Note: Descriptions are shown in the official language in which they were submitted.
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DRILLING FLUID, APPARATUS, AND METHOD
TECHNICAL FIELD OF THE INVENTION
The invention is in the area of drilling fluids used in connection with
drilling
wells, such as oil wells and water wells. The invention is also directed
towards a drilling
apparatus and process.
BACKGROUND OF THE INVENTION
In drilling a well or other similar borehole, a drill bit is operatively
coupled,
usually by a drill string, to a drive which rotates the drill bit to cause the
drill bit to bore
into the earth. A drilling fluid, or drilling mud, is circulated through the
borehole
annulus. . The drilling fluid passes through the drilling string and to the
surface through
the drill bit for cooling and lubricating the drill bit and for carrying rock
cuttings
generated by the cutting action of the bit to the surface. The drilling fluid
may be a gas,
2 5 but more typically is a liquid.
Many liquids suitable for use as drilling fluids are known. Some drilling
fluids
are oil-based. Such oil-based fluids suffer from a number of drawbacks,
particularly,
their adverse effects on the environment. Oil-based fluids also can be costly
to purchase
and to dispose of.
2 0 Other drilling fluids are water-based or constitute an emulsion of oil in
water or
water in oil. Such fluids often are inexpensive compared to oil-based fluids,
and are less
costly to dispose of. Water-based fluids also pose less of a risk to the
environment than
do oil-based fluids. One drawback associated with water-based fluids is that
the water
in the fluid tends to promote borehole instability, particularly when shale is
encountered
2 5 in the drilling process. The water-based fluid may adsorb and absorb into
pores in the
shale, thus causing the shale to swell and thereby tending to cause the
borehole to
collapse.
In recognition of this drawback, water-based drilling fluids have incorporated
an
allcyl glycoside, such as methyl glucoside, into the drilling fluid. It is
known that methyl
3 0 glucoside serves as a borehole stabilizing agent that functions by
inhibiting shale
swelling. The mechanism of action of methyl glucoside is not fully understood,
but is
believed to be associated with gel formation or an ion exchange phenomenon. It
is
generally believed that the methyl glucoside, in adding gel strength to the
drilling fluid,
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2
causes more rapid formation of filter cake on the borehole wall thereby
allowing less
water filtrate to reach the surrounding shales. This is believed to reduce
swelling and
sloughing of the shale.
While known drilling fluids that include methyl glucoside are satisfactory,
there
remains room for improvement in such fluids in the area of borehole stability.
It is a
general object of the invention to provide a drilling fluid that is suitable
for use in
borehole drilling. Another general object is to provide a drilling apparatus
and process
that incorporate the drilling fluid of the invention.
1 o THE INVENTION
It has now been discovered that both maltodextrins, on the one hand, and
hemicellulose-containing materials, on the other hand, function to assist
glycosides in
promoting borehole stability in a drilling fluid. It has.further been found
that
carboxyalkyl starches, in particular carboxymethyl starches, also function to
assist
glycosides in promoting borehole stability. Surprisingly, these ingredients
promote
borehole stability more so than other organic species of similar origin or
chemical
structure when used in conjunction with an alkyl glucoside. In accordance with
the
invention, a drilling fluid comprises a liquid base, an alkyl glycoside, which
preferably is
methyl glucoside; and a borehole stability promoter that comprises a
maltodextrin, a
2 0 carboxyalkyl starch, and/or hemicellulose. Also encompassed by the
invention is a
drilling fluid that includes methyl glucoside and cellulose. The invention
also
encompasses a drilling apparatus and a process for drilling. The drilling
apparatus
comprises a drilling string that is fluidically coupled to a source of
drilling fluid, the
drilling fluid including in one embodiment a liquid base, an alkyl glycoside,
and one or
2 5 more of a maltodextrin, a carboxyalkyl starch, and a hemicellulose-
containing material
and, in another embodiment, a liquid base, an alkyl glycoside, and cellulose.
The
process of the invention includes the steps of circulating the drilling fluid
of the
invention through a drill string as a borehole is cut into the earth,
optionally in
conjunction with hemicellulose, a maltodextrin, a carboxyalkyl starch and/or
cellulose.
3 0 It has further been found that desugared molasses functions effectively as
a
borehole stabilizing agent. In accordance with another embodiment of the
invention, a
drilling fluid comprises a liquid base, optionally an alkyl glucoside, and a
borehole
stabilizing agent that comprises desugared molasses solids. Also encompassed
by this
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3
embodiment of the invention are a drilling apparatus and a process for
drilling. More
generally, the various boreholes stabilizing agents discussed hereinabove may
be
combined with the alkyl glucoside to form a drilling fluid. Thus, for
instance, the
drilling fluid may comprise an alkyl glucoside, desugared molasses solids, and
one or
more of hemicellulose, a maltodextrin, and a carboxyalkyl starch.
Alternatively, the
molasses solids may be solids from a molasses that has not been desugared.
It has further been found that sorbitol functions as a borehole stabilizing
agent,
alone in a liquid base or in combination with molasses solids, an alkyl
glucoside, andlor
a borehole stability promoter. In accordance with one embodiment of the
invention, a
drilling fluid comprises a liquid base, sorbitol, and one or both of an alkyl
glucoside and
molasses solids, optionally in conjunction with a borehole stability promoter.
In
accordance with another embodiment, a drilling apparatus includes a drill
string that is
fluidically coupled to a source of drilling fluid, the drilling liquid
comprising a liquid
base and sorbitol. In yet another embodiment of the invention, a process for
drilling
includes the steps of circulating a drilling fluid through a drill string as a
borehole is
being cut into the earth, the drilling fluid including a liquid base and
sorbitol.
Other features and embodiments of the invention are discussed hereinbelow and
are set forth in the pending claims.
2 0 BRIEF DESCRIPTION OF THE DRAWING
The Figure is a schematic representation of an oil well drilling apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The drilling fluid of the invention generally comprises in one embodiment a
2 5 liquid base, an alkyl glycoside, and a borehole stability promoter, and
may include other
components and additives as may be deemed appropriate. In another embodiment,
the
drilling fluid comprises a liquid base, molasses solids, optionally in
conjunction with an
alkyl glucoside or a borehole stability promoter, and further optionally
including other
components and additives as may be deemed appropriate.
3 0 The liquid base used in the drilling fluid of the invention comprises
water, a
water-miscible liquid, or a mixture of a water-miscible liquid with water. If
the liquid
base includes water, the water may be provided from any suitable source. For
example,
when the oil drilling apparatus is off shore or near the ocean, sea water is
the preferred
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4
liquid base inasmuch as it is freely available. The water may also comprise
treated
water, softened water, tap water, natural or artificial brine, or other
suitable water source.
The water miscible liquid may be glycerine, polyglycerine, a polyether, a
polyol, or other
suitable water miscible liquid. The liquid base may be present in any amount
suitable to
carry, dissolve and/or suspend the components of the drilling fluid.
Preferably, the
liquid base is present in the drilling fluid in a total amount ranging from
about 5 to about
7.5, more preferably, about 5.5 to about 6 lbs./gallon. It is further
contemplated that the
liquid base may be used in an oil-based system that comprises an emulsion of
oil in
water or water in oil.
The drilling fluid of the invention in one embodiment further includes an
allcyl
glycoside. Alkyl glycosides are a known class of industrial chemicals and are
formed by
the substitution of the hemiacetal hydroxyl group of a lower order saccharide
(i.e., a
polysaccharide having a degree of polymerization loss than about 7) with an
alkyl
radical having from one to four carbon atoms. The alkyl radical may be methyl,
ethyl,
propyl, isopropyl, n-butyl, s-butyl or t-butyl, and the saccharide may be, for
example,
glucose, maltose, maltotriose, or maltotetraose.
The alkyl glycoside used in conjunction with the invention is preferably
methyl
glucoside. Most preferably, the methyl glucoside is provided in the form of
MeG-206,
an aqueous methyl glucoside solution sold by Grain Processing Corporation of
2 0 Muscatine, Iowa. MeG-206 is a 60% aqueous solution of methyl glucoside,
the methyl
glucoside being present in a 2:1 ratio of a:(3 isomers (this ratio should be
regarded as
approximate). The methyl glucoside also may be provided in the form of MeG-
365,
also sold by Grain Processing Corporation of Muscatine, Iowa. MeG-365 is a 65%
aqueous solution of methyl glucoside which exists in the solution as a 2:1
ratio of a:(3
2 5 isomers (this ratio also should be regarded as approximate). Another
suitable methyl
glucoside may be provided as a 70% 1:1 (approximate) mixture of a:~i methyl
glucoside
isomers. More generally, any other suitable mixture of methyl glucoside
isomers may
be employed in conjunction with the invention.
The alkyl glycoside may be present in any amount effective to inhibit shale
3 0 swelling. Preferably, when the alkyl glycoside is methyl glucoside, the
methyl glucoside
is present in the drilling fluid in an amount ranging from about 2 to about 4
lbs./gallon
of the drilling fluid (dry basis MeG).
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In another embodiment of the invention, the drilling fluid comprises or
includes
molasses solids. It is contemplated that either molasses solids from molasses
that has
not been desugared or molasses solids from desugared molasses may be employed
in
this embodiment. Molasses is the by-product of the process used to extract
sugar from
5 sugar beet or cane sugar molasses or from other types of molasses (e.g.,
sorghum or
citrus molasses). Preferred embodiments of the invention make use of desugared
sugar
beet molasses or sugar cane molasses (this molasses generally has not been
desugared).
With respect to sugar beet molasses, as is well known in the art, sugar beets
are
used to produce commercial grade sugai that serves as a substitute for the
often more
expensive cane sugar. The older of the two most widely used processes of
removing
sugar from sugar beets involves cleaning the beets and slicing them into thin
chips. The
sliced beets are then subjected to a sugar extraction process whereby hot
water is passed
over the beets for approximately one hour. This process removes most, but not
all, of
the sugar from the beets in the form of beet "juice." The beets are then
pressed in screw
presses to remove the remaining juice therefrom. The juice is then subjected
to a
process called carbonation, whereby small clumps of chalk are provided in the
juice to
filter out any non-sugars. The chalk is then filtered from the juice, which is
then
evaporated a syrup. The syrup is then boiled until sugar crystals form
therein. Once the
crystals form, the resulting mixture is centrifuged to separate the crystals
from the
2 0 remaining product, which remaining product is characterized as molasses.
Desugared
sugar beet molasses preferably is prepared by a process known as the Steffen
process, in
which a calcium precipitate is formed to remove additional sugar. This process
is
described briefly in U.S. Patent No. 5,639,319 to Daly, which purports to
teach the use
of desugared sugar beet molasses as a tire ballast. Another process for
desugaring
2 5 molasses involves an ion exchange reduction of the sugar content. With
respect to cane
sugar molasses and desugared sugar cane molasses, these products may be
obtained via
any method or process known in the art or otherwise found to be suitable.
Likewise,
sugar beet or other types of molasses may be obtained via any other method
known in
the art or found to be suitable.
3 0 In either instance, the molasses is a liquid that contains approximately
60 to 80%
solids, often 60 to 75% solids. The solids contained in the sugar beet or
other molasses
are not particularly well characterized, but generally speaking, the molasses
generally
includes residuals, organic acids, salts, proteinaceous material, and other
materials. In
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6
some embodiments of the invention, molasses or desugared molasses is used
alone as
the drilling fluid in a drilling process or apparatus. For this embodiment,
the, molasses
can be said to comprise a liquid base (water) in which is carried desugared
molasses
solids or, more generally, molasses solids. It should be noted that although
the invention
encompasses embodiments wherein molasses solids are obtained via drying a
molasses
solution to solids, the invention is not limited thereto, and the "liquid
base" and
"molasses solids" or "desugared molasses solids" may together comprise either
conventional molasses or conventional desugared molasses that has been
diluted. More
preferably, the desugared sugar beet molasses or other molasses or desugared
molasses
is diluted with a~ liquid base such as water to a solids content of about 20%
to about
60%. In accordance with a highly preferred embodiment of the invention, the
drilling
fluid includes both an alkyl glucoside and desugared molasses solids. In this
embodiment, the alkyl glucoside and the desugared sugar beet molasses solids
may be
present in any proportion with respect to each other and preferably are
present in a total
solids content in the drilling fluid ranging from about 40% to about 80%.
In some embodiments, the drilling fluid includes sorbitol, in lieu of or in.
addition to molasses solids or an alkyl glucoside. Sorbitol may be obtained
commercially, or may be prepared by hydrogenating glucose. The sorbitol may be
used
in the drilling fluid in any amount effective to inhibit shale swelling.
Preferably, the
2 0 sorbitol is present in an amount of 40-50% solids; more preferably, about
50-70%
solids. One preferred drilling fluid includes 60% sorbitol.
In accordance with preferred embodiments of the invention, the drilling fluid
further includes a borehole stability promoter, sometimes called a stability
agent,
sometimes call a stability agent that is selected from among maltodextrins,
2 5 carboxymethyl starches, and hemicellulose. With respect to hemicellulose,
hemicellulose is a term used to refer to a wide variety of
heteropolysaccharides found
in association with cellulose in plant species. The hemicellulose functions to
inhibit
shale swelling, and may further function as a fluid loss control agent. The
hemicellulose may be added in a purified form. Most preferably, the
hemicellulose-
3 0 containing material is produced in accordance with the teachings of U.S.
Patent
4,038,481 (.Antrim et al.), which discloses the alkaline hydrolysis of corn
hulls to yield
plural phases including a hemicellulose-rich fraction. The hemicellulose-rich
fraction
prepared in accordance with the teachings of this patent may be used as the
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7
hemicellulose-containing material without subsequent isolation or
purification, or this
fraction may be concentrated or otherwise modified. The alkaline hydrolysis
itself
preferably is conducted using potassium hydroxide as the alkaline hydrolyzing
species. Potassium is itself believed to function as a shale stability
enhancer in a
drilling fluid, and thus the potassium hydroxide digest of corn hulls is
believed to be
particularly suitable for use in conjunction with the invention. More
economically, an
unrefined aqueous slurry (for example, an alkaline digest of corn hulls) may
be used.
More generally, hemicellulose may be provided in an unpurified, somewhat
"crude"
form or in a highly purified form with the purer hemicellulose being preferred
from a
technical standpoint, but with cruder forms being more economical. In some
instances a greater amount of the crude hemicellulose may be desired to
achieve the
same results as by adding a purer form of hemicellulose. One form of
hemicellulose
is known as "wood molasses." Wood molasses may be obtained commercially; one
wood molasses is sold under the trademark TEMULOSE by Temple-Inland Forest
Products Corp. of Diboll, Texas.
The hemicellulose-containing material is used to provide hemicellulose in the
drilling fluid in an amount effective to inhibit swelling of shale.
Preferably, if the
drilling fluid does not include a maltodextrin, the hemicellulose is present
in an
amount ranging from about 0.002 to about 0.2 lbs./gallon by dry basis weight.
In this
2 0 embodiment of the invention, these amounts are irrespective of the amount
of any
cellulose in the drilling fluid.
The drilling fluid may also include a maltodextrin in lieu of or in addition
to the
hemicellulose-containing material. Maltodextrins are oligo- or poly-
saccharides in
which the saccharides are linked exclusively or predominantly by 1-4 linkages.
In
2 5 preferred embodiments, at least 50 percent of the saccharide units in the
maltodextrin
are linked via 1-4 linkages. More preferably, at least about 60 percent of the
saccharide units are linked via 1-4 linkages; even more preferably, at least
about 80
percent of the saccharide units are so linked. While the drilling fluid may
incorporate
any maltodextrin or mixture of maltodextrin species, the invention is
particularly
3 0 applicable to mixtures of maltodextrin species in which at least a portion
of the
maltodextrins in the mixture have a degree of polymerization (DP) greater than
5.
Preferably, at least one of the maltodextrin species in the mixture has a DP
of 8 or
more. More preferably, at least one species has a DP of at least 10. For
example, in
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8
some embodiments of the invention, a maltodextrin mixture in which at least 80
percent of the maltodextrin species in the mixture have a DP greater than 5.
is used,
and in some such embodiments, preferably at least 60 percent have a DP greater
than
8. In another embodiment, a maltodextrin in which at least 80 percent of the
maltodextrin species have a DP greater than 10 is used. In some embodiments of
the
invention, the DP profile of the maltodextrin is such that at least 75 percent
of the
maltodextrin species in the mixture have a DP greater than 5 and at least 40
percent of
the species in the mixture have a DP greater than 10. The maltodextrins may
include
saccharide species having an odd DP value, and the profile may be partially
defined
by a saccharide species having a DP value of 1, for example, dextrose or
sorbitol. The
mixture further may include other saccharide species or other components. Such
starting materials may be obtained conventionally, for example, by the partial
hydrolysis of starch.
Suitable maltodextrins are sold under the trademark MALTR1N~ by Grain
Processing Corporation of Muscatine, Iowa. The MALTRIN~ maltodextrins are
mixtures of malto-oligosaccharides. Each MALTRIN~ maltodextrin is
characterized by
a typical dextrose equivalent value (DE) and DP profile. Suitable MALTRIN
maltodextrins that may be incorporated as borehole stability promoters in
accordance
with the invention, include, for example, MALTRIN~ M040, MALTRIN~ MO50,
2 o MALTRIN~ M100, MALTRIN~ M150, and MALTRIN~ M180. Typical
approximate DP profiles for the subject Maltrin maltodextrins are set forth in
the
following table (the DP profiles being approximate as indicated in the Table):
CA 02463714 2004-04-13
WO 2004/020546 PCT/US2003/025116
o ~ o o ~ a o 0
+I+I +I II +I1-i+I -II+I
0
~r
0
II
O d' ~ M V d; O~ M W
n . . O
o N cV .- ,--,- ~ O
o
0 0 ~ o o o o o o
_ _ _ _ _ _ _
-1-I-I-I-1-I-I-I-I-I-i-I+I -I-I-1-I
O
O
v~
II
V1 V1 d~ M ~ O 00 . W
00
.-r.-i~ .-~.-.iO O A
.b
0 0 0 0 0 0
o ~ V'7~P'1~i'1~ Vo
~ o
_ _ _ _
"O -f'I'E'l-i'1+I -f'I'H -I'I-i'1-t'I
o O
O O
II
V1 O ~ M t~ N V1 I~ W
M ' A
\pd W VO M d N O
U
0 0 0
o ~ V1 ~ V7V'1V1 0 0
+I+I +I +I -t-I+i +~ +I +I
O
V1
II
00 .~ ~ I~V~ I~ 00 M W O
d' O~ oo ~ we W ~t
D
_
0
O
I
~
o ~ ~ o ~ 0 0 0
_
+I~ ~ ~I +I
O
II
9F
~
p yn ~' O~d: M N ~ W
, ' 0
d'M O~ ~--~V ~O 0 lp
1
aE
4: #
~7E
M !~,
L~ O
O
r1 n o0 t wD v1'd'M N
~
N
A ~ A A
CA 02463714 2004-04-13
WO 2004/020546 PCT/US2003/025116
Other suitable maltodextrins as may be known or discovered also may be
considered
useful in conjunction with the invention.
The maltodextrin may be present in any amount effective to inhibit shale
swelling. When the drilling fluid includes a maltodextrin borehole stability
promoter
5 and does not include hemicellulose, the maltodextrin preferably is present
in a total
amount ranging from about 0.002 to about 0.2 lbs./gallon, more preferably
about 0.01 to
about 0.15 lbs./gallon by dry basis weight of the maltodextrin. In this
embodiment of
the invention, these amounts are irrespective of the amount of cellulose in
the drilling
fluid.
10 The borehole stability promoter alternatively or additionally may comprise
a
carboxyalkyl starch, preferably a carboxymethyl starch. Carboxymethyl starches
are
known in the art, and the preparation of such starches is described in M~~lifi
.d Star .hew
Prc,nertie~ ~nc~ i lies (Wurzburg, O.B., Ed.) 1986 p. 187-88. When the
drilling fluid .
includes a carboxymethyl starch but does not include any other borehole
stability
promoter, the carboxymethyl starch preferably is present in the drilling fluid
in an
amount ranging from about 0.002 to about 0.2 lbs./gallon, more preferably
about 0.01 to
about 0.15 lbs./gallon. In this embodiment, these amounts are irrespective of
the
amount of cellulose in the composition. The carboxyalkyl starch may have a
degree of
substitution (DS) of any suitable value. Adequate results may be obtained when
the
2 o starch has a DS of about 0.2.
The drilling fluid of the invention may incorporate a borehole stability
promoter
that includes a maltodextrin and hemicellulose in any combination of two or
more of the
foregoing. In such case, the total amount of the combined borehole stability
promoter
present in the drilling fluid preferably ranges from about 0.002 to about 0.2
lbs./gallon
2 5 by dry basis weight, irrespective of the amount of cellulose in the
drilling fluid, with the
maltodextrin, starch, and hemicellulose being present in any amount relative
to one
another. More generally, the borehole stability promoter may be present in any
amount
effective to inhibit shale swelling.
The drilling fluid further preferably includes a salt, preferably sodium or
3 0 potassium chloride. Salts are believed to assist the alkyl glycoside or
molasses solids or
sorbitol and/or the borehole stability promoter in inhibiting shale swelling.
When sea
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11
water is used as the liquid base, or when the bore formation includes salt
water, salt will
be present in the form of sodium chloride. Other salts that may be
incorporated in the
composition of the invention include potassium chloride, calcium chloride,
sodium
acetate, potassium acetate, calcium acetate, and the like. The salt is
preferably present in
the drilling fluid in an amount ranging from about 0.15 to about 0.8
lbs./gallon by dry
basis weight but, more generally, may be present in any amount effective to
assist in
inhibiting shale swelling.
The drilling fluid may include fiu-ther additives as may be appropriate.
Examples of additives that are known in the art include barite, and other
weighting
agents, bentonite, low-and-medium-yield clays, salt water clay, iron oxide,
calcium
carbonate, starch, carboxymethylcellulose, acrylonitrile, gums, molecularly
dehydrated
phosphate, tannin compound; quebracho, lignins, lignosulfate, mica, sugar cane
fibers,
and granular materials. Generally, the drilling fluid may contain other
ingredients such
as weighting agents, viscosifiers, fluid loss reducing additives, Theological
modifying
additives, emulsifiers, seepage loss control additives, lubricity additives,
defoamers, pH
control additives, dispersants, .and so forth, all of such materials being
solubilized,
suspended or dispersed in the drilling fluid in such amounts as may be
appropriate. It is
generally contemplated that any other suitable additive as is known or as may
be
discovered may be employed in connection with the invention.
2 0 The invention further encompasses a drilling fluid additive composition
that
includes in one embodiment an alkyl glycoside and a borehole stability
promoter that is
selected from among a maltodextrin, a carboxyallcyl starch, hemicellulose, and
mixtures
of the foregoing and that includes in another embodiment molasses solids in
conjunction
with one or more of the foregoing borehole stability promoters and/or in
conjunction
2 5 with an allcyl glycoside. In yet another embodiment, the additive includes
sorbitol in
conjunction with one or more the foregoing borehole stability promoters. In
another
embodiment, the additive includes sorbitol in combination with an alkyl
glucoside or in
conjunction with molasses solids. In accordance with this embodiment of the
invention,
the liquid base is not present, or is present in a smaller amount than is
intended in the
3 0 final drilling composition. The composition may be supplied to drillers,
for example, to
be used as an additive to seawater or brine in forming a drilling fluid
imsihi, or may be
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12
supplied to fabricators of drilling fluid to be blended with a liquid base. In
accordance
with this embodiment of the invention, the hemicellulose, starch, and/or
maltodextrin
preferably are present in an amount ranging from about 0.1 % to about 5% by
the dry
basis weight of the alkyl glucoside or molasses solids (or total dry weight of
the
molasses solids and alkyl glucoside). The composition may be dry or may be in
liquid
form, with the hemicellulose, starch, and maltodextrin being dissolved in a
liquid. The
composition of this embodiment of the invention may include other ingredients,
such as
salts or other additives, which other ingredient may be employed in such
amounts as
may be desired.
The invention also encompasses a drilling fluid that includes methyl glycoside
or
other alkyl glycoside and cellulose, the alkyl glycoside being present in at
least an
amount effective to inhibit shale swelling, and the cellulose being present in
an amount
of at least about 0.1 % by weight of the alkyl glycoside. It is contemplated
that cellulose
may assist the alkyl glycoside in promoting borehole stability. Preferably,
the cellulose
is present in an amount of from about 0.1% to about 5% by weight of the alkyl
glycoside. In this embodiment of the invention, the amount of cellulose in the
drilling
fluid is irrespective of the amount of dry hemicellulose or maltodextrin in
the drilling
fluid. In another embodiment, a drilling fluid comprises molasses solids and
cellulose,
the cellulose being present in an amount ranging from about 0.1% to about 5%
by
2 0 weight of the molasses solids. Also encompassed is a drilling fluid that
includes sorbitol
and cellulose.
The invention also encompasses a drilling apparatus. With reference to the
Figure, the apparatus is shown generally at 10 and includes a drill string 1
l, the drill
string 11 generally including a drive 12, a drill stem 14, and a drill bit 15
(the drive 12 is
2 5 shown as a top drive, but other configurations, such as a rotary table,
are possible). The
drill stem 14 may include components such as drill collars, drill pipe and a
kelly (not
separately shown). The drill string 11 is fluidically connected to a source 16
of drilling
fluid which comprises the drilling fluid of one or more embodiments of the
invention.
Generally, the source 16 will be suction tanks 17 that are fluidically coupled
to mud
3 0 pumps 18 and optionally a mud pit (not shown). The mud pump circulates
fluid through
the drill string 11, i.e., through and around the drill bit and/or through the
annulus
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13
between the drill stem and the borehole. The apparatus generally may take any
other
conventional or otherwise suitable form and is not limited to the
configuration shown in
the Figure.
The invention also encompasses a process for drilling. The process includes
the
step of circulating the drilling fluid of one or more embodiments of the
present invention
through the drill string of a drilling apparatus during drilling operations.
No special
apparatus is contemplated by the process of the invention, but instead the
process is
contemplated to be useful in connection with any suitable drilling apparatus.
The following examples are provided to illustrate the present invention, but
1 o should not be construed as limiting in scope.
EXAMPLES
VOLCLAY clay bentonite tablets (American Colloid Company, Skokie, Illinois)
were soaked in various drilling fluids and observed over a period of time to
simulate the
effect of the drilling fluid on shale iri a well bore. The stability of each
bentonite pellet
was evaluated according to the following scale:
1= unaltered
2= hard, intact but loose on surface
3= swollen, softening, still intact
2 0 4= together, but no integrity
5= dissolved
These evaluations were designed to evaluate the drilling fluids as against one
another,
rather than to directly evaluate efficiency in actual borehole conditions.
The drilling fluids were prepared using as alkyl glycosides MeG-206 (a 60%
2 5 aqueous solution of methyl glucoside existing as a 2:1 ratio of oc: (3
ratio isomers). MeG-
365 (a 65% aqueous solution of methyl glucoside existing as a 2:1 ratio of
a:(3 isomers),
and a 70% aqueous solution of methyl glucoside existing as a 1:1 ratio of a:
(3 ratio)
(designated hereunder as MeG-207). As borehole stability promoters, MALTRIN~
M040, M100, and M180 (maltodextrins available from Grain Processing
Corporation of
3 o Muscatine, Iowa) and the soluble fraction resulting from alkaline
treatment of corn hulls
(designated hereunder as "HC") were used. As a control, drilling fluids were
prepared
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14
using only water and using only MeG-365 or MeG-207, without the addition of
hemicellulose, maltodextrin, or molasses. All of the drilling fluids were
prepared at an
initial pH of 7 unless otherwise indicated.
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Drilling fluids were prepared with MeG-365 and MeG-207. The stability of the
bentonite pellets in each fluid was evaluated. The stability of the pellets in
pure water
also was evaluated. The following results were obtained.
5
Drillin Fluid 1 hr. 2 hr. 4 hr. 8 hr. 24 hr.
HO 4 4.5 5 5 5
365 2 2.5 3 4.5 5
207 1 1 1.5 2 3
Drillin Fluid 1 hr. 2 hr. 4 hr. 20 30 hr.
hr.
365 2 2 3.5 4.5 5
207 1 1 1.5 2.5 3
Drillin Fluid 1 hr. 4 hr. 8 hr. 24 hr. 32 hr. 56 hr.
365 1.5 3 3.5 4.5 --- --=
207 1 1.5 .2 3.5 4 5
Drillin Fluid 1 hr. 2 4 8 24 hr. 48 hr
hr. hr. hr.
365 ~ 1.5 2 3 3.5 4.5 ---
207 1 1 1.5 1.5 3 ---
1 o The bentonite pellets were substantially unstable in water, and fared only
somewhat
better in the drilling fluids that included methyl glucoside and water but
that did not
include maltodextrin, hemicellulose, or molasses.
EXAMPLE 1
15 MeC'T + Maltndextrin
Drilling fluids were prepared using methyl glucoside and maltodextrin, and the
bentonite stability test was repeated for each fluid. The following results
were obtained.
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16
Maltodextrin percentages in these tables express weight percent maltodextrin
by dry
basis of methyl glucoside.
Drillin Fluid 1 hr. 2 hr. 4 hr. 8 hr. 24 hr.
365 + 5% M040 1 1 1.5 1.5 2
365 + 5% M100 1 1 1.5 1.5 2.5
365 + 5% M180 1.5 1.5 2 2 4
Drillin Fluid 1 2 hr. 4 hr. 20 30 hr.
hr. hr.
365 + 1% M040 1.5 2 2.5 4 4
365 + 3% M040 1 1.5 1.5 2.5 3
Drillin Fluid 1 hr. 4 hr. 8 hr. 24 hr.
365 + 0.5% 1.5 2 3.5 4
M100
365 + 1% M100 1 1.5 1.5 3.5
As set forth above, the bentonite pellets generally were more stable in the
drilling fluids
of Example 1 than in the control drilling fluids.
E~~AMPLE 2
MeC'T + Maltndexirin + NaC'.1
Drilling fluids were prepared using MeG, maltrodextrin, and sodium chloride.
The bentonite stability test was repeated' for each fluid, and the following
results were
obtained. Sodium chloride percentages in these tables express weight percent
sodium
chloride by dry basis weight of methyl glucoside.
Drillin Fluid 1 hr. 2 hr. 4 hr. 8 hr. 24 hr.
365 + 5% M040 + 10% 1 1 1 1.5 2
NaCI
365 + 5% M100 + 10% 1 1 1.5 1.5 2
NaCI
365 + 5% M180 + 10% 1 1.5 1.5 2 4
NaCI
Drillin Fluid 1 hr. 2 hr. 4 hr. 20 30 hr.
hr.
365 + 1% M040 + 5% 1.5 1.5 1.5 2 3
NaCI
365+3%M100+5%NaCI 1 1 1.5 2 3
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Drillin Fluid 1 hr. 4 hr. 8 hr. 24
hr.
365 + 0.5% M040 + 2% 1.5 1.5 2.5 3.5
NaCI
365 + 1% M100 + 2% NaCI 1 1.5 1.5 3
365 + 0.5% M100 + 5% 1.5 2 2 3.5
NaCI
365 + 1% M100 +5% NaCI 1 1.5 1.5 3.5
As seen, the addition of sodium chloride to the drilling fluid rendered the
fluid retention
less aggressive toward the bentonite pellets.
EXAMPLE 3
Me(~T + T~('.
Drilling fluids were prepared using MeG and the hemicellulose fraction of
allcaline treated corn hulls. The bentonite stability tests were repeated, and
the following
examples were obtained. Hemicellulose percentages in these tables are
expressed as
weight percent dry hemicellulose provided in the HC solution by dry basis MeG.
Drillin Fluid 1 hr. 2 hr. 4 hr. 8 hr.
365 + 0.6% hemicellulose1 1 1 1.5
365 + 0.6% hemicellulose~ 2.5 3.5 4 4.5
solution diluted to
50%
Drillin Fluid 1 hr. 2 4 hr. 20 30 hr.
hr. hr.
365 + 1% hemicellulose1 ~ 1 1 2 2.5
Drillin Fluid 1 hr. 2 4 hr. 8 hr. 24 hr. 48
hr. hr.
207 + 0.5% hemicellulose1 1 1 1 1.5 1.5
365 + 0.6! hemicellulose1 1 1 1.5
As seen, the bentonite pellets were substantially more stable in the drilling
fluids
prepared using MeG and hemicellulose than in the drilling fluids prepared
using only
MeG.
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EXAMPLE 4
MeC'T + HC'. + NaC'.1
Drilling fluids were prepared using MeG, the hemicellulose and sodium
chloride. The bentonite stability tests were repeated and the following
results were
obtained.
Drillin Fluid 1 2 4 20 hr. 30 hr.
hr. hr. hr.
365 + 1% hemicellulose1 1 1 1.5 2
+ S% NaCI '
Drillin Fluid 1 4 hr. 8 hr. 24 32 56 hr.
hr. hr. hr.
365 + 0.5! hemicellulose1 1.5 2 2 2.5 3
+ 2% NaCI
365 + 1% hemicellulose1 1 1.5 1.5 2 2.5
+ 5% NaCI
As seen, the bentonite pellets were substantially more stable in the drilling
fluids thus
prepared then in the control drilling fluids. Addition of salt to the drilling
fluid reduced
the aggressiveness of the fluid towards the bentonite pellets.
Drilling fluids were prepared using MeG and other organic additives in
accordance with the following table. The bentonite stability test was repeated
for each
drilling fluid, giving the following results:
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19
Drillin Fluid 1 2 4 hr. 8 ~24
hr. hr. hr. hr.
365 + 10% NaCI* 2 2.5 3.5 4 5
365 at H 10 2.5 3 3.5 4 5
365 + 5% h drox - ro 1 2 2.5 3 3 ---
starch*
365 + 2% corn starch* 2 2.5 2.5 4 ---
365 + 2% solubilized starch*1.5 2 2.5 3.5 4.5
365 + 2% of eth lene oxide*2 2.5 3.5 4 4.5
365 + 2% ethos lated starch*1.5 2.5 3.5 4 4.5
365 + 2% acid modified 1.5 2 3 4 4.5
starch*
365 + 2%~cationic starch*1.5 2 3.5 4 4.5
365 + 2% arabic* 1.5 2 3 4.5 ---
365 + 2% * 1 1 1.5 2 ---
*dry basis MeG.
As seen, the bentonite pellets generally were not as stable in the drilling
fluids of
the comparative examples as in the drilling fluids of the invention. These
results
. demonstrate the surprising benefits of using maltodextrin andlor
hemicellulose as a
borehole stability promoter as compared with other organic species.
EXAMPLE 5
1 o The water activity, or relative humidity that exists in the space above
the drilling
fluid in an enclosed container, was evaluated for each of the drilling fluids
of the
invention and for control drilling fluids. It is believed that the stability
of wellbore
formations in a drilling fluid generally improves as the water activity value
of the
drilling fluids decreases.
The following results were obtained:
Drillin Fluid Control Water activi 25C
Pure H 0 1.01 as measured
MeG-365 0.864
MeG-207 ~ 0.789
MeG-207 diluted to 65% 0.851
solids
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Drillin Fluid vention Water Activi 25
C
MeG-207 + 0.5% hemicellulose~l~ 0.780
MeG-365 + 0.5% hemicellulose ~l~ 0.889
MeG-365 + 1% hemicellulose ~l~ 0.836
MeG-365 + 2% hemicellulose ~l> 0.816
MeG-365 + 0.5% hemicellulose ~l> 0.810
+ 2% NaCh2>
MeG-365 + 0.5% hemicellulose ~l> 0.727
+ 5% NaCl~2>
MeG-365 + 1% hemicellulose Vii) 0.768
+ 5% NaCl~2~
MeG-365 + 0.5% Maltodextrin~a~ 0.844
MeG-365 + 1% Maltodextrin~2~ 0.855
MeG-365 + 2% Maltodextrinia~ 0.845
MeG-365 + 0.5% Maltodextrin~2~ 0.820
+ 2% NaCI(2~
MeG-365 + 0.5% Maltodextrin~2~ 0.759
+ 5% NaCh2~
MeG-365 + 1% Maltodextrin~a~ + 0.811
2% NaCh2~
MeG-365 + 1% Maltodextrin~2~ + 0.756
5% NaC~2~1
(1) by net basis, on dry MeG basis.
(2) On dry basis MeG.
5 RXAMPT,R f
A drilling fluid comprising MeG-365, 5% MALTRIN~ M040 (on dry basis
MeG), and 0.6% hemicellulose (on dry basis hemicellulose) is prepared.
10 A drilling composition comprising 50% polyglycerine, 20% water, 1%
hemicellulose (dry basis), and 29% MeG (2:1 a: (3)(dry basis) is prepared. The
MeG is
obtained from MeG-365.
15 A drilling composition comprising 50% polyglycerine, 20% water, 1%
maltodextrin (MALTRIN~ M180) (dry basis), and 29% MeG (2:1 a.:(3)(dry basis)
is
prepared. The MeG is obtained from MeG-360.
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21
A composition comprising 65% MeG and 2.5% hemicellulose is prepared
(balance water). The composition is suitable for addition to seawater to form
a drilling
fluid.
A drilling fluid comprising the following ingredients is prepared:
350 lbs. Fresh Water
20 lbs. Bentonite
4 lbs. Lime
3 lbs. Pol saccharide deflocculant
0.75 1b. KOH
1-2lbs. Drillin Starch
0.251b. Li 'te
10-301bs. MeG 2:1
0.1-0.3 lbs. Hemicellulose
A composition comprising the following ingredients is prepared:
350 lbs. Fresh Water
lbs. Bentonite
4 lbs. Lime
3 lbs. Pol saccharide Deflocculant
0.75 1b. KOH
1-2lbs. Drillin Starch
0.251b. Li 'te
10-301bs. MeG 2:1
0.1-0.3 lbs. Maltodextrin MALTRIN R
M040
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22
A composition comprising the following ingredients is prepared:
250 lbs. Sea Water
11 lbs. KCl
100 lbs. Bentonite
0.50 1b. NaOH
1-4lbs. Drillin Starch
10-301bs. MeG 2:1
0.1-0.3 lbs. Hemicellulose
RXAMPT.R 1 "~
A composition comprising the following ingredients is prepared:
250 lbs. Sea Water
11 lbs. KCl
100 lbs. Bentonite
0.50 1b. NaOH
1-4lbs. Drillin Starch
10-301bs. MeG 2:1
0.1-0.3 lbs. Maltodextrin
Corn hulls from a corn wet milling operation are wet screened through a LT.S.
No. 6 screen at about 50° C using sufficient water to substantially
remove the fine fiber,
most of the starch and some of the protein and lipid material present. The
hulls
remaining on the screen are then slurried in water and the pH of the slurry is
adjusted
with lime to pH 6.5 and treated at 79 °C for 1 hour with a B. subtilis
alpha-amylase
(obtained from Genencor International) at a dosage of about 3 liquefons/g
(units as
defined by Genencor) of hull solids. The hulls are filtered, washed and dried
to a
moisture range of 5 to 10 percent in a forced air oven at 70° C.
Fifty-two grams (50.6 g d.b.) of the hulls are slurned in 1000 ml of 69
percent
aqueous ethanol (v/v) containing 5 g of reagent grade NaOH, and the slurry is
heated in
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23
a Parr model 4522 pressure reactor at 100° C for 3 hours. The reaction
mixture, at a
temperature of about 50° C, is then filtered through a Buchner fiuuiel
using Whatman
No. 3 filter paper.
The filter cake is then extracted by refluxing at about 82 °C with 1000
ml of 69
percent aqueous ethanol (v/v) for one hour, and the mixture is filtered at a
temperature
of about 50 °C through a Buchner funnel using Whatman No. 3 paper. The
filter cake is
next slurried in 1000 ml of 69 percent aqueous ethanol (v/v), and the slurry
is adjusted
with diluted HCl to pH 2 and is filtered as above. The filtrate is next
combined with the
filtrates from the two previous filtrations. The combined filtrates then are
adjusted to
pH 2 with HCl, and evaporated to dryness. The residue is dried in a vacuum
oven at 70°
C.
To extract the hemicellulose, the filter cake from the above procedure is
slurried
in 1000 ml of deionized water, held at room temperature for about two hours,
and
filtered through a coarse sintered glass funnel. This procedure is repeated a
second time.
The filtrates from these two extractions are combined and concentrated to
about 10
percent solids by evaporation of the water on a vacuum rotary evaporator at a
temperature of 40° C and a vacuum of about 20 inches of mercury. The
concentrated
hemicellulose solution is then dried on a drum drier having a surface
temperature of
130° C, and the dried hemicellulose is ground in a Waning blender.
2 0 T'he hemicellulose is added to 10 kg MeG-365 in an amount of 2.5%
hemicellulose (on dry basis MeG) to form a drilling fluid.
Various drilling fluids were prepared as set forth in detail below. The
ability of
2 5 each fluid to stabilize shale was evaluated by measuring the amount of
time required for
a bentonite clay pellet to break down (as was determined when the pellet had
reached or
passed "4" on the scale discussed in the earlier Examples). For control
purposes, drilling
fluids that included methyl glycoside but that did not include a borehole
stability
promoter were evaluated. The compositions of the drilling fluids that were
prepared and
3 0 the results of the stability tests are set forth below.
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24
Drillin Fluid Time to ellet breakdown
365 <1 da
_
207 I ~ days
Drillin Fluid Time to ellet breakdown
365 + 4% M040 + 4% KOH 7 da s
365 + 4% CMS + 4% KOH >25 da s
365 + 2% CMS + 4% KOH 5 da s
365 + 1 % CMS + 4% KOH 4 da s
365 + 2% CMS +2% KOH 4 da s
365 + 1 % CMS + 2% KOH 3 da s
CMS is carboxymethyl starch having a DS of 0.2
It is thus seen that both the maltodextrin and the carboxymethyl starch tested
functioned
as borehole stability promoters.
As a control for Examples 16 through 20, the following drilling fluids were
evaluated.
Drillin Fluid 4 8 hr. 16
hr. hr.
MeG-206 3 3.5 4
MeG-207 1.5 2 2
Five hundred g dry basis corn hulls containing 766 g water was added to
sufficient water to give a total weight of 5000 g. The stirred slurry was
heated and
maintained at 82° C to 96° C for two hours. The hot slurry was
then filtered through a
No. 60 Mesh A.S.T.M.E. Standard Testing Sieve. The retained solids were
subjected to
a second treatment of slurrying, stewing, and filtering, and then to a third
treatment of
slunying, stewing, and filtering. The retained solids were crumbled, placed on
screens,
and allowed to air-dry at room temperature.
One hundred g dry basis of the treated corn hulls thus obtained were added to
a
solution already containing 1610 mL 190 proof ethanol, 390 xnl, water, and 20
g 50%
NaOH in a reaction flask equipped with a reflux condenser and mechanical
stirring. The
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stirred reaction mixture was heated to the reflex temperature and then
refluxed for three
hours at the reflex temperature of 78° C. The reaction miXture was
cooled to 40° C, and
then it was vacuum filtered across a 40-60° C fritted glass funnel. The
retained solids
were returned to the reaction flask and reslurried in a solution already
containing 1610
5 mL 190 proof ethanol and 390 mL water. The slurry was heated to reflex
temperature
and then refluxed for one hour at the reflex temperature of 78° C. The
reaction mixture
was cooled to 20° C, and then it was vacuum filtered across a 40-
60° C fritted glass
funnel. The retained solids were reslurried in a solution already containing
1610 mL
190 proof ethanol and 390 mL water at 20° C, and then the pH of the
slurry was adjusted
1 o to 6.5 with 5.8N hydrochloric acid. The slurry was then vacuum filtered
across a 40-60°
C fritted glass funnel.
The retained solids were reslurried in 2000 mL water in a reaction flask
equipped with a reflex condenser and mechanical stirring. The stirred mixture
was
heated to the reflex temperature and then refluxed for two hours at the reflex
15 temperature of 98° C. The mixture was cooled to 50° C, and
then was vacuum filtered
across a 40-60° C fritted glass funnel. The filtrate, referred to as
FILTRATE A, which
contained corn hull hemicellulose, was retained. The retained solids were
reslurried in
2000 mL water in a reaction flask equipped with a reflex condenser and
mechanical
stirring. The stirred mixture was heated to the reflex temperature and then
refluxed for
2 o two hours at the reflex temperature of 98° C.
The mixture was cooled to 50° C, and then it was vacuum filtered
across a 40-
60° C fritted glass funnel. The filtrates referred to as FILTRATE B,
containing the corn
hull hemicellulose, was retained. The retained solids were reslurned in 2000
mL water
in a reaction flask equipped with a reflex condenser and mechanical stirring.
The stirred
2 5 mixture was heated to the reflex temperature and then refluxed for two
hours at the
reflex temperature of 98° C. The mixture was cooled to 50° C,
and then it was vacuum
filtered across a 40-60° C fritted glass funnel. The filtrate, referred
to as FILTRATE C,
containing the corn hull hemicellulose was retained. The combined FILTRATES A,
B,
and C containing the corn hull hemicellulose were assayed to contain 54.5 g
solids.
3 0 Combined filtrates A, B, and C then were spray dried. The resulting
hemicellulose was
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26
formulated into an adhesive paste by mixing 15 parts weight hemicellulose of
the spray-
dried hemicellulose with 85 parts water.
A drilling fluid comprising 48.5% MeG-206 (60% solids), 46.5% desugared
sugar beet molasses, and 3% hemicellulose was prepared as described above and
evaluated for bentonite pellet stability. The following results were obtained.
4 hr. 8 hr. 16 hr.
1.5 2 2
As seen, this product established satisfactory results.
~ FXAMPT,R 17
A drilling fluid composed of 48% MeG-206 (60% solids), 48% desugared sugar
beet molasses (60% solids) and 4% corn hull hemicellulose prepared as in
Example 16
was prepared and evaluated for bentonite pellet stability. The following
results were
obtained.
4 hr. 8 hr. 16 hr.
2 1.5 1.5
As seen, this product exhibited excellent results.
2 0 A drilling fluid composed of 97% MeG-206 and 3% corn hull hemicellulose
prepared as in Example 16 was prepared and evaluated for bentonite pellet
stability.
The following results were obtained.
4 hr. 8 hr. 16 hr.
2 3 3.5
2 5 As seen, this product exhibited somewhat satisfactory results.
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A drilling fluid comprising 50% MeG-206 and 50% desugared sugar beet
molasses was prepared and evaluated for bentonite pellet stability. The
following results
were obtained.
4 hr. 8 hr. 16 hr.
1.5 2.5 2.5
As seen, this product exhibited satisfactory results.
FXAMPT,R 7O
A drilling fluid comprising 49% MeG-206, 49% desugared sugar beet molasses,
and 2% corn hull hemicellulose prepared in accordance with the teachings of
U.S.
Patent 6,063,178 to McPherson et al., assignor to Grain Processing Corporation
of
Muscatine, Iowa was prepared and evaluated for bentonite pellet stability. The
~ following results were obtained.
4 hr. 8 hr. 16 hr.
1 1.5 1.5
As seen, this product exhibited excellent results.
E,5 AMPT.R?_1
The following drilling fluids were evaluated for bentonite pellet stability at
16
hours. The results are shown following the description of the drilling fluid.
In this
example, the hemicellulose was a dry solid prepared in accordance with the
description
provided in prior U.S. Patent 6,063,178.
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28
Drillin Fluid 16
hr.
MeG-206 4
Desu aced Su ar Beet Molasses 60% 2.5
solids
98% MeG-206 + 2% hemicellulose 3
98% Desugared Sugar Beet Molasses 2
(60% solids) +
2% hemicellulose
A drilling fluid comprising desugared cane sugar molasses that has been
diluted
to 30% solids with salt water is circulated through a drill string.
The following drilling fluids were prepared and evaluated for shale stability
as in
the foregoing examples.
Example 23A Meg 206
Example 23B Sorbitol (60% aqueous solution)
Example 23C Meg 206, 3% crude hemicellulose (as is)
Example 23D Sorbitol + 3% crude hemicellulose (as is)
The following results were observed.
Example 1 hr. , 2 hr. 4 hr. 6 hr. 8 hr.
23A 1.5 1.5 3 3.5 4
23B 2 2 2 2.5 3
23C 1 1 1 1 1
23D 1 ~1 1 1 1
Thus, the foregoing general objects have been satisfied. The invention
provides
2 0 a drilling fluid that is suitable for use in connection with borehole
drilling. The
invention further provides a drilling apparatus and method that incorporate
the improved
drilling fluid.
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29
While particular embodiments of the invention have been shown, it will be
understood that the invention is not limited thereto since modifications may
be made by
those skilled in the art, particularly in light of the foregoing teachings.
For instance, the
pH or salt content of the disclosed fluids may be modified, or, more
generally, other
components may be altered. It is therefore contemplated that the invention
encompasses
the subject matter of the following claims and equivalents thereof. All
references cited
herein are hereby incorporated by reference in their entireties.
