which are also manifest in the chemical behavior, e.g.
in the respective stabilities to hydrolysis of both classes of co~pounds, the :Language used in practice is ambiguous. Thus, in the pertinent litera~ure the term sulfonate is frequently used when, in reality, sulfates are intended to be described. Thus, for example, there is reported of sulfonation products which are relatively poorly stable to acids and alkalis, if, besides the formation of true sulfonic acids, above all unstable sulfuric acid esters are formed; hereto cf., for example, DE 12 46 71~ and the summarizing treatise by H.L~ Sanders "Sulfoils - The Resurgent Surfactants", SOAP/COSMETICS~C~E~ICAL SPECIALTIES, May 1975, 39/40.
Also in the field of drilling fluid systems which the invention relates tol and more particularly of the so-called inverted fluids, this definition in unprecise language is frequently used; hereto cf., for example, the U.S. Patent Specification No. 3,642,623, column 6 :. :
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D 92~3 - 8 - Mar. 04, 1991 lines 26 to 28. The preparation of true sulfonates com-prising predominantly organically bonded sulfur from esters of unsaturated carboxylic acids, and especially unsaturated fatty acids, with mono- or polyhydric alcohols has been known since long. Reference may be made, for example, to the DE 12 46 717 as already quoted and to the DE-A1-3~ 37 443. Thus, for exa~,ple, true sulfonates may be obtained under compara~ly mild wor~ing conditions from unsaturated oils of vegetable and/or animal origin, highly diluted sulfur trio~ide/air mixtures are employed for sulfation. Upon subsequent neutralization, well electrolyte-resistant water-soluble compounds are obtained which have been described as storage-stable acid-resistant and alkali-resistant emulsifiers. Fields of technical use include, for example, leather oiling agents, greasing agents for the textile industry, the manufacture of metal processing oils and the production of electrolyte-resistant emulsions for the most ~arious intended uses. As to details, cf. the literature already quoted.

Ester sulfonates confor~ing to the definition according to the invention, and more specifically the combination thereof with ecologically compatible oil phases o~ an increased degradability have so far not been proposed for the field of use of the drilling hole treatment agents which the instant invention relates to.

The class of the so called fatty acid sulfonates within the wide meaning of the term as explained herein~
above indeed plays an important role in practice and in the literature as an emulsifier component for building O/W a~d W/O emulsions for the field of drilling hole ~luids and for drilling hole treatment agents. However, 2 i~

D 9243 - 9 - Mar. 04, 1991 here in the first place the corresponding sulfation products of unsaturated carboxylic products have been described, but not so the esters within the definition according to the invention. Moreover, sulfonates having a dif~erent constitution play an important role, in which sulfonates especially the sulfo grouping has been introduced into the emulsifier molecule via aromatic molecular moieties. Compounds of this type are not compatible with the goal according to the invention o~
an increased ecological compatibility. Reference may be made, by way of an extract from the voluminous prior art printed literature, to DE 12 ~ 289 and to the U.S.
?atent Specifications ~os. 3,476,912, ~,012,329, 3,89~,431, 3,340,188, 3,878,111 and, as already quoted, 3,642,623. In these printed publications there have been mentioned, inter alia, petroleum sulfonates, tall oil pitch sulfonates, combinations of sodium oleic acid sulfonate and titanates and further combination systems.

In the practice of, more particularly, water-based fluid systems and comparable liquid phases the so-called Turkey-red oil plays a remarXable role as an emulsifier component. Said material is ~nown to be a sulfated, castor oil-based oil; hereto cf. in detail, for example, Rompp Chemie-Lexikon, 7th Edition (1977), 3707.

In contrast thereto, the teaching of the invention provides the use of sur~ace-active salts of esters from mono- and/or polyolefinically unsaturated carboxylic acids having at least g carbon atoms and lower mono-and/or polyhydric alcohols, which esters have been sulfonate~ in (an) inner position(sj and comprise sulfur that has been organically bonded to an at least pre-dominant degree, as ecologically compatible emulsifiers , ....
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D 9243 - 10 - Mar. 04, 1991 of the W/O type and/or o/w type. In comparison to the salts of unsaturated carboxylic acids or salts thereof which have been correspondingly sulfonated in (an) inner position(s) to form C-S bonds, the substance class proposed according to the invention is distinguished by the additional ester bond and, hence, the alcohol moiety included in the molecule. The free carboxylic group, thus, has been prevented from undergoing an immediate salt formation. At the same time the respective pre-deter~ined alcohol moiety allows a wide variation of the base molecule. -hus, mn C5m bination with the deliberate control of the degree of sulfonation which will in greater detail be described hereinbelow, hereby the possibility is created of synthesizing emulsifier molecules exhibiting a distribution as wide as possible of the ratio of lipophilic to hydrophilic properties of the material. Hence, in combination with further possibilities o~ variation to be discussed hereinbelo~, this implies the chance of taking an improved technical action without havlng to compromise the ecological advantages of _he emulsifie3r class as involved here.
There~ore, the teach~ng of the invention makes il possible to tho_oughly and persistently stabilize oil~
based W/O inverted emulsions without using the N-containing emulsifier systems as widely used today, the ecological compatibility of which, especially in the highly sensitive marine eco-system, is no~ undisputed.

The ester sulfonate salts to be emplox~d accordinq to the invention Ester sulfcnate salts preferred for a use according to the invention are derived from unsaturated monocarb-oxylic acids of natural and/or synthetic origin which ~ ~ 3 ~

D 9243 - ll - Mar. 04, l991 comprise from lO to 40 carbon atoms and preferably are within the range of Cl2_32.

Starting materials which are inexpensive and available in large amounts may be the respective fatty acid glyceride esters of natural origin. The prevailing portion of the carboxylic acid moieties as here con-templated is within the range of appropriate fatty acids having from 16 to 24 carbon atoms and from l to 5 double bonds. Examples for such ester oils of natural origin are fatty acid glycerol esters, and especially the ~espective triglycerides based on coriander oil, chaulmoogra oil, sunflower oil, cottonseed oil, olive oil, peanut oil, linseed oil, lard ol, meadow foam oil, hog's lard or fish oil. Of particular importance as a starting material for the production of the sulfonated fatty acid esters to be used according to the invention is fresh rapeseed oil which is rich in oleic acid.
Certain selected tri~lycerides may be employed as well as any optional mixture of various origins. Admixtures of natural and synthetic esters are as well usable.

The term o~ the fatty acid glycerol esters includes the mono-, di- and tri-esters and the mixtures thereof, as may be obtained by esterification of one mole of glycerol with from one to three moles of fatty acids and/or fatty acid mixture or by the transesterification of unsaturated triglycerides with, more specifically, from 0.3 to 2 moles of glycerol. The term of the unsaturated fatty acid esters and the sulfonates obtain-ed therefrom, respectively, expressly includes also those native and/or synthetic esters and ester mixtures, the fatty acid component of which is not completely, but only partially composed of unsaturated fatty acids.

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D 9243 - 12 - Mar. 04, 19~' Further included is the range of mixtures, and more particularly of those commercial mixtures ob~ained in practice, of various unsaturated or largely unsaturated fatty acid glycerol esters with each other. In all of these cases it is preferred that in the ester or ester mixture, respectively, the portion of the mono- and/or polyunsaturated carboxylic acids comprises at leat about 50% by mole - relative to the mixture of carboxylic acids. The use in combination of saturated fatty acids in minor or at most equal amounts is expressly included in the teaching of the invention.

The ester-forming alcohol component especiall~
comprises the moieties of mono- to tetrahydric alcohols comprising preferably up to 5 carbon atoms. Thus, important esters may be derived from methanol, ethanol and, if desired, also hiqher alcohols. Thus, under the aspect of the use of sulfonated esters of monofunctional alcohols, it may be expedient for reasons to be discuss-ed hereinafter, to employ sufficiently lo~-volatile alcohcl components so that a potential ester cleavage during practical use will induce no inhalation-toxico-logical danger. Nevertheless, said aspect which will be discussed hereinbelow in the context of ester oils is or minor importance in connection with the emulsifiers.
These emulsifier components anyway ar~ employed only in comparably restricted amounts so that the respective endangerment is a priori of minor significance. The aspect of a potèntial inhalation-toxicological danger is in fact irrelevant in the case of use of esters derived from polyfunctional alcohols due to the low volatilities thereof. Thus, here diols such as ethylene glycol, 1,2-and 1,3-propanediol or the respective butanediols are to be considered. Nevertheless, of particular importance :

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~i~ 3~ jJ~ i i D 3243 - 13 - Mar. 04, 1991 is glycerol, already quoted as an ester-forming poly-functional alcohol component.

More specifically, such esters derived from poly-functional alcohol provide the options of modifying, by introducing the sulfo group, only one or several or all of the carboxylic acid moieties present in combination with the alcohol .olecule. In a per se known manner the hydrophilic character will be the more pronounced, the higher the number of sulfonate groups per ester molecule will be. This is to be taken into special consideration also if esters of polyunsaturated carboxylic acids will be employed which are basically accessible to a multiple sulfonation reaction.

Under this aspect of the facts it is preferred according to the invention to use ester sulfonate salts having a molar ratio of sulfonate/carboxylic acid moiety of a maximum value of about 1 (statistical mean value).
Nevertheless it r~ay be particularly preferred here to employ lower values of said molar ratio. In the way as intimated here t:-e lipophilic por~ion of the ester molecule will be strengthened. This fact may be de-liberately utilized for the formation of particularly suitable W/O emulsifiers. Thus, for example, molar ratios of sulfonate/carboxylic acid moiety within the ranqe of from 0.25 to 0.7 may be preferred. In the case of the triglyceride-based ester sulfonate salts the preferred molar ratios of the kind indicated are within the range of from about 0.3 to 1 (statistical mean value), i.e. within the range of from about 1 sulfonate group per molecule to a degree of conversion allowing one sulfonate group at each carboxylic acid moiety.

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~'~J ~ ) J ') ,~, `'' D 9243 - 14 - Mar. 04, 1991 The preparation of the substance group as especial-ly important according to the invention of the ester sulfonate salts based on unsaturated mono-, di- and/or triglycerides derived from fatty acids having from 16 to 24 carbon atoms and from 1 to 5 double bonds at a proportion of unsaturated fatty acids of more than 50%
by weight, in an improved embodiment, is the subject matter of applicants older German patent application P 39 36 001.6 (D 8902). The disclosure of said older patent application is incorporated herein by reference.
Ester sulfonates of this kind, in preferred -mbodiments ~ay be derived to a degree of more than 50~ by weight from oleic acid and/or linoleic acid and especially ori~inate from rapeseed oil which is rich in oleic acid.

In the manner described in said older application -hereto also cf. J. Falbe (Ed.) "Surfactants in Consumer Products", Springer Verlag, Berlin-Heidelberg 1987, page 61 - a largely selective introduction of sulfonate groups is successfully achieved with a s~multaneous significant suppression of the introduction of sulfate groups into the ester molecule, the partial occurrence of which is inevitable.

The emulsifiers based on ester sulfonate salts as praferred according to the invention comprise a ratio of sulfonate groups to sulfate groups of at least 60/40.
Higher sulfonation ratios, especially those in excess of 70/30, are preferred. In the prac~ice of the technical process, upon the use of the described ester oils of natural and/or synthetic origin, ratios of sulfonate groups to sulfate groups within the range of from about 75/25 ~o 85/15 are achievable at a reasonable technical expense. Ester sulfona~es of this ~ind are especially 2ag~0.~

D 9243 - 1~ - Mar. 04, 1991 suitable materials for the use on a commercial large scale within the scope of the invention.

One important possibility for modifying the emulsifier properties and, more specifically, for influencing the .iLB value of ;he respective ester sulfonate salts is constituted by the choice of the salt-forming cations. Thereby also the water and oil solubilities may be especially affected. Generally there is ap~licable that water-scluble salts of monovalent cations, more specifically the al.`~ali metal and/or ammoniu~ salts, will result in favoring the hydrophilic properties, ~hereas the ~se of ?oly~alent cations may reduce the water-solubility. Then in compounds of this kind the lipophilic character may become more pronounced, so that compounds of this kind are particularly suitable fOL^ a use in the field of the W/O inverted emulsions. Polyvalent cations a-e derived especially from the al~aline earth metals and aluminum.
In the class of the polyvalent cations, calcium is of special importance, whereas sodium and a~monium are of predo~inant im?ortance as mor.ovalent cations. It ~
~e apparent that the structure of the ester sulfonate salts selected according to the invention cc-.prises a multiplicity of parameters to be purposefully influenced such as to allow controlling the emulsifier action and, thus, an optimization of the desired effec.s. Under this aspect, ester sulfonate sal~s within the scope of the invention, are much more flexibly modifiable than the corresponding sulfonate salts of unsaturated mono-carboxylic acids of natural and/or synthetic origin which have been sulfonated in the inner positions.

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D 9243 - 16 ~ Mar. 04, 1991 In the practical operation there is the further possibility of utilizing an in situ formation of such ester sulfonate salts of pol~alent cations. This may be illustrated by way of the following example:

The aqueous dispersed phase in oil-based drilling fluids of the inverted type is generally loaded ~ith dissolved salts, especially calcium salts such as calcium chlorid, in practical use. If such aqueous phases containing dissolved alkaline earth metal salts are used in forming 'che inverted emulsion, then the corresponding alkaline earth metal salts of tne ester sulfonates will be formed even if said e~ulsifier components are initially employed in the form of their sodium salts. Not only does this allow a particularly economical realization of the teaching according to the invention, but it has also heen shown that rheologically highly stable inverted emulsions are accessible by such an in situ formation of the alkaline earth metal salts which are especially active as ~/0 emulsifiers. It will be right apparent in the case of such a salt-exchange reaction as shown here that also the ootassium salts may have particularly importance as feedstock material: In the reaction with the meaning as described last, there is formed potassium chloride besides the calcium salts that are active as W/O emulsifiers, which potassium 5 chloride transits in the aqueous dispersed phase and here is a known preferred constituent for ~he inhibition of water-swellable clays within the exploitation of geological resources.

The ester sulfonate salt-based emulsifiers, in a preferred embodiment, are employed as the essential components forming the type of emulsion and stabilizing :

D 9243 - 17 - Mar. 04, 1991 the emulsion. Nevertheless the teaching according to the invention also includes mixed systems in which ester sulfonate salts are used together with other emulsifier components. It is preferred that these other emulsifier components on their own are ecologically compatible; in this context reference may be made to applicant's older application P 40 03 028.8 (D 8158) wherein selected ether-based emulsifiers for oil-based inverted emulsions have been described. Another example for suitable co-emulsifiers is provided by the surface-active alpha-sulfofatty acid derivatives and al~yl glycoside com-pounds described in the parallel pending Ger~an Patent Applicatlons P 40 24 659.0 and P 40 24 658.2 (D 9222 and D 9223).

Salts - and more specifically corresponding alXali metal or alkaline earth metal salts - of sulfonated and/or unsulfonated unsaturated and/or saturated fatty acids of natural and/or syr~thetic orgin can be especial-ly suitable co-emulsifiers. Thus, the invention in-cludes admixing any optional fatty acids or fatty acid salts as co-emulsifiers to the respective compositions of active ingredients, in which case, more specifically, it has been shown that no problems are caused by a use, in combinatioll, of unsatured straight-chain and/or branched fatty acids.

If such emulsifier mixtures are used, then in preferred embodiments of the invention the ester sulfon-ate salts constitute at least 10% by weight, and prefer-ably at least 50% by weight, of the respective emulsi-fier system.

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:~ 2 ~ 3 ~j D 9243 - 18 - Mar. 04, 1991 The ester sulfonate salts may be used in amounts of from about 0.1 to 10% by weight, relative to ths sum of the liquid phases water and oil. Preferred amounts are within the range of from about 0.5 to 5% by weight of the emulsifier components, while the range of from about 1 to 3% by weight of the emulsifier - again relative to the sum of water + oil - is of particular importance.

The economical production of the emulsifiers according to the invention is significantly facilitated by omitting the step of bleaching the reaction products as primarily o~tained, which step in prior art as evidenced by the pertinent printed publications is considered as an essential process step. Thus, the production process for compositions of active substances containing ester sulfonate salts within the scope of the invention may be restrictecl to the process steps of sulfonation and salt-formation. The cruda reaction product may be directly put into a commercial use.

In the preferred embodil~ents as especially ~eatured in the introduction, the appropriate oil phases are constituted by the ecologically compatible ester oils, oleophilic alcohols and/or ethers described in appli-cant's older applications as quoted. When said agents are used, the invention relates to the drill-hole treat-ment agents which are fluid and pumpable within the temperature range of from 5 C to 20 C, and more specifically drilling fluids based on ~ either a continuous oil phase, especially in admixture with a dispersed aqueous phase (W/O
inverted type) - or a dispersed oil phase in a continuous aqueous phase (O/W emulsion type).

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D 9243 - 19 - Mar. 04, 1991 The ecologically compatible oils and oil phases, with respect to the possible physical properties there-of, covers a wide range. The invention comprises, on the one hand, oil phases which are fluid and pumpable also at low temperatures. These, more particularly, include representatives suitable for the preparation of W/O emulsions. However, on the other hand, highly viscous to solid oil phases and materials of this type may also be included in the use within the scope of the teaching according to the invention. This may be exemplified by the following deliberations:

For water-based 0/~ emulsion fluids a high mobility of the dispersed oil phase is not required and, as the case may be, not even desirable. For example, to ensure good lubricating properties, oil phases adjusted such as to be comparably viscous may be advantageous. Another possible use of highly visc:ous or even solid ecological-ly compatible oil phases may be constituted, if the respective oil phase involved in the final product is only partially formed by said highly viscous to solid representatives of degradable esters, alcohols and/or ethers which themselves have been admixed with comparab-ly highly liquid oils of this kind.
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Nevertheless, there is consistently applicable to all oil phases or mixed oil phases to be used according ` to the invention that ~lash points of at least about 100 C and preferably flash points of above about 135 'C
are demanded for reasons of safety in operations.
Values that are distinctly higher, particularly those above 150 ~C, may be especially expedient. rurthermore~
there is consistently applicable ~o the oil phases as potentially susceptible to hydxolysis that may be used . ` `" - .
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D 92~3 - 20 - Mar. 04, 1991 within the scope of the invention not onLy that the requirement of the ecological compatibility will have to be met by the compound put into use, i.e., for example, the respectively selected ester oil or ester oil mix-ture, but also that no toxicological and especially no inhalation-toxicological danger will be induced upon a partial saponification in practical use. Within the scope of the mentioned older applications there has been described in great detail that here, more particularly, the various representatives of ester oils are referred to, with the monofunctional alcohols from the esters formed being again of particular significance here. In comparison to ?olyfunctional alcohols, the lo~er members of the monofunctional alcohols are highly volatile, so that here a partial hydrolysis may cause exposure to secondary danger. Accordingly, in the classes of the various ester oils those monofunctional alcoholâ
included in the use, or the moieties of such alcohols, have been chosen so that they have at least 6 carbon atoms, and preferably at least 8 carbon atoms, in t~.e molecule thereof.

The inverted drilling fluids of the ~ind involve according to the invention, irrespectively of a definite property of the continuous oil phase, in preferred embodiments have a plastic viscosity (PV) wi~hin t~.e range of from 10 to 60 mPa.s and a flow limit (yield ~oint, YP) within the range of from 5 to 40 lb/100 ft each determined at 50 C.

As an oil phase which is ecologically compatible and well fluid at low temperature, there have proven to be useful, more specifcally, ester oils o~ monocarboxyl-ic acids which then, in a preferred embodiment of the ;' ~ , ;

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D 9243 - 21 - Mar. 04, l991 invention, are derived from at least one of the follow-ing subclasses:

a) Esters of Cl 5-monocarboxylic acids and mono-and/or polyfunctional alcohols, whereof the moieties of monohydric alcohols comprlse at least 5 carbon atoms and preferably at least 8 carbon atoms and the polyhydric alcohols preferably have from 2 to 6 carbon atoms in the ~olecule, b) Esters of monocarboxylic acids of synthetic and/or natural origin co~prising from 6 to 16 carbcn atoms, and ~ore specifically esters of aliphatic saturated monocarboxylic acids and ~.ono- and/cr polyfunctional alcohols of the kind .~.entioned a), c) Esters of olefinically mono- and/or polyunsaturated monocarboxylic acids having at least 16, and especially 16 to 24 carbon atoms and es?eciall~
monofunctiona} straight-chain and/or branched alcohols.

Starting materials for recovering numerous .~.ono-carboxylic acids falling under these subclasses, especially those having a higher number of carbcn atoms, are vegetable and/or animal oils. There may be -.ention-ed coconut oil, palm kernel oil and/or babassu oil, ` especially as feedstock for ~he recovery of .~nocarb-oxylic acids of the prevailing range up to Cl3 and of essentially saturated components. Ester oils of vegetable origin based on olefinically mono- and option-ally poly-unsaturated carboxylic acids of the range of Cl6 24 are, for ex~mple, palm kernel oil, peanut oil, :~ :

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D 9243 - 22 - Mar. 04, 1991 castor oil, sunflower oil, and especially rapeseed oil.
sut also components synthetically recovered are import-ant structural elements for ecologically compatible oil phases on the side of the carboxylic acids as well as on the side of the alcohols.

Additives to the oil-based and/or water-based fluid Inverted drilling muds conventionally contain, together with the continuous oil phase, the finely dispersed aqueous phase in a~ounts of from ~ to 50% by weight. In water-based emulsion fluids the dispersed oil phase is usually present in amounts of f-om at least about 1 to 2~ by weight, frequently in amounts of from at least about 5% by weight with an upper limit of the oil portion of about from 40 to 50% by weight - the percentage by weight in all cases being based on the sum of the unloaded liquid portions of oil/water.

Besides the water content, there are to be taken into consideration all of the additives provided for comparable types of fluids. Said additives may be wa~er-soluble, oil-soluble and/or water-dispersible and/or oil-dispersible.

Conventional additives, besides the emulsifiers defined according to the invention, include, for example, fluid-loss additives, soluble and/or insoluble materials to build-up structural viscosity, alkali reserve, agents for inhibiting an undesirable water exchange between drilled formations - e.g. water-swell-able clays and/or salt layers - and the, e.g., water-based drilling fluid, wetting agents for an improved ~trike of the emulsified oil phase on solid surfaces, e.g. for improving the lubricating effect, but also for D 9243 - 23 - Mar. 0~, 1991 improving the oleophilic closure of exposed rock formations, e.g. rock surfaces, biocides, for example for inhibiting bacterial onset and growth of o/w emulsions and the like. In detail, reference is here to be made to pertinent prior art such as described, for example, in the technical literature as initially quoted; cf., more specifically, Gray and Darley, loc.
cit., Chapter 11, "Drilling Fluid Components". Just by way of an excerpt, there may be quoted:

Finely dispersed additives for increasi..g the der.sity of the fluid: ~idely used is barium sulfate (baryte), but also calcium carbonate (calcite) or the mixed carbonate of calcium and magnesium (dolomite) are used.

Agents for a build-up of structural viscosity which simultaneously will act as fluid-loss additives': Here, bentonite of hydrophobized bentonite are to be mentioned in the first place. For salt water fluids, other com-parable clays, and more specifically attapulgite and sepiolite are of considerable importance in prac-ice.

Also the use in combination of organic polymer ~o~pounds of naturàl and/or synthetic origin may be of considerable importance in this connection. There may be especially mentioned starch or chemically -.odified starches, cellulose derivatives such as carboxymethyl-cellulose, guar gum, xanthan gum, or also merely synthetic water-soluble and/or water-dispersible polymer compounds, especially of the type of the high .~.olecular weight polyacryl amide components with or without an-ionic or cation modifications, respectively.

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D 9243 - 24 - ~ar. 04, l991 Diluents for regulatlng the viscosity: The so-called diluents (thinners) may be organic or inorganic in n~ture. Examples for organic thinners are tannin and/or quebracho extract. Further examples are lignite and lignite derivatives, especially lignosulfonates.
However, as has been set forth hereinabove, in a pre-ferred embodiment, just here no toxic compounds will be included in the use, among which in the first place the respective salts with toxic heavy metals such as chromium and copper are to be mentioned. ~olyphosphate compowlds constitute an exa-?le of inorganic thinners.

Additives inhibiting the undesirable ~ter-exchange with, for example, clays: Here to be consi~ered are the additives known from prior art for oil- an~ water-based drilling fluids. These include halides and/or carbonates of the alkali and/or alkaline earth metals, whereof the potassium salts, optionally in combination with lime, may be of particular importance.

R~ference may be made, for example, to the relevant publications in "Petroleum Engineer In~ernational", September 1987, 32-40, and "World Oil", November 1983, 93-97.

Alkali reserves: Here to be taken into consider-ation are inorganic and/or organic bases adjusted to match the total behavior of the fluid, and more part-icularly basic salts or hydroxides of alkali and/or alkaline earth metals as well as organic bases. Kind and amount of these basic components will have been selected and mutually adjus~ad in a known manner so that the drilling hole treating agen~s will be adjusted to a pH value within the range of from about neutral to . .

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D 9243 - 25 - Mar. 04, 1991 moderately basic, especially to the range of from about 7.5 to 11.

3asically, the amounts of each of the auxiliary materials and additives is within the conventional range and, thus, may be learnt from the relevant literature as quoted.

E X A M P L E S

In the following Examples 1 ar.d 2, by observation of a standard formulation for oil-based drilling fluid systems of the W/o type there are set forth appropriate drilling fluid systems, wherein each continuous oil phase is formed by a selected oleophilic carboxylic acid ester of the following definition:

An ester mixture comprising substantially saturated fatty acids based on palm kernel and 2-ethylhexanol which to the by far predominating part is derived from C12/14-carboxylic acids and confor.-..s to the following specification:
C8: from 3.5 to 4.5% by weight C10: from 3.5 to 4.5% by weight C12: from 65 to 70 ~ by weisht C14: from 20 to 24 % by weight C16 about 2 % by weight C18: from 0.3 to 1 % by weight The ester mixture is a bright yellow liquid which has a flash point in excess of 165 C and a viscosity (Brookfield, 20 C) of from 7 to 9 cP.

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D 9243 - 26 - Mar. 04, 1~91 The viscosity characteristics are determined with unaged and aged material as follows:

Measurement of the viscosity at 50 C in a Fann-35-viscosimeter from the company Baroid Drilling Fluids, Inc.. In a ~ se known manner there have been deter-mined the plastic viscosity (PV), the yield point (YP) and the gel strength (lb/100 ft2) after 10 seconds and after 10 minutes. In Example 1 there is further deter-mined the fluid loss value (HTHP).

Ageing of the respective drilling fluid is effected by way of a treatment at 125 'C in an autoclave - in a so-called roller oven - for 16 hours.

', The drilling fluid systems are composed in a per seknown manner in accordance with the following basic formulation:
230 ml of carboxylic acid ester oil 26 ml of water 6 g of organophilic ~entonite (GELTONE from the company Baroid Drilling Fluids, Inc . ) 12 g of organophilic lignite (DURATONE from the company Baroid Drilling Fluids, Inc.) 2 g of lime 12 g of emulsifier based on ester sulfonate sal.s 346 g of baryte g.a g of CaC12 . 2 H2O
;

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9.j D 9243 - 27 - Mar. 04, l991 Example 1 An unsaturated C16 24-triglyceride obtained from rapeseed oil is allowed to react with gaseous S03 (about 5% by weight of 5O3 in nitrogen or air~ within a temperature interval of from 70 C to 80 C at a feed ~olar ratio of triglyceride ester to SO3 of 1 : 1.2.
This is followed by an alkaline hydrolysis to a constant pH value. Then the products are adjusted to a pH value of from 6.5 to 8.5. There is obtained an aqueous con-centrate of the low-sulfonated rapeseed esters which has the following characteristic values:
Active substance: 39.7 % by weight Unsaturated portions: 27.1 % by weight Water: 58.9 % by weight Na2S04: 1.4 % by weight This reaction product is employed as the "emulsi-fier based on ester sulfonate salts" in the basic form-ulation quoted above.

The characteristic values determined of the unaged and of the aged r.~aterials - as indicated above - are summarized in the following Table.

Unaged Aged Material Material Plastic viscosity (PV) ~1 ;8 Yield point (YP) 4 23 Gel strength (lb/100 ft2) lO seconds 3 17 10 minutes 5 36 HTHP 6 ml .

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D 9243 - 28 - Mar. 04, 1991 Example 2 As the emulsifier there is employed a rapeseed oil which now has been sulfonated to a higher degree. The following data apply to the sulfonation step: Ratio of triglyceride ester to SO3 of 1 : 3; process temperature 80 'C to 90 'C. The aqueous sulfonate salt product employed as "emulsifier" in the basic formulation quoted above has the following cha~acteristic values:
~ctive substance: 53.9 % by weight Unsaturated portions: 1,.6 -O by weight Water: 44.4 % by weight Na25O4: 1.7 % by weight The values determined of the unaged and of the aged materials are as follows.
Unaged Aged Material Material Plastic viscosity (PV) 45 52 Yield point (YP) 8 22 Gel strength tlb/100 ft2) 10 seconds 6 19 10 minutes 14 33 HTHP 18 ml Examples 3 and 4 .
With the use of the ester sulfonate salt-based emulsifiers of the Examples 1 and 2, W/o inverted fluid systems were prepared based on pure mineral oil as common in practice (commercial product BP 83 HF) in a ~ se known manner according to the following form-; ulation:

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D 92~3 - 29 - Mar. 04, 1991 204 ml of mineral oil 7.2 g of emulsifier based on ester sulfonate salts 3.6 g of lime 6 g of organophilic lignite (DURATONE from the company Baroid Drilling Fluids, Inc.) 3.6 g of co-emulsifier based on C18-fatty acid 105.6 g of aqueous calcium chloride solution (9-2 g of CaC12 . 2 H2O) 4.8 g of organophilic bentonite (GELTONE from the company Baroid Drilling Fluids, Inc.) 216 g of baryte In the Example 3, there is used the comparably lower-sulfonated emulsifier based on sulfonated rapeseed ; oil according to Example 1, while Example 4 employs the corresponding higher-sulfonated emulsifier based on sulfonated rapeseed oil according to Example 2.

~ he characteristic values determined of the unaged and of the aged fluid systems are as follows:

Example 3 :
Unaged Aged MaterialMaterial Plastic viscosity (PV)37 47 Yield point (YP) 19 10 Gel strength (lb/100 ft2) ~ 10 seconds 9 2 :, 10 minutes 11 3 .

HTHP 7 ml . - .
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D 9243 - 30 - Mar. 04, l991 Example 4 UnagedAged Material Material Plastic viscosity (PV) 40 82 Yield point (YP) 29 60 Gel strength (lb/lO0 ft2) 10 seconds 13 18 lO minutes 29 61 HTHP 6 ml The values determined of the unaged and of ~he aged materials are as follows.
Unaged Aged Material Material Plastic viscosity (PV) 38 35 Yield point (YP) 13 10 Gel strength (lb/lO0 ft2) 10 seconds 7 lO minutes 14 9 Example 5 In the following Example 5 a water-based emulsion fluid using a complex oleophilic polycarboxylic acid ester having a lubricant character as the dispersed oil phase is prepared according to the following procedure:

First, a homogenized slurry containing 6% by weight of bentonite is produced from a commercially available `, :

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D 9243 - 31 - Mar. 04, l991 bentonite (non-hydrophobized) and tap water and the pH
value thereof is adjusted to from 9.2 to 9.3 with caustic soda solution.

This pre-swollen bentonite phase is charged and, in subsequent process steps - each with thorough mixing - , the individual components of the water-based ester-oil emulsion are incorporated in accordance with the ~ollow-ing formulation:
350 g of 6% by weight bentonite solution l.S g of co~ercial carboxymethylcellulose (of lo~ viscosity) (~elatin U 300 S 9 g of sodium chloride g of complex ester 6 g of emulsifier of ~xample 2 219 g of baryte As an oleophilic ester oil phase there is employed the reaction product of trimethylolpropane (14% by weight), a co~mercially available dimer fa'ty acid mixture (24% by weight) and oleic acid as the balance.
The dimer fatty acid mixture contains 77% by ~eight of dimer acids and tri- and higher polycarboxylic acids as the balance - here % by weight relative to the dimer fatty acid mixture.

The viscosity of the OJW emulsion fluid thus prepared is determined as follows:
.
First the plastic viscosity (PV), the yieId point , (YP) and the gel strength after 10 seconds and lO minutes of the unaged emulsion fluid are determined at room temperature.

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D 9243 - 32 - Mar. 04, 1991 Then the emulsion fluid is aged under static conditions at 90 C for 16 hours in order to test the influence of the tPmperature on the stability of the emulsion. Then the viscosity values are once more determined at room temperature.

Unaged Aged Material Material .
Plastic viscosity (PV) 19 18 Yield point (YP) 99 110 Gel strength (lb/100 ft ) 10 seconds 49 ~3 10 minutes 50 ;6 .

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Claims

C L A I M S :

1. Use of surface-active salts of esters from mono-and/or polyolefinically unsaturated carboxylic acids having at least 8 carbon atoms and lower mono- and/or polyhydric alcohols, which esters have been sulfonated in (an) inner position(s) and comprise sulfur that has been organically bonded to an at least predominant degree, (briefly: ester sulfonate salts) as ecologically compatible emulsifiers of the W/O type and/or O/W type in fluid and pumpable drilling fluids and other fluid drilling-hole treatment agents which comprise a con-tinuous or a dispersed oil phase together with an aqueous phase and which are suitable for an environ-mentally acceptable exploitation of geological resources, for example oil or natural gas deposits.

2. An embodiment according to claim 1, characterized in that ester sulfonate salts of unsaturated monocarb-oxylic acids of natural and/or synthetic origin com-prising from 10 to 40 carbon atoms, preferably com-prising the range C12-32 and especially the range C16-24, are used while, more specifically, mixtures of various carboxylic acid moieties may be present in the ester sulfonate salt.

3. An embodiment according to claims 1 and 2, characterized in that ester sulfonate salts are employed, the alcohol component(s) of which are derived from mono- to tetrahydric alcohols having preferably up to 5 carbon atoms, and especially from mono- to tri-hydric alcohols having up to 3 carbon atoms.

4. An embodiment according to claims 1 to 3, characterized in that at least partially ester sulfonate salts are used of mono-, di- and/or triglycerides of natural and/or synthetic origin which have been sulfon-ated in (an) inner position(s).

5. An embodiment according to claims 1 to 4, characterized in that ester sulfonate salts are used, the carboxylic acid moieties of which are also portion-wise derived from saturated carboxylic acids, while the mono- and/or polyunsaturated carboxylic acids comprise at least 50% by mole - relative to the mixture of carb-oxylic acids.

6. An embodiment according to claims 1 to 5, characterized in that ester sulfonate salts of mono-, di- and/or especially triglycerides of natural origin, preferably based on vegetable and/or animal oils are used.

7. An embodiment according to claims 1 to 6, characterized in that ester sulfonate salts are used which comprise a maximum molar ratio of sulfonate moiety to carboxylic acid moiety of about 1 (statistic mean value), while lower values - e.g. from 0.25 to 0.7 - may be preferred for said molar ratio and, in the case of the triglyceride-based ester sulfonate salts the molar ratio, more particularly, is within the range of from about 0.3 to 1.

8. An embodiment according to claims 1 to 7, characterized in that triglyceride-based ester sulfonate salts are used wherein the ratio of sulfonate groups to sulfate groups is at least about 60/40 and preferably is above 70/30 and, more particularly, is within the range of from about 75/25 to 85/15.

9. An embodiment according to claims 1 to 8, characterized in that ester sulfonate salts are used which are based on unsaturated mono-, di- and tri-glycerides as well as mixtures thereof, which have been derived from fatty acids having from 16 to 24 carbon atoms and from 1 to 5 double bonds at a proportion of unsaturated fatty acids of more than 50% by weight, where ester sulfonate salts may be preferred, more of 50% by weight of the fatty acid component(s) of which are derived from oleic acid and/or linoleic acid and more particularly have originated from rapeseed oil rich in oleic acid.

10. An embodiment according to claims 1 to 9, characterized in that water- and/or oil-soluble ester sulfonate salts of the alkali metals, alkaline earth metals and/or ammonium are employed, whereof the use of the respective sodium, calcium and/or magnesium salts is preferred and calcium salts are especially used in the preparation and stabilization of W/O emulsions.

11. An embodiment according to claims 1 to 10, characterized in that the ester sulfonate salts con-stitute the at least prevailing portion of emulsifier, while they may be also employed together with other, especially with biologically compatible W/O and O/W
emulsifiers, respectively, and wherein especially the corresponding salts of sulfonated and/or non-sulfonated fatty acids may be employed as co-emulsifiers.

12. An embodiment according to claims 1 to 11, characterized in that the ester sulfonate salts are employed in amounts of from about 0.1 to 10% by weight, preferably from 0.5 to 5% by weight, and especially in amounts of from about 1 to 3% by weight - weight per-centage relative to the sum of water plus oil.

13. An embodiment according to claims 1 to 12, characterized in that the ester sulfonate salt-based emulsifiers are employed in combination with ecologic-ally compatible oil phases, while here ester oils of monocarboxylic acids and/or polycarboxylic acids with mono- and/or polyfunctional alcohols, corresponding ester oils of carbonic acid, oleophilic alcohols and/or corresponding ethers are preferred oil phases and, more particularly, are selected so that in practical use even upon a partial saponification of the esters no toxico-logical, especially no inhalation-toxicological endangerment will be induced.

14. An embodiment according to claims 1 to 13, characterized in that the ester sulfonate salts are used together with oil phases and mixed oil phases, respect-ively, exhibiting flash points of at least 100 °C, and preferably in excess of about 135 °C.

15. An embodiment according to claims 1 to 14, characterized in that the ester sulfonate salt-based emulsifiers are employed in fluid and pumpable inverted systems having a continuous oil phase which have solid-ification values (pour point and setting point) below 0 °C, and preferably below -5 °C and have a Brookfield (RVT) viscosity at from 0 °C to 5 °C of not more than 55 mPa.s, and preferably of not more than 45 mPa.s, while upon the use of the emulsifiers in O/W emulsions the dispersed oil phase may have a Brookfield (RVT) viscosity at 20 °C of up to about 3,000,000 mPa.s, and preferably of up to about 1,000,000 mPa.s.

16. An embodiment according to claims 1 to 15, characterized in that ecologically acceptable ester sulfonate salt emulsifiers are used together with an oil phase which at least partially contains ester oils of monocarboxylic acids from at least one of the following subclasses:
a) Esters of C1-5-monocarboxylic acids and mono-and/or polyfunctional alcohols, whereof the moieties of monohydric alcohols comprise at least 6 carbon atoms and preferably at least 8 carbon atoms and the polyhydric alcohols preferably have from 2 to 6 carbon atoms in the molecule, b) Esters of monocarboxylic acids of synthetic and/or natural origin comprising from 6 to 16 carbon atoms, and more specifically esters of aliphatic saturated monocarboxylic acids and mono- and/or polyfunctional alcohols of the kind mentioned in a), c) Esters of olefinically mono- and/or polyunsaturated monocarboxylic acids having at least 16, and especially 16 to 24 carbon atoms and especially monofunctional straight-chain and/or branched alcohols.

17. Inverted drilling fluids suitable for an environ-mentally acceptable exploitation of geological resources and comprising, in a continuous oil phase, a dispersed aqueous phase together with emulsifiers and further con-ventional auxiliary agents such as thickness, fluid-loss additives, weighting agents, water-soluble salts and/or alkali reserves, characterized in that they con-tain surface-active ester sulfonate salts as indicated in claim 1 as emulsifier or as an emulsifier component together with an ecologically compatible continuous oil phase.

18. Inverted drilling fluids according to claim 17, characterized in that they contain ester oils, oleo-philic alcohols and/or corresponding ethers as the eco-logically compatible continuous oil phase.

19. Inverted drilling fluids according to claims 17 and 18, characterized in that they have a plastic viscosity (PV) within the range of from about 10 to 60 mPa.s and a flow limit (yield point, YP) within the range of from about 5 to 40 lb/100 ft2 - each determined at 50 °C.

20. Inverted drilling fluids according to claims 17 to 19, characterized in that upon the use, in combination, of ester oils in the continuous oil phase, and more specifically of corresponding esters of monocarboxylic acids, of polycarboxylic esters and/or of carbonic acid, said ester oils comprise at least one third, and prefer-ably the predominant portion of this ecologically com-patible oil phase.

21. Inverted drilling fluids according to claims 17 to 20, characterized in that the dispersed water portion thereof comprises about from 5 to 50 % by weight, and preferably about from 10 to 30% by weight, and especial-ly contains salts of the kind of CaCl2 and/or KCl in the dissolved state.

22. Inverted drilling fluids according to claims 17 to 21, characterized in that the oil phase of the inverted mud has a Brookfield (RVT) viscosity within the range of from 0 °C to 5 °C, below 50 mPa.s, and preferably not higher than 40 mPa.s.