NO301340B1 - The use of selected ester oils in water-based drilling flushes of the oil / water emulsions type and similar drilling flushing liquids with improved ecological acceptability - 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

The present invention relates to new drilling fluids on the basis of water-based oil/water emulsions and on these built up oil/water emulsion drilling mud which is characterized by high ecological acceptability and at the same time good durability and use properties. An important area of application for the new drilling flushing systems is sea-based drilling for the exploitation of oil and/or natural gas deposits, whereby the invention here primarily aims to provide technically usable drilling flushing with high ecological acceptability. The application of the new drilling flushing systems is of particular importance in the maritime area, but is not limited to this. The new drilling flushing systems can generally also be used for land-based drilling, i.e. also here for the exploitation of oil and/or natural gas deposits. However, they are also new and valuable tools for example in geothermal drilling, water drilling, geoscientific drilling and drilling in the mining industry. In principle, it applies that the ecotoxic problem area is substantially simplified with the help of the invention's selected new water-based oil/water drilling fluids.

State of the art

Liquid flushing systems for the lowering of boreholes in rock during the simultaneous installation of released drill cuttings are, as is known, limited to thickened, pourable systems that can be assigned to one of the three following classes: Clean-aqueous drilling flushing fluids, oil-based drilling flushing systems which are usually used as so-called invert-emulsion muds and constitute preparations of the type water/oil emulsions where the aqueous phase is heterogeneously and finely dispersed in the continuous oil phase. The third class of the known drilling fluids are built up on water-based oil/water emulsions, that is to say on liquid systems which in a continuous aqueous phase contain a heterogeneous finely dispersed oil phase. The invention describes improved systems of this latter kind.

Drilling fluids from such oil/water emulsion systems occupy, in terms of their usage properties, an intermediate position between the purely aqueous systems and the oil-based invert flushes. The advantages, but also the shortcomings of the purely aqueous systems connect with the advantages and disadvantages of the oil-based invert emulsions described to date. Detailed case information can be found in the available specialist literature, for example, reference should be made to a book by George R. Gray and H.C.H. Darley, "Composition in Properties of Oil Well Drilling FLuids", 4th ed., 1980/81, Gulf Publishing Company, Houston and the extensive case and patent literature cited therein, as well as to the handbook "Applied Drilling Engineering", Adam T. Bourgoyne , Jr. et al., First Printing Society of Petroleum Engineers, Richardson, Texas (USA).

One of the main weaknesses of the water-only drilling fluid systems lies in the interaction between water-sensitive and especially water-swellable rock and/or salt formations with the aqueous drilling fluid and the resulting secondary consequences, especially borehole stability and thickening of the drilling fluid. Numerous proposals have dealt with a limitation of this problem circle and have, for example, led to the development of the so-called inhibitory water base muds, see for example "Applied Drilling Engineering", mentioned above, chapter 2, Drilling Fluids, 2.4 and Gray and Darley, mentioned above , Chapter 2, especially the subchapter on pages 50 to 62 (Muds for "Heaving Shale", Muds for Deep Holes, Non-Dispersed Polymer Muds, Inhibited Muds: Potassium Compounds).

In later practice, particularly oil-based drilling flushes to overcome the described shortcomings have asserted themselves, consisting of the three-phase system oil, water and finely divided solids and which are preparations of the water/oil emulsion type. Oil-based drilling fluids were originally built on diesel oil fractions with a content of aromatics. For detoxification and reduction of the resulting ecological problems, it was proposed to use as dispersed oil phase 1"extensively aromatic hydrocarbon fractions, today also referred to as "non-polluting oils", here reference should be made to the publication by E.A. Boyd et al., "New Base Oil Used in Low Toxicity Oil Muds", "Journal of Petroleum Technology", 1985, 137-143 as well as by R.B. Bennett, "New Drilling Fluid Technology - Mineral Oil Mud", "Journal of Petroleum Technology", 1984, 975 -981, as well as the literature cited therein.

Drilling fluids of the water-based oil/water emulsion system type also currently use pure hydrocarbon oils as dispersed oil phase, here reference should be made to Gray and Darley, cited above, page 51/52 under the chapter "Oil Emulsion Muds" as well as the tabular arrangement on page 25 (table 1-3) with information in connection with water-based emulsion rinses of the type Salt Water Muds, Lime Muds, Gyp Muds and CL-CLS-Muds.

In this context, it is known in particular that water-based oil/water emulsion flushing means in many respects a significant improvement of the pure water-based drilling flushing systems. In recent times, however, the advantages and disadvantages of such water-based emulsion flushing compared to the oil-based invert systems have also become quite critical. The reason for this is the significant ecological concerns that currently exist against the currently used oil-based invert flushes.

These ecological concerns can be divided into two problem areas: All water- and/or oil-based drilling flushing systems need, in addition to the basic ingredients oil and water, a number of additives to set the desired performance characteristics. Only emulsifiers or emulsifier systems, weighting agents, fluid-loss additives, wetting agents, alkali reserves, viscosity-regulating agents, possibly auxiliaries for inhibiting excavated cake with increased water sensitivity, disinfectants and the like shall be mentioned here as examples. A detailed statement can be found, for example, in Gray and Darley, cited above, chapter 11, "Drilling Fluid Components". From today's point of view, practice has thereby developed ecologically harmless additives, but also ecologically questionable and even ecologically undesirable additives.

The second problem circle is determined by the oil phases used within the scope of such drilling flushing. Even the hydrocarbons today designated as "non-polluting oils" and largely aroma-free are not without problems when released into the environment. A further reduction of the environmental problem, triggered by the liquid oil phases of the kind described here, seems absolutely necessary. This is particularly valid for the installation of sea-based drilling, especially for the exploitation of oil and natural gas deposits, because the marine ecosystem reacts particularly sensitively to the installation of toxic and difficult-to-degrade substances.

Some proposals to reduce this latter problem stem from more recent times. Thus, US-PS 4,374,737 and 4,481,121 describe oil-based invert drilling fluids in which non-polluting oils are used. As non-polluting oils are mentioned next to each other and as equivalent aroma-free mineral oil fractions and plant oils of the type peanut, soybean, linseed, corn and rice oil, or also oils of animal origin such as whale oil, and all the time it revolves around the here mentioned ester oils of vegetable and animal origin or triglycerides of natural fatty acids which, as is known, have a high environmental tolerance and which, in relation to hydrocarbon fractions, even when these are aroma-free, are completely superior from ecological considerations.

In the aforementioned US patents, however, no concrete example is described of the use of such natural ester oils in invert drilling fluids. All the time, mineral oil fractions are used as continuous oil phase. In reality, oils of vegetable and/or animal origin of the aforementioned type do not come into consideration for invert drilling flushes, for practical reasons. The rheological properties of such oil phases are not controllable for the wide and practically required temperature ranges of 0 to 5°C on the one hand and up to 250°C and above on the other hand.

Older proposals from the present applicant

A number of older applications from the present applicant describe the use of easily biodegradable and ecologically harmless ester oils as continuous oil phase in water/oil invert drilling flushing systems. Reference must be made here in particular to the older publications NO 171.562-B and NO 171.601-B as well as the development of usable ester oils in accordance with what is stated in the older publications NO 171.501-B and NO 171.502-B.

The subject of these older publications is the use of ester oils based on monocarboxylic acids selected in each case, respectively monocarboxylic acid mixtures and monofunctional and possibly multifunctional alcohols as a continuous oil phase in water/water-invert systems. The older publications describe that with the esters or ester mixtures described there, not only can satisfactory rheological properties be set in the newly produced drilling fluids, but that it is also possible, with the combined use of selected, known alkali reserves, to work in the drilling fluids without thereby having to fear unwanted thickeners by a partial ester hydrolysis.

An important further development of such ester oil-based invert drill flushes is the subject of the older publication NO 179.487-B from the same applicant.

The teaching in this older publication is based on the concept in invert drilling fluids based on ester oils also to use a further additive which is suitable to keep the desired rheological data for drilling fluids within the required range even when increasing amounts of free are formed during use carboxylic acids by partial ester hydrolysis. The aim is here to co-use basic amine compounds of a distinctly oleophilic nature and with maximally limited water solubility and with the ability to form salts with carboxylic acids, as an additive in the oil phase.

The task of the invention and the technical solution

The present invention is based on the task of providing drilling flushing systems with the highest possible and, in this form, hitherto unknown ecological acceptability, which at the same time exhibit good usability and a satisfactory application, especially also in problem areas. The invention thereby deliberately abandons the type of oil-based invert drilling flush systems and returns to the type of oil-modified, water-based oil/water emulsion systems. Thereby, however, the aids described in the aforementioned older publications and the associated ecological benefits should also find application in this class of drilling flushing systems.

The invention will thus, in a first embodiment, utilize the advantages of oil/water emulsion flushing systems in relation to the pure water-based drilling flushes, while at the same time, however, replacing the mineral oil phase at least in a significant proportion, preferably completely, with ecologically harmless ester oils.

In a further embodiment, the invention will also ecologically remedy the second circle of problems with additives and auxiliaries, by choosing from the large range of additives known here at least predominantly and preferably completely such auxiliaries that are distinguished by ecological problem-freeness.

According to this, the object of the invention in a first embodiment is the use of water-emulsifiable, liquid at working temperature or at least plastically moldable and having a flash point of at least 80°C esters of monocarboxylic acids with up to 5 carbon atoms and monohydric alcohols with at least 6 C atoms and /or polyhydric alcohols, whereby in the case of esters of monohydric alcohols, the carboxylic acid residues are at least partially derived from monocarboxylic acids with up to 36 carbon atoms, as at least the predominant component in the dispersed oil phase of water-based oil/water emulsion drilling fluids for an environmentally friendly utilization of geological formations, and which, if desired, contain insoluble, finely divided weighting agents for the formation of water-based oil/water emulsion drilling muds and/or further additives such as emulsifiers, fluid-loss additives, wetting agents, alkali reserves and/or auxiliaries for inhibiting drilled rock with high water sensitivity.

In a further embodiment, the invention relates to water-based oil/water emulsion drilling fluids for rock drilling in geological formations, which in a homogeneous aqueous phase contain a stable dispersed oil phase in amounts of 5 to 50 wt-#, calculated on the sum of unweighted water and oil phase , together with dissolved and/or dispersed auxiliaries for drilling fluids for rock drilling in geological formations (emulsifiers, fluid-loss additives, wetting agents, finely divided weighting substances, salts, alkali reserves and/or disinfectants), and which are characterized by

at least in the predominant proportion of the dispersed oil phase is formed by water-emulsifiable, liquid at working temperature or at least plastically moldable and showing a flash point of at least 80°C ester oils of monocarboxylic acids with up to 5 C atoms and monohydric alcohols with at least 6 C atoms and/or polyhydric alcohols, whereby in the case of esters of monohydric alcohols, the carboxylic acid residue is at least partially

can also originate from monocarboxylic acids with up to 36 C atoms.

For both embodiments of the teachings of the invention, the further preferred precaution applies that at least predominantly such inorganic and/or organic auxiliaries and additives are co-used for water-based emulsion drilling washes or emulsion drilling muds, which are ecologically and toxicologically at least largely without problems. Thus, in the most important embodiments of the invention, the use of aids based on soluble toxic heavy metal compounds is waived.

The preferred embodiments of the invention The mixing ratios for the ester oil/water phases emphasize the usual range for the currently known oil/water emulsion drilling fluids based on mineral oil. The lower limit values for the oil phase are usually at least approx. 5 weight # and preferably between approx. 5 and 10 weight-#, for example ie at 7 or 8 weight-#, the weight percentage amount each time being calculated on the total weight of the liquid phases ester oil plus water, both in an unencumbered state. Minimum amounts of the specified order of magnitude ensure that you can take advantage of the type-characteristic properties for an oil/water emulsion rinse. The upper limit value for the content of ester oils is usually approx. 50 weight # or something over that, for example at a maximum of approx. 65 weight #. Under the assumption of a sufficiently uniform droplet size for the dispersed oil phase, the area for the densest packing has thus already been reached, so that the transition in flushing type for the water/oil invert flushing seems close or sensible.

The upper limit for the ester oil content in the oil/water rinses of the invention is generally determined by cost/benefit considerations and is usually at approx. 45 weight #, preferably below this value, for example at approx. 40 weight

An ester oil quantity within the range of approx. 10 to 40 weight #, weight # calculated as above, and especially amounts of ester oils in the range of approx. 15 to 35 weight #, gives the opportunity to utilize numerous known and also so far not described advantages of such emulsion rinses. Oil content of, for example, 20 or at most 30 wt-# provides the basis for high-quality drilling fluids which in their function at least come very close to the oil-based invert flushes, but which even then need much less ester oil phase.

Define. ion of the esterol used in the invention. ier

For the selection and adaptation of the ester oil to the areas of application in question, the following general considerations apply in the first instance: The ester oils must be pourable at ambient temperature, but also under the conditions of use, whereby the range of pourability also includes such materials which are at least plastically malleable at ambient temperature and which at the usual elevated working temperatures it softens to pourability. For reasons of ease of workability in practice, preference is given to ester oils whose solidification values (pour and solidification points) are below 10°C and suitably below 0°C. Corresponding ester oils with solidification values of no more than -5°C are particularly suitable. Furthermore, account must be taken of the fact that the drilling fluids are usually produced on site using, for example, seawater with a comparatively low water temperature.

For reasons of operational safety, it must be required that the ester oils have a flash point of at least 80°C, preferably, however, a higher flash point of at least 100°C and significantly higher values, for example values of over 150 or 160°C.

Furthermore, important for the optimal utilization of the invention's objective is the requirement that the ester oils exhibit a biologically or ecologically acceptable constitution, that is to say, in particular, that they are free of unwanted toxic components. In the preferred embodiment of the invention, according to this, ester oils are used which are free of aromatic components and which in particular exhibit saturated and/or olefinically unsaturated, straight and/or branched hydrocarbon chains. The use of components exhibiting cycloaliphatic structural constituents is possible from ecological considerations, but has less importance for economic reasons.

Carboxylic acid esters of the type in question here undergo, as a highly dispersed oil phase in a continuous aqueous phase, a hydrolytic ester cleavage on a limited scale with the simultaneous release of the ester-forming components carboxylic acid and alcohol. For the usage properties of the ester oils within the context of the invention, one must here take into account two points of view that stand in a certain internal context, namely considerations with a view to possible inhalation toxicity for released components, especially the alcohol components, as well as the change in the composition of emulsion rinses and the associated possible changes in the performance characteristics.

For an understanding of the teachings of the invention, these considerations must be considered separately for the ester-forming basic constituents, on the one hand the alcohols and on the other hand the carboxylic acids.

According to the invention, both monohydric and polyhydric alcohols are suitable as ester-forming alcohol components, whereby any mixtures of these types can also be used. A further differentiation of the alcohols can be carried out based on considerations regarding the solubility ratio in water. The alcohols can be water-soluble and/or water-insoluble.

In a first group, the polyhydric alcohols are considered. Preference is given here in particular to the technically readily available lower, polyfunctional alcohols which form esters with suitable rheology and which have 2 to 5 and preferably 2 to 4 hydroxyl groups and especially 2 to 6 C atoms.

Characteristic representatives are ethylene glycol, the propanediols and especially glycerol.

Polyhydric alcohols of the type described here are characterized by high water solubility and thereby also by such low evaporation values that concerns with regard to inhalation toxicity can usually be neglected.

Polyhydric lower alcohols of the type described here can find use as a fully esterified oil component and/or as partial esters with partially free hydroxyl groups in and/or in practical use constitute the emulsion rinse of the invention. As long as the resulting partial esters retain their at least largely water-insoluble character in the oil phase, no significant changes occur with regard to the oil/water ratio in the emulsion rinse. It becomes something else only when the state of water-soluble hydrolysis products, in particular the free lower polyhydric alcohols, is reached. However, the change occurring in practical operation in such emulsion flushing from this source is negligible. Firstly, under the working conditions of the invention, a comparatively high stability of the ester bond is ensured. 01je/water emulsion rinses, as is known, usually work in pH ranges from approximately neutral to somewhat alkaline, especially in the pH range approx. 7.2 to 11 and in particular approx. 7.5 to 10.5, so that from such considerations there is no aggressive hydrolytic attack on the ester bond. In addition and beyond this, however, the following must also be taken into account: In practical use of the drilling mud and the associated progress of the drilling in ever deeper layers of soil, there is a constant consumption of drilling mud and especially also of the oil phase used in the drilling mud. Emulsion flushing is known for, and here lies a very important point for their use, that the emulsified oil phase attracts solid surfaces and thereby causes both a sealing of the filter layer on the walls of the borehole and also prevents an interaction between the drilled cuttings and the aqueous phase in the drill flushing, or even prevents it. This continuous consumption of drilling fluid and especially of the oil phase requires a continuous supply of oil fluid. In practice, a state of equilibrium is quickly established within the scope of the drill flushing which controls and enables continuous operation over long periods of time.

With a view to certain points of view, further considerations should be carried out when it comes to the co-use of monohydric alcohols in the ester oils. Hereby, only the lower levels of these alcohols are water-soluble or miscible with water in unlimited quantities. In addition, however, volatility also plays a not insignificant role with these alcohols. In practical operation at a borehole, at least somewhat elevated temperatures are quickly established in the circulated drilling fluid, so that the portions exposed during repumping for the removal of drilling cuttings, for example, exhibit a temperature in the range of 50 to 70°C. Inhalation toxicological considerations should be made here. Already C^alcohols, for example isobutyl alcohol, can be so volatile under the working conditions that exist on the drilling platform that there is a risk for the crew. According to the invention, when using ester oils with the co-use of monohydric alcohols, a lower carbon number limit of 6 is preferably chosen for these monohydric alcohols, whereby working with esters of monofunctional alcohols with at least 8 C atoms can be particularly preferred.

However, the selection and limitations of the number of carbon atoms in the ester-forming alcohol lead at the same time, with a view to the composition in the ester oil phase taking into account a partial hydrolysis in operation, to the following result: The hydrolyzing proportion of such ester oils is converted into free alcohol which remains as a practically water-insoluble mixture component in the dispersed ester oil phase. Here, very special advantages can be triggered for the functionality of the dispersed oil phase. Oil-based invert drill flushing systems based on pourable and especially monofunctional alcohol with high ecological acceptability are described in the applicant's publication NO 300.043-B1. The use of these alcohols as application material for oil/water emulsion rinses of the kind comparable to the present invention is the subject of a parallel application. The teaching according to the present invention is connected with the parallel-running application so that it would not be necessary to go into it in more detail.

In addition, however, the consideration set out above also applies here that in practical operation at equilibrium setting a quasi-static state is quickly established for the composition of the ester oil phase which is characterized by a predominant content of non-hydrolysed ester oil.

A number of considerations are also necessary when it comes to the carboxylic acids formed by partial hydrolysis of the ester oil rinse.

Depending on the particular constitution of the carboxylic acids used, a distinction can be made here between two principle types, with a liquid transition: carboxylic acids that lead to carboxylic acid salts with an emulsifying effect, as well as inert salts.

Decisive here is in particular the chain length present in each case for the carboxylic acid molecule that becomes free. Also to be taken into account is the salt-forming cation usually present via the alkali reserve in the drilling fluid.

In general, the following rules apply here: Lower carboxylic acids, for example those with 1 to 5 carbon atoms, lead to the formation of inert salts, for example to the formation of corresponding acetates or propionates. Fatty acids with a longer chain length and especially those from the area » lead to compounds with an emulsifying effect.

With a suitable choice of ester oils and, to a certain extent, also the salt-forming cations in the emulsion rinse, the targeted management of the secondary products in the ester rinse is enabled, which can have a significant influence on the nature and effect of this. Here too, however, what has been said above applies: Not only the dispersed organic phase, but also the aqueous phase is subject to continuous consumption and the necessity of supplementation in practical operation. During stationary operation, controllable equilibrium states will therefore be quickly established, also with regard to the reaction products discussed here based on ester-forming carboxylic acids.

General information for the definition of suitable ester oils

Preferred as ester oils within the framework of the invention are the corresponding reaction products of monocarboxylic acids with monofunctional and/or polyfunctional alcohols of the specified type. However, the co-use of polyvalent carboxylic acids is not excluded, especially for cost reasons, however, their use is of secondary importance.

The carboxylic acids can thereby be of natural and/or synthetic origin, they are furthermore, as already indicated, preferably straight-chain and/or branched and optionally cyclic, but not aromatic. The ester-forming carboxylic acids can be saturated or unsaturated, whereby unsaturated compounds in particular mean olefinically unsaturated compounds which can be once, but also several times olefinically unsaturated. Olefinically unsaturated components can have a special significance for setting pre-given rheology values. As is known, olefinically longer chain compounds are suitable for the formation of esters with lower melting points than corresponding saturated components.

The preferred range for the number of carbons in the carboxylic acids is from 1 to 36 and especially from 2 to 36. Not least because of the easy availability, the upper limit for the carbon number can be approx. 22 to 24. The choice of the relevant chain length in the ester-forming carboxylic acid component takes place, in accordance with the nature of the alcohol component(s) used, taking into account the numerous considerations already mentioned above and which do not only apply to the ester and/or its rheology immediately, but also the reaction by-products formed especially by partial hydrolysis.

Suitable alcohols are, as stated, both monofunctional alcohols, taking into account the stated limitations, and also polyfunctional alcohols, especially lower polyfunctional alcohols with 2 to 6 carbon atoms and preferably with a maximum of 4 hydroxyl groups.

Also, the alcohol components can thereby be of natural and/or synthetic origin, be straight-chain or branched and, especially in the case of monofunctional alcohols, be saturated and/or also olefinically unsaturated. Monofunctional alcohols in particular have up to 36 carbon atoms, preferably up to approx. 24 carbon atoms. Alcohols with 6 to 18, and especially 7 to 15 C atoms of natural and/or synthetic origin, can be of particular importance in forming the ester oil phase.

Particularly important ester oils are, within the framework of the context of the invention, environmentally friendly ester oils as described, for example, in the aforementioned older publications NO 171.562-B, NO 171.601-B, NO 171.501-B and NO 171.562-B. In order to complete the description of the invention, essential characteristic data for such ester oils and ester mixtures shall be summarized below.

According to this, the dispersed ester oil phase contains carboxylic acid esters from at least one of the following subclasses: a) Esters of C^_g-monocarboxylic acids and mono- and/or polyfunctional alcohols, whereby residues of monohydric alcohols exhibit at least 6 and preferably at least 8 C atoms and the polyhydric alcohols preferably have 2 to 6 C atoms in the molecule; b) esters of monocarboxylic acids of synthetic and/or natural origin with 6 to 16 C atoms, especially esters of corresponding aliphatically saturated monocarboxylic acids and mono- and/or polyfunctional alcohols of the type mentioned under a); and c) esters of olefinically mono- and/or polyunsaturated monocarboxylic acids with at least 16 and especially 16 to 24 C atoms and especially monofunctional straight-chain and/or branched alcohols.

The latter esters of olefinically mono- and/or polyunsaturated monocarboxylic acids with at least 16 C atoms (c) are preferably assigned to at least one of the following subclasses: cl) Esters which in an amount of more than 45 wt-# , preferably more than 55 wt-#, are derived from di- and/or polyunsaturated olefinically unsaturated C^^_<g>4<-m>onocarboxylic acids; and c2) esters which in an amount of not more than 35% by weight are derived from doubly or more olefinically unsaturated acids and thereby preferably at least approx. 60 wt-# once olefinically unsaturated.

Starting materials for obtaining the numerous monocarboxylic acids included in this subclass with a particularly high carbon number are vegetable and/or animal oils. Mention should be made of coconut, palm kernel and/or babassu oil, especially as substances used for obtaining monocarboxylic acids with the predominant range up to C^g and of essentially saturated components. Vegetable ester oils, especially for olefinically mono- or optionally polyunsaturated carboxylic acids from the range C^^_g^ are, for example, palm, peanut, castor and especially beet oil. Carboxylic acids of animal origin of this type are particularly similar to mixtures of fish oil such as herring oil.

The teachings of the invention expressly also and precisely include the use of monocarboxylic acid triglycerides and thereby especially the use of special glyceride oils of natural origin. Here, however, the following must be taken into account: Natural oils and fats usually exist in such a highly contaminated form, for example with free carboxylic acids or other accompanying substances, that their immediate processing into oil/water emulsion rinses of the type described here is usually excluded . If such natural application materials are added to water-based drilling fluids in the usual commercial form, there is, so to speak, immediately such a strong foaming of the drilling fluid in use that the result is a serious obstacle and even renders the drilling fluid unusable. However, this may be different when purified and/or synthetically obtained selected triglycerides are used as dispersed oil phase. Here, too, in this area, the teachings of the invention can be realized. In principle, however, one must always, with such esters of higher alcohols, expect a not insignificant foaming tendency. Partial esters of glycerol, mono- or diglycerides, are known to be effective emulsifier components.

As already indicated, for the purposes of the invention, not only relatively thin-flowing ester oils are suitable within the context of the older applications in the field of ester oil-based invert drilling flushes, within the framework of oil/water emulsion flushes particularly comparatively viscous-flowing ester oils can be of advantage as a dispersed phase. They are, for example, valuable aids for closing fine pores in filter cakes in the borehole or when inertizing swelling-capable rock, the lubrication ability of such ester oils with comparatively higher viscosity even at elevated temperatures in the borehole, especially also with deviated boreholes, is possibly clearly better than the comparatively thinner ester oils. An influence of the drilling technology is not triggered by a dispersed ester oil phase of comparatively higher viscous ester oils, the rheology in the total system is determined by the closed aqueous phase. In this connection, it may be preferred to use ester oils as dispersed phase which have a Brookfield viscosity of approx. 500,000 mPas or more, for example up to 1,000,000 or even 2,000,000 (determined at room temperature). Here lies an important extension to the teachings of the older publications in the area of oil-based invert drill flushes on an ester oil basis.

In one embodiment of the invention, branched components and in particular α-branched alcohols and/or carboxylic acids can have a special meaning. As is well known, branching of this type is on the one hand responsible for an influence on the rheology, usually the formed ester becomes more mobile with such chain branching. In addition to this, such a "branching" can also have effects in the direction of increased hydrolysis stability under the working conditions, which is exploited in the use of the invention.

The aqueous phase

All types of water are suitable for producing the oil/water emulsion rinses of the invention. According to this, these can be built up on the basis of fresh water and especially on the basis of salt water, here especially sea water in the case of sea-based drilling.

Additives in the emulsion rinse

In principle, all additives intended for comparable flushing types are taken into account here, the addition of which is normally associated with a particularly desired characteristic picture for the drilling flushing. The additives can, for example, be water-soluble, oil-soluble and/or water- or oil-dispersible.

Classic additives for water-based oil/water emulsion flushing can be, for example: Emulsifiers, fluid-loss additives, structural viscosity-building soluble and/or insoluble substances, alkali reserves, agents for inhibiting unwanted water yield between drilled formations, for example water-swellable clays and/or salt layer, and the water-based flushing liquid, wetting agents for better attraction of the emulsified oil phase on solid surfaces, for example to improve the lubrication effect, but also to improve the oleophilic closure of exposed rock formations, for example rock surfaces, further disinfectants, for example to inhibit bacterial attack on such oil/water emulsions and the like. In detail, reference must be made here to the available known technique as described, for example, in the literature mentioned at the outset, in particular reference must be made here to Gray and Darley, cited above, chapter 11, "Drilling Fluid Components". Only examples should therefore be mentioned: Finely dispersed additives to increase the flushing density: Barium sulphate (baryte) is widely used, but calcium carbonate (calcite) or the mixed carbonate and calcium and magnesium (dolomite) are also used.

Means for building up structural viscosity which at the same time also act as fluid-loss additives: In the first line here, mention should be made of bentonite which is known to be used in water-based flushing in an unmodified form and which is thereby ecologically problem-free. For saltwater washes, other comparable clays, especially attapulgite and sepiolite, are of considerable practical importance.

The co-use of organic polymer compounds of natural and/or synthetic origin can also be of great importance in this context. Particular mention should be made here of starch or chemically modified starches, cellulose derivatives such as carboxymethyl cellulose, guar gum, xanthan gum or also pure synthetic water-soluble and/or water-dispersible polymer compounds, especially of the type of high-molecular polyacrylamide compounds with or without anionic or cationic modification.

Thinners for viscosity regulation: The so-called thinners can be organic or inorganic, examples of organic thinners are tannins and/or Oebracho extract. Further examples are lignite and lignite derivatives, especially lignosulfonates. However, as indicated above, in a preferred embodiment of the invention, the co-use of toxic components is dispensed with precisely here, whereby the corresponding salts with toxic heavy metals such as chromium and/or copper should be mentioned in the first line. An example of inorganic diluents are polyphosphate compounds.

Emulsifiers: For the teachings of the invention, two special features must be taken into account here. It has been shown that a stable dispersion of ester oils can be much more easily possible than the corresponding dispersion of pure mineral oils as these are used according to the known technique. Here is already a first lead. Furthermore, account must be taken of the fact that effective oil/water emulsifiers are formed by partial saponification of the ester oils under the influence of suitable alkali reserves using longer-chain carboxylic acid esters, which contributes to the stabilization of the system.

Additives that inhibit the unwanted water exchange with, for example, clays: The known additives for water-based drilling fluids come into consideration here. In particular, this refers to halides and/or carbonates of alkali and/or alkaline earth metals, whereby corresponding potassium salts may possibly have a certain significance in combination with lime. Here, for example, reference should be made to the corresponding publications in "Petroleum Engineer International", September 1987, 32-40 and "Word Oil", November 1983, 93-97.

Alkali reserves: Here, the inorganic and/or organic base, in particular corresponding basic salts or hydroxides of alkali and/or alkaline earth metals as well as organic bases, are taken into consideration for the overall behavior of the flushing.

In the area of organic bases, a distinction must be made between water-soluble organic bases, for example compounds of the diethanolamine type, and practically water-insoluble bases with a pronounced oleophilic character as described in the initially mentioned older publication NO 179.487-B as an additive in invert drilling mud on an ester oil basis. Precisely the co-use of such oil-soluble bases within the scope of the invention lies within the new teaching. Oleophilic bases of this type, which are particularly distinguished by at least one longer hydrocarbon residue with, for example, 8 to 36 carbon atoms, are however not dissolved in the aqueous phase, but in the dispersed oil phase. Here, the basic components have several meanings. On the one hand, they can immediately act as alkali reserves. On the other hand, the dispersed oil droplets provide a certain positive charge state and thus lead to an increased interaction with negative surface charges such as can be encountered, for example, especially with hydrophilic clays that have the ability to ion exchange. According to the invention, the influence on the hydrolytic cleavage and the oleophilic closure of water-reactive rock layers can thereby be removed.

The quantity of the auxiliaries and additives used in each case is in principle within the usual limits and can be found in the indicated available literature.

EXAMPLES

First, using commercial bentonite (non-hydrophobic), a 6 wt # homogenized bentonite slurry was prepared with tap water while setting a pE value of 9.2 to 9.3 using caustic soda.

Based on this pre-swollen aqueous bentonite phase, the individual components of the water-based ester oil emulsion are incorporated in the following process steps, each time during intensive mixing, according to the following recipe:

350 g 6 weight-^-ig bentonite solution

1.5 g technical carboxymethyl cellulose of the low-viscosity type

(Relatin U 300 59)

35 g of sodium chloride

70 g of ester oil (according to the definition given below)

1.7 g emulsifier (sulphated castor oil "turkey oil" unless otherwise stated)

219 g baryte

On the oil/water emulsion rinses produced in this way, viscosity determinations are carried out as follows: On the emulsion rinse, the plastic viscosity (PV), yield strength (YP) and gel strength are first determined at 50°C on non-aged material after 10 seconds and after 10 minutes.

The emulsion rinse is then aged for 16 hours at 125°C in an autoclave in a so-called "Roller-Oven" to test the influence of temperature on emulsion stability. The viscosity values are then determined again at 50°C. In the following examples, the type of ester oil used, information about the emulsifier, the values determined on non-aged and aged material and, if necessary, general remarks are summarized in each case.

Example 1

Ester oil used: 2-ethylhexyl ester of a C 8 -^^ fatty acid mixture (essentially saturated).

Turkey red oil as an emulsifier.

Example 2

The batch from example 1 is repeated, however, the co-use of emulsifiers (turkey red oil) is waived.

The viscosity values measured on non-aged and aged material are as follows:

Already in the freshly prepared batch, a slight droplet formation can be determined on the surface, after aging the solid tends to deposit.

Example 3

Ester oil used: oleic acid isobutyl ester

Emulsifier: Turkish red oil

The viscosity values measured on non-aged and aged material are as follows:

Example 4

The batch from example 3 is repeated, but soy lecithin (commercial product "Drilltread") is used as an emulsifier in an amount of

1.7 g. The viscosity values measured on unaged and aged drilling mud are as follows:

Example 5

When Turkish red oil is used as emulsifier, propylene glycol monooleate is used as ester oil. The following viscosity values are determined:

Example 6

As Turkish red oil is once again used as an emulsifier, trimethylolpropane trifatty acid ester is used as the ester oil phase. The values measured on non-aged and aged material are the following:

Example 7

Within the framework of the teachings in example 6, a corresponding glycerol trifatty acid ester is used as the ester oil phase. The values determined for non-aged and aged emulsion drilling fluid are the following:

Example 8

Using Turkish red oil as an emulsifier, the n-hexanol esterified residue from the fatty acid dimerization (monomer fatty acid "Åliphat 47") is incorporated as the ester oil phase. The viscosity values determined on non-aged and aged material are as follows:

Claims (26)

1. Use of water-emulsifiable, liquid at working temperature or at least plastically malleable and having a flash point of at least 80 °C esters of monocarboxylic acids with up to 5 carbon atoms and monohydric alcohols with at least 6 C atoms and/or polyhydric alcohols, whereby in the case of esters of monohydric alcohols, the carboxylic acid residues are at least partially derived from monocarboxylic acids with up to 36 carbon atoms, which are at least the predominant component of the dispersed oil phase of water-based oil/water emulsion drilling fluids for an environmentally friendly exploitation of geological formations, and which, if desired, contain insoluble, finely divided weighting agents agents for the formation of water-based oil/water emulsion drilling mud and/or further additives such as emulsifiers, fluid-loss additives, wetting agents, alkali reserves and/or auxiliaries for inhibiting drilled rock with high water sensitivity. 2. Use according to claim 1 of the dispersed ester oil phase in quantities of at least 5 wt-56, preferably at least 8 wt-# in the oil/water rinse, the weight-# being calculated on the sum of non-weighted liquid parts of ester oil/water, thereby constituting preferably not more than 50 wt-#, especially not more than 40 wt-#, wt-# calculated as above. 3. Use according to claims 1 and 2 of esters of monofunctional alcohols of natural and/or synthetic origin and pronounced oleophilic character with at least 8 C atoms. 4. Use according to claims 1 to 3 where, when using or co-using ester oils based on multifunctional alcohols, full and/or partial esters of water-soluble polyols with preferably up to 4 OH groups in the molecule are also used, especially esters of ethylene glycol, propylene glycol and/or glycerol . 5 . Use according to claims 1 to 4 of ester oils whose solidification values (pour and solidification points) are below 0°C and preferably below -5°C and exhibit a flash point of at least 100°C. 6. Use according to claims 1 to 5 where the dispersed oil phase uses ester oils which, as a continuous oil phase at 20°C, exhibit a Brookfield-RVT viscosity of no more than 1,000,000 mPas. 7. Use according to claims 1 to 6 of ester oils which are at least largely free of toxicologically "considerable molecular constituents, especially aromatic portions, whereby the preferred ester oils originate from straight-chain and/or branched carboxylic acids and preferably also corresponding alcohols. 8. Use according to claims 1 to 7, where the dispersed ester oil phase contains carboxylic acid esters from at least one of the following subclasses: a) esters of C 1 -g monocarboxylic acids and mono- and/or polyfunctional alcohols, whereby residues of monohydric alcohols exhibit at least 6 and preferably at least 8 C atoms and the polyhydric alcohols preferably have 2 to 6 C atoms in the molecule; b) esters of monocarboxylic acids of synthetic and/or natural origin with 6 to 16 C atoms, especially esters of corresponding aliphatically saturated monocarboxylic acids and mono- and/or polyfunctional alcohols of the type mentioned under a); and c) esters of olefinically mono- and/or polyunsaturated monocarboxylic acids with at least 16 and especially 16 to 24 C atoms and especially monofunctional straight-chain and/or branched alcohols. 9. Use according to claims 1 to 8 of the ester oils present in the dispersed phase according to claim 8, c) which can at least be assigned to one of the following subclasses: cl) Esters which in an amount of more than 45% by weight, preferably more than 55 wt-#, is derived from doubly and/or more olefinically unsaturated (^^^-monocarboxylic acids; and c2) esters which in an amount of not more than 35 wt-# are derived from doubly or more olefinically unsaturated acids and thereby preferably at least approx. 60 wt-# once olefinically unsaturated. 10. Use according to claims 1 to 9, where in the dispersed oil phase, basic amine compounds of distinctly oleophilic character and very limited water solubility are used as additives. 11. Use according to claims 1 to 10 where oleophilic amine compounds are used which are at least predominantly free of aromatic components and whose water solubility at room temperature does not amount to more than 1% by weight. 12. Use according to claims 1 to 11 where basic amine compounds are used as additives, which at least have a long-chain hydrocarbon residue with preferably 8 to 36 C atoms. 13. Use according to claims 1 to 12 where work is carried out with dispersed ester oil phase whose content of oleophilic amine compounds amounts to up to 10 wt-# and preferably in the range 0.1 to 2 wt-56, calculated on esterol je. 14. Use according to claims 1 to 13 where ester oils with increased saponification stability are used which in particular exhibit at least one branched ester-forming component, preferably in the form of an α-branching. 15. Application according to claims 1 to 14 where the homogeneous aqueous phase is fresh water or water containing dissolved or suspended salts, especially halides and/or carbonates of alkali and/or alkaline earth metals, which can also, if desired, be modified seawater. 16. Use according to claims 1 to 15 where the dispersed ester oils together with the known inorganic and/or organic excipients are used to limit rock hydration of the mineral layer disposed for this purpose. 17. Water-based oil/water emulsion drilling fluids for rock drilling in geological formations, containing in a homogeneous aqueous phase a stable dispersed oil phase in amounts of 5 to 50 wt-#, calculated on the sum of unencumbered water and oil phase, together with dissolved and/ or dispersed auxiliary substances for drilling flushing fluids for rock drilling in geological formations (emulsifiers, fluid-loss additives, wetting agents, finely divided weighting substances, salts, alkali reserves and/or disinfectants), characterized in that at least in the predominant proportion the dispersed oil phase is formed from water emulsifiable, at working temperature liquid or at least plastically malleable and having a flash point of at least 80 "C showing ester oils of monocarboxylic acids with up to 5 C atoms and monohydric alcohols with at least 6 C atoms and/or polyhydric alcohols, whereby in the case of esters of monohydric alcohols, the carboxylic acid residue can at least partially also originate from monocarboxylic acids with up to 36 C atoms. 18. Emulsion drilling fluids according to claim 17, characterized in that the dispersed esterol phase at least constitutes at least 8 and preferably no more than 40 wt-#, whereby the proportion of emulsified ester oil phase is preferably in the range 10 to 35 wt-#. 19. Emulsion drilling fluids according to claims 17 and 18, characterized in that the ester-forming alcohols and carboxylic acids are free of ecologically questionable and especially aromatic components. 20. Emulsion drilling fluids according to claims 17 to 19, characterized in that the ester oils can at least partially be assigned to one or more of the following subclasses: a) Esters of C.j_g-monocarboxylic acids and mono- and/or polyfunctional alcohols, whereby residues of monohydric alcohols exhibit at least 6 and preferably at least 8 C atoms and the polyhydric alcohols preferably have 2 to 6 C atoms in the molecule; b) esters of monocarboxylic acids of synthetic and/or natural origin with 6 to 16 C atoms, especially esters of corresponding aliphatically saturated monocarboxylic acids and mono- and/or polyfunctional alcohols of the type mentioned under a); and c) esters of olefinically mono- and/or polyunsaturated monocarboxylic acids with at least 16 and especially 16 to 24 C atoms and especially monofunctional straight-chain and/or branched alcohols. 21. Emulsion drilling fluid according to claims 17 to 20, characterized in that when there are ester oils from subclass c), these can at least partially be assigned to one of the following subclasses: cl) Esters which in an amount of more than 45 wt-#, preferably more than 55% by weight, is derived from di- and/or polyolefinically unsaturated C1-4-monocarboxylic acids; and c2) esters which in an amount of not more than 35% by weight are derived from doubly or more olefinically unsaturated acids and thereby preferably at least 60% by weight is once olefinically unsaturated. 22. Emulsion drilling fluids according to claims 17 to 21, characterized in that the present ester oils are based on monofunctional, practically water-insoluble alcohols with a pronounced oleophilic character. 23. Emulsion drilling fluids According to claims 17 to 22, characterized in that in the dispersed ester oil phase, basic amine compounds with a pronounced oleophilic character and very limited water insolubility, which are free of aromatic components and which preferably exhibit a long-chain hydrocarbon residue with preferably 8 to 36 C atoms, are also used. 24. Emulsion drilling fluids according to claims 17 to 23, characterized in that the usual auxiliaries and additives for water-based emulsion drilling fluids are also selected under criteria for ecological acceptability and are especially free of toxic heavy metal compounds. 25. Emulsion drilling fluids according to claims 17 to 24, characterized in that they contain additives for inhibiting the absorption of water in swelling rock layers or clays. 26. Emulsion drilling fluids according to claims 17 to 25, characterized in that they are adjusted to a pH value in the range of approx. neutral to moderately basic, especially to the 7.5 to 11 range.