Note: Descriptions are shown in the official language in which they were submitted.
CA 02192998 1996-12-13
H 1394 PCT
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
CA 02192998 1996-12-13
H 1394 PCT 2
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-
. ~,;...
CA 02192998 1996-12-13
H 1394 PCT 3
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
CA 02192998 1996-12-13
H 1394 PCT 4
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
CA 02192998 1996-12-13
H 1394 PCT 5
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.._....,......
CA 02192998 1996-12-13
H 1394 PCT 6
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-
CA 02192998 1996-12-13
H 1394 PCT 7
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
CA 02192998 1996-12-13
H 1394 PCT 8
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,
CA 02192998 1996-12-13
H 1394 PCT 9
In one important embodiment,
a) LAOS flowable and pumpable at temperatures of 0 to
20 C and more particularly at temperatures of 0 to
10 C
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-
~
CA 02192998 1996-12-13
H 1394 PCT 10
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
CA 02192998 2006-03-16
11
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.
CA 02192998 1996-12-13
H 1394 PCT 12
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
CA 02192998 1996-12-13
H 1394 PCT 13
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
CA 02192998 1996-12-13
H 1394 PCT 14
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
~
CA 02192998 1996-12-13
H 1394 PCT 15
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
CA 02192998 1996-12-13
H 1394 PCT 16
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
CA 02192998 1996-12-13
H 1394 PCT 17
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.
CA 02192998 2006-03-16
18
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
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CA 02192998 1996-12-13
H 1394 PCT 19
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
~
CA 02192998 1996-12-13
H 1394 PCT 20
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'.
_~..=
CA 02192998 2006-03-16
21
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.
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CA 02192998 2006-03-16
22
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
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CA 02192998 1996-12-13
H 1394 PCT 23
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.
~
CA 02192998 1996-12-13
H 1394 PCT 24
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.
CA 02192998 1996-12-13
H 1394 PCT 25
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.
