CA2192998C - Free-flowing borehole servicing preparations containing linear alpha-olefins, more particularly corresponding drilling fluids - Google Patents

Abstract

The invention relates to the use of at least predom-inantly linear hydrocarbon compounds olefinically un-saturated in the alpha-position with flashpoints of at least about 80°C as the oil phase or as part of the oil phase of oil- or water-based free-flowing borehole servicing preparations. It also relates to a drilling fluid composition comprising an auxillary fluid compris-ing such linear hydrocarbon compounds olefinically unsaturated in the alpha-position and to processes for sinking a bore in a rock. Particular significance is attributed to corresponding drilling fluids which, together with the alpha-olefins, contain other oil phases from the field of borehole servicing preparations and are distinguished by ecological compatibility, being degrad-able under both aerobic and anaerobic conditions.
Suitable mixture components for the oil phase are, in particular, oleophilic alcohols, ethers and corresponding esters selected from carboxylic acid esters and/or carbonic acid esters.

Description

Free-flowing borehole servicing preparations containing linear alpha-olefins, more particularly corresponding drilling fluids Field of the Invention This invention relates to new borehole servicing preparations which flow freely under normal conditions and which are made up using an oil phase. As a charac-teristic example of servicing preparations of the type in question, the invention is described hereinafter with reference to drilling fluids and drilling muds based thereon which may be used both in land-supported drilling and in offshore drilling. However, the modification according to the invention of auxiliary fluids of the type in question is by rio means limited to this par-ticular application. The many other auxiliary fluids used in the specialist field in question, for example spotting fluids, spacers, packer fluids, auxiliary workover, stimulation and fracturing fluids, may also be correspondingly modified.
The invention is concerned both with auxiliary fluids of the type mentioned which are based on oils, i.e. which work with a continuous oil phase, and with auxiliaries in which the oil phase is emulsified in a continuous phase, more particularly an aqueous continuous phase. Drilling fluids and drilling muds based thereon are characteristic examples of the various corresponding possibilities.
On the one hand, water-based drilling fluids con-taining around 1 to 50% of emulsified oil phase in addition to other typical auxiliaries encountered in drilling fluids are known and are also referred to as o/w emulsion fluids. On the other hand, oil-based drilling fluids in which the oil forms the fluid phase or at least a substantial part of the fluid phase as a continuous oil phase are widely used in practice. Particular signifi-cance is attributed in this regard to so-called invert drilling muds which - on the basis of w/o emulsions -contain a disperse aqueous phase in the continuous oil phase. The content of disperse aqueous phase is typical-ly in the range from about 5-10o by weight to about 50-60o by weight. In addition to these w/o invert drilling muds, however, there are also the so-called true oil muds of which the liquid phase consists almost entirely of a continuous oil phase and which contain at most small quantities - normally not more than 5 to 10% by weight -of dispersed aqueous phase.
The invention relates equally to the two fields in question, namely oil-based drillirig fluids and water-based drilling emulsions.
The use of the new borehole servicing fluids is of particular significance for the development of oil and gas occurrences, particularly in the marine sector, but is by no means limited to this particular field of application. The new systems may also be generally used in land-supported drilling operations, for example in geothermal drilling, water drilling, geoscientific drilling, so-called river-crossing drilling and mine drilling. Irrespective of this broad range of applications of the principles according to the inven-tion, the technical teaching is described hereinafter with reference to drilling muds.

Background of the Invention It is known that drilling fluids for sinking bores in rock and bringing up the rock cuttings are slightly thickened, fluid systems which may be assigned to one of the following three classes:

water-based drilling fluids, oil-based drilling fluids (true oil muds and so-. ~,;...

called w/o invert emulsion muds) and water-based o/w emulsions which contain a hetero-geneous finely dispersed oil phase in a continuous aqueous phase.
Drilling fluids on a continuous oil basis, more particularly w/o invert emulsions, are generally made up of a three-phase system, namely: oil, water and fine-particle solids. The aqueous phase is present in the continuous oil phase in heterogeneous fine dispersion.
There are a whole range of additives, including in particular emulsifiers, weighting agents, fluid loss additives, alkali reserves, viscosity regulators and the like. Full particulars can be found, for example, in the Article by P.A. Boyd et al. entitled "New Base Oil Used in Low-Toxicity Oil Muds" in Journal of Petroleum Techno-logy, 1985, 137 to 142 and in the Article by R.B. Bennet entitled "New Drilling Fluid Technology -Mineral Oil Mud"
in Journal of Petroleum Technology, 1984,, 975 to 981 and the literature cited therein.
Drilling fluids based on aqueous o/w emulsion systems occupy an intermediate position between water-based systems and oil-based irivert: muds in terms of their performance properties. Detailed information can be found in the relevant specialist literature, cf. for example the book by George R. Gray and H.C.H. Darley entitled "Composition and Properties of Oil Well Drilling Fluids", 4th Edition, 1980/81, Gulf Publishing Company, Houston, and the extensive specialist and patent litera-ture cited therein and the manual entitled "Applied Drilling Engineering" by Adam T. Borgoyne, Jr. et al., First Printing, Society of Petroleum Engineers, Richard-son, Texas (USA).
In practice, the oil phases of drilling fluids of the type described in these references and other borehole servicing preparations of comparable composition have until very recently been formed almost exclusively by selected mineral oil fractions. Accordingly, consider-able environmental pollution occurs when, for example, the drilling muds enter the environment either directly or via the drilled rock. Although mineral oils are aerobically degradable in the presence of suitable bacterial strains, the degradation process is relatively slow. Anaerobically, mineral oils are virtually non-degradable and, accordingly, may be regarded as causing long-term pollution.
These problems have been known to experts for years.
Thus, US patents 4,374,737 and 4,481,121 describe oil-based invert drilling fluids in which so-called non-polluting oils are said to be used. De-aromaticized mineral oil fractions and ester oils of vegetable and animal origin are named alongside one another as non-polluting oils of equal rank. The ester oils are trigly-cerides of natural fatty acids which, ecologically, are known to be safe and distinctly superior in this respect to hydrocarbon fractions. These proposals cannot be put into practice for the particularly important field of oil-based w/o invert emulsion drilling fluids. The primary and secondary hydrolysis products of these triglyceride esters, which are formed in use, lead to uncontrollable changes in the fluidity of the w/o emul-sions. More particularly, complete thickening occurs in a very short time.
In a relatively large number of earlier patent applications, applicants describe proposals for replacing the mineral oil fractions by ecologically safe, compara-tively readily degradable oil phases. Four different types of replacement oils are disclosed and may even be used in admixture with one another. The substitutes in question are selected oleophilic carboxylic acid esters, at least substantially water-insoluble alcohols which flow freely under working conditions, corresponding ethers and selected carbonic acid esters, cf. the follow-ing German patent applications which have become part of the prior art literature in the form of the DE-Al speci-fications: 38 42 659, 38 42 703, 39 07 391, 39 07 392, 39 03 785, 39 03 784, 39 11 238, 39 11 299, 40 18 228 and 40 19 266. All these documents are concerned with oil-based drilling fluids, more particularly of the w/o invert type. Water-based emulsion drilling fluids using oil phases of increased degradability are described in the following German patent applications identified by the publication numbers of the DE-A1 specifications: 39 15 876, 39 15 875, 39 16 550 and the already cited 40 18 228 and 40 19 266.
Other proposals have also been put forward with a view to replacing mineral oils in borehole servicing preparations of the type described herein by other oil phases, cf. US 5,189,012. This document proposes the use of synthetic hydrocarbon compounds from the group of branched-chain oligomex=s which have been produced by oligomerization. of C2_14 olefins to average molecular weights of the oligomer in the range from 120 to 1,000.
The Examples of this document describe tests to determine the toxicity of these branched hydrocarbon oligomers to-wards selected test organisms (Mysidopsis Bahia). There is no reference to tests for determining the degradabil-ity and, in particular, the anaerobic degradability of these branched hydrocarbon compounds which are also known among experts as "poly-alpha-olefi.ns". Applicants' in-vestigations of these problems have indicated that poly-alpha-olefins show little or no anaerobic degradability.
By contrast, oil phases based on the ester oils described in the documents cited above arid corresponding oleophilic alcohols are distinguished by surprisingly good degradability both under aerobic conditions and in particular under anaerobic conditions. Starting out from this fact, selected monocarboxyl:ic acid esters are now ~

... ,.~...~,..~...e,. .,, n......... ., .,.. ,. õw, ,w .. .... _ .. ..,......
...~...._..._m.._....,......

used worldwide as replacement oils, more particularly for drilling muds, in the field of offshore drilling. At the present time, particular significance is attributed in this regard to the esters of saturated monocarboxylic acids containing 12 to 16 carbon atoms and monohydric alcohols which are described in DE-Al 38 41 703.

The problem addressed by the invention and its technical solution The invention sought to broaden the range of techni-cal possibilities preserltly available for alternative oil phases in the field of application in question. More particularly, the problem addressed by the present invention was to increase the ability of liquid and, in particular, water-containing borehole servicing prepara-tions to withstand high temperatures without at the same time compromising their degradability both under aerobic conditions and under anaerobic conditions. The following basic observations are relevant in this regard:
The alternative oil phases based on carboxylic acid esters widely used today combine optimal results under typical in-use conditions both from the point. of view of operational efficiency and from the point of view of ecological compatibility as reflected in their anaerobic degradability. Despite the basic susceptibility to hydrolysis, even water-containing systems of this type, more particularly the w/o invert systems, are astonish-ingly stable up to relatively high temperatures at the bottom of the borehole. However, if extreme tempera-tures, for example of the order of 200 C or higher, are reached, inreasing ester hydrolysis can occur to the detriment of the process.
Oleophilic alcohols are not susceptible to hydroly-sis and combine this advantage with ready aerobic and anaerobic degradability. However, alcohol-based w/o muds show flow properties which may ca.ll for particular atten-tiveness in operation, presumably on account of their tendency to form hydrogen bridges, so that hitherto hydrolysis-resistant oil phases based on oleophilic alcohols have not been successfully used in practice.
Summary of the Invention The problem addressed by the teaching according to the invention was to enable selected hydrocarbon com-pounds to be used as the oil phase or, more particularly, as a mixture component of the oil phase in the field in question. By virtue of their structure, the selected hydrocarbon compounds would largely achieve the required combination of good performance properties and ecological compatibility, particularly in the form of anaerobic degradability. The teaching according to the invention is based on the additional concept that certain deficien-cies in the technical performance propex=ties are accep-table. By mixing the pure hydrocarbon compounds with alternative oil phases of the type mentioned above and, more particularly, with oils based on esters and/or on oleophilic alcohols, certain weaknesses can be inter-cepted and corrected. The teaching according to the invention is based in particular on the observation that corresponding mixtures are capable of combining optimal technical performance properties without in any way comprising the advantage of ecological compatibility as reflected in aerobic and/or anaerobic degradability.
The teaching of the invention described hereinafter is based on the fact that at least substantially linear hydrocarbon compounds olefinically unsaturated in the alpha position - hereinafter also referred to as "linear alpha-olefins (LAOS)" - can also be anaex=obically degra-ded using microorganism strains occurring in practice on the seabed. Reference is made in this connection to the article by B. Schink entitled "Degradation of Unsaturated Hydrocarbons by Methanogenic Enrichment Cultures" in FEMS

Microbiology Ecology 31 (1985), 69-77, published by Else-vier. It can be seen from this publication that alpha-olefins with a chain length of interest to the applica-tion according to the invention, for example alpha-hexadecene, can even be degraded under anaerobic condi-tions using anoxic marine sediments as inoculation medium.
In one of the general aspects, the invention relates to a drilling fluid composition comprising an auxiliary fluid, the auxiliary fluid consisting essentially of:
(a) a water phase; and (b) an oil phase containing oil components selected from the group consisting of linear alpha-olefins and mixtures of linear alpha-olefiris with an ecologically safe water-insoluble oil.
In another aspect this invention relates to a process for sinking a bore in rock comprising contacting the bore with a drilling fluid, during the drilling process, wherein the drilling fluid comprises an auxili-ary fluid consisting essentially of:
(a) a water phase; and (b) an oil phase containing oil components selected from the group consisting of linear alpha-olefins and mixtures of linear alpha-olefins with an ecologically safe water-insoluble oil.

Detailed Description of the Invention The invention will now be described with reference to its most preferred embodiments.
In a first embodiment, therefore, the present invention relates to the use of at least substantially linear hydrocarbon compounds olefinically unsaturated in the alpha-position (linear alpha-olefins LAOS) with flashpoints of at least 80 C as a constituent of oil- or water-based free-flowing borehole servicing preparations.
In one important embodiment, In one important embodiment, a) LAOS flowable and pumpable at temperatures of 0 to 20 C and more particularly at temperatures of 0 to or b) solutions or mixtures of LAOS in ecologically safe water-insoluble oils which are flowable and pumpable at temperatures in the ranges mentioned above are used as the continuous or disperse oil phase of oil-or water-based drilling fluids or other free-flowing borehole servicing preparations. In the case of oil-based servicing preparations, particular practical significance is attributed to the above-described w/o invert emulsions which contain a disperse aqueous phase in the continuous oil phase as defined in accordance with the invention.
In one particularly important embodiment, the in-vention relates to borehole servicing preparations, more particularly drilling fluids, flowable and pumpable at temperatures of 5 to 20 C based either on a continuous oil phase, optionally in admixture with a limited quan-tity of a disperse aqueous phase (w/o invert type) , or on an o/w emulsion with a disperse oil phase in the continu-ous aqueous phase, these preparations optionally contain-ing typical dissolved and/or dispersed auxiliaries, such as viscosifiers, emulsifiers, fluid loss additives, wet-ting agents, fine-particle weighting agents, salts, alkali reserves and/or biocides. This embodiment of the borehole servicing preparations according to the inven-tion is characterized in that the preparations contain at least predominantly linear hydrocarbon cornpounds olefini-cally unsaturated iri the alpha position (LAOS) with flashpoints of at least 80 C and preferably of at least 90 C in their oil phase. Particularly irnportant embodi-~

ments of the invention are characterized by the presence of oil-based servicing preparations of the type mentioned which, in their continuous oil phase, contain the LAOS
homogeneously mixed with other oil phases from the field of borehole servicing preparations which, in particular, are ecologically safe, i.e. are preferably degradable both under aerobic and under anaerobic conditions.
Particulars and preferred embodiments of the invention At least predominantly linear alpha-olefins are known commercial products for various applications, cf.
for example the chapter entitled "LINEAR ALPHA-OLEFINS"
of Chemical Economics Handbook-SRI International (1993).
They may be based on natural substances. More particu-larly, however, they are also synthetically produced on a large scale. LAOS based on natural substances are ob-tained by dehydration of native fatty alcohols as linear products with an even number of carbon atoms. Syntheti-cally obtained LAOS -- produced by oligomerization of ethylene - also frequently contain even numbers of carbon atoms in the chain, although there are also known proces-ses for the production of odd-numbered alpha-olefins, cf.
the cited article in Chemical Economics Handbook.
Even-numbered LAOS may used with advantage for the application according to the invention although the teaching according to the invention is not limited to even-numbered LAOS. By virtue of their volatility, LAOS
as defined in accordance with the invention generally contain at least 10 and preferably at least 12 to 14 carbon atoms in the molecule. The upper limit for LAOS
flowable at room temperature is C18_20 . However, this upper limit is not restrictive so far as the suitability of this class of compounds for use in accordance with is concerned. This is clear from the preferred variant of the invention where the LAOS are used in. admixture with other, more par=ticularly ecologically safe, oil phases.
~F{3 In mixtures such as these, comparatively small quantities of LAOS can have important effects so far as the proper-ties of the mixed oil phase are concerned. Accordingly, the upper limit of suitable LAO compounds for the appli-cation with which the teaching according to the invention is concerned is distinctly above the C18_20 limit mentioned above and, for example, may reach C30. However, for oil-based borehole servicing preparations and, in particular, for w/o invert drilling muds, a chain length range of about 12 to 24 and, more particularly, 14 to 20 carbon atoms will generally be of particular significance.
As already mentioned, the rheological properties of the LAOS move into the background when mixtures of these components with other oil phases from the field of borehole servicing preparations are used. In this case, comparatively small or at least minor quantities of LAOS
may be used in admixture with one or more other oil components. However, it can also be useful - depending on the particular requirements of the borehole in ques-tion - to form at least the predominant part of the free-flowing oil phase by the LAO component(s). Basically, the LAO content of the oil phase may be at least 2-5o by weight to 95-98o by weight. In preferred embodiments, the LAO content is at least 20% by weight to less than 50o by weight and, more particularly, at least about 50%
by weight. Preferred upper limits to the LAO content of the oil phase are 90 to 95o by weight and, more particu-larly, 70 to 75% by weight. All these figures apply to the described embodiment in which the LAOS are used in admixture with other oil phases. So far as their identi-fication is concerned, reference is made to applicants' above-cited specifications on the use of esters, ethers and alcohols and oil phases in borehole servicing prepar-ations.

LAO-containing oil phases of which the rheological properties are tailored to the particular application are preferably used in accordance with the invention. Thus, where the oil. phases are used as a continuous oil phase, it is possible to use corresponding oils or oil mixtures of which the solidification values (flow and pour point) are preferably below 0 C and mo:re preferably below -5 C
and which, in addition, preferably have a Brookfield (RVT) viscosity at 0 to 5 C of not more than 55 mPas and preferably not more than 45 mPas. In the case of o/w emulsion muds or servicing preparations, the oil phase -which of course is now present as a disperse phase - may be defined far more broadly in its rheological proper-ties. Oils with a Brookfield (RVT) viscosity of up to about 3 million mPas and preferably up to about 1 million mPas are suitable in their case.
Where mixtures of the LAOS with other soluble oil phases are used, the other soluble oil phases are prefer-ably selected so that the mixed oi.l phases also have flashpoints of at least 80 C, preferably at least about 90 C and, more particularly, above 100 C. Higher flash-points of the mixed oil phases are preferred for safety reasons. Thus, flashpoints above 1:35 C rnay generally be established.
The chemical nature and preferred selection criteria of the other selected oil phases to be used together with the LAOS are discussed in applicants' above-cited speci-fications on the particular type of oil. As mentioned above, the classes of monocarboxylic acid esters, poly-carboxylic acid esters, carbonic acid esters, oleophilic alcohols and corresponding ethers are particularly suitable in this regard. The classes of ester compounds first listed can be formed in practice by partial hydro-lysis of, in particular, volatile alcohol components.
Accordingly, it is preferred to use mixture components which do not involve any toxicological risks, more particularly inhalation-toxicological risks, even in the event of partial saponification under in-use conditions.
So far as the discusse(i classes af ester compounds are concerned, this means in particular that monohydric alcohols of these esters of natural and/or synthetic origin should preferably contain at least 6 carbon atoms, and, more preferably, at least 8 carbon atoms.
Carboxylic acid esters of polyhydric alcohols are known to be safe from the point of view of inhalation-toxicological risks. This applies iri particular to corresponding esters of natural o:rigin which are avail-able in numerous forms as fats and/or oils of vegetable and/or animal origin and which - taking into account the further parameters defined in connection with the dis-closure of the irivention - are also suitable for the purposes of the invention.
To complete the disclosure of the invention, suit-able mixture components are briefly summarized once more in the following.
Preferred ester oils of monocarboxylic acids belong to at least one of the following subclasses:
a) esters of C1_5 monocarboxylic acids and monohydric and/or polyhydric alcohols, residues of monohydric alcohols containing at least 6 and preferably at least 8 carbon atoms and the polyhydric alcohols preferably containing 2 to 6 carbon atoms in the molecule, b) esters of monocarboxylic acids of synthetic and/or natural origin containing 6 to 16 carbon atoms, more particularly esters of corresponding aliphatically saturated monocarboxylic acids, and monohydric and/or polyhydric alcohols of the type mentioned under a); corresponding esters of C12_16 monocar-boxylic acids may also be free from residues of polyhydric alcohols, c) esters of mono- and/or poly-olefinically unsaturated monocarboxylic acids containing at least 16 carbon atoms and, more particularly, 16 to 24 carbon atoms and, in particular, monohydric linear and/or branch-ed alcohols. However, corresponding esters of polyhydric: alcohols of the type mentioned under a) are also particularly suitable; corresponding esters of glycerol can be of particular significance.
Characteristic examples of such esters are glyceride oils of vegetable and/or animal origin which may be employed in technologically useful form in admixture with the LAO component, even in the embodiment of the w/o invert drilling fluids containing a dis-persed aqueous phase. However, it is known that natural substances of the type in question are not confined to glycerol as the ester-forming alcohol component, particularly in the field of animal oils.
Correspondingly, the teaching according to the invention is also not limited in this regard.
A definition of sui_table polycarboxylic acid esters can be found in the above-cited DE-Al 40 19 266. Parti-cularly important mixture components for mixing with the LAOS in accordance with the teaching of the invention can be carbonic acid diesters of the type described in DE-Al 40 18 228. Esters of carbonic acid are distinguished from the outset by increased resistance to hydrolysis under working conditions. By mixirig with LAOS, it is even possible to obtain high-temperature-stable borehole servicing preparations which can be i.ised at temperatures of up to 300 C or even higher, but which nevertheless have the required ecological compatibility.
As already mentioned on more than one occasion, the oleophilic alcohols described in DE-Al 38 11 238 (= EP-Al 0 391 252) can be of particular importance as mixture components. At least substantially water-insoluble monohydric and/or polyhydric alcohols of natural and/or synthetic origin, which are flowable and pumpable at ~

temperatures of 0 to 5 C, and mixtures thereof in eco-logically safe water-i.nsoluble oils are particularly suitable mixture components.
In the above-described embodiment where polycar-boxylic acid esters are used, the following modification can be particularly important. Highly viscous complex esters with a pronounced lubricant character based on polybasic carboxylic acids and polyhydric alcohols and optionally co-condensed monohydric alcohols and/or monocarboxylic acids may be used to obtain substantial improvements in the lubricity of the oil phase, even in comparatively small quantities of, for example, 2 to 150 by weight, based on the oil phase as a whole. More particularly, the pure hydrocarbon oils in the form of the LAO compounds do of course generally show unsatisfac-tory lubricity and are clearly surpassed in this regard by ester oils. In addition, however, it is clear from the example described here that the use of multicomponent mixtures containing more than only two components as the oil phase - taking the general principles of the inven-tion into account - can lead to important technical optimizations without compromising ecological compatibil-ity as reflected in particular in aerobic and anaerobic degradation.
If the borehole servicing preparations according to the invention are formulated as invert drilling muds of the w/o type, preferred contents of their disperse aqueous phase are in the range from about 5 to 60% by weight and more preferably in the range from about 10 to 50o by weight, based on the free-flowing components.
Around 10 to 45% by weight of disperse aqueous phase are values for oil-based w/o invert muds suitable for a broad range of applications.
In the case of the water-based o/w emulsion muds, the quantity of disperse oil phase is adapted to the particular technical requirements. In general, the oil ,~t content is in the range from about 1 to 50% by weight and preferably in the range from about 8 to 50% by weight, again based on the liquid component of the mud.

Additives in the oil-based or water-based drilling fluid The general rules apply to the composition of the particular servicing fluids for which exemplary data are presented in the following with reference to correspond-ing drilling muds.
Invert drilling muds normally contain the finely dispersed aqueous phase in quantities of around 5 to 45a by weight and preferably in quantities of around 5 to 2506 by weight together with the continuous oil phase.
The following rheological data apply to the rheology of preferred invert drilling niuds according to the invention: plastic viscosity (PV) in the range from about 10 to 60 mPas and preferably in the range from about 15 to 40 mPas; yield point (YP) in the range from about 5 to 40 lb/100 ft2 and preferably in the range from about 10 to 25 lb/100 ft2 - determined in either case at 50 C.
The determination of these parameters, the methods used and the otherwise standard composition of the invert drilling muds described herein are covered in the prior art cited at the beginnirig and are described in detail, for example, in "Manual of Drilling Fluids Technology"
published by NL-Baroid, London, GB, cf. in particular the chapter entitled "Mud Testing - Tools and Techniques" and also "Oil Mud Technology", which is freely available to those interested.
In emulsion drilling fluids, the dispersed oil phase is typically present in quantities of at least about 1 to 2% by weight, frequently in quantities of at least about 506 by weight and preferably in quantities of at least about 7 to 8% by weight in the case of an o/w emulsion.
The percentage oil content should preferably be no more than about 50% by weight and, in particular, no more than about 40o by weight, based on the sum total of the unweighted liquid components oil/water.
In addition to water, it is possible to use any of the additives designed for comparable types of drilling fluids, of which the addition is normally intended to provide the fluid with a specific property spectrum. The additives may be water-.soluble, oil--soluble and/or dispersible in water or oil.
Conventional additives include emulsifiers, fluid loss additives, soluble and/or insoluble substances which build up pseudoplasticity, alkali reserves, additives for inhibiting the unwanted exchange of water between drilled formations - for example water-swellab:Le clays and/or salt layers - and the drilling fluid (for example based on water), wetting agents for improving the absorption of the emulsified oil phase by solid surfaces, for example for improving lubricity, and also for improving the oleophilic sealing of exposed rock formations or rock surfaces, biocides, for example for inhibiting the bacterial contamination of o/w emulsions and the like.
Full particulars can be found in the relevant prior art as represented, for example, by the specialist literature cited at the beginning, cf. in particular Gray and Darley, loc. cit., chapter 11, "Drilling Fluid Compo-nents", of which the following are only a few examples:
Finely dispersed additives for increasing the density of the drilling fluid: barium sulfate (barite) is widely used, although calcium carbonate (calcite) or the mixed carbonate of calcium and magnesium (dolomite) are also used.
Agents for building up pseudoplasticity which also act as fluid loss additives: bentonite and hydrophobi-cized bentonite are mentioned iri particular. For salt water muds, considerable significance is attributed in practice to other comparable clays, more particularly attapulgite and sepiolit.e.

Considerable significance can also be attributed in this regard to the co-use of organic polymer compounds of natural and/or synthetic origin, including in particular starch or chemically modified starches, cellulose deriva-tives, such as carboxymethyl cellulose, guar gum, xanthan gum, or even purely synthetic water-soluble and/or water-dispersible polymer compounds, more particularly of the high molecular weight polyacrylamide compound type with or without anionic or cationic modification. Polyalkyl methacrylates, for example the products marketed under the name of "VISCOPLEX" by Rohm GmbH, have also proved to be particularly suitable viscosity generators based on organic synthetic polymer compounds for LAO-based oil phases.
Diluents for controlling viscosity. The so-called diluents may be organic or inorganic. Examples of organic diluents are tannins and/or quebracho extract.
Further examples are lignite and lignite derivatives, more particularly lignosulfonates. As mentioned above, however, one preferred embodiment of the invention dispenses with the use of toxic components in this very connection, the corresponding salts with toxic heavy metals, such as chromium and/or copper, being mentioned above all in this regard. One example of inorganic diluents are polyphosphate compounds.
Emulsifiers: the emulsifiers used are critically determined by the type of drilling fluid. Emulsifiers suitable for use in practice for forming w/o emulsions are, in particular, selected oleophilic fatty acid salts, for example those based on amidoamine compounds. Ex-amples of such emulsifiers can be found in the above-cited US-PS 4,374,737 and in the literature cited there-in.
Other emulsifiers are required for the formation of o/w emulsions, as known per se. However, it has been found that stable dispersion to form an o/w dispersion is *Trade-mark very much easier than the corresponding dispersion of pure mineral oils of the type used in the prior art.
This represents a first simplification. Another factor to be taken into consideration is that, where ester oils are used, effective o/w emulsifiers are subsequently formed by partial saponification under the effect of suitable alkali reserves where relatively long-chain carboxylic acid esters are used and, hence, contribute towards stabilizing the system.
Additives inhibiting the unwanted exchange of water, for example with clays: suitable additives of this type are the additives known from the prior art on oil- and water-based drilling fluids. The additives in question are in particular halides and/or carbonates of the alkali and/or alkaline earth metals, particular significance being attributed to corresponding potassium salts, optionally in conjunction with lime.
Further particulars can be found, for example, in the corresponding Articles in "Petroleum Engineer Inter-national", September 1987, 32-40 and "World Oil", Novem-ber 1983, 93-97.
Alkali reserves: suitable alkali reserves are inorganic and/or organic bases adapted to the overall behavior of the drilling fluid, more particularly corre-sponding basic salts and hydroxides of alkali metals and/or alkaline earth metals and organic bases. The type and quantity of these basic components are selected and adapted to one another in known mariner in such a way that the borehole servicing preparations are adjusted to a pH
value in the neutral to moderately basic range, more par-ticularly to a pH value in the range from about 7.5 to 11.
So far as organic bases are concerned, a distinction has understandably to be drawn between water-soluble organic bases, for example compounds of the diethanol-amine type, and substantially water-insoluble bases of ~

decidedly oleophilic character of the type described as additives in invert drilling muds based on ester oils in applicants above-cited published application DE-Al 39 03 785. The co-use of oil-soluble bases such as these also falls within the scope of the teaching according to the invention. However, oleophilic bases of this type, which are distinguished in particular by at least one relative-ly long hydrocarbon radical, for example containing 8 to 36 carbon atoms, are not dissolved, in the aqueous phase, but rather in the oil phase. These basic components are important in several respects. On the one hand, they may act directly as an alkali reserve. On the other hand, they provide the dispersed oil droplet with a certain positive charge and hence lead to increased interaction with negative surface charges of the type encountered in particular in hydrophi:Lic clays capable of ion exchange.
According to the invention, it is possible in this way to influence hydrolytic cleavage and the oleophilic sealing of water-reactive rock layers.
Basically, the quantities in which the particular auxiliaries and additives are used are within the usual limits and, accordingly, may be taken from the relevant literature cited in the foregoing.

E x a m p l e s In Examples 1 to 4 below and the associated Com-parison Example, corresponding mixtures are prepared in known manner on the basis of a comparatively water-rich standard formulation for oil-based drilling muds of the w/o type, the continuous oil phase in Examples 1 to 4 corresponding to the definition according to the inven-tion. In the Comparison Example, the commercial product "PETROFREEO" is used as the continuous oil phase. This oil phase, which is widely used in practice, is known to be readily degradable both under aerobic and under an-aerobic conditions and is largely based on saturated C12_14 A'.
_~..=

monocarboxylic acid esters.
The viscosity characteristics of the material are determined as follows before and after ageing: measure-ment of viscosity at 50 C in a Fann-35 viscosimeter (SR12) of Baroid Drilling Fluids, Inc. The plastic vis-cosity (PV), yield point (YP) and gel strength (lb/l00 ft2) after 10 secs. and 10 mins. are determined in known manner.
The drilling fluids are aged by treatment for 16 h at 200 C in a so-called roller oven.
In all the Examples, the drilling fluids tested are prepared in known manner on the basis of the following formulation:
193 ml continuous oil phase 8 g w/o emulsifier (EZ-Muli, a product of Baroid Drilling Fluids, Inc.) 3 g viscosifier (Rilanit Spezial a product of Henkel KGaA) 2 g lime (calcium hydroxide) 82 ml water g CaC12= 2HzO
2 g organophilic bentonite (GELTONE, a product of Baroid Drilling Fluids, Inc.) 211 g barite (barium sulfate) Examples 1 to 4 In Examples 1 to 4 according to the invention, the linear alpha-olefin (LAO) used is a corresponding C-18 LAO (Shop C-18, a product of Shell). The composition of the oil phases from Examples 1 to 4 and from the Compari-son Example is set out in Table 1 below.

*Trade-mark Table 1 Example 1 2 3 4 Comparison Example C-18 LAO ml 193 145 96.5 96.5 Guerbet C16 alcohol ml 48 Di-n-octyl ether ml 96.5 PETROFREE* ml 96.5 193 Table 2 below shows the data of the drilling fluids (plastic viscosity (PV), yield point (YP) and gel strength after 10 secs. (10") and 10 mins. (10')) deter-mined at 50 C for Examples to 1 to 4 and for the Com-parison Example.

Table 2 Examples 1 2 3 4 Comparison Example PV (mPas) 28 62 29 44 47 YP (lb/100 ft2) 26 139 28 47 91 10"/10' gel strength (lb/100 ft2) 11/13 73/74 14/17 20/25 39/41 Table 3 below shows the same data after ageing for 16 h at 200 C in a roller oven.

Table 3 Examples 1 2 3 4 Comparison Example PV (mPas) 21 38 18 59 Cannot be determined YP (lb/100 ft2) 7 23 6 55 Cannot be determined 10"/10' gel strength (lb/100 ft2) 6/7 3/9 4/6 22/25 57/75 *Trade-mark Comparison of the figures set out in Tables 2 and 3 shows that mixtures of the C-18 LAO in particular with other ecologically safe oil phases lead to results of practical interest.
The invert drilling fluid based on the pure ester oil PETROFREE aged under high-temperature conditions is so seriously damaged by ester hydrolysis occurring in situ under the selected working conditions of the water-rich invert drilling fluid that neither the plastic viscosity nor the yield point can be determined (Com-parison Example). Mixing of this ester oil phase with the C-18 olefin in a ratio of 1:1 leads to such a high degree of stabilization that, even after ageing for 16 hours at 200 C, acceptable rheological data can still be measured.
Although the incorporation of comparatively small quantities of the C-16 Guerbet alcohol in the C-18 LAO
leads to considerable thickening of the w/o invert drilling fluid in the fresh state, the values can still be determined. However, ageing of the corresponding drilling fluid (Example 2) at high temperatures leads to very good rheological values which can have an advantage-ous effect in many respects in practice by comparison with the drilling fluid based on pure C-18 LAO.
Examples 5 to 8 Mixtures of linear alpha-olefins (LAO) containing 16 and 14 carbon atoms, i.e. C-16 LAO and C-14 LAO (products of Shell), with a C,z/,e fatty alcohol mixture and with technical oleyl alcohol (iodine value 80/85) were used as the continuous oil phase in the basic formulation de-scribed above. The composition of the oil phase is shown in Table 4.

~

Table 4 Example 5 6 7 8 C-16 LAO ml 128.7 96.5 128.7 C-14 LAO m.1 128.7 C12/le Fatty alcohol ml 64.3 96.5 Oleyl alcohol ml 64.3 64.3 Table 5 below shows the drilling fluid data for these Examples as determined at 50 C after ageing in a roller oven for 16 h at 2000C.

Table 5 Example 5 6 7 8 PV (mPas) 22 43 25 20 YP (lb/100 ft2) 43 73 41 34 10"/10' Gel strength (lb/100 ft2) 16/14 31/31 15/16 13/13 Examples 9 and 10 C-14 LAO (commercial product of Shell) is mixed with different quantities of refined rapeseed oil in these two Examples. In Example 9, the mixed oil phase contains the C-14 LAO in a quantity of 66.6% by weight; in Example 10, the quantity of C-14 LAC) is 50% by weight: - % by weight in both cases based on the mixture of the C-14 LAO and the added rapeseed oil.
Using these two oil phases, corresponding mixtures are prepared in accordance with the standard formuation for oil-based drilling fluids of the w/o type given at the beginning of the Examples. As in the preceding Examples, the plastic viscosity (PV) of the drilling fluids, their yield point (YP) and their gel strength after 10 secs. and 10 mins. are determined before and after ageing. In this case, too, the drilling fluids were aged by treatment in an autoclave for 16 hours at 200 C as in the preceding Exam-ples.

The data determined on the drilling fluids before and after ageing are set out in Tables 6 (freshly prepared drillirig fluid) and 7 (aged drilling fluid).

Table 6 (before ageing) Examples 9 10 PV (mPas) 54 93 YP (lb/100 ft2) 125 98 10"/10' gel strength (lb/100 ft2) 73/73 81/59 Table 7 (after ageing for 16 h/2001C) Examples 9 10 PV (mPas) 40 49 YP (lb/100 ft2) 28 30 10"/10' gel strength (lb/100 ft2) 4/4 3/4 Those skilled in the art will. recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the embodiments of the invention described specifically above. Such equivalents are intended to be encompassed in the scope of the following claims.

Claims (26)

1. A drilling fluid composition comprising an auxiliary fluid, the auxiliary fluid consisting essentially of:

(a) a water phase; and (b) an oil phase containing linear alpha-olefins or mixtures of linear alpha-olefins with an ecologically safe water-insoluble oil.

2. The composition of claim 1 wherein the linear alpha-olefins contain from 12 to 30 carbon atoms.

3. The composition of claim 2 wherein the linear alpha-olefins contain from 14 to 20 carbon atoms.

4. The composition of claim 1 wherein the ecologically safe water insoluble oil is a monocarboxylic acid ester, polycarboxylic acid ester, oleophilic alcohol, oleophilic ether, carbonic acid ester, or a mixture thereof.

5. The composition of claim 1 wherein the linear alpha-olefins are present in the oil phase in an amount of from at least 5% by weight up to 90% by weight, based on the total weight of the oil phase.

6. The composition of claim 5 wherein the oil phase of the auxiliary fluid is a mixture of linear alpha-olefins with an ecologically safe water-insoluble oil, wherein the linear alpha-olefins are present in the oil phase in an amount of from 20% by weight to 50% by weight, based on the total weight of the oil phase.

7. The composition of claim 5 wherein the oil phase has a solidification value below 0°C, and a Brookfield viscosity at from 0 to 5°C of up to 55 mPas.

8. The composition of claim 4 wherein the monocarboxylic acid esters are esters of monocarboxylic acids containing from 1 to 24 carbon atoms with monohydric alcohols containing at least 6 carbon atoms, esters of monocarboxylic acids containing from 1 to 24 carbon atoms with polyhydric alcohols having from 2 to 6 carbon atoms, or mixtures thereof.

9. The composition of claim 5 wherein the oil phase has a flash point of at least 80°C.

10. The composition of claim 9 wherein the oil phase has a flash point above about 135°C.

11. The composition of claim 1 wherein the water phase is present in the auxiliary fluid in an amount of from 5 to 60% by weight, based on the weight of the auxiliary fluid.

12. The composition of claim 1 wherein the oil phase is present in the auxiliary fluid in an amount of from 1 to 50% by weight, based on the weight of the auxiliary fluid.

13. The composition of claim 1 further comprising a viscosifier, emulsifier, fluid loss additive, wetting agent, fine-particle weighing agent, salt, alkali reserve, biocide, or a mixture thereof.

14. A process for sinking a bore in rock comprising contacting the bore with a drilling fluid, during the drilling process, wherein the drilling fluid comprises an auxiliary fluid consisting essentially of:

(a) a water phase; and (b) an oil phase containing linear alpha-olefins or mixtures of linear alpha-olefins with an ecologically safe water-insoluble oil.

15. The process of claim 14 wherein the linear alpha-olefins contain from 12 to 30 carbon atoms.

16. The process of claim 15 wherein the linear alpha-olefins contain from 14 to 20 carbon atoms.

17. The process of claim 14 wherein the ecologically safe water insoluble oil is a monocarboxylic acid ester, polycarboxylic acid ester, oleophilic alcohol, oleophilic ether, carbonic acid ester, or a mixture thereof.

18. The process of claim 14 wherein the oil phase of the auxiliary fluid is a mixture of from 5% by weight up to about 90% by weight, based on the total weight of the oil phase, of linear alpha-olefins with an ecologically safe water-insoluble oil.

19. The process of claim 18 wherein the linear alpha-olefins are present in the oil phase in an amount of from 20% by weight to 50% by weight, based on the total weight of the oil phase.

20. The process of claim 18 wherein the oil phase has a solidification value below 0°C, and a Brookfield viscosity at from 0 to 5°C of up to 55 mPas.

21. The process of claim 17 wherein the monocarboxylic acid esters are esters of monocarboxylic acids containing from 1 to 24 carbon atoms with monohydric alcohols containing at least 6 carbon atoms, esters of monocarboxylic acids containing from 1 to 24 carbon atoms with polyhydric alcohols having from 2 to 6 carbon atoms, and mixtures thereof.

22. The process of claim 18 wherein the oil phase has a flash point of at least 80°C.

23. The process of claim 22 wherein the oil phase has a flash point above about 135°C.

24. The process of claim 14 wherein the water phase is present in the auxiliary fluid in an amount of from 5 to 60% by weight, based on the weight of the auxiliary fluid.

25. The process of claim 14 wherein the oil phase is present in the auxiliary fluid in an amount of from 1 to 50% by weight, based on the weight of the auxiliary fluid.

26. The process of claim 14 wherein the drilling fluid further comprises a viscosifier, emulsifier, fluid loss additive, wetting agent, fine-particle weighing agent, salt, alkali reserve, biocide, or a mixture thereof.