IE920305A1

IE920305A1 - The use of surface-active carboxylic acid complex esters as¹emulsifiers in oil-based drilling fluids and other well¹servicing fluids

Info

Publication number: IE920305A1
Application number: IE030592A
Authority: IE
Original assignee: Henkel Kgaa
Priority date: 1991-01-31
Filing date: 1992-01-30
Publication date: 1992-07-29
Also published as: ZA92668B; MX9200455A; DE4102908A1; AU1167992A; TR25713A; WO1992013926A1; CA2101757A1; JPH06504801A

Abstract

The description relates to the use of complex esters from the reaction of: (a) di and/or tricarboxylic acids or their derivatives capable of ester formation; with (b) polyvalent alcohols with up to 6 and preferably with up to 4 OH groups and/or their oligomers; and (c) monocarboxylic acids; which have an initial molar ratio b/a somewhat corresponding to the number of carboxyl groups per mol of reactant (a), are largely free of unreacted carboxyl groups but may have residual free OH groups, as ecologically acceptable emulsifiers of the W/O type in fluid and pumpable drilling muds or other borehole treatment agents which have a dispersed aqueous and/or water miscible alcoholic phase in a closed oil phase and are suitable for the environmentally friendly opening of deposits, e.g. of petroleum or natural gas. The invention also relates to invert drilling muds which are suitable for the environmentally friendly opening of geological deposits and contain, in a closed oil phase, a dispersed aqueous and/or water miscible alcoholic phase together with emulsifiers and other customary auxiliaries, e.g. thickening agents, fluid-loss additives, fillers, water-soluble salts and alkaline reserves, characterized by the fact that, together with an ecologically acceptable closed oil phase, they contain surface-active complex esters of the kind described above as emulsifiers or emulsifier components.

Description

COMPLETE SPECIFICATK N ·>. CASE, V/.

THE USE OF SURFACE-ACTIVE CARBOXYLIC ACID COMPLEX ESTERS AS EMULSIFIERS IN OIL-BASED DRILLING FLUIDS AND OTHER HELL SERVICING FLUIDS HENKEL KOMMANDITGESELLSCHAFT AUF AKTIEN, a company organised and existing under the laws of the Federal Republic of Germany, of Henkelstrasse 67, 4000 Dusseldorf, Federal Republic of Germany 5015 D 9441 PCT The use of surface-active carboxylic acid complex esters as emulsifiers in oil-based drilling fluids and other well servicing fluids This invention relates to the use of selected emulsifiers having increased ecological compatibility for the production of free-flowing disperse systems which are present as invert w/o emulsions having a continuous oil phase and which are suitable for use as free-flowing well servicing fluids. The invention is described hereinafter with reference to oil-based drilling fluids and drilling muds based thereon as a characteristic example of fluids of the type in question. However, the modification of auxili10 ary fluids of the type in question in accordance with the invention is by no means confined to this particular application, instead it may be used in particular in the fields of spotting fluids, spacers, auxiliary fluids for workover and stimulation and for fracturing.

More particularly, the problem addressed by the present invention is substantially to influence the ecological compatibility of these auxiliaries, which are now industrially used worldwide, by using selected and, in particular, ecologically safe emulsifiers. In its prefer20 red embodiment, the present invention seeks to use these biologically safe emulsifiers in conjunction with oil phases of increased environmental compability and, in particular, biodegradability.

Prior art So-called invert drilling muds which, as w/o emulsions, contain a disperse aqueous phase in the continuous oil phase are at present of major importance in the field of drilling fluids for sinking wells in rock and bringing D 9441 PCT 2 up the loose drillings. The content of disperse aqueous phase is typically between about 5 and 50% by weight.

Stabilization of the dispersion formed requires the use of corresponding emulsifiers of the w/o type (invert fluids). The relevant specialist literature on the subject is represented, for example, by G.R. Gray, H.C.H. Darley Composition and Properties of Oil Well Drilling Fluids, 4th Edition, Gulf Publishing Co., Houston, London, 1981, more particularly pages 64 and 320 et seq.

In practice, the oil phases of drilling fluids of the described type and other well servicing fluids of comparable composition are now almost exclusively formed by mineral oil fractions. This involves considerable pollution of the environment if, for example, the drilling fluids enter the environment either directly or via the drilled rock. Mineral oils are difficult and, anaerobically, virtually impossible to degrade and hence must be regarded as long-term pollution. Even though these oil phases as the main constituent or at least a substantial constituent of the drilling fluid are an important starting point for ecological considerations, corresponding attention must also be devoted to the other components of these multicomponent mixtures. Emulsifiers are particularly important in this regard. By definition, compounds of this type are highly active substances, even in low concentrations, which are known to be capable of intensively interacting with the vegetable or animal organism.

Problem addressed by the invention The problem addressed by the present invention was to improve drilling fluids of the described type based on continuous oil phases in admixture with disperse aqueous phases, taking their ecological compatibility into account, to a considerable extent in relation to typical drilling fluids. More particularly, the invention set out to D 9441 PCT 3 provide emulsifiers or emulsifier components which had never been used in the field in question. In the preferred embodiment of the invention, these environmentally compatible emulsifiers of the w/o type are used together with oil/water phases in which the oil phases in turn show increased ecological compatibility and, in particular, can be degraded in an environmentally friendly manner by natural degradation mechanisms.

Solution to the problem addressed by the invention To solve the first problem, the invention proposes using selected carboxylic acid complex esters of the type described hereinafter, which may be classified as w/o emulsifiers by virtue of their constitution and their. interaction with the surrounding system, as ecologically compatible or rather safe compounds having an emulsifying effect.

In a first embodiment, therefore, the present invention relates to the use of complex esters from the reaction of (a) di- and/or tricarboxylic acids or ester-forming derivatives thereof with (b) polyhydric alcohols containing up to 6 OH groups and preferably up to 4 OH groups and/or oligomers thereof and (c) monocarboxylic acids 30 in which the molar ratio of (b) to (a) substantially corresponds to the number of carboxyl groups per mol of reactant (a) and which are substantially free from unreacted carboxyl groups, but may contain residual contents of free OH groups, D 9441 PCT 4 as ecologically compatible emulsifiers of the w/o type in free-flowing and pumpable drilling fluids or other well servicing fluids which contain a disperse aqueous phase in a continuous oil phase and which are suitable for the environmentally friendly development of geological deposits, for example oil and gas pools.

Of particular importance in this regard are corresponding invert drilling fluids which, in a continuous oil phase, contain a disperse aqueous phase together with emulsifiers and typical other auxiliaries, such as thickeners, fluid loss additives, weighting agents, soluble salts and/or alkali reserves. In this embodiment of the invention, selected surface-active complex esters are used as emulsifier or as at least part of an ecologically safe. emulsifier system.

The emulsifiers selected in accordance with the invention are suitable for use as the oil phase together with typical mineral oil fractions. In one preferred embodiment, however, these emulsifiers are used together with environmentally compatible ester oils, oleophilic alcohols and/or corresponding ethers as the continuous or disperse oil phase, cf. in particular relevant developments by applicants who, in a relatively large number of earlier patent applications, describe proposals for replacing the hitherto usual mineral oil fractions by ecologically safe, readily degradable oil phases. Various types of replacement oils are mentioned in these patent applications and may even be used in admixture with one another. The replacement oils in question are selected oleophilic mono30 carboxylic acid esters, selected polycarboxylic acid esters, at least substantially water-soluble alcohols capable of flowing under the particular working conditions, corresponding ethers and selected carbonic acid esters. The earlier patent applications in question are P 38 42 659.5 (D 8523), P 38 42 703.6 (D 8524), P 39 07 391.2 (D D 9441 PCT 5 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 these earlier applications relate to oil-based drilling fluid systems, more particularly of the invert w/o type.

In its most important embodiment, the invention relates to the combined use of the above-described emulsifiers from the class of surface-active carboxylic acid complex esters together with disperse or continuous oil phases of the last-mentioned type. The disclosure of the earlier applications cited above is hereby specifically included in the disclosure of the present invention.

Particulars of the teaching according to the invention In their specific embodiment for the particular application, the complex esters used for the purpose according to the invention may be present in various modifications through the choice and corresponding adaptation of the above-defined constituents (a), (b) and (c) of the molecule. The basic structure of the complex esters is the same for all these specific embodiments, being derived primarily from the definition of the basic constituents (a) to (c) and hence their functionality, the molar ratios in which the components (a) to (c) are used in the synthesis of the complex ester molecule and the particular way in which the molecule is built up. The following graphic formula applies to the idealized structural formula of the complex esters used in accordance with the invention. The centrally arranged polycarboxylic acid constituent (a) is esterified at its carboxyl groups with the polyhydric alcohols (b) which, in turn, are at least partly reacted through their free hydroxyl groups with the monocarboxylic acids (c) to form ester groups. By virtue of the polyfunctionality of the reactants (a) and (b), it can immedi35 ately be seen that, although compounds having this idealIE 920305 D 9441 PCT 6 ized structural formula are present to a considerable extent in the reaction mixture, structurally further development reaction products may also be present at the same time. This is not of fundamental importance to the practical value of the complex esters for the purposes of the teaching according to the invention.

Within the context of the models of the complex ester molecule under discussion here, particular significance is attributed to two embodiments of specific complex ester types for the teaching according to the invention.

In the first of these embodiments, the w/o emulsifiers used are complex esters at least partly containing trihydric and/or tetrahydric alcohols and/or oligomers thereof as reaction component (b) , so that a plurality of free. hydroxyl groups is available at the particular structural element of the complex ester for the final attachment of the monocarboxylic acids (c). The use of trihydric alcohols and/or oligomers thereof as constituent (b) of the complex ester molecule can be particularly important in this regard. Special significance is attributed to glycerol as the trihydric alcohol and/or oligomer thereof as reaction component (b).

In the second important category of the complex esters used in accordance with the invention, reaction component (b) is formed at least partly and, preferably, predominantly or even exclusively by oligomers of lower diols, more particularly oligomers of diols containing up to 6 carbon atoms and preferably up to 3 carbon atoms, particular significance being attributed to ethylene glycol, propane30 1,2-diol and/or propane-1,3-diol. This embodiment of the complex esters used in accordance with the invention is characterized in that only one free hydroxyl group is available for the subsequent reaction with the monocarboxylic acids (c) at the particular point of attachment of the complex ester molecule. As already mentioned, the two D 9441 PCT 7 sub-principles under discussion here regarding the specific character of the reaction components (b) from the preparation of the complex ester may be combined with one another, the mixing ratios used extending virtually over the entire range of the mixtures of, on the one hand, diols and, on the other hand, higher polyhydric alcohols.

Suitable diol oligomers are, in particular, corresponding compounds having average molecular weights of up to about 500, preferably in the range from about 12 0 to 4 00 and, more preferably, in the range from about 150 to 350. These figures are based in particular on ethylene glycol as the oligomer-forming dihydric alcohol and may be similarly applied to dihydric alcohols containing a larger number of carbon atoms.

Preferred polycarboxylic acids (a) for the purposes of the invention are corresponding compounds containing up to about 36 carbon atoms and, more particularly, about 4 to 18 carbon atoms. Particular significance is attributed in this regard to corresponding dicarboxylic acids or dicar20 boxylic acid mixtures and/or ester-forming derivatives thereof, non-aromatic polycarboxylic acids being preferred for ecological reasons. Straight-chain and/or branchedchain polycarboxylic acids of the stated type are particularly suitable for the purposes of the invention and, above all as technical polycarboxylic acid mixtures and, more particularly, corresponding technical dicarboxylic acid mixtures, may form the basis of the complex esters to be used in accordance with the invention. Commercially available technical dicarboxylic acid mixtures predominant30 ly containing 4 to 6 carbon atoms and/or corresponding dicarboxylic acid mixtures predominantly containing 8 to 12 carbon atoms are particularly important as reaction component (a) in the context of the teaching according to the invention.

Reaction component (c) is preferably selected from D 9441 PCT 8 saturated and/or unsaturated monocarboxylic acids of natural and/or synthetic origin. These monocarboxylic acids preferably contain at least 6 carbon atoms and, more preferably, at least 8 carbon atoms in the molecule. Mono5 carboxylic acids containing 8 to 24 carbon atoms are especially important both for reasons of accessibility and, in particular, for reasons of specific development of the desired w/o emulsifier characteristic. The monocarboxylic acids or corresponding mixtures of monocarboxylic acids may be linear and/or branched. They nay be at least partly mono- and/or polyolefincally unsaturated and, particularly in the case of the monocarboxylic acids of natural origin, have chain lengths of predominantly 12 to 22 carbon atoms. Technical fatty acid mixtures, for example those based on· tallow, rapeseed oil and tall oil, are suitable representatives of the class of substances in question here. However, the invention is not confined to these particular starting materials. Suitable fatty acid sources of natural origin are, for example, palm oil, coriander oil, chaul20 moogra oil, sunflower oil, cottonseed oil, olive oil, peanut oil, linseed oil, lard oil, meadowfoam oil, lard or fish oil. So-called new rapeseed oil rich in oleic acid is a particularly important starting material for the preparation of the complex esters to be used in accordance with the invention.

According to the invention, the condensation and synthesis of the complex esters is preferably controlled in such a way that the residual acid value of the product to be used as emulsifier is kept as low as possible. Complex esters having residual acid values below 60 and preferably not above 40 are the preferred representatives of the complex esters according to the invention. Complex esters or corresponding mixtures which have even lower residual acid values of preferably not more than 2 5 and, more preferably, below 10 to 15 have proved to be particularly D 9441 PCT 9 suitable in practice.

So far as the structure of the complex esters is concerned, particular significance may be attributed to any residues of free hydroxyl groups present therein. This applies in particular to the above-mentioned sub-category of complex esters in which polyfunctional alcohols having a functionality of more than 2 are used as reaction component (b) . The situation touched upon here will become clearer from the following considerations: The classification of emulsifiers on the one hand in the class of the w/o emulsifiers desired in accordance with the invention or, on the other hand, in the class of the o/w emulsifiers which are not required in accordance with the invention for forming a disperse oil phase in a con15 tinuous aqueous phase is determined in known manner by the ratio of the oleophilic components in the particular molecule to the hydrophilic component. The particular emulsifier molecule in question may be assigned to one or the other class on the basis of the so-called HLB value, typical w/o emulsifiers being characterized by comparatively low HLB values, for example in the range from 3 to 11 or 12, and typical o/w emulsifiers being characterized by higher HLB values. The same classification is also used for the well servicing fluids according to the invention, cf. for example the above-cited literature reference Gray, Darley loc. cit. page 321.

The preferred performance of the complex esters as defined in accordance with the invention derives from their structural elements. In addition to the hydrocarbon chains of the reactants (a), the oleophilic parts of the molecule are in particular the corresponding acid residues of the monocarboxylic acids (c) . More hydrophilic parts of the molecule are the ester groups and, as known per se, particularly free hydroxyl groups which may readily be left as unreacted residual constituents in the complex ester D 9441 PCT 10 molecule. It is clear that, in each individual case, the oleophilic and hydrophilic parts of the molecule and their ratio to one another can be very finely controlled, thus enabling the desired w/o emulsifier property to be optim5 ized. The structure of the oil of natural and/or synthetic origin to be used as the continuous phase may also be included in these considerations, the activity of the complex esters as w/o emulsifiers in drilling muds based on mineral oil differing from their activity in drilling muds based on ester or ether oils. According to the invention, however, it is also possible through the described controllability of the emulsifier properties from the structure of the complex esters to produce standard emulsifiers which provide the properties required in practice both in pure mineral-oil-based drilling muds and in drilling muds based, for example, on ester or ether oils. General chemical knowledge may be used to regulate the emulsifier effect by displacing the hydrophilic and lipophilic parts of the molecule towards one another.

It has been found that, in the use of the complex esters having the structure according to the invention, it can be of advantage, even in cases where higher alcohols are used as reaction component (b), to use those reaction products which, on average, contain no more than 3 free OH groups and preferably no more than 2 free OH groups per complex ester molecule. However, the desired adaptation of the hydrophilic constituents to the lipophilic parts of the molecule can also be achieved without any free hydroxyl groups or with hardly any free hydroxyl groups in the final complex ester molecule. This applies in particular to the above-described sub-class of complex esters in which reaction component (b) is formed by diol oligomers which in turn - at least on the case of the lower diols, such as ethylene glycol or propanediol - introduce a considerable degree of hydrophilicity into the molecule. Accordingly, D 9441 PCT 11 the present invention also specifically encompasses those complex esters in which the described hydrophilic/lipophilic adaptation has been carried out without the use of free hydroxyl groups.

Complex esters of the type used in accordance with the invention are compounds known per se which have been proposed for various applications of which the field of lubricants is mentioned as just one example. Their use as a w/o emulsifier in accordance with the invention for stabilizing flowable and pumpable drilling muds or other well servicing fluids which contain a disperse aqueous and/or water-miscible alcoholic phase in a continuous oil phase and which are suitable for the environmentally friendly development of reserves, for example oil and gas. pools, has not been described. For ecological reasons and particularly for reasons of the degradability of the emulsifiers in question, complex esters of the type according to the invention are important new constituents in fluids of the last-mentioned type. The complex esters preferably form at least the predominant part of the emulsifier, although they may also be used together with other, more particularly biologically compatible w/o emulsifiers. In a number of earlier applications, applicants describe corresponding classes of compounds for the particular purpose in question here, cf. in particular earlier patent applications P 40 03 028.8 (D 8158), P 40 24 658.2 (D 9223), P 40 24 659.0 (D 9222) and P 40 24 892.5 (D 9243). Selected emulsifiers based on ethers, α-sulfonated fatty acid disalts, alkyl glycoside compounds and surface-active ester sulfonate salts are described as w/o emulsifiers in these earlier applications. Compounds of this type are suitable for mixing with the complex esters used as w/o emulsifiers in accordance with the present invention.

Other suitable co-emulsifiers are salts, more par35 ticularly corresponding alkaline earth metal salts, of D 9441 PCT 12 sulfonated and/or non-sulfonated unsaturated and/or saturated fatty acids of natural and/or synthetic origin. Where emulsifier mixtures of the type described here are used, the complex esters form at least about 10% by weight and preferably at least about 50% by weight of the particular emulsifier system in preferred embodiments of the invention.

The complex esters may be used in quantities of from about 0.1 to 10% by weight based on the sum of the water and oil liquid phases. Preferred quantities of the emulsifier component are about 0.5 to 5% by weight, particular significance being attributed to quantities of from about 1 to 3% by weight, again based on the sum of water and oil.

In the preferred embodiment particularly emphasized at the beginning, the particular oil phases were formed by the ecologically compatible ester oils, oleophilic alcohols and/or ethers described in applicants' earlier applications cited above. Accordingly, using these oil phases, the invention relates to well servicing fluids flowable and 0 pumpable at temperatures of 5 to 20°C, more particularly drilling fluids based on the continuous oil phase, more particularly in admixture with a disperse aqueous phase (invert w/o type).

The ecologically compatible oils or oil phases cover a wide range so far as their possible physical quality is concerned. In this regard, the invention encompasses oil phases which are flowable and pumpable even at relatively low temperatures, as represented by those which are suitable for the production of w/o emulsions. However, highly viscous to solid oil phases or materials of this type may also be partly used in accordance with the teaching of the invention. This is exemplified by the following considerations : One possibility of using highly viscous or even solid, ecologically compatible oil phases exists when the particIE 920305 D 9441 PCT 13 ular oil phase of the end product is formed only partly of these highly viscous to solid representatives of degradable esters, alcohols and/or ethers which, in turn, are mixed with comparatively thinly liquid oils of this type or other types.

However, one requirement which all the oil phases or mixed oil phases used in accordance with the invention have to satisfy is that, for safety reasons, they should have flash points of at least about 100°C and preferably above about 35°C. Distinctly higher flash points, particularly those above 150°C, can be particularly valuable. Another requirement is that the emulsifiers based on the complex esters should be able to be used in flowable and pumpable invert systems with continuous oil phases which have solidification points (flow and pour point of the oil phase) below 0°C and preferably below -5°C and a Brookfield (RVT) viscosity at temperatures of 0 to 5 °C of no more than 55 mPa.s and preferably no more than 4 5 mPa.s. Another requirement which the various potentially hydrolyzable oil 0 phases used in accordance with the invention have to satisfy is that not only should the need for ecological compatibility be fulfilled for the compound used, i.e. for example the particular ester oil or mixture of ester oils selected, there should also be no toxicological risk and, in particular, no inhalation-toxicological risk, even in the event of partial hydrolysis in practical application. According to the earlier applications cited above, the various representatives of the ester oils in particular are being addressed in this regard, special significance again being attributed to monofunctional alcohols from the esterforming reaction. By comparison with polyfunctional alcohols, monofunctional alcohols, particularly lower types, are highly volatile so that secondary risks can arise through partial hydrolysis. In the classes of the various ester oils, therefore, the monofunctional alcohols D 9441 PCT used or rather the corresponding residues of these alcohols are preferably selected so that they contain at least 6 carbon atoms and preferably at least 8 carbon atoms in the molecule. Hydrolysis-stable ethers can be particularly important for practical application as the continuous oil phase of the well servicing fluids.

Irrespective of the particular quality of the continuous oil phase, invert drilling muds of the type targeted by the present invention preferably have a plastic viscosity (PV) in the range from about 10 to 60 mPa.s and a yield point (YP) in the range from 5 to 40 lb/100 ft2 , as determined in either case at 50°C.

In addition to ethers from alcohols of natural and/or synthetic origin, ester oils of monocarboxylic acids have. proved to be ecologically compatible oil phases with good flow properties at low temperatures, being derived in a preferred embodiment of the invention from at least one of the following sub-classes: a) esters of C^ monocarboxylic acids and monohydric and/or polyhydric alcohols, residues of monohydric alcohols containing at least 6 and preferably at least 8 carbon atoms and the polyhydric alcohols preferably containing 2 to 6 carbon atoms in the molecule, b) esters of monocarboxylic acids of synthetic and/or natural origin containing 6 to 16 carbon atoms, more particularly esters of corresponding, aliphatically saturated monocarboxylic acids and monofunctional and/or polyfunctional alcohols of the type mentioned in a) , c) esters of olefinically mono- and/or polyunsaturated monocarboxylic acids containing at least 16 and more particularly 16 to 24 carbon atoms and, in particular, D 9441 PCT 15 monofunctional linear and/or branched alcohols.

Starting materials for many of the monocarboxylic acids belonging to these sub-classes, particularly those containing relatively large numbers of carbon atoms, are vegetable and/or animal fats and/or oils. Tallow, coconut oil, palm kernel oil and babassu oil are mentioned in particular as starting materials for monocarboxylic acids predominantly containing up to 18 carbon atoms and substan10 tially saturated components. Vegetable ester oils, more particularly for olefinically monounsaturated and, optionally, polyunsaturated carboxylic acids in the C16.24 range are, for example, palm oil, peanut oil, castor oil, sunflower oil and, in particular rapeseed oil. However,. synthetic components are important structural elements for ecologically compatible oil phases both from the carboxylic acid side and on the alcohol side.

Additives in the oil-based drilling fluid Invert drilling fluids normally contain the finely disperse aqueous phase in quantities of about 5 to 50% by weight together with the continuous oil phase. In addition to water, suitable additives are any of those typically used in comparable fluids. These additives may be water25 soluble, oil-soluble and/or dispersible in water or oil.

In addition to the emulsifiers defined in accordance with the invention, typical additives are, for example, fluid loss additives, soluble and/or insoluble substances for building up pseudoplasticity, alkali reserves, agents for inhibiting the unwanted exchange of water between drilled formations, for example water-swellable clays and/or salt layers, and the drilling fluid, wetting agents for improving absorption of the oil phase onto solid surfaces, for example for improving the lubricating effect and also for improving the oleophilic sealing of exposed D 9441 PCT 16 rock formations or rock surfaces, biocides, for example for inhibiting bacterial infestation of the emulsions and the like. Further information on typical additives of the type in question can be found in the relevant prior art as represented, for example, by the specialist literature cited at the beginning, cf. in particular Gray and Darley, loc. cit., Chapter 11, Drilling Fluid Components. Accordingly, the following additives are mentioned purely by way of extract: Finely disperse additives for increasing the density of the fluid: barium sulfate (baryta) is widely used, although calcium carbonate (calcite) or the mixed carbonate of calcium and magnesium (dolomite) are also used.

Agents for building up pseudoplasticity which also act as fluid loss additives: hydrophobicized bentonite is mentioned above all. Considerable significance is also attributed in this connection to the co-use of organic polymer compounds of natural and/or synthetic origin.

Additives inhibiting the unwanted exchange of water, for example with clays: the additives known from the prior art on oil-based drilling fluids may be used for this purpose.

These are, in particular, halides and/or carbonates of the alkali and/or alkaline earth metals, considerable significance being attributed to corresponding potassium salts, optionally in combination with lime. More recent proposals concern the use of lower water-soluble alcohols, such as glycerol and/or propanediol, see for example GB 2,223,255A. Reference is also made, for example, to the Articles in Petroleum Engineer International, September 1987, 32 - 40 and World Oil, November 1983, 93 - 97.

Alkali reserves: suitable additives of this type are D 9441 PCT 17 inorganic and/or organic bases adapted to the overall behavior of the drilling fluid, more particularly corresponding basic salts or hydroxides or alkali and/or alkaline earth metals and also organic bases. Lime is a particularly important representative of this class. The type and quantity of these basic components are adapted to one another in known manner.

The particular auxiliaries and additives selected are 10 basically used in the usual quantities, cf. the relevant literature cited above.

The production of the complex esters used as w/o emulsifiers in accordance with the invention (no protection is being claimed for their production in the present application) is carried out in known manner by a multistage process which may be carried out, for example, as follows in two reaction steps: 1st Reaction step: The polycarboxylic acid component(s) and the polyol component(s) are reacted with one another under reduced pressure and at elevated temperatures, for example in a water jet vacuum at temperatures above 150°C, until the residual acid value has fallen to a level in the lower range desired. However, the esterification reaction may also be carried out in the absence of esterification catalysts. If, for example, the esterification reaction is carried out in a water jet vacuum at 170°C, there is no need to add an esterification catalyst.

As mentioned above, the molar quantity of polyol component(s) used is adapted to the quantity of polycarboxylic acid(s) initially introduced in such a way that there is 1 mol of the polyol component(s) per mol of a carboxyl group intended for esterification. By using a slight excess of the polyol component(s), the residual acid D 9441 PCT 18 values can be reduced particularly effectively in this first step, for example to values below 20. To this end, the polyol component may be used in an excess of approximately 5% for example. 2nd Reaction step: The reaction product from the first reaction step containing the now terminally positioned free hydroxyl groups of the polyhydroxy ester formed is reacted with the predetermined quantities of monocarboxylic acids or monocarboxylic acid derivatives capable of esterification. Providing the volatility of the corresponding monocarboxylic acids is sufficiently high, as is the case for example where corresponding fatty acids having C chain. lengths in the higher range are used, this esterification step may also be carried out in a water jet vacuum at elevated temperatures, for example at 170°C, in the absence of additional catalysts. However, typical catalysts may also be used.

The production process may be modified where comparatively low-boiling reactants, for example corresponding low-boiling polyol components, are used. In this case, a preliminary reaction may be carried out at sufficiently high temperatures, for example again at 170°C, but initial25 ly under only moderately reduced pressures in the range from about 200 to 300 mbar until a sufficient initial reaction has taken place. The reaction is then continued under a full water jet vacuum.

In the following Examples, the complex esters A and B which are characterized in the following by the basic formulation of their reaction constituents (a), (b) and (c) and by selected product parameters are used as w/o emulsifiers . g glycerol (4 mol) g of a C4.6 dicarboxylic acid mixture (2 mol) g rapeseed oil fatty acid (6 mol) 234.2 97.7 81.6 D 9441 PCT Emulsifier A prepared from 368.4 270.4 1,726.2 Residual acid value Saponification value Iodine value OH value Emulsifier B prepared from 515.8 378.6 1,611.1 Acid value Saponification value Iodine value OH value g glycerol (5.6 mol) g C<,-6 dicarboxylic acid mixture (2.8 mol) g rapeseed oil fatty acid (5.6 mol) 26.9 204.9 113.4 100.3 The mixture based on the C4.6 dicarboxylic acids which is used as the dicarboxylic acid component (a) is commer25 cially available as Sokalan DCS (BASF) and has an acid value of 830.

Examples Examples 1 and 2 below using a standard formulation for oil-based drilling fluids of the w/o type illustrate corresponding drilling fluids in which the continuous oil is formed by a selected oleophilic carboxylic acid ester corresponding to the following definition: D 9441 PCT 20 Ester mixture of substantially saturated fatty acids based on palm kernel oil and 2-ethyl hexanol of which by far the predominant part is based on C12/1A fatty acids and which corresponds to the following specification: C8: 3.5 to 4. 5% by weight Cio* 3.5 to 4 . 5% by weight C12: 65 to 70 % by weight C14: 20 to 24 % by weight C16: approx. 2% by weight Cie: 0.3 to 1% by weight.

The ester mixture is in the form of a pale yellow liquid having a flash point above 165°C and a viscosity (Brookfield 20°C) of 7 to 9 cp.

The viscosity characteristics of the material are determined as follows before and after ageing: Measurement of viscosity at 50°C in a Fann 35 viscosimeter (a product of Baroid Drilling Fluids Inc.). The 20 plastic viscosity in mPas (PV), the yield point in lb/100 ft2 (YP) and the gel strength (lb/100 ft2) after 10 seconds and 10 minutes are determined in known manner. In addition, the fluid loss value (HTHP) is determined in Examples and 2.

The particular drilling fluids are aged by treatment for 16 h at 125°C in an autoclave (so-called roller oven).

The drilling fluid systems are made up in known manner using the following basic formulation: 230 ml carboxylic acid oil ml water g organophilic bentonite (GELTONE, a product of Baroid Drilling Fluids Inc.) g organophilic lignite (DURATONE, a product of Baroid Drilling Fluids Inc.) D 9441 PCT g lime g emulsifier based on complex ester 346 g baryta 9.2 g CaCl2 · 2 HZO.

The characteristic values determined on the material before and after ageing, as mentioned above, are shown in the following Table.

Example 1 In this Example, complex ester A is used as the emulsifier. Unaged material Aged material Plastic viscosity (PV) 55 56 Yield point (YP) 25 26 Gel strength (lb/100 ft2) 10 seconds 10 9 10 minutes 16 22 HTHP 5 ml Example 2 In this Example, complex ester B is used as the emulsifier. Unaged material Aged material 30 Plastic viscosity (PV) 46 55 Yield point (YP) Gel strength (lb/100 ft2 ) 33 37 10 seconds 13 16 10 minutes 27 45 35 HTHP 6 ml D 9441 PCT Examples 3 and 4 Using the emulsifiers based on complex ester of Examples 1 and 2, invert w/o drilling fluids based on a pure mineral oil (commercial product BP 83 HF) typically used in practice are made up in known manner in accordance with the following formulation: 204 ml mineral oil g emulsifier based on complex ester 3.6 g lime g organophilic lignite (DURATONE, a product of Baroid Drilling Fluids Inc.) 3.6 g co-emulsifier based on C18 fatty acid 105.4 g aqueous calcium chloride solution (9.2 g CaCl2 · H2O) 4.8 g organophilic bentonite (GELTONE, a product of Baroid Drilling Fluids Inc.) 216 g baryta Emulsifier A is used in Example 3 while the corresponding emulsifier B is used in Example 4.

The characteristic data determined on the drilling fluids before and after ageing are as follows: Example 3 Unaged material Aged material Plastic viscosity (PV) 33 31 Yield point (YP) 12 18 Gel strength (lb/100 ft2 ) 10 seconds 12 6 10 minutes 18 10 HTHP 5 D 9441 PCT 23 Example 4 Unaged material Aged material Plastic viscosity (PV) 35 38 Yield point (YP) 15 7 Gel strength (lb/100 ft2) 10 seconds 11 6 10 minutes 17 7 HTHP 5 ml D 9441 PCT

Claims

1. The use of complex esters from the reaction of (a) di- and/or tricarboxylic acids or ester-forming 5 derivatives thereof with (b) polyhydric alcohols containing up to 6 OH groups and/or oligomers thereof and (c) monocarboxylic acids in which the molar ratio of (b) to (a) substantially corresponds to the number of carboxyl groups per mol of reactant (a) and which are substantially free from un15 reacted carboxyl groups, but may contain residual contents of free OH groups, as ecologically compatible emulsifiers of the w/o type in free-flowing and pumpable drilling fluids or other well servicing fluids which contain a disperse aqueous phase in 2. 0 a continuous oil phase and which are suitable for the environmentally friendly development of geological deposits, for example oil and gas pools.

2. The use claimed in claim 1, characterized in that the complex esters used contain as reaction component (b) 25 polyhydric alcohols with up to 4 OH groups and, preferably at least partly, trihydric and/or tetrahydric alcohols and/or oligomers thereof, more particularly lower trihydric alcohols and/or oligomers thereof, complex esters based on glycerol and/or its oligomers as reaction component (b) 30 being particularly preferred.

3. The use claimed in claim 1, characterized in that complex esters of which the reaction component (b) is formed at least partly by oligomers of lower diols, more particularly by ethylene glycol oligomers preferably having D 9441 PCT 25 average molecular weights of up to about 500 are used.

4. The use claimed in claims 1 to 3, characterized in that the complex esters used are based on polycarboxylic acids containing up to about 36 carbon atoms and, more 5. Particularly, about 4 to 18 carbon atoms, preferably nonaromatic polycarboxylic acids and, more preferably, linear and/or branched polycarboxylic acids, as component (a).

5. The use claimed in claims 1 to 4, characterized in that the complex esters used as based on technical dicar10 boxylic acid mixtures for example mixtures of dicarboxylic acids containing predominantly 4 to 6 carbon atoms and/or containing predominantly 8 to 12 carbon atoms.

6. The use claimed in claims 1 to 5, characterized in that the complex esters used contain co-condensed saturated 15 and/or unsaturated monocarboxylic acids containing 8 to 24 carbon atoms as a reaction component (c), preference again being attributed to technical carboxylic acid mixtures, particularly of natural origin, which contain predominantly 12 to 22 carbon atoms in the molecule and are at least 20 partly mono- and/or polyolefinically unsaturated, fatty acid mixtures based on rapeseed oil and/or tall oil being particularly preferred.

7. The use claimed in claims 1 to 6, characterized in that complex esters having residual acid values below 60, 25 preferably not above 40 and, more preferably, not above 25 are used.

8. The use claimed in claims 1 to 7, characterized in that the complex esters used have a pronounced w/o emulsifier characteristic, the hydrophilic/lipophilic balance 30 being determined by the ratio of polar molecule constituents, including any free hydroxyl groups, to the molecule constituents of pronounced oleophilic character.

9. The use claimed in claims 1 to 8, characterized in that the complex esters used contain on average no more 35 than 3 free OH groups and preferably no more than 2 free OH D 9441 PCT 26 groups per complex ester molecule.

10. The use claimed in claims 1 to 9, characterized in that the complex esters used have been produced by a twostage synthesis in which the polyfunctional reaction 5 components (a) and (b) are first reacted with one another and the monocarboxylic acids (c) are subsequently reacted off with free OH groups, complex esters prepared from dicarboxylic acids, approximately 2 mol (per mol dicarboxylic acid) glycerol and/or oligoglycerol and long-chain, 10 at least partly olefinically unsaturated monocarboxylic acids of the fatty acid range preferably being used.

11. The use claimed in claims 1 to 10, characterized in that the complex esters form at least the predominant part of the emulsifier, but may also be used together with15 other, more particularly biologically compatible, w/o emulsifiers.

12. The use claimed in claims 1 to 11, characterized in that the w/o emulsifiers based on the complex esters are used in quantities of 0.1 to 10% by weight, preferably in 20 quantities of 0.5 to 5% by weight and, more preferably, in quantities of from about 1 to 3% by weight, based on the sum of water and oil.

13. The use claimed in claims 1 to 12, characterized in that the emulsifiers based on the complex esters are used 25 together with ecologically compatible oil phases, ester oils of monocarboxylic acids and/or polycarboxyl ic acids with monohydric and/or polyhydric alcohols, corresponding ester oils of carbonic acid, oleophilic alcohols and/or corresponding ethers being preferred oil phases and being 30 selected in particular so that no toxicological, particularly inhalation-toxicological, risks arise in practical application, even in the event of partial ester hydrolysis.

14. The use claimed in claims 1 to 13, characterized in that the complex esters are used together with oil phases 35 or mixed oil phases having flash points of at least about D 9441 PCT 100°C and preferably above about 135°C.

15. The use claimed in claims 1 to 14, characterized in that the emulsifiers based on complex esters are used in flowable and pumpable invert systems with continuous oil 5 phases which have solidification values (flow and pour point of the oil phase) below O’C and preferably below -5°C and a Brookfield (RVT) viscosity at 0 to 5°C of not more than 55 mPa.s and preferably not more than 45 mPa.s.

16. The use claimed in claims 1 to 15, characterized in 10 that the emulsifiers based on the complex esters are used with oil phases which may also be formed at least partly by mineral oil fractions, but are preferably based at least partly on ethers and/or esters, preferred ester oils of monocarboxylic acids being those from at least one of the 15 following sub-classes: a) esters of C^ monocarboxylic acids and monohydric and/or polyhydric alcohols, residues of monohydric alcohols containing at least 6 and preferably at least 20 8 carbon atoms and the polyhydric alcohols preferably containing 2 to 6 carbon atoms in the molecule, b) esters of monocarboxylic acids of synthetic and/or natural origin containing 6 to 16 carbon atoms, more 25 particularly esters of corresponding, aliphatically saturated monocarboxylic acids and monofunctional and/or polyfunctional alcohols of the type mentioned in a) , 30 c) esters of olefinically mono- and/or polyunsaturated monocarboxylic acids containing at least 16 and more particularly 16 to 24 carbon atoms and, in particular, monofunctional linear and/or branched alcohols.

17. Invert drilling fluids suitable for the environmentalIE 920305 D 9441 PCT 28 ly friendly development of geological deposits and containing in a continuous oil phase a disperse aqueous and/or water-miscible alcoholic phase together with emulsifiers and other typical auxiliaries, for example thickeners, 5 fluid loss additives, weighting agents, water-soluble salts and alkali reserves, characterized in that, together with an ecologically compatible continuous oil phase, they contain surface-active complex esters of the type claimed in claim 1 as emulsifier or as an emulsifier component. 10

18. Invert drilling fluids as claimed in claim 17, characterized in that they at least partly contain ester oils, oleophilic alcohols and/or ethers as the ecologically compatible continuous oil phase.

19. Invert drilling fluids as claimed in claims 17 and 18, 15 characterized in that they have a plastic viscosity (PV) in the range from about 10 to 60 mPa.s and a yield point (YP) in the range from about 5 to 40 lb/100 ft 2 , as determined in either case at 50’C.

20. Invert drilling fluids as claimed in claims 17 to 19, 20 characterized in that, where ester oils are used in the continuous oil phase, more particularly corresponding esters of monocarboxylic acids, polycarboxylic acids and/or carbonic acid, or where ethers are used, the ester oils or the ethers make up at least about one third, but preferably 25 at least the predominant part of the ecologically compatible oil phase.

21. Invert drilling fluids as claimed in claims 17 to 20, characterized in that they have a disperse water content of about 5 to 50% by weight and preferably about 10 to 30% by 30 weight and, in particular, contain salts of the CaCl 2 and/or KCl type and/or water-soluble lower polyhydric alcohols in dissolved form.

22. Invert drilling fluids as claimed in claims 17 to 21, characterized in that the oil phase of the invert drilling 35 fluid has a Brookfield (RVT) viscosity at 0 to 5’C of below 50 mPa.s and preferably not more than 40 mPa.s.

23. Invert drilling fluid composition, substantially as described herein by way of example.