NZ233683A - Oil-in-water emulsion drilling fluid containing a carboxylic acid ester, preparation and use thereof - Google Patents

Abstract

The description relates to the use of water-emulsifiable esters of saturated and/or unsaturated carboxylic acids with up to 36 C atoms, which are liquid or at least plastically deformable at the working temperature and have flash-points of at least 80 DEG C, and mono and/or polyvalent alcohols as at least the major component of the dispersed oil phase of water-based O/W emulsion drilling fluids which are suitable for the environmentally acceptable exploitation of geological formations and may, if desired, contain insoluble, finely divided fillers to form water-based O/W emulsion drilling muds and/or further additives like emulsifiers, fluid-loss additives, wetting agents, alkaline reserves and/or aids for the inhibition of highly water-sensitive drilled rock.

Description

New Zealand Paient Spedficaiion for Paient Number £33683 t. % m ,o> I'i'fO! iks.-n 23368 ?? .f.iiic.ii-■-->"i Class: (>.}.CQ%&zl<XL;..£J.Qm/-J.&ioQ; £2)Mti>Sk f-u. jica-Utn 0:!o: P.O. Jou»\ia!, No: 70BVW ZIjEI ^%ry^} v *- ■ Lf i ii/"i y t»'« w <e? NEW ZEALAND PATENTS ACT, 1953 NEW 2EALANO PATENT OFFICE J 5 MAY 1990 RECEIVED .1 ■? .1 No: Date: COMPLETE SPECIFICATION DRILLING FLUIDS #We HENKEL KOMMANDITGESELLSCHAFT AUF AKTIEN, HenkelstraBe 67, 4000 Dtisseldorf-Holthausen, Federal Republic of Germany, a German cor.porat.ion hereby declare the invention for which X/we pray that a patent may be granted to rosv'us, and the method by which it is to be performed, to be particularly described in and by the following statement (followed by page la) - u. 2 33683 BACKGROUND OF THE INVENTION 1) Field of the Invention The invention relates to new drilling fluids in the form of water-base oil-in-water (0/W-) emulsions, and to O/W-emulsion drilling muds base' thereon, which are distinguished by high ecological acceptability arr at the same time have good standing and application properties. 2) Description of the Prior Art Liquid mud systems used in the sinking of rock bores for bringing tc the surface the detached drill cuttings are flcwable systems thickenec to a limited extent. They can be classified into one of the three following groups, thus: purely aqueous drilling fluids; drilling rmr systems based on oil (which as a rule are used in the form of the sc called invert emulsion muds, and represent preparations of the W/0-emulsion type in which the aqueous phase forms a heterogeneous fine dispersion in the continuous oil phase); and water-based O/W-emulsions ^ (these are fluid systems which contain a heterogeneous, finely- dispersed oil phase in a continuous aqueous phase). The invention concerns improved systems of this latter type.

The application properties of drilling fluids of the O/W-emulsion type take an intermediate position between the purely aqueous systems anc W* the oil-based invert fluids. The advantages, but also thf disadvantages, of the purely aqueous systems are connected with the advantages and disadvantages of the oil-based invert-emulsions described hitherto. Detailed information on this subject can be founc in the relevant specialist literature - see, for example, the textbook by George R. Gray and H.C.H. Darley, "Composition and Properties of Oil Well Drilling Fluids", 4th. edition, 1980/1981, Gulf Publishing Company, Houston, and the extensive specialist and Patent literature 2 33683 cited therein, and see also the Manual "Applied Drilling Engineering", Adam T. Bourgoyne, Jr. et al., First Printing Society of Petroleum Engineers, Richardson, Texas (USA).

One of the main weaknesses of purely water-based drilling mud systems lies in the interaction of water-sensitive, particularly water-swellable, rock and/or salt formations with the drilling fluid, and in the secondary effects initiated thereby, in particular bore-hole instability and thickening of the drilling fluid. Many proposals are concerned with the reduction of this range of problems, and have, for example, resulted in the development of the so-called inhibitive water-based muds - cf., for example, "Applied Drilling Engineering", loc. cit., Chapter 2, Drilling Fluids, 2.4 and Gray and Darley loc. cit., Chapter 2, in particular the sub-section on pages 50 to 62 (Muds for "Heaving Shale", Muds for Deep Holes, Non-Dispersed Polymer Muds, Inhibited Muds: Potassium Compounds).

In more recent times drilling fluids based on oil, which consist of a 3-phase system of oil, water and finely particulate solids, and are preparations of the W/O-emulsion type, have been used successfully to overcome the difficulties described above. Oil-based drilling fluids were originally based, as regards the continuous oil phase, on diesel oil fractions containing aromatics, but for detoxification, and to reduce the ecological problems created thereby, it was then proposed to use hydrocarbon fractions which were largely free of aromatics - now also known as "non-polluting oils" - see, for example, the publications by E.A. Boyd et a^l. "New Base Oil Used in Low Toxicity Oil Muds", Journal of Petroleum Technology, 1985, 137 - 143, and R.B. Bennet "New Drilling Fluid Technology - Mineral Oil Mud", Journal of Petroleum Technology, 1984, 975 - 981 and the literature cited therein.

The drilling fluids of the water-based O/W-emulsion system type have also hitherto used pure hydrocarbon oils as the dispersed oil phase -cf., for example, Gray, Darley loc. cit., p. 51/52 under the section "Oil Elnulsion Muds" and the tabular summary on p. 25 (Tables 1-3) with details for water-based emulsion fluids of the salt-water mud, lime mud, gyp mud and CL-CLS mud type, In this context in particular it is known that water-based O/W-emulsion fluids represent a substantial improvement in many respects over the purely water-based drilling mud systems. Particularly in mare recent times, however, the advantages and disadvantages of such water-based emulsion fluids have also been examined critically in comparison with the oil-based invert-systems, due to the considerable ecological reservations new felt towards the oil-based invert drilling fluids oornnonly used today. These ecological reservations can be subdivided into two main problem areas.

Firstly, in addition to the basic constituents - oil and water - all drilling fluid systems based on water and/or oil require a large number of additives for establishing the desired application properties, typically emulsifiers or emulsifier systems, weighting agents, fluid-loss additives, wetting agents, alkali reserves, and viscosity regulators, and in some cases auxiliary agents for the inhibition of drilled rock with high water-sensitivity (water swellable), disinfectants and the like. A detailed summnry can be found, for example, in Gray and Darley, loc. cit., Chapter It, "Drilling Fluid Components". Tne industry has developed additives which currently appear ecologically harmless, bit unfortunately it also uses additives which are ecologically questionable, or even ecologically undesirable.

The second problem area is determined by the oil phases used in such drilling fluids. Even the hydrocarbon fractions which are largely free from aromatics, currently known as "non-polluting oils", are not totally harmless when released into the environment. A further reduction in the environmental problems - caused by the fluid oil phases of the type referred to here - appears urgently necessary. This is true in particular for the sinking of off-shore wells, e.g., for the development of petroleum or natural gas deposits, because the serine eco-system reacts particularly sensitively to the introduction of tcscic and poorly degradable substances.

There have recently been same proposals for reducing these latter problems. For exaqple, US Patent Specifications Kb®. 4#|74^3f ooi 4,481,121 disclose oil-based invert-drilling fluids in which non-polluting oils are to be used, and suggest for this purpose, as being of equal value, mineral oil fractions which are free from aromatics, and vegetable oils, such as groundnut oil, soybean oil, linseed oil, corn oil, rice oil, and even oils of animal origin, such as whale oil. These named ester oils of vegetable and animal origin are all, without exception, triglycerides of natural fatty acids, which are known to have high environmental acceptability, and are clearly superior from the ecological point of view to hydrocarbon fractions - even when these do not contain aromatic hydrocarbons. In these above US Patent Specifications, however, not one concrete example actually describes the use of such natural ester oils in invert drilling fluids. Without exception mineral oil fractions are used as the continuous oil phase -and in fact, oils of vegetable and/or animal origin of the type mentioned are not considered for invert drilling fluids for practical reasons, for the rheological properties of such oil phases cannot be controlled over the wide temperature range generally required in practice, frcm 0 to 5°C on the one hand, up to 250°C and more on the other.

A series of earlier Patent Applications by the present Applicant describes the use of easily biodegradable and ecologically harmless ester oils as the continuous oil phase in W/O-invert drilling mud systems (see, in particular, the applicant's New Zealand Patent Nos. 231 826 and 231 827, and the modifications of the ester oils that can be used as disclosed in the applicant's earlier PCT Patents PCT/EP 90/00 342 and PCT/K3 90/00 343.

) The subject of these earlier Applications is the use as the continuous oil phase in W/O-invert systems of ester oils based on selected monocarboxylic acids (and mixtures thereof) and mono- or polyfunctional alcohols. The earlier Applications show that, using the esters and ester mixtures disclosed therein, not only can satisfactory rheological properties be established in the fresh drilling fluid, but it is also possible, by the additional use of selected, known alkali reserves in the drilling fluid, to work without fearing undesired thickening effects when there is partial ester •T OFFICE SEP 1991 hydrolysis.

An important further development of such invert drilling fluids based on ester oils is the subject of the Applicant's earlier Patent PCT/EP 90/00 167 (WO 90/00 417). The teaching of this Application starts with the concept of additionally using in invert drilling fluids based on ester oils a further additive which is suitable for keeping the desired rheological data of the drilling fluid in the required range, even when in use larger and larger amounts of free carbaseylic acids are formed by partial ester hydrolysis. The Application provides for the additional use as such additives in the oil phase, of basic amine compounds, which are capable of forming salts with carboxylic acids and have a marked oleophilic nature and at most limited water-solubility.

BRIEF SUMMARY 0P THE INVe^TIVE OOHCEPT Ttie present invention starts with the problem of providing drilling mud systems of the highest ecological acceptability which simultaneously have good application properties and also make satisfactory use possible in difficult areas. The invention thus positively rejects the oil-based type of invert drilling mud systems, and returns to the oil-modified water-based type of O/W-emulsion systems. The auxiliary agents described in the Applicant's cited earlier Patent Applications, and the ecological advantages associated therewith, are now, hewever, also to be used in this class of drilling mud systems.

As one object, then, the invention seeks to make use of the advantages of O/W-emulsion mud systems over purely water-based drilling fluids, but at the same time to replace the mineral-oil phase at least to a substantial amount with ecologically harmless ester oils.

As a second object, the invention seeks to oodecate the ecological concerns of the second problems area, associated with the atMiti^ts and auxiliary agents in drilling fluids, by selecting from the wide range of additives known in this field, at least to a iarge extent and preferably universally, those auxiliary agents which are distinguished by their ecologically harmless nature.

In one aspect, therefore, the invention provides a water-based 0/W-emulsion drilling fluid in which the dispersed oil phase is at least largely one or more water-emulsifiable ester of a saturated and/or unsaturated carboxylic acid having up to 36 carbon atoms and an mono-and/or polyfunctional alcohol, which ester is fluid and/or at least plastically deformable at working temperature and has a flash point of at least 80°C.

The drilling fluids of the invention may, of course, if desired contain insoluble, finely particulate weighting agents for the formation of water-based O/W-emulsion drilling muds, and/or further additives, such as emulsifiers, fluid-loss additives, wetting agents, alkali reserves and/or auxiliary substances for the inhibition of drilled rock with high water-sensitivity (water swellable). Any inorganic and/or organic auxiliary and loading substances used in the drilling fluids of the invention are, very preferably, those which are at least predominantly ecologically and toxicologically harmless. The term "ecologically harmless" as used herein means the auxiliary agents should have a high environmental acceptability and should not cause any damage to the environment. Accordingly, in the most important embodiments of the invention the use of auxiliary agents based on soluble toxic heavy-metal compounds is avoided.

DETAILED DESCRIPTION OF THE INVENTIVE CONCEPT The water-based O/W-emulsion drilling fluids of the invention preferably contain, stably dispersed in a homogeneous aqueous phase, the oil phase in amounts of about 5 to 50% by weight - the percentage by weight referring to the sum of the unweighted water phase and oil phase1 The proportions of the various constituents The mixture ratios of the ester oil water phases cover the usual rarige^ for O/W-emulsion drilling fluids based on mineral oils. The lcwer-limit values for the oil phase are usually at least about 5%^by weight, I 3 "•"7 or preferably between about 5 and 10% by weight (e.g. 7 or 8% by weight) based on the total weight of the fluid oil and water phases (each in the unweighted state), and minimum amounts of the order given ensure that use can be made of the characteristic peculiarities of an O/W-emulsion fluid. The upper limit value for the oil content is usually about 50% by weight or even slightly higher (e.g., a maximum of about 65% by weight; assuming that the droplet size of the dispersed oil phase is sufficiently even, the range of most dense packing is then already achieved, and therefore conversion into the w/O-invert fluid type is likely to occur). The preferred upper limit for the content of the ester oil in the O/W-fluids of the invention is generally determined primarily by cost/benefit considerations, and is, for example, about 45% by weight, or even slightly less (e.g., about 40% by weight). Most preferably, therefore, an ester oil amount of frcm about 10 to 40% by weight, and in particular of from about 15 to 35% by weight, offers the possibility of making use of the many known (ard unknown) advantages of these O/W-emulsion fluids. Oil contents of, for example, 20% by weight (or, in an extreme case, 30% by weight) provide the basis of high-quality drilling fluids which very closely approach the oil-based invert fluids in the way they function, but require very much less alcohol or ester-oil phase.

The ester components The following general considerations are of initial importance in the selection of the ester oiis:- The ester oils should be fluid both at ambient temperature and under their conditions of use, though the acceptable fluidity range allows the inclusion of those materials which are at least plastically deformable at ambient temperature and which soften to become fluid at the usually high working temperatures. For reasons of easier processability, in practice there are preferred ester oils with solidification values (pour point and setting point) below 10°C, usefully belcw 0°C, and especially not above -5°C (it should be noted that drilling fluids are usually produced on site using, for example, 2 3:683 sea water at comparatively lew temperatures).

For reasons of industrial safety, the ester oils must have flash points of at least 80°C. Higher flash points - of at least 100°C, and even above 150 or 160 °C - are much preferred.

A further important requirement is that the ester oils have a biologically or ecologically acceptable constitution - i.e. in particular that they are free from undesired toxic constituents. In the preferred embodiment of the invention there are therefore used ester oils which are free from aromatic constituents, and which in particular have saturated or olefin-unsaturated, straight or branched hydrocarbon chains. Hie use of components containing cycloaliphatic structural constituents is possible fran the ecological point of view, but for reasons of cost will be of less significance in practice.

Carboxylic acid esters used as the highly dispersed oil-phase in a continuous aqueous phase are subject to a limited degree of hydrolytic ester-cleavage, with liberation of the ester-forming constituents (the carboxylic acid and the alcohol). It follows that two closely linked issues should be taken into account as regards the application properties of the ester oils according to the invention, namely the possible inhalation-toxicity of the liberated oonqponents, in particular of the alcohol components, and also the change in the composition of the emulsion fluid and the associated possible change in its application properties. For comprehension of the teaching according to the invention, these considerations will be dealt with separately for each of the ester-forming basic constituents - firstly the alcohols* and secondly the carboxylic acids.

According to the invention, both monoftydric alcohols and poXybydric alcohols are suitable as the ester-forming alcohol ooraponents, and any mixtures of these types can also be used. A further distinction can be made between alcohols froe a consideration of tbtir solubility behaviour in water; they can be soluble or insoluble. 9 2 3^0 33 In a first group are the polyhydric alcohols. Preferred here are in particular the industrially easily available lower, polyfunctions 1 alcohols with 2 to 5, preferably 2 to 4 hydroxy 1 groups and in particular 2 to 6 carbon atoms, which form esters with a suitable rheology. Characteristic representatives are ethylene glycol, the propanediols and (in particular) glycerin.

Polyhydric alcohols of this type are distinguished by their high water-solubility and by such low volatilization values that considerations of the exclusion of toxic hazards on inhalation are usually not applicable. The polyhydric lower alcohols can be used as totally esterified oil components and/or as partial esters (with same free hydraxyl groups). Provided that the partial esters formed retain the at least largely water-insoluble character of the oil phase, no substantial change takes place as regards the oil/water ratio in the emulsion fluid. The situation is only different when water-soluble hydrolysis products form - in particular therefore the free lower polyhydric alcohols. Hie changes which occur in practical operation in such emulsion fluids from this cause are, however, insignificant. Firstly, a conparatively high stability of the ester bond is ensured under the working conditions according to the invention. O/W-emulsion fluids are known to operate usually in the pH-range of around neutral to moderately alkaline - for exanple, in the pH-range of about 7.2 to 11, and in particular about 7.5 to 10.5 - so that for these considerations alone there is no aggressive hydrolytic attack on the ester bond. In addition, and moreover, the following is in particular also true:- In the practical use of the drilling fluid, and the associated driving forward of the bore into ever deeper earth strata, there is a continual consumption of the drilling fluid, and in particular of the oil-phase used in the drilling fluid. Emulsion fluids are known - and this is an important point of value in their use - for the fact that the emulsified oil phase clings on to solid surfaces and therefore both effects the sealing of the filter layer to the wall of the bore shaft and hinders, or even prevents, interaction between the drilled rodk. and 2?"'3* the aqueous phase of the drilling fluid. This continual consumption of drilling fluid, and in particular of the oil-phase, necessitates a continual supply of oil-based mud. In practical operation, a state of equilibrium is therefore rapidly established in the drilling fluid which prevails over, and makes possible, a continuous operation for long periods of time.

A second group of ester-forming alcohols is the monohydric alcohols. Her® only the lower representatives of these alcohols are water-soluble or water-miscible. In addition, however, volatility is a not unimportant consideration in the case of these alcohols. In the practical operation of a bore, at least moderately increased temperatures are rapidly established in the circulated drilling fluid so that the parts brought to the surface and exposed to the ambient air Airing the recirculation for removal of the drill cuttings may have a temperature in the range of 50 to 70 °C. Considerations of the t Kicological effects on inhalation must therefore be borne in mind. Even C4-alcohols, such as isobutyl alcohol, can be so volatile under th© operating conditions on the drilling platform that hazards to personnel must be taken into account. According to the invention, therefore, when ester oils are employed together with monohydric alcohols they should contain not less than 6, and very preferably at least 8, carbon atoms.

Hxls selection and limitation of the number of carbon atoms in the ester-forming alcohol, however, means - as regards the composition of the ester-oil phase when taking into account a partial hydrolysis during operation - that when the hydrolyzing parts of the ester oils are converted to the free alcohol this latter remains as a practically water-insoluble mixture constituent in the dispersed ester-oil phase. This confers definite functional advantages on that phase. Oil-based invert drilling-mud systems based on fluid, particularly monofunctional, alcohols of high ecological acceptability are disclosed in the Applicant's earlier German Patent Application P 39 11 238.1 [D 8511 J. ltie use of these alcohols as a material for O/tf-enulsion fluids of the type described in the present invention is the subject of WMVd New Zealand Patent 233 682 by the Applicant. To this extent the teaching of the present invention is connected with that of the parallel Application, and therefore this aspect is not dealt with in further detail here. Essentially, hcwever, it is true here, too, that in use the composition of the ester oil phase is in a quasi-static state, adjusting rapidly by equilibrium and characterized by large contents of non-hydrolyzed ester oil.

A number of points must also be considered with regard to the carboxylic acids formed by the partial hydrolysis of the ester oils. Here it is possible, depending on the specific constitution of the carboxylic acids used, to distinguish between two basic types - those which give rise to carboxylic acid salts with an emulsifier effect, and those which give rise to inert salts.

The respective chain-length of the liberated carboxylic acid molecule is decisive here. Moreover, the salt-forming cation usually present in the alkali reserves of the drilling fluid should also be considered. In general, the following rules apply. Lower carboxylic acids, for example those with 1 to 5 carbon atoms, give rise to the formation of inert salts - thus, to the formation of corresponding acetates or propionates. Fatty acids of higher chain-length, and in particular those with fran 12 to 24 carbon atoms, result in compounds with an emulsifier effect. By selecting suitable ester oils - and to a certain extent also the salt-forming cations in the emulsion fluid - the specific control of the secondary products in the emulsion fluid is therefore possible, which can also have considerable influence on the nature and effect of the emulsion fluid. What has previously been stated also applies here: the aqueous phase, too, is subject to continual consumption in practice, and thus requires replacement. In stationary operation, therefore, rapidly controllable states of equilibrium will be established, even with regard to the reaction byproducts based on the ester-forming carboxylic acids as discussed here.

The preferred ester oils for use in the drilling fluids of the invention are the reaction products of monocarboxylic acids with N.Z. PATENT OFFICE SEP 1991 RECf'V'E-D 2 Z7 5 33 rnonofunctional or poly functional alcohols of the type given (the additional use of polyvalent carboxylic acids is not excluded, but they ar© of less significance, particularly for reasons of cost).

Th® carboxylic acids involved here can be of natural or synthetic origin; they can, as already indicated, be straight or branched, and optionally cyclic, but should not be aromatic in structure. They can be saturated or unsaturated, and in the latter case are preferably ■on©- or poly-olefin-unsaturated. Olefin-unsaturated components can be of particular significance for attaining the predetermined rheology values. It is known that olefinic longer-chain compounds are suitable as corresponding saturated components for the formation of esters with lower melting points.

His preferred range for the muter of carbon atoms in the carboxylic acids extends from 1 to 36, and in particular from 2 to 36. For reasons of easy availability, an upper limit is about 22 to 24 carbon atoms. Tft© selection of the respective chain length in the ester-foraing carboxylic acid carponents is carried exit - depending on the nature of the alcohol canponent(s) used - from a consideration of the various issues already discussed (and so refers not only to the ester and/or its rheology directly, but also to the reaction by-products formed in particular by partial hydrolysis).

Suitable alcohols are, as indicated, both rnonofunctional alcohols -taking into consideration the limitations listed above - and polyfunctional alcohols, particularly lower polyfunctional alcohols with 2 to 6 carbon atoms and preferably with a maximum of 4 hydroxy 1 groups, The alcohol components here can also be of natural or synthetic origin, straight or branched, and - in particular in the case of the rnonofunctional alcohols - saturated or olefin-unsaturated. The preferred rnonofunctional alcohols have up to 36 carbon atoms, preferably up to about 24 carbon atoms. Alcohols with 6 to 18, in particular 7 to 15 carbon atoms, whether of natural or synthetic origin, are of particular significance in the formation of the ester oils.

Particularly important ester oils for use in the invention are the ecologically-acceptable ester oils described in the aforementioned earlier New Zealand Patents 231 827 and 231 826 and PCT Patent Nos.

PCT/EP 90/00 342 and PCT/EP 90/00 343.

For completion of the present invention disclosure, the essential characteristics of these ester oils or ester mixtures are briefly summarized in the following.

The ester-oils are carboxylic acid esters from at least one of the following sub-classes:- a) Esters of C-j _cj-monocarboxylic acids and mono- and/or polyfunctional alcohols, wherein the monohydric alcohols contain at least 6, and preferably at least 8, carbon atoms, and the polyhydric alcohols contain 2 to 6 carbon atoms. b) Esters of rnonocarboxylie acids of synthetic and/or natural origin having from 6 to 16 carbon atoms, in particular esters of aliphatic-saturated monocarboxylic acids and mono- and/or polyfunctional alcohols of the type indicated under a). c) Esters of olefin mono- and/or poly-unsaturated monocarboxylic acids having at least 16, and especially from 16 to 24, carbon atoms, and in particular rnonofunctional straight or branched alcohols.

These latter esters of olefinic mono- or poly-unsaturated monocarboxylic acids are preferably either c1) esters which derive, by more than 45% by weight, and preferably by more than 55% by weight, from di- and/or poly-olef in-unsaturated Cjg_24-monocarboxylic acids, or c2) esters which derive, by not more than 35%, from di- and poly-olef in-unsaturated acids, and are preferably at least about 60% by weight rrono-olefin-unsaturated.

N.Z. PATENT OFFICE SEP 1391 RECEiVEO 2 31683 The raw materials for producing many of the monocarboxylic acids in these sub-classes, in particular those with a higher number of carbon atoms, are vegetable and/or animal oils. Coconut oil, palm kernel oil and/or habassu oil are particularly useful for providing essentially saturated monocarboxylie acids predominantly having up to 18 carbon atoms. Examples of vegetable ester oils, in particular for olefinic mono- and optionally poly-unsaturated carboxylic acids with from 16 to 24 carbon atoms, are palm oil, groundnut oil, castor oil and especially colza oil. Carboxylic acids of animal origin of this type are corresponding mixtures of fish oils, such as herring oil.

It® present invention expressly and preferably also includes the use of monocarboxylic acid triglyceride ester oils, and therefore in particular alas the use of corresponding glyceride oils of natural origin. Here, however, it must be remembered that natural oils and fats usually occur in a form so highly contaminated with free carboxylic acids or other accompanying substances, for example, that there is as a rule no question of immediately processing them in O/W-emulsion fluids of the type referred to here. If such natural materials are added in the commercially-available form to water-based drilling fluids, then almost immediately such a large amount of foam forms in the drilling fluid being used as to constitute a serious hindrance or even to result in the complete unuseability of the drilling fluid. This may not be the case if cleaned and/or synthetically-obtained selected triglycerides are used in the dispersed oil phase, and the invention can be realized without exception with these. In principle, however, with such esters of high-grade alcohols there is always to be anticipated a not-inconsiderable tendency to foam formation. Partial esters of glycerin - the mono- or di-glycerides -are known to be effective emulsifier components.

As already indicated, it is not only the comparatively thin-bodied ester oils - as in the disclosure of the aforementioned earlier Ratent Applications in the field of invert drilling fluids, based on ester-oils - which are suitable for the purposes of the invention, but* within the framework of O/H-^aaulsicn fluids, even oofaneivtly viscous »*l "c»r» T ,/C Z j^oo. ester oils can be of advantage as the dispersed phase. They are, for example, valuable auxiliary agents for sealing of the finest pores in the filter cake of the bore shaft, or in rendering inert swellable rock. Moreover, the lubricating ability of such comparatively high viscosity ester oils, even at the elevated temperatures experienced in the bore shaft {and in particular in deviated bore-holes), is in some cases distinctly better than the comparatively thin-bodied ester oils. A dispersed ester oil phase of comparatively high-viscosity ester oils does not cause any detrimental effect on the drill-technology, for the rheology of the system as a whole is determined by the continuous aqueous phase. In this sense it may be preferred to use ester oils as the dispersed phase which have a room temperature Brookfield viscosity of up to about 500,000 mPa.s or even higher - thus, preferably up to about 1 million mPa.s or even 2 million mPa.s. This constitutes an important extension of the teaching in the aforement ioned.. ear Her— Patent Applications that relate to oil-based invert drilling fluids based on ester^olls.

In one embodiment of the invention, branched-chain components, and in particular alpha-branched-chain alcohols and/or carboxylic acids, can be of particular significance. Branched materials of this type are known both to influence the rheology - usually the esters formed by such a chain-branching are more mobile - and to provide increased hydrolysis stability under working conditions.

The aqueous phase All types of water are suitable for the production of the O/W-emulsion fluids according to the invention. These can therefore be based on either fresh or salt water - particularly sea water (which is especially useful when drilling off-shore wells).

Additives in the emulsion fluid In principle there may be employed any of the additives provided for comparable drilling fluid types in connection with achieving a specific 2 3j633 desired range of properties for the drilling fluid. Hie additives can be water- and/or oil- soluble and/or dispersible. Classical additives for water-based O/W-emulsion fluids are eraulsifiers, fluid-loss additives, structure-viscosity building soluble and/or insoluble substances, alkali reserves, agents for the inhibition of undesired water-exchange between drilled formations - e.g. water-swellable clays and/or salt strata - and the water-based drilling fluid, wetting agents for better adhesion of the emulsified oil phase on to solid surfaces, e.g. for improving the lubricating effect, but also for the improvement of the oleophilic seal of exposed rock formations, and disinfectants, e.g. for inhibiting the bacterial attack on such O/W-emulsions. For details, see, the relevant prior art, as described in the specialist literature cited above, and in particular Gray and Darley, loc. cit.. Chapter 11, "Drilling Fluid Components".

Examples of the various materials are as follows.

Weighting agents: Barium sulfate (barite) is widely used, but calcium carbonate (calcite) or the mixed carbonate of calcium and magnesium (dolomite), can be employed.

Viscosity builders and fluid-loss additives: Bentonite is ccnroonly used in water-based fluids in a non-modified form, and is therefore ecologically safe. For salt-water fluids other oonparable clays, in particular attapulgite and sepiolite, are in practice of considerable significance.

The additional use of organic polymer compounds of natural and/or synthetic origin can also be of considerable importance in this context. Typical materials are: starch or chemically raodified starches; cellulose derivatives, such as carixxxymethyloellulose; gpar gum; xanthan gun; or also purely synthetic water-soluble and/or %ater-dispersible polymer compounds, in particular of the high saoiecaslar weight polyacrylaaide type with or without anionic or cationic acidification. 2 33 6 8* Thinners for viscosity-regulation: The so-called thinners can be of organic or inorganic nature. Examples of organic thinners are tannins and/or quebracho extract. Further examples are lignite and lignite derivatives, particularly lignosulfonates. As indicated above, in a preferred embodiment of the invention the use of toxic components is particularly to be excluded, and here the corresponding salts with toxic heavy metals, such as chromium and/or copper, are to be avoided. Examples of inorganic thinners are polyphosphate compounds.

Emulsifiers: For use in the invention, two features are to be considered here. Firstly, it has emerged that a stable dispersion of ester oils is very much easier to attain than the corresponding dispersion of pure mineral oils as used in the state of the art. Secondly, it should be noted that by the partial esterification of the ester oils under the additional effect of suitable alkali reserves, when longer-chain carboxylic acid esters are used, effective 0/W-emulsifiers are also formed, and contribute to the stabilization of the system.

Water exchange control agents: The additives kncwn from the state of the art for water-based drilling fluids can be considered here. Thus, they may be alkali and/or alkaline-earth metal halides and/or carbonates, especially the potassium salts, optionally in combination with lime. Reference is made, for example, to the corresponding publications in ''Petroleum Engineer International",. Septefiiber 1987, 32 - 40, and "World Oil", November 1983, 93 - 97.

Alkali reserves: Inorganic arid/or organic bases adapted to the total behaviour of the fluid can be considered, in particular corresponding alkali and/or alkaline-earth metal or organic base basic salts or hydroxides.

In the field of organic bases, a conceptual distinction must be drawn between water-soluble organic bases - for example, compounds of the diethanolamine type - and practically water-insoluble bases of marked oleophilic character as described in the Applicant's earlier Patent _ 18 - :i;w, a.i PCT/EP 90/00 167 cited above as additives in invert drilling muds based on ester oil. The use of such oil-soluble bases in the framework of the present invention in particular falls within the new teaching. Oleophilic bases of this type, which are primarily distinguished by at least one longer hydrocarbon radical with, for exanple, 8 to 36 carbon atoms, are, however, not dissolved in the aqueous phase, but in the dispersed oil phase. Here these basic components are of great significance. Specifically, not only do they act as alkali reserves, they give the dispersed oil droplets a positive charge, and therefore result in increased interaction with negative surface charges which can be met particularly in hydrophilic clays which ar® capable of ion-exchange. In this way influence can be brought to bear on the hydrolytic cleavage and the oleophilic sealing of water-reactive rode strata.

Hie amount of auxiliary substances and additives used in each case fluctuates essentially within the usual boundaries, and can therefore be taken from the cited relevant literature.

An important area of use for the new drilling fluids of the invention is in off-shore wells for the development of petroleum and/or natural gas deposits, for one particular aim of the invention is to make available industrially usable drilling fluids with a high ecological acceptability. However, while the new drilling fluids have especial significance in a marine environment, their use is not limited thereto. They can, for example, also be put to quite general use in land-based drilling - thus, for the development of petroleum and/or natural gas deposits, and in the drilling of geothennal wells, tratter bore-holes, and geoscientific bores, and in drilling for the mining industry generally. In all these areas potential ecotoxic problems are substantially sijnplified by the new water-based O/W-drilling fluids of the invention.

DETAILED DESCRIPTION Examples : Preparation and use of ester oil-containing O/W-emulsion drilling fluids A) Preparation of the emulsion Firstly, a 6% by weight homogenized bentonite suspension is prepared using carmercially available bentonite (not hydrophobized) with tap water, and adjusting the pH value to 9.2 to 9.3 by means of sodium hydroxide solution. Starting with this pre-swollen aqueous bentonite phase, in successive stages of the process - each under intensive intermixing - the individual components of the water-based ester-oil emulsion according to the following formulation are incorporated 350 g (6% by weight) bentonite solution 1.5 g industrial carboxymethylcellulose low-viscosity (Relatin U300S9) 35 g sodium chloride 70 g ester oil (according to the definition given below) 1.7 g emulsifier (sulf. castor oil "Turkey-red oil", unless otherwise indicated) 219 g barite B) Testing of the emulsion Viscosity measurements were carried out on the thus-prepared O/W-emulsion fluids as follows: Firstly, the plastic viscosity (PV), the yield point (YP) and the gel strength (after 10 sec. and after 10 min.) of the emulsion fluid was determined at 50°C on the unaged material.

Following this, the emulsion fluid was aged for 16 hours at 125°C in an autoclave in the so-called "roller-oven" to examine the effect of temperature on the stability of the emulsion. Then, the viscosity 2 3~ 683 values at 50^ were determined once again.

In the following Exanples in each case the nature of the ester oil used, details of the emulsifier, the values determined for the unaged and aged material, and - if necessary - general coiments are given.

Example 1 Ester oil used; 2-ethylhexylester of a Cg^^-fatty acid mixture (essentially saturated) Turkey-red oil as the emulsifier Vx**pl* 2 111® formulation of Example 1 is repeated, but without using the emulsifier (Turkey-red oil).

Even in the fresh formulation a slight droplet formation can be seen on the surface, after ageing the solid substance tends to settle.

Example 3 Ester oil used; Oleic acid isobutylester Emulsifier: Turkey-red oil Example 4 The formulation in Example 3 was repeated using 1.7g of soybean lecithin (coranercial product: "Dri11tread") as the emulsifier.

Example 5 Ester oil used: Propylene-glycol-mono-oleate ESmilsifier: Turkey-red oil J - 683 Example 6 Ester oil used: A trimethylolpropane tri-fatty-acid ester Bnulsifier: Turkey-red oil Example 7 Ester oil used: A glycerin tri-fatty-acid ester {of Example 6} Example 8 Ester oil used; Residue from the fatty-acid dimerization of "Aliphat 47", esterified with n- hexanol.

Bailsifier: Turkey-red oil 2 Th© results of all the Examples are given in the following Table. w \Q r i> K) fS| Example 1 unaged aged plastic viscosity [mPa.s] 8 14 yield point [Pa] 19.2 13.4 gel strength [Pa] sec. 13.4 9.6 min. 16.3 23.0 Example 5 unaged aged plastic viscosity [mPa.s] yield point [Pa] gel strength [Pa] sec. min.

C 14 .1 16.3 .8 12.5 24.9 24.9 o Example 2 Example 3 Example 4 unaged aged 11 10 16.8 18.2 18.2 16.3 .9 24.0 Example 6 unaged aged 16 17.7 15.8 13.9 12.9 .6 23.0 unaged aged 11 13 18.2 12.9 12.5 9.6 .8 18.7 Example 7 13 12 8.6 8.1 8.6 6.2 9.1 5.8 unaged aged 11 12 12.5 14.9 12.5 6.2 8.6 16.3 Example 8 14 16 17.2 14.4 12.0 9.1 12.9 22.5 unaged aged unaged aged

Claims (53)

WHAT WE CLAIM IS:

1. The use of water-dispersible esters, which are fluid or at least plastically deformable at working temperature and have flash points of at least 80°C, derived from saturated and/or unsaturated carboxylic acids with up to 36 carbon atoms and mono- and/or polyhydric alcohols, as at least the main constituent of the dispersed oil phase in a homogeneous aqueous phase of water-based O/W-emulsion drilling fluids which are suitable for the development of geological formations and which contain, if desired, insoluble, finely particulate weighting agents for the formation of water-based O/W-emulsion drilling muds and/or further additives.

2. The use according to claim 1, characterized in that the further additives are selected from emulsifiers, fluid-loss additives, wetting agents, alkali reserves and auxiliary substances for the inhibition of drilled rock of high water-sensitivity.

3. The use according to claim 1 or 2, characterized in that the dispersed ester-oil phase is used in amounts of at least 5% by weight in the O/W-fluid percentages by weight referred to the sum of the unweighted liquid parts of ester-oil/water - and constitutes not more than 50% by weight - percentage by weight calculated as before,

4. The use according to claim 3, characterized in that the dispersed ester-oil phase is used in amounts of at least 8% by weight in the O/W-fluid and constitutes not more than 40% by weight.

5. The use according to any one of claims 1 to 4, characterized in that, as the dispersed ester-oil phase, at least predominantly monocarboxylic acid esters from mono- and/or polyhydric alcohols are used, and can also take the form of partial esters. fe ftf 'V

6. The use according to claim 5, characterized in that the polyhydric alcohol radicals are derived from lower alcohols with 2 to 6 carbon atoms with up to 4 OH-groups in the molecule.

7. The use according to any one of claims 1 to 6, characterized in that fU. esters are used which are derived at least partly from rnonofunctional alcohols of such low volatility under working conditions that, when there is a partial ester-cleavage in practical use, cleavage products are formed which are toxicologically harmless when inhaled.

8. The use according to any one of claims 1 to 7, characterized in that esters of rnonofunctional alcohols of natural and/or synthetic origin and an oleophilic character with at least 6 carbon atoms are used.

9. The use according to claim 8, characterized in that esters of rnonofunctional alcohols of natural and/or synthetic origin and an oleophilic character with at least 8 carbon atoms are used.

10. The use according to any one of claims 1 to 9, characterized in that when esters based on polyfunctional alcohols are used or added, complete and/or partial esters of water-soluble polyols are used.

11. The use according to claim 10, characterized in that esters of ethylene glycol, propylene glycol and/or glycerin are used.

12. The use according to any one of claims 1 to 11, characterized in that esters are used which have solidification values (pour point and setting point) below 0°C, and at the same time have flash points of at least 100°C.

13. The use according to claim 12, characterized in that esters are used^. which have solidification values below -50°C. 'Y -J . - 8 JUNI992 -25 -

14. The use according to any one of claims 1 to 13, characterized in that, as the dispersed oil phase, esters are used which, as the dispersed oil phase, have a Brookfield RVT viscosity at 20°C of not more than 1 million mPa.s.

15. The use according to any one of claims 1 to 14, characterized in that esters are used, which are free from aromatic constituents.

16. The use according to claim 15, characterized in that the esters are derived from straight-chain and/or branched carboxylic acids and corresponding alcohols.

17. The use according to any one of claims 1 to 16, characterized in that the esters are derived at least in part from carboxylic acids with up to 24 carbon atoms.

18. The use according to claim 1.7, characterized in that the ester oils are at least largely derived from carboxylic acids with up to 24 carbon atoms.

19. The use according to any one of claims 1 to 18, characterized in that the dispersed oil phase contains carboxylic acid esters from at least one of the following sub-classes: a) esters from C,.5-monocarboxylic acids and mono- and/or polyfunctional alcohols, in which radicals of monohydric alcohols have at least 6 carbon atoms, and the polyhydric alcohols have 2 to 6 carbon atoms in the molecule, b) esters from monocarboxylic acids of synthetic and/or natural origin with 6 to 16 carbon atoms and mono- and/or polyfunctional alcohols of the type indicated under a), and c) esters of mono- and/or polyunsaturated monocarboxylic acids with at least 16 carbon atoms and rnonofunctional straight-chain and/qr ' v ■ . ^ ^ branched alcohols. '-j *24 SEP 1992 -26 ■ ?3 Z6 8 3

20. The use according to claim 19, characterized in that in sub-class a) said radicals of monohydric alcohols have at least 8 carbon atoms.

21. The use according to claim 19, characterized in that the esters of sub-class b) are esters of corresponding aliphatic saturated monocarboxylic acids and mono- and/or polyfunctional alcohols of the type indicated under a).

22. The use according to claim 19, characterized in that esters of sub-class c) are esters of mono- and/or polyunsaturated monocarboxylic acids with 16 to 24 carbon atoms and rnonofunctional straight-chain and/or branched alcohols.

23. The use according to claim 19 or 22, characterized in that esters in the dispersed phase as in sub-class c) can be assigned to at least one of the following sub-classes: cl) esters which are derived by more than 45% by weight from di- and/or poly-olefin-unsaturated C16jW-monocarboxylic acids, and c2) esters which are derived by not more than 35% by weight from di- and poly-olefin-unsaturated acids and which are at least 60% by weight mono-olefin-unsatu rated.

24. The use according to claim 23, characterized in that esters of subclass cl) are derived by more than 55% by weight from di- and/or polyolefin-unsaturated Ci^-monocarboxylic acids.

25. The use according to any one of claims 1 to 24, characterized in that in the dispersed oil phase, basic amine compounds of an oleophilic character and which have a water-solubility at room temperature of not more than 1% by weight are also used as additives.

26. The use according to of claim 25, characterized in that oleophilic amine compounds are used as additives which are free from aromatic constituents.

27. The use according to claim 25 or 26, characterized in that oleophilic basic amine compounds are used as additives which have at least one long-chain hydrocarbon radical with 8 to 36 carbon atoms.

28. The use according to any one of claims 25 to 27, characterized in that a dispersed oil phase is used containing up to 10% by weight of oleophilic amine compounds referred to the oil.

29. The use according to claim 28, characterized in that a dispersed oil phase is used containing from 0.1 to 2% by weight of oleophilic amine compounds.

30. The use according to any one of claims 1 to 29, characterized in that esters are used which have at least one branched ester-forming component.

31. The use according to claim 30, characterized in that said at least one branched ester-forming component is in the form of an alpha branch.

32. The use according to any one of claims 1 to 31, characterized in that as the homogeneous aqueous phase, fresh water or water containing dissolved or suspended salts is used, which can also, if desired, be modified sea water.

33. The use according to claim 32, characterized in that the dissolved or suspended salts are halides and/or carbonates of the alkali and/or alkaline earth metals.

34. The use according to any one of claims 1 to 33, characterized in that as additives inorganic and/or organic auxiliary agents are used for the . \ \ ^ water-based emulsion drilling fluids or emulsion drilling muds which are ecologically and toxicologic;!]ly harmless.

35. The use according to any one of claims 1 to 34, characterized in that the dispersed oils are used together with known inorganic and/or organic auxiliary substances for limiting the rock-hydration of mineral strata which are prone thereto.

36. Water-based O/W-emulsion drilling fluids which contain in a homogeneous aqueous phase an oil phase in stable dispersion in amounts of 5 to 50% by weight referred to the sum of the unweighted water phase and oil phase - together, if desired, with dissolved and/or dispersed auxiliary substances, characterized in that the predominant part of the dispersed oil phase is formed by water-emulsifiable esters which are fluid or at least plastically deformable at working temperature and have flash points of at least 80°C, from saturated and/or unsaturated carboxylic acids with up to 36 carbon atoms and mono-and/or polyfunctional alcohols.

37. Emulsion drilling fluids according to claim 36, wherein the dissolved and/or dispersed auxiliary substances are selected from emulsifiers, fluid-loss additives, wetting agents, finely particulate weighting agents, salts, alkali reserves, and disinfectants.

38. Emulsion drilling fluids according to claim 36 or 37, characterized in that the dispersed oil phase constitutes at least 8% by weight and not more than 40% by weight thereof.

39. Emulsion drilling fluids according to claim 38 characterized in that the dispersed oil phase constitutes from 10 to 35% by weight thereof. -29-

40. Emulsion drilling fluids according to any one of claims 36 to 39, characterized in that the ester-forming alcohols and carboxylic acids are free from aromatic constituents.

41. Emulsion drilling fluids according to any one of claims 36 to 40, characterized in that the esters can be assigned at least in part to one or more of the following sub-classes: a) esters from Ci_5-monocarboxylic acids and mono- and/or polyfunctional alcohols, such that radicals from monohydric alcohols have at least 6 carbon atoms and the polyhydric alcohols have 2 to 6 carbon atoms in the molecule, b) esters from monocarboxylic acids of synthetic and/or natural origin with from 6 to 16 carbon atoms and mono- and/or polyfunctional alcohols of the type indicated under a), and c) esters of mono- and/or polyunsaturated monocarboxylic acids with at least 16 carbon atoms and rnonofunctional straight-chain and/or branched alcohols.

42. Emulsion drilling fluids according to claim 41, characterized in that in subclass a) said radicals from monohydric alcohols have at least 8 carbon atoms.

43. Emulsion drilling fluids according to claim 41, characterized in that the esters of sub-class b) are esters of corresponding aliphatic saturated monocarboxylic acids and mono- and/or polyfunctional alcohols of the type indicated under a).

44. Emulsion drilling fluids according to claim 41, characterized in that esters of subclass c) are esters of mono- and /or polyunsaturated monocarboxylic acids with 16 to 24 carbon atoms and rnonofunctional straight-chain and/or branched alcohols. ■■ •; . ? -30-

45. Emulsion drilling fluids according to claim 41 or 44 characterized in that when ester oils of the sub-class c) are present, these can be assigned at least in part to one of the following sub-classes: cl) esters which are derived by more than 45% by weight from di- and/or poly-olefin-unsaturated Cj^-monocarboxylic acids, and c2) esters which are derived by not more than 35% by weight from di- and poly-olefin-unsaturated acids and which are at least 60% by weight mono-olefin-unsaturated.

46. Emulsion drilling fluids according to claim 45, characterized in that the esters of subclass cl) are derived by more than 55% by weight from di-and/or poly-olefin-unsaturated Ci^-monocarboxylic acids.

47. Emulsion drilling fluids according to any one of claims 36 to 46, characterized in that esters are present which are based on rnonofunctional, water insoluble alcohols of an oleophilic character.

48. Emulsion drilling fluids according to any one of claims 36 to 47, characterized in that constituents of rnonofunctional alcohols present in the esters are selected such that when a partial ester-hydrolysis occurs in use, alcohols are formed in practical use which do not constitute a toxicological hazard when inhaled.

49. Emulsion drilling fluids according to any one of claims 36 to 48, characterized in that in the dispersed oil phase, basic amine compounds of an oleophilic character and which have a water-solubility at room temperature of not more than 1% by weight are also used as additives, which are free from aromatic constituents and have at least one long-chain hydrocarbon radical with; 8 to 36 carbon atoms. , v- -31 -

50. Emulsion drilling fluids according to any one of claims 36 to 49, characterized in that the auxiliary substances of water-based emulsion drilling fluids are ecologically and toxicologically harmless.

51. Emulsion drilling fluids according to any one of claims 36 to 50, characterized in that they contain auxiliary substances for the inhibition of the water-absorption of swellable rock strata or clays.

52. Emulsion drilling fluids according to any one of claims 36 to 51, characterized in that they are adjusted to a pH value from 7.5 to 11.

53. Water-based O/W emulsion drilling fluids according to any one of claims 36 to 52, substantially as herein described with reference to any example thereof. Htoket {({mwndityttflitchaft ct(/f RKtJfn By fcfe / their authorised Ager A.J. PARK & SON.