Note: Descriptions are shown in the official language in which they were submitted.
2006009
Patent
Docket No. D 8524
DRILLING FLUIDS lIND MUDB
CONTAINING SELECTED E8TER OILS
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. Statement 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
solids. Such emulsions are of the w/o emulsion type, i.e.
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 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
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.
Oil-based drilling fluids were originally made from
1
2006009
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, ~. 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 arid 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
U.S. patents cited above mentions the use of such natural
ester 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
mentions 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-purity tall oil tatty acids. An ester of a
* Trade-mark
2
A'
2006009
monofunctional alcohol and monofunctional carboxylic acids,
mentioned for the first time here, is described as
equivalent to triglycerides of natural origin and/or de-
aromaticized hydrocarbon fractions.
The cited U.S. patent does not contain any
reproducible Examples relating to the use of such an ester
of monofunctional 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 of the above type 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-
cohols derived from those oils or fats are suitable for the
production of such drilling fluids. The second key obser-
3
2006009
-- vation 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 having chain
lengths of up to about C24, more especially the relatively
long-chain acids in the range from about C16 to C22, 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, lead 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
emulsion 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 alkanol wherein the monocarboxylic acid
contains from 12 to 16 carbon atoms and is
aliphatically saturated,
B. a disperse aqueous phase,
C. at least one emulsifier,
D. at least one weighting agent,
4
2i10~i~09
,.~.,A 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-C12, more especially C4-C12 alcohols
(alkanols) and saturated aliphatic C12-C16 monocarboxylic
acids or mixtures thereof with at most equal quantities of
other 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 together with emulsifiers, weighting agents, fluid
loss additives and, if desired, other standard additives
30
4a
;~oo~oo~
....a.
such as gellants.
In another embodiment, the invention relates to
mineral-oil-free invert drilling muds which are suitable
for the offshore development of oil and gas sources and, in
a continuous oil phase based on ester oils, contain a dis-
perse aqueous phase together with emulsifiers, weighting
agents, fluid loss additives and, if desired, other stand-
ard additives, wherein the oil phase consists at least
substantially of esters of monofunctional C2_~2 alcohols and
saturated aliphatic C~Z_~6 monocarboxylic acids. According
to one preferred element of the invention, the ester oils
of the continuous oil phase have a Brookfield (RVT)
viscosity of no more than 50 mPa.s at a temperature in the
range from 0 to 5C.
In one particularly preferred embodiment of the two
embodiments of the invention as described above, at least
the predominant part, i.e. at Ieast 50$, preferably at
least 60$, of the ester oils used is based on saturated
aliphatic C~2-C~' monocarboxylic acids.
In one important embodiment, the ester oil contains
only saturated aliphatic monocarboxylic acids of the
broader C~2_~6 range mentioned, but more especially of the
C~2_~4 range. However, the invention is by no means confined
to this. It can be of advantage to use esters of other
carboxylic acids in at most substantially the same quantity
as the above esters, but preferably in smaller quantities.
Where other esters are present, esters of relatively short-
chain aliphatic monocarboxylic acids and/or esters of
relatively long-chain carboxylic acids can be present.
However, in cases where esters of relatively long-chain
carboxylic acids are used, it is preferred at least partly
to use corresponding mono- and/or polyolefinically
unsaturated, relatively long-chain carboxylic acid
derivatives. In this embodiment, suitable mixture
components are, especially, mono- and/or polyolefinically
unsaturated C~6.Zi and more especially C~a_u monocarboxylic
acid esters.
5
2006ppg
.~.~.
In another important and preferred embodiment of the
invention which is discussed in more detail hereinafter,
significant quantities of strong hydrophilic bases, such as
alkali metal hydroxides and/or diethanolamine, are not used
in the invert drilling mud where the ester oils defined
herein are present.
It is known that state-of-the-art invert drilling muds
incorporating a continuous oil phase always contain an
alkali reserve, particularly for protection against
inrushes of C02 and/or H2S into the drilling mud and hence
for protecting metal parts of the drill pipe against
corrosion. A useful alkali (alkaline) reserve in the
context of the teaching of the invention comprises the
addition of lime (calcium hydroxide) or the co-use of more
weakly basic metal oxides, for example of the zinc oxide
type and/or other zinc compounds. Further particulars of
these elements of the teaching of the invention are given
hereinafter. 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 the predominant part thereof are discussed first in
the following.
The ester oils used in accordance with the invention
of monofunctional alcohols and selected monocarboxylic
acids can be derived from either straight or branched
hydrocarbon chains. Preferred are the esters of straight-
chain acids. Saturated C~2_~6 and more especially
monocarboxylic acids and monofunctional alcohols having the
C chain lengths defined in accordance with the invention
3o can form ester oils which show adequate rheologic
properties, even down to temperatures in the range of from
0 to 5'C, and in particular are flowable and pumpable in
that temperature range. In the context of the invention,
preferred esters for the oil phase of drilling muds are
saturated compounds which have a Brookffeld (RVT) viscosity
at a temperature of 0 to 5'C of no more than 50 mPa.s and
preferably of no more than 40 mPa.s. By selecting suitable
6
A.
2oosflc~~
components for the ester-forming reaction, it is possible
to adjust the viscosity at temperatures in the above-
mentioned range to values of at most 30 mPa.s, for example
in the range of from 10 to 20 mPa.s. It is clear that this
affords important advantages for offshore drilling where
the surrounding water can have very low temperatures.
In a preferred embodiment, the ester oils used in
accordance with the invention based on selected individual
components or on ester mixtures have solidification values
to (pour point and setting point) below -10C and more
especially below -15C. Despite this high mobility at low
temperatures, the molecular size of the ester oil in
accordance with the invention ensures that the flash points
of the ester oils are sufficiently high, being at least
80C, but generally exceeding a temperature limit of about
100C. Ester oils having flash points above 150-160C are
preferred. It is possible to produce ester oils of the
described type which have flash points of 185'C or higher.
In another important embodiment, the ester oils of the
range required in accordance with the invention for the
saturated Ciz.~b monocarboxylic acids are derived from
materials of predominantly vegetable origin. Carboxylic
acids or carboxylic acid mixtures predominantly containing
saturated monocarboxylic acids within the stated range can
be obtained, for example, from renewable triglycerides,
such as coconut oil, palm kernel oil and/or babassu oil.
Fatty acid mixtures of this origin normally contain a
limited quantity of lower fatty acids (Cs_~o) of generally at
most about 15%. Their content of C~2_ acids is by far
predominant, generally making up at least 50% and normally
60% or more of the carboxylic acid mixture. The small
remainder consists of higher fatty acids, with unsaturated
components playing a considerab?.e role. Accordingly,
carboxylic acid mixtures of this type, by virtue of their
natural structure, readily lead to materials having
satisfactory rheologic properties.
In one embodiment of the invention, suitable mixture
7
2oosoo9
components likewise of natural origin are, in particular,
monofunctional ester oils of the type described in co-
pending Canadian application Serial No. 2,006,010, filed
of even date herewith, "The Use of Selected Ester Oils in
Drilling Fluids and Muds". In the context of the teaching
of the present invention, however, these mixture components
are preferably used in small quantities (at most about 49%,
based on the ester oil mixture). To complete the
disclosure of the invention, this class of possible mixture
components is briefly discussed in the following. Further
particulars can be found in the above co-pending
application.
These possible mixture components are esters of
monofunctional CZ_~2 alcohols and mono- and/or polyolefini-
cally unsaturated 06_24 monocarboxylic acids. In this case,
too, the carboxylic acids can be derived from unbranched or
branched hydrocarbon chains, particular significance again
being attributed the straight-chain acids. Esters of the
higher chain lengths in question here are flowable and
pumpable down to temperatures of 0 to 5'C, providing an
adequate level of olefinically unsaturated ester
constituents is guaranteed. In the preferred embodiment of
the invention, therefore, esters of this type, of which
more than 70% by weight and preferably more than 80% by
weight are derived from olefinically unsaturated C
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 provides
benefits in addition to a single ethylenic double bond in
the molecule.
These esters of unsaturated, relatively long-chain
8
A
2oosoo9
monocarboxylic acids used as a mixture component with the
esters of the present invention preferably have
solidification values (pour point and setting point) below
-10'C and more especially below -15'C. By virtue of the
size of their molecule, these mixture components also have
flash points in the desired range, i.e. at least above
80C, preferably above 100'C and more especially above
160'C. In the preferred embodiment, mixture components of
this type have Brookfield (RVT) viscosities at 0 to 5C of
no more than 55 mPa.s and preferably of at most 45 mPa.s.
Among these highly unsaturated mixture components,
there are two sub-classes of particular importance.
The first of these sub-classes is based on unsaturated
06_24 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
polyunsaturated carboxylic acid residues in the ester oil
is comparatively limited. Within this sub-class, however,
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 practical signifi-
cance is derived from C~6_2' monocarboxylic acid mixtures of
which more than 45% by weight and preferably more than 55%
by weight are derived from diolefinically and/or polyole-
finically unsaturated acids within the C range mentioned.
The most important monoethylenically unsaturated car-
boxylic acids within the range in question here are hexa-
decenoic acid [palmitoleic acid (C~6), oleic acid (C~8), the
related ricinoleic acid (C~a) and erucic acid (Cu)]. The
most important di-unsaturated carboxylic acid within the
range in question here is linoleic acid (C~a) while the most
important triethylenically unsaturated carboxylic acid is
linolenic acid (C~a) .
Selected individuals of the ester type formed from an
unsaturated monocarboxylic acid and a monoalcohol may be
used as mixture component. One example of such esters are
9
2006009
the esters of oleic acid, for example of the oleic acid
isobutyl ester type. So far as the Theology of the system
is concerned and/or for reasons of availability, it is
frequently desirable to use acid mixtures.
Vegetable oils of natural origin, of which the
hydrolysis or transesterification gives mixtures of
carboxylic acids or carboxylic acid esters of the first
sub-class mentioned above are, for example palm oil, peanut
oil, castor oil and, in particular, rapeseed oil. Suitable
to 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.
Carboxylic acid mixtures of the second sub-class
mentioned above are also widely available from natural fats
of vegetable and/or animal origin. Classic examples of
oils which have a high content of C~6_~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. A
typical example of an animal starting material for the
production of corresponding carboxylic acid mixtures is
fish oil, particularly herring oil.
Another factor to be taken into consideration in the
choice of the saturated ester oils used in accordance with
the invention, particularly the mixtures of ester oils with
the unsaturated ester oils described above, is that
saturated carboxylic acid esters containing 16 and more C
atoms can have comparatively high boiling points and hence
readily give rise to rheologic difficulties. According to
the invention, therefore, saturated carboxylic acids
containing 16-18 or more C atoms preferably make up no more
than about 20% by weight and, in particular, no more than
about 10% by weight of the ester oils of the invention.
By contrast, the presence of saturated carboxylic
acids containing less than 12 carbon atoms is more accept-
2oosoo~
able. On the contrary, they can be valuable mixture
components for the ester oil phases selected in accordance
with the invention. Their esters are as invulnerable to
oxidation under practical in-use conditions as the
saturated principal ester components of the invention,
particularly in the C~2_~4 range. The rheologic properties
of the lower fatty acid esters promote the objective of the
invention, namely to replace the pure hydrocarbon oils
hitherto solely used in practice at least partly,
preferably predominantly or even completely by ester oils
or ester oil fractions.
The alcohol radicals of the esters or ester mixtures
of the invention are preferably derived from straight-
chain and/or branched-chain saturated alcohols, preferably
alcohols containing at least 4 C atoms and, more preferably
to alcohols 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 invention 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 can be partly or
completely replaced by corresponding components of
synthetic origin. Typical examples of alcohols are the
corresponding oxo alcohols (branched alcohols) and the
linear alcohols obtained by the Ziegler process.
Similarly, monocarboxylic acid components present in par-
ticular in carboxylic acid mixtures can be derived from
petrochemical synthesis. However, the advantages of start-
ing 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
anaerobically degradable.
11
20flfl009
However, another important aspect of using ester oils
of the present invention as sole or predominant
constituents in invert oil muds has to be taken into
consideration. This concerns the difficulty mentioned at
the beginning that, in principle, the carboxylic acid
esters are vulnerable to hydrolysis and, accordingly,
behave differently from the pure hydrolysis-stable
hydrocarbon oils hitherto used.
Invert drilling muds of the present type 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. 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 present
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 of from
pH 8.5 to 9 and higher.
In oil muds based on pure hydrocarbon fractions as the
oil phase, strongly alkaline and, at the same time, highly
hydrophilic inorganic or organic additives are generally
used in practice without any difficulty. The alkali metal
hydroxides and, in particular, sodium hydroxide as well as
highly hydrophilic organic bases, e.g. diethanolamine
and/or triethanolamine are particularly typical additives
for binding impurities of H2S. In addition to and/or
instead of the above highly hydrophilic inorganic and
12
;~oo~oc~~
organic bases, lime or even more weakly basic metal oxides,
especially zinc oxide and other zinc compounds, are
particularly important as the alkali reserve. Lime in par-
ticular is widely used as 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 ester-based oil muds of the present
invention requires a departure from standard practice so
l0 far as these variables are concerned. It is of course
necessary in the present 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 an
alkaline 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 alkaline 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 metal hydroxides or
highly hydrophilic amines of the diethanolamine and/or
triethanolamine type. Lime can be effectively used as the
alkali reserve. In that case, however, it is best to limit
the maximum 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 mud). In addition to or
instead of lime, it is also possible to use other known
alkaline reserves, including in particular the less basic
metal oxides of the zinc oxide type. 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 invention prevents or at least limits the
formation of unwanted quantities of highly active o/w
13
2oosao9
emulsifiers to such an extent that the favorable rheologic
properties are maintained for long periods in operation,
even in the event of thermal ageing. Zn relation to the
recommendations of the prior art which have hitherto
remained in the realm of theoretical considerations, this
represents a significant advance in the art 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 saturated C~2_~6 monocarboxylic
acids defined in accordance with the invention, which flow
and can be pumped at temperatures in the range from 0 to
5C, generally make up at least about half the continuous
oil phase of the drilling mud. However, preferred oil
phases are those in which esters 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. As
discussed above, components suitable for mixing with the
ester oils defined in accordance with the invention are the
ester compounds described in the above co-pending
application 2,006,010. The invention also encompasses
mixtures with such other selected ester oils.
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 lb/100 ft2 and
preferably in the range of from 10 to 25 lb/100 ftt, 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., ~. 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
14
A
;~oosoo9
fullness of disclosure, the following descriptions of other
components of the drilling muds of the invention are given.
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 previously cited U.S.
4,374,737 and the literature cited therein. One
particularly suitable type of emulsifier is the product
marketed under the name of "EZ-MULt"'" by BAROID DRILLING
FLUIDS, iNC., of Aberdeen, Scotland. Emulsifiers of this
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, hence, for forming 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.
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 baryta
which is added in quantities adapted to the particular
conditions to be expected in the well. For example, it is
possible by addition of baryta to increase the specific
gravity of the drilling mud to values of up to 2.5 and
preferably in the range of from 1.3 to 1.6.
In invert drilling muds of the present type, the
disperse aqueous phase is charged with soluble salts,
2006009
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 discussed above
can also be used to improve the oil wettability of the in-
organic weighting materials. In addition to the amino-
amides already mentioned, alkyl benzenesulfonates and imi-
dazoline compounds are as 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
and muds is in offshore drilling for the development of oil
and/or gas sources. The drilling fluids and muds of the
invention have high ecological compatibility. The use of
the new drilling fluids and muds is of particular
importance in, but is not limited, to, the offshore sector.
The new drilling fluids and muds can also be used quite
generally for land-supported drilling, including for
2o 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 to the above advantages, the drilling
fluids based in accordance with the invention on the use or
co-use of ester oils of the described type are also dis-
tinguished 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 in
accordance with the invention have a distinctly better
lubricating effect than the mineral oils hitherto used,
which is an important advantage of the teaching of the
invention.
16
2006009
The invention will be illustrated but not limited by
the following examples.
EXAMPLES
In Examples 1 and 2 below and the Comparison Examples,
distilled lauric acid/n-hexyl ester is used as the ester
oil for forming the continuous oil phase. It is a whitish-
yellow liquid with a flash point above 165'C, a pour point
below -5'C, a density (20'C) of from 0.857 to 0.861, an
iodine value and an acid value both below 1, a water
content below 0.3% and the following viscosity data
(Brookfield mPa.s): 22.5 to 25.5 at -5°C; 15 to 18 at +2°C;
to 18 at +5'C; approx. 15 at +10'C; 12 to 14 at 20°C.
15 EXAMPLE 1
A water in oil invert drilling mud was prepared in
known manner from the components listed below, after which
the viscosity data of the material before and after ageing
were determined as follows:
Measurement of viscosity at 50'C in an NL Baroid Fann
35 viscosimeter. Plastic viscosity (PV), yield point (YP)
and gel strength (lb/100 ftz) after 10 secs. and 10 mins.
were determined in known manner.
The measurements were carried out both before and
after ageing of the material, ageing being obtained by
treatment in an autoclave - in a so-called roller over
for 16 h at 125'C.
The following composition was selected for the
drilling mud:
230 ml ester oil
26 ml water
6 g organophilic bentonite (GELTONEt'"II, a product
of BAROID DRILLING FLUIDS, INC.)
3 5 6 g organophi 1 is 1 ignite ( DURATONEt", a product of
BAROID DRILLING FLUIDS, INC.j
1 g lime
6 g water in oil emulsifier (EZ-MULa", a product
of BAROID DRILLING FLUIDS, INC.)
17
X006009
346 g barite
9.2 g CaCl2 x 2H20
In this formulation, approximately 1.35 g lime
correspond to the limit of 2 lb/bbl.
The characteristic data determined on the material
before and after ageing as described above are shown in the
following Table:
Unaged Aged
material material
Plastic viscosity (PV) 28 28
Yield point (YP) 11 14
Gel strength (lb/100 ft2)
10 seconds 5 6
10 minutes 7
COMPARISON EXAMPLE 1
The invert drilling mud of Example 1 Was prepared
using the same quantities except that, on this occasion,
the quantity of lime was increased three times (3 g).
The characteristic data determined before and after
ageing of the material are shown in the following Table:
Unaged Aged
material material
Plastic viscosity (PV) 31 72
Yield point (YP) 8 59
Gel strength (lb/100 ft2)
10 seconds 5 13
10 minutes 7 74
EXAMPLE 2
A particularly heavily weighted invert drilling mud
18
2006009
was prepared in accordance with the following formulation:
184 ml ester oil
ml water
2 g organophilic bentonite (GELTONEt"' II, a
5 product of BAROID DRILLING FLUIDS, INC.)
g organophilic lignite (DURATONEt"', a product
of BAROID DRILLING FLUIDS, INC.)
l0 1 g lime
10 g water in oil emulsifier (EZ-MULt'", a product
of BAROID DRILLING FLUIDS, INC.)
15 568 g barite
4.8 g CaCl2 x 2 A20
The characteristic data of the material were
20 determined before and after ageing as in Example 1. The
values obtained are shown in the following Table:
Unaged Aged
material material
Plastic viscosity (PV) 20 81
Yield point (YP) 12 16
Gel strength (lb/100 ft2)
10 seconds 8 8
l0 minutes 10 11
In this Example, approximately 1.04 g lime correspond
to the limit of 2 lb/bbl.
COMPARISON EXAMPLE 2
The heavily weighted formulation of Example 2 was
repeated, except that the lime content was doubled (2 g).
The characteristic data of the material before and
after ageing were again determined and are shown in the
following Table:
Unaged Aged
material material
19
20U60~9
Plastic viscosity (PV) 78 73
Yield point (YP) 37 59
Gel strength (lb/100 ftz)
seconds 12 18
10 minutes 16 27
The ester oil used to form the continuous oil phase in
Examples 3 and 4 below is an ester mixture of substantially
saturated fatty acids based on palm kernel oil and 2-ethyl
hexanol, of which by far the predominant part is made up of
C~2_~4 fatty acids and which corresponds to the following
composition:
C8 . 3.5 to 4.5% by weight
Coo: 3.5 to 4.5% by weight
C~2: 65 to 70% by weight
2o C~': 20 to 24% by weight
C~6: Approx . 2 % by weight
B: 0.3 to 1% by weight
The ester mixture is present in the form of a light
yellow liquid with a flash point above 165°C, a pour point
below -10°C, a density (20°C) of 0.86 and an acid value
below 0.3. In the low-temperature range, the ester mixture
shows the following viscosity data (Brookfield, Mass.):
-5°C 20 to 22: 0°C 16 to 17; +5°C 13 to 15; +10°C
approx. 11:
20°C 7 to 9.
EXAMPLE 3
As in the preceding Examples, a w/o invert drilling
mud was prepared from the following components. The
viscosity data of the material were determined before and
after ageing.
.The following composition was selected for the
drilling mud:
230 ml ester oil
6 g emulsifier 1 (INVERMULt'NT, a product of
NL Baroid of Aberdeen, Scotland)
2006009
26 g water
6 g organophilic bentonite (GELTONEt"')
12 g organophilic lignite (DURATONEt"')
1.5 g lime
6 g emulsifier 2 (EZ-MULt'")
346 g barite
9.2 g CaCl2 X 2HZ0
The characteristic data determined on the material
before and after ageing are shown in the following table:
Unaged Aged
material material
Plastic viscosity (PV) 37 30
Yield point (YP) 16 14
Gel strength (lb/100 ft2)
10 seconds 7 5
10 minutes 10 g
EXAMPLE 4
A 40% water-containing w/o invert drilling mud having
the following composition was prepared using the ester oil
of Example 3.
350 ml ester oil
20 g emulsifier (EZ-MULt~)
8 g organophilic lignite (DURATONEt')
4 g lime
6 g organophilic bentonite (GELTONEt'j
234 ml water
99 g CaCl2 X 2H20
150 g barite
The material showed the following plastic viscosity
and yield point values before and after ageing:
Unaged Aged
material material
21
Image
