Note: Descriptions are shown in the official language in which they were submitted.
200601 0
Patent
Docket No.: D 8523
THE U8E OF SELECTED ESTER OILS IN
DRILLING FLOID8 AND MUD8
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to new drilling fluids based on
ester oils and to invert drilling muds based thereon which
combine high ecological compatibility with good stability and
performance properties.
2. State of Related Art
It is known that liquid drilling fluids for sinking bores
in rock and bringing up the rock cuttings are slightly
thickened, water-based or oil-based fluid systems. Oil-based
systems are being increasingly used in practice, particularly
in offshore drilling or in the penetration of water-sensitive
layers.
Oil-based drilling fluids are generally used in the form
of so-called invert emulsion muds which consist of a three
phase system, namely: oil, water and finely divided additives,
including in particular emulsifiers and emulsifier systems,
weighting agents, fluid loss additives, alkali reserves,
viscosity regulators and the like, for stabilizing the system
as a whole and for establishing the desired performance
properties. 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 the Journal of Petroleum
Technology, 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.
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Oil-based drilling fluids were originally made from
diesel oil fractions containing aromatic constituents. For
the purposes of detoxification and reducing the ecological
problems thus created, it was then proposed to use hydro-
carbon fractions substantially free from aromatic compounds
- now also known as "nonpolluting oils" - as the continuous
oil phase, c~. the literature cited above. Although cer-
tain advances were achieved in this way through elimination
of the aromatic compounds, a further reduction in the envi-
ronmental problems caused by drilling fluids of the above
type seems to be urgently required. This applies in
particular to the sinking of offshore wells for the de-
velopment of oil and gas sources because the marine ecosys-
tem is particularly sensitive to the introduction of toxic
and non-readily degradable substances.
The relevant technology has for some time recognized
the significance of ester-based oil phases for solving
these problems. Thus, U.S. Patents 4,374,737 and 4,481,121
describe oil-based drilling fluids in which nonpolluting
oils are said to be used. Non-aromatic mineral oil
fractions and vegetable oils of the peanut oil, soybean
oil, linseed oil, corn oil and rice oil type, and even oils
of animal origin, such as whale oil, are mentioned
alongside one another as nonpolluting oils of equivalent
rank. The ester oils of vegetable and animal origin
mentioned here are all triglycerides of natural fatty acids
which are known to be environmentally safe and which,
ecologically, are distinctly superior to hydrocarbon
fractions, even where they have been de-aromaticized.
Interestingly, however, not one of the Examples in the
US patents cited above mentions the use of such natural es-
ter oils in invert emulsion drilling muds. Mineral oil
fractions are used throughout as the continuous oil phase.
In its general descriptive part, U.S. 4,481,121 men-
tions not only triglycerides, but also a commercial product
"Arizona 208'~~ of the Arizona Chemical Company, Wayne, N.J.,
which is a purified isooctyl-monoalcohol ester of high-
* Trade-mark
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2006010
purity tall oil fatty acids. An ester of a monofunctional
alcohol and monofunctional carboxylic acids, mentioned for
the first time here, is described as equivalent to trigly
cerides of natural origin and/or de-aromaticized hydrocar
bon fractions.
The cited US patent does not contain any reproducible
Examples relating to the use of such an ester of monofunc-
tional components.
DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where
otherwise indicated, all numbers expressing quantities of
ingredients or reaction conditions used herein are to be
understood as modified in all instances by the term
"about".
The investigations on which the present invention is
based have shown that the use of readily degradable oils of
vegetable and/or animal origin, which was considered in the
prior art, is not feasible for practical reasons. The
rheologic properties of such oil phases cannot be
controlled for the wide temperature range required in
practice of 0 to 5C on the one hand up to 250C and higher
on the other hand.
The teaching of the present invention is based on the
observation that it is in fact possible to produce oil-
based invert drilling fluids based on ester oils of high
environmental compatibility which correspond in their
storage and in-use behavior to the best of the hitherto
known oil-based drilling fluids, but have the additional
advantage of increased environmental compatibility. Two
key observations in this regard dominate the teaching
according to the invention:
The triglycerides accumulating in the form of natural
oils are not suitable for the production of mineral-oil-
free oil-based invert drilling fluids, whereas the esters
of monofunctional carboxylic acids with monofunctional al-
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2006010
cohols derived from those oils or fats are suitable for the
production of such drilling fluids. The second key observation
is that ester oils of the present type do not in fact show the
same in-use behavior as the mineral oil fractions used hitherto
based purely on hydrocarbons. In practical application, the
ester oils of monofunctional components of the invention
undergo partial hydrolysis, resulting in the formation of free
fatty acids. These free fatty acids react in turn with the
alkaline constituents always present in invert drilling fluids,
for example with the alkali reserve used to prevent corrosion,
to form the corresponding salts. However, salts of highly
hydrophilic bases and the acids in the range of from scout C16
to C24 commonly encountered in fats and oils of natural origin
are known to be compounds having comparatively high HLB values
which lead in particular to the formation and stabilization of
o/w emulsions. Use is made of this to a very considerable
extent in the field of detergents and cleaning preparations.
However, the formation of undesirably large quantities of such
o/w emulsifier systems must interfere with the w/o emulsions
required for solving the problem addressed by the invention
and, hence, leads to problems. The teaching of the present
invention as described in the following shows how invert
drilling fluids based on ester oils can be effectively used in
practice despite these difficulties inherent in the system.
Thus the present invention provides an invert drilling
mud free of mineral oil comprising
A. a continuous oil phase composed predominately of
at least one monocarboxylic acid ester of a C2-C12
monofunctional alcohol wherein the monocarboxylic acid
contains from 16 to 24 carbon atoms and is
olefinically mono- or poly-unsaturated,
B. a disperse aqueous phase,
C. at least one emulsifier,
D. at least one weighting agent,
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E. at least one fluid loss additive, and
F. a mild alkaline reserve.
In a first embodiment, therefore, the present
invention relates to the use of selected esters - flowable and
pumpable at temperatures in the range of from 0 to 5'C - of
monofunctional C2-12 alcohols (alkanols) and olefinically
mono- and/or polyunsaturated C16-24 monocarboxylic acids or
mixtures thereof with small quantities of other, more
especially saturated monocarboxylic acids as the oil phase,
or at least a substantial part of the oil phase, of invert
drilling muds which contain in a continuous oil phase a
disperse aqueous phase and also emulsifiers, weighting
agents, fluid loss additives and, if desired, other stand-
30
4a
CA 02006010 2004-03-17
and additives together with an alkali (alkaline) reserve,
with the proviso that strong hydrophilic bases, such as
alkali metal hydroxides and/or diethanolamine, are not used
in significant quantities. Lime (calcium hydroxide) is often
added as the alkali reserve, more especially for protection
against inrushes of COZ and/or HZS into the drilling fluid
and hence for protection against corrosion. An addition of
lime such as this may be used as the alkali reserve in
accordance with the invention. However, it is important to
ensure that only comparatively small quantities of this
alkaline component are incorporated. The maximum addition of
lime is of the order of about 2 lb/bbl (line/oil mud) and is
thus distinctly below the quantities typically used in
practice in oil-based invert drilling fluids.
In another embodiment, the invention relates to
mineral-oil-free invert drilling fluids which are suitable
for the offshore development of oil and gas sources and, in
a continuous oil phase based on ester oils, contain a
disperse aqueous phase together with emulsifiers, weighting
agents, fluid loss additives and, if desired, other standard
additives. The new drilling fluids are characterized in that
the oil phase consists at least substantially of esters of
monofunctional C2_1z alcohols and olefinically mono- and/or
polyunsaturated Cls-z4 monocarboxylic acids and in that the
w/o emulsion is mildly alkalized and, where lime is added,
this alkali reserve does not exceed quantities of about 2
lb/bbl (lime/oil mud). The lime content is preferably
slightly below this limit.
In a further embodiment, the invention relates to an
invert drilling fluid that is free of mineral oil and is
substantially free from highly hydrophilic basic materials
selected from the group consisting of alkali metal
hydroxides and amines selected from diethanolamine and
triethanolamine, said fluid consisting of (A) a continuous
oil phase composed of at least one monocarboxylic acid ester
CA 02006010 2003-08-06
of a CZ-C1z monofunctional alcohol wherein the monocarboxylic
acid contains from 16 to 24 carbon atoms and comprises at
least about 60% by weight of mono-olefinically unsaturated
acids and no more than about 35% by weight of di- and poly-
olefinically unsaturated acids, (B) a disperse aqueous
phase, and (C) a mildly alkaline alkali reserve component
consisting essentially of lime in a quantity not exceeding
above about 2 lb/bbl of said drilling fluid.
The ester oils selected in accordance with the
invention which are intended to form the entire continuous
oil phase of the invert drilling muds or at least a
substantial part thereof (i.e. over 50% by weight thereof)
are discussed first in the following.
As already stated, an important criterion lies in the
choice of esters which may be assigned to the class of
reaction products of monofunctional carboxylic acids with
5a
~00~010
mono functional alcohols. In addition, however, it is in-
tended in accordance with the invention exclusively or at
least predominantly to use C~6-CZ4 carboxylic acids within
this class. The carboxylic acids may be derived from un-
branched or branched hydrocarbon chains, preferably linear
chains. Monocarboxylic acids of this type and of the C~6 to
CZ4 range and esters thereof are unsuitable as predominantly
saturated hydrocarbon compounds due to their comparatively
high solidification points. Even then, however, esters of
this type are flowable and pumpable down to temperatures of
0 to 5C providing an adequate level of olefinically
unsaturated ester constituents is guaranteed. In the
preferred embodiment of the invention, therefore, esters of
the described type of which more than 70% by weight and
preferably more than 80% by weight are derived from
olefinically unsaturated C~b.Z,~ carboxylic acids are used.
Important natural starting materials are carboxylic acid
mixtures which contain at least 90% by weight olefinically
unsaturated carboxylic acids in the above C range. The
unsaturated carboxylic acids may be mono- and/or
polyolefinically unsaturated. Where carboxylic acids or
carboxylic acid mixtures of natural origin are used, the
double ethylenic double bond in particular and, to a lesser
extent, even a triple ethylenic double bond per carboxylic
acid molecule plays a role in addition to a single
ethylenic double bond in the molecule. Particulars of this
are given in the following.
In conjunction with the choice of esters of monofunc-
tional reactants in accordance with the invention, the
choice of such a comparatively highly unsaturated carbox-
ylic acid component in the ester oils ensures that the es-
ter oils and, ultimately, the final invert emulsions show
the rheologic properties required in practice, particularly
at relatively low temperatures. The comparatively highly
unsaturated ester oils containing 16 to 24 C atoms in the
monocarboxylic acid component, which are used in accordance
with the invention, have solidification points (pour point
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and setting point) below -10'C and more especially below
-15'C in the preferred embodiment. Despite this high mo-
bility at low temperatures, the molecular size of the ester
oil prescribed in accordance with the invention ensures
that the flashpoints of the ester oils are sufficiently
high, being at least 80'C, and generally exceeding a tem-
perature limit of approximately 100'C. Ester oils having
flashpoints above 160'C are preferred. Ester oils of the
described type showing high mobility, even at low temper-
atures, and having flashpoints of 185'C or higher can be
produced without difficulty.
In conjunction with these high flashpoints determined
by the size of the molecule, it is possible at the same
time to ensure that the viscosity values are within the
required limits. Thus, preferred ester oils of the des-
cribed type show a Brookfield (RVT) viscosity at a temper-
ature of 0 to 5'C of not more than 50 mPa.s and preferably
of at most 45 mPa.s or lower. It is possible to adjust
values of 30 or even higher, for example in the range of
from 20 to 25 mPa.s, at temperatures in the range
indicated.
Among the unsaturated ester oils suitable for use in
accordance with the invention, there are two sub-classes of
particular importance.
The first of these sub-classes is based on unsaturated
4 monocarboxylic acids of which no more than about 35%
by weight are diolefinically and, optionally, polyolefinic-
ally unsaturated. In their case, therefore, the content of
di-and polyunsaturated carboxylic acid residues in the
ester oil is comparatively limited. Within this sub-class
it is preferred that at least about 60% by weight of the
carboxylic acid residues are monoolefinically unsaturated.
In contrast to the first sub-class described above,
the second sub-class of ester oils of particular signifi-
cance is derived from C~6.2,~ unsaturated nonocarboxylic acid
mixtures of which more than 45% by weight and preferably
more than 55% by weight are derived from diolefinically
7
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and/or polyolefinically unsaturated acids within the above
C range.
The most important monoethylenically unsaturated car-
boxylic acids within the above carbon range are hexa-
decenoic acid (palmitoleic acid (C~6) ) , oleic acid (C~8) ,
the
related ricinoleic acid (C~e) and erucic acid (CZZ) . The
most important di-unsaturated carboxylic acid within the
range in question here is linoleic acid (C~8) while the most
important triethylenically unsaturated carboxylic acid is
linolenic acid (C~8) .
Selected individual esters formed from an unsaturated
monocarboxylic acid and a monoalcohol can be used as the
ester oil in accordance with the invention. One example of
such esters are the esters of oleic acid, for example of
the oleic acid isobutyl ester type. So far as the rheology
of the system is concerned and/or for reasons of
availability, it is frequently desirable to use esters from
acid mixtures. This is of importance so far as meeting the
above-stated specifications of the two sub-classes for
preferred ester oils is concerned.
As already mentioned, the first of these two sub-
classes is distinguished by the fact that its content of
di-unsaturated and polyunsaturated acids is limited and
does not exceed about 35% by weight. Vegetable oils of
natural origin, of which the hydroly$is or transesterifi-
cation gives mixtures of carboxylic acids or carboxylic
acid esters of the type required here, are for example
palm oil, peanut oil, castor oil and, in particular, rape-
seed oil. Suitable rapeseed oils are both traditional
types of high erucic acid content and also the more modern
types of reduced erucic acid content and increased oleic
acid content.
Ester oils of the first sub-class which correspond to
this definition are particularly important for the simple
reason that problems possibly arising from the lack of
stability to oxidation are reduced. In practice, the
drilling fluid is of course continuously pump-circulated
8
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and, in the process, is brought constantly into contact
with atmospheric oxygen, often over a large area and at at
least slightly elevated temperatures, for the purpose of
separating out the rock cuttings brought up, for example by
sieving.
However, carboxylic acid mixtures of the second sub-
class mentioned above are also of considerable practical
significance for use in accordance with the invention.
This is attributable in part to their broad accessibility
from natural fats of animal and/or vegetable origin. Clas-
sic examples of oils which have a high content of C~b_~8 or
06_22 carboxylic acids and which, at the same time, contain
at least about 45% of at least diethylenically unsaturated
carboxylic acids are cottonseed oil, soybean oil, sunflower
oil and linseed oil. The tall oil acids isolated during
the recovery of cellulose also fall within this range.
However, starting materials of the last type are generally
distinguished by more or less large additional contents of
resin constituents. A typical animal starting material for
the production of corresponding carboxylic acid mixtures is
fish oil, particularly herring oil.
As already mentioned, the ester oils used in accor-
dance with the invention can be certain selected individual
esters corresponding to the above definition. However,
mixtures of esters of corresponding monocarboxylic acids
and monoalcohols will normally be present. In this regard,
the scope of the invention encompasses above all those mix-
tures which, on the one hand, meet the viscosity require-
ment according to the invention and of which, on the other
hand, at least 50% comprise the monofunctional esters of
the olefinically mono- and/or polyunsaturated C~6_2' car-
boxylic acids. Ester constituents and, in particular, car-
boxylic acid esters of monofunctional alcohols and mono-
functional carboxylic acids of different constitution may
be present as minor constituents of the mixture providing
the mixture has the required property profile. This is im-
portant where carboxylic acid mixtures of natural origin
9
~~~so~.o
are used. Natural starting materials such as these gener-
ally also contain more or less large proportions of satu-
rated carboxylic acids, often including linear C
car-
~6_~a
boxylic acids. Saturated fatty acids of this type and
their esters readily give rise to rheologic difficulties
due to their comparatively high melting points. According
to the invention, therefore, saturated C~6_~8 carboxylic
acids preferably make up no more than 20% by weight and
in
,
particular, no more than 10% by weight of the ester oils.
By contrast, the presence of saturated carboxylic
acids containing less than 16 carbon atoms and
more
,
especially, from 12 to 14 carbon atoms is more acceptable.
In small quantities, the contents of such lower, fully
saturated fatty acids often present in natural starting
materials are frequently valuable mixture components in the
context of the problem addressed by the invention. Their
esters are not vulnerable to oxidation under practical in-
use conditions and their rheologic properties promote the
objective of the invention, namely to replace the
pure
hydrocarbon oils hitherto solely used in practice b
est
y
er
oils or ester oil fractions.
The alcohol radicals of the esters or ester mixtures
according to the invention are preferably derived from
straight-chain and/or branched-chain saturated alcohols,
particular significance being attributed to alcohols c
-
on
taining at least 3 C atoms and, more especially, to alco-
hols containing up to about 10 C atoms. The alcohols
can
also be of natural origin, in which case they have normally
been obtained from the corresponding carboxylic acids or
their esters by hydrogenating reduction. However
the in-
,
vention is by no means limited to starting materials of
natural origin. Both on the monoalcohol side and on the
monocarboxylic acid side, the starting materials of natural
origin may be partly or completely replaced by correspond-
ing components of synthetic origin. Typical examples of
alcohols are the corresponding oxo alcohols (branched
alcohols) and the linear alcohols obtained by the Ziegler
2006010
process. Similarly, monocarboxylic acid components present
in particular in carboxylic acid mixtures can be derived
from petrochemical synthesis. However, the advantages of
starting materials of natural origin lie in particular in
their proven lower toxicologic values, their ready
degradability and their ready accessibility. The natural
destruction of the used oil mud ultimately required
presupposes that ester oils of the type described herein be
both aerobically and anaerobicaliy degradable.
l0 However, one important limitation is associated with
the use of these ester oils in invert oil muds of the type
used in the present invention. This limitation arises out
of the difficulty mentioned at the beginning that, in
principle, the carboxylic acid esters are vulnerable to
hydrolysis and, accordingly, have to behave differently
than the pure hydrocarbon oils hitherto used.
Invert drilling muds of the type used herein contain
the finely disperse aqueous phase, normally together with
the continuous oil phase, in quantities of from 5 to 45% by
weight and preferably in quantities of from 5 to 25% by
weight. Particularly preferred is the range of 10 to 25%
by weight of disperse aqueous phase. This precondition
from the constitution of conventional drilling muds also
applies to the ester-based invert drilling muds of the
invention. It is clear that, in continuous practical
operation, disturbances of the equilibrium can occur in the
multiphase system as a result of partial ester hydrolysis.
The situation is complicated by the fact that, in
practice, drilling muds of the present type always contain
an alkali reserve. This alkali reserve is particularly
important in affording protection against corrosion caused
by unexpected inrushes of acidic gases, particularly C02
and/or H2S. The danger of corrosion to the drill pipe
requires the safe establishment of pH values at least in
the mildly alkaline range, for example in the range from pH
8.5 to 9 and higher.
In oil muds based on pure hydrocarbon fractions as the
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2006010
oil phase, strongly alkaline and, at the same time, highly
hydrophilic inorganic or organic additives are generally
used in practice without any difficulty. Particular signi-
ficance can be attributed to the alkali hydroxides and
in
,
particular, to sodium hydroxide on the one hand or t
o
highly hydrophilic organic bases, diethanolamine and/or
triethanolamine being particularly typical additives for
binding impurities of H2S . In addition to and/or instead of
the highly hydrophilic inorganic and organic bases me
-
n
tinned here, lime or even more weakly basic metal oxides,
especially zinc oxide or comparable zinc compounds, are
particularly important as the alkali reserve
Lime in
-
.
par
ticular is widely used an inexpensive alkalizing agent. It
may safely be used in comparatively high quantities of, for
example, from 5 to 10 lb/bbl (lime/oil mud) or even higher.
The use of the ester-based oil muds of the invention
requires a departure from standard practice so far as these
variables are concerned. It is of course necessary in this
case, too, to ensure that the pH value of the drilling mud
is kept at least in the mildly alkaline range and that a
sufficient quantity of alkali reserve is available for
unexpected inrushes of, in particular, acidic gases. At
the same time, however, the ester hydrolysis should not be
undesirably promoted and/or accelerated by such an alkali
content.
Thus, in the preferred embodiment of the invention, no
significant quantities of highly hydrophilic, inorganic
and/or organic bases are used in the oil mud. In particu-
lar, the invention does not use alkali hydroxides or highly
hydrophilic amines of the diethanolamine and/or triethanol-
amine type. Lime may be effectively used as the alkali re-
serve. In that case, however, it is best to limit the max-
imum quantity of lime used in the drilling mud to around 2
lb/bbl or slightly lower, for example to between 1 and 1.8
lb/bbl (lime/drilling mudj. In addition to or instead of
lime, it is also possible to use other known alkali
reserves, including in particular the less basic metal
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oxides of the zinc oxide type and other comparable zinc
compounds. However, even where acid-binding agents such
as
these are used, it is important not to use excessive
amounts to prevent unwanted premature ageing of the
drilling mud accompanied by an increase in viscosity and
hence a deterioration in the rheologic properties. The
particular aspect of the teaching according to the inv
-
en
tion prevents or at least limits the formation of
unwanted
quantities of highly active o/w emulsifiers to such
an
extent that the favorable rheologic properties are
maintained for long periods in operation, even in the event
of thermal ageing. In relation to the recommendations of
the prior art which have hitherto remained in the realm of
theoretical considerations, this represents a significant
surplus which actually enables the low toxic properties of
ester oils of the present type to be utilized in practice
for the first time.
The esters based on olefinically unsaturated C~6_z4
monocarboxylic acids defined in accordance with the inven-
tion, which flow and can be pumped at temperatures in the
range from 0 to 5'C, generally make up at least about half
the continuous oil phase of the drilling mud. However,
preferred oil phases are those in which esters or ester
mixtures of the type according to the invention are very
much predominantly present. In one particularly important
embodiment of the invention, the oil phase consists almost
entirely of such ester oils. Components suitable for mix-
ing with the ester oils defined in accordance with the in-
vention are, in particular, selected other ester oil frac-
3 0 tiOns which are described in copending Canadian application
Serial No. 2,006,009 "Drilling Fluids and Muds Containing Selected
Ester oils", filed of even date herewith. The invention
also encompasses mixtures with such other selected ester
oils. These ester oils, which are described in the above
copending application,
are esters of monofunctional Cz.~z alcohols and saturated
aliphatic C~z_~6 monocarboxylic acids.
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The following rheologic data apply to the rheology of
preferred invert drilling muds according to the invention:
plastic viscosity (PV) in the range of from 10 to 60 mPa.s
and preferably in the range of from 15 to 40 mPa.s, yield
point (YP) in the range of from 5 to 40 1b/100 ft2 and
preferably in the range of from 10 to 25 1b/100 ftz
as
,
measured at 50'C. Full information on the determination of
these parameters, on the measurement techniques used and on
the otherwise standard composition of the invert oil muds
described herein can be found in the prior art cited above
and, for example, in "Manual of Drilling Fluids Technology"
published by BAROID DRILLING FLUIDS, INC., cf. in
particular the Chapter entitled "Mud Testing - Tools and
Techniques" and "Oil Mud Technology", which is freely
available to interested experts. In the interests of
fullness of disclosure, the following summary observations
may be made:
Emulsifiers suitable for use in practice are systems
which are capable of forming the required w/o emulsions.
Selected oleophilic fatty acid salts, for example those
based on amidoamine compounds, are particularly suitable,
examples being described in the already cited U.S. Patent
No. 4,374,737 and the literature cited therein. One
particularly suitable type of emulsifier is the product
marketed under the name of "EZ-MULi'" by BAROID DRILLING
FLUIDS, INC.
Emulsifiers of the above type are marketed in the form
of concentrates and can be used, for example, in quantities
of from 2.5 to 5% by weight and more especially in
quantities of from 3 to 4% by weight, based in each case on
the ester oil phase.
In practice, organophilic lignite is used as a fluid-
loss additive and forms an impervious coating in the form
of a substantially water-impermeable film over the walls of
the well. Suitable quantities are, for example, in the
range of from 15 to 20 lb/bbl or in the range of from 5
to 7% by weight, based on the ester oil phase.
14
20~16~.(~
In drilling muds of the present type, the thickener
normally used to create viscosity is a cationically
modified, finely divided organophilic bentonite which can
be used in quantities of from 8 to 10 lb/bbl or in the
range of from 2 to 4% by weight, based on the ester oil
phase. The weighting agent normally used in practice to
establish the necessary pressure equalization is barite
which is added in quantities adapted to the particular
conditions to be expected in the well. For example, it is
l0 possible by addition of barite to increase the specific
gravity of the drilling mud to values of up to about 2.5
and preferably in the range from 1.3 to 1.6.
In invert drilling muds of the present type, the
disperse aqueous phase is charged with soluble salts,
generally calcium chloride and/or potassium chloride, the
aqueous phase preferably being saturated with the soluble
salt at room temperature.
The emulsifiers or emulsifier systems mentioned above
can also be used to improve the oil wettability of the in-
organic weighting materials. In addition to the amino-
amides already discussed, alkyl benzenesulfonates and imi-
dazoline compounds are further examples. Additional
information on the relevant prior art can be found in the
following literature references: GB 2,158,437, EP 229 912
and DE 32 47 123.
One important application for the new drilling
fluids is in offshore drilling for the development of oil
and/or gas sources, to provide technically useful drilling
fluids of high ecological compatibility. The use of the
new drilling fluids is of particular importance in, but is
not limited to, the offshore sector. The new drilling
fluids can also be used quite generally for land-supported
drilling, including for example geothermal drilling, water
drilling, geoscientific drilling and mine drilling. In
this case, too, the ester-based drilling fluids selected in
accordance with the invention basically simplify ecotoxic
problems to a considerable extent. In addition, the
zoosolo
drilling fluids based in accordance with the invention on
the co-use of ester oils of the described type are also
distinguished by distinctly improved lubricity. This is
particularly important when the path of the drill pipe and
hence the well deviate from the vertical during drilling,
for example at considerable depths. In such cases, the
rotating drill pipe readily comes into contact with the
well wall and embeds itself therein. Ester oils of the
type used as oil phase in accordance with the invention
have a distinctly better lubricating effect than the
mineral oils hitherto used, which is an important advantage
of the present invention.
The invention will be illustrated but not limited by
the following examples.
EXAMPLES
EXAMPLE 1
An invert drilling mud was prepared using an undistil
led isobutyl rapeseed oil ester as the continuous oil
phase. This rapeseed oil ester was based on a mixture of
predominantly unsaturated, straight-chain carboxylic acids
which correspond substantially to the following
distribution: 60% oleic acid, 20% linoleic acid, 9 to 10%
linolenic acid, olefinically unsaturated Czo-z2
monocarboxylic acids approximately 4%, remainder saturated
monocarboxylic acids predominantly in the C~b_~8 range.
The rapeseed oil ester used had the following charac-
teristic data: density (20'C) 0.872 g/cm3; pour point below
-15°C; flash point (DIN 51584) above 180'C; acid value
(DGF-C-V 2) 1.2; viscosity at 0°C 32 mPa.s, viscosity at
5°C 24 mPa.s; no aromatic compounds.
An invert drilling mud was conventionally prepared us-
ing the following mixture constituents:
230 ml rapeseed oil fatty acid ester
26 ml water
6 g organophilic bentonite (GELTONEt", a product
of BAROID DRILLING FLUIDS, INC. of Aberdeen,
Scotland)
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X006010
0.2 g lime
6 g water in oil emulsifier ("EZ-MULt'~~, a product
of BAROID DRILLING FLUIDS, INC.)
340 g barite
9.2 g CaClz x 2H20
20 g organophilic lignite ("DURATONEL"'", a product
of BAROID DRILLING FLUIDS, INC.)
Plastic viscosity (PV), yield point (YP) and gel
strength after 10 seconds and 10 minutes were first deter-
mined on the material before ageing by viscosity measure-
ment at 50°C.
The invert drilling mud was then aged for 16 h at
125°C in an autoclave in a so-called "roller oven" to
determine the effect of temperature on the stability of the
emulsion. The viscosity values were then redetermined at
50°C.
The following results were obtained:
Unaged Aged
material material
Plastic viscosity (PV) 35 62
Yield point (YP) 21 24
Gel strength (1b/100 ft2)
10 seconds 12 12
10 minutes 14 15
COMPARISON EXAMPLE 1
Another invert drilling mud was prepared in the same
way as in Example 1, except that on this occasion the quan-
tity of lime was increased to 4 g, i.e. drastically beyond
the limit of approximately 2 lb/bbl.
Once again, the viscosity values and gel strength of
the material were determined before and after ageing. The
following results were obtained:
17
2006010
Unaged Aged
material material
Plastic viscosity (PV) 41 cannot
be meas-
ured
Yield point (YP) 22 cannot
be meas-
ured
Gel strength (1b/100 ft2)
10 seconds 11 74
10 minutes 17 72
EXAMPLE 2
Another invert drilling mud was prepared with a
continuous oil phase. The oil phase consisted of distilled
oleic acid isobutyl ester which has the following
characteristic data: density (20°C) 0.86 g/cm3; viscosity
(20°C) 8 to 10 mPa.s; pour point below -25°C; flash point
(DIN 51584) above 185°C; acid value (DGF-C-V 2) below 1; no
aromatic compounds.
A drilling mud of the following composition was
prepared:
210 ml isobutyl oleate
6 g fatty-acid-based emulsifier (INVERMULtma
product of BAROID DRILLING FLUIDS, INC.)
6 g organophilic bentonite (GELTONE Iltm a product
of BAROID DRILLING FLUIDS, INC.)
13 g organophilic lignite (DURATONEt', a product
of BAROID DRILLING FLUIDS, INC.)
1 g lime
3 g water in oil emulsifier (EZ-MULt', a product
of BAROID DRILLING FLUIDS, INC.)
270 g barite
58.2 g saturated aqueous CaCl2 solution
18
CA 02006010 2003-02-21
Plastic viscosity, yield point and gel strength after
seconds and 10 minutes were determined before and after
ageing (16h at 125°C in a roller oven) in the same way as in
Example 1. The results obtained are shown below. In the
5 formulation used here, 1.9 g added lime substantially
corresponds to the limit of 2 lb/bbl of alkali reserve.
Unaged Aged
material material
Plastic viscosity (PV) 46 41
Yield point (YP) 35 32
Gel strength (1b/100 ftz)
10 seconds 17 18
10 minutes 21 29
EXAMPLE 3
Another invert drilling oil emulsion was prepared using
the formulation of Example 2, except that the addition of lime
was increased to 2 g and hence to within the limit of about 2
lb/bbl of alkali reserve. The plastic viscosity, yield point and
gel strength of the material before and after ageing are shown in
the following:
Unaged Aged
material material
Plastic viscosity (PV) 53 46
Yield point (YP) 61 45
Gel strength (1b/100 ft2)
10 seconds 33 24
10 minutes 40 29
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