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Description  |
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This invention pertains to an aqueous drilling fluid. More particularly it
pertains to a drilling fluid containing a copolymer of lignosulfonate and
a polyacrylate to increase the yield of bentonite and subbentonite clays.
Drilling fluids are used in drilling of wells and have a number of
functions which include the removal of cuttings from the well, seal off
formation of gas, and to hold the cuttings and weighting materials in
suspension in the event of shutdown in drilling. These fluids are
generally thixotropic systems having proper viscosity for circulation
through the well bore to carry the cuttings from the bottom of the hole
and a proper gel rate and strength to prevent the settling of the cuttings
or weighting materials when it becomes necessary to discontinue
circulation of the fluid. Dispersed clay slurries having thixotropic
properties have been most commonly used as a drilling fluid.
In the last few years, low-solids drilling fluids have gained in importance
due to the faster drilling rates which may be obtained by the use of these
fluids. The drilling rate increases with a decrease in concentration of
the solids present in the fluid. Since water free of colloidal materials
will not function adequately as a drilling fluid in many situations,
drilling fluids containing a low colloidal solids content are being
increasingly used. These fluids generally contain a small amount of
bentonite or subbentonite clay and a polymer or copolymer which when added
to the drilling fluid will increase the yield of the bentonitic clay to
provide the desired viscosity and gel characteristics to the drilling
fluid. Many of these polymers while increasing the yield of bentonite have
a flocculating effect on other clays which aids in flocculation and
removal of drilled clays and solids other than bentonite. The "yield" of a
clay is defined as the number of barrels of 15 centipoise clay dispersion
or mud which can be prepared from a ton of clay. The use of polyacrylates
and graft copolymers of acrylic acid and polyhydroxy polymeric derivatives
of cellulose or certain polysaccharides for this purpose are disclosed in
U.S. Pat. Nos. 3,558,545 and 3,640,826.
It is, therefore, an object of this invention to provide a copolymer of
lignosulfonate capable of beneficiating bentonite. A further object is to
provide a low-solids drilling fluid containing a copolymer of
lignosulfonate to beneficiate or increase the yield of bentonite present
in the drilling fluid. A still further object is to provide a drilling
fluid containing a copolymer of lignosulfonate and polyacrylate.
The above and other objects are attained by a drilling fluid composition
comprising bentonite or subbentonite clay and a water soluble copolymer of
lignosulfonate and a polyacrylate in a sufficient amount to increase the
yield of the clay. The copolymer is obtained by polymerization of the
acrylate monomer with the lignosulfonate in a weight ratio of 2:1 to 1:5
of the acrylate monomer to lignosulfonate. It has the property of
beneficiating bentonitic clays to increase their yield and functions as a
flocculating agent for low yield clays generally encountered in drilling
operations.
The reaction or polymerization of the acrylate monomer with the
lignosulfonate is effected using conventional grafting techniques of
polymerizing vinyl monomers to polymers with free radical type reactions.
The reaction is generally carried out by polymerization of the acrylate
monomer in the presence of the lignosulfonate. Preferably an aqueous
medium is used. In carrying out the reaction with free radical generation,
an association of the acrylate copolymer with the lignosulfonate is
obtained characteristic of graft type copolymers. Preferably, free radical
initiators such as benzoyl peroxide, alpha-azobisisobutyronitrile, cumene
hydroperoxide, and other free radical initiators such as hydrogen
peroxide-metal redox system are used. High energy radiation such as
gamma-radiation is also effective for most reactions and may be used.
While the reaction is preferably carried in an aqueous medium, other
solvents such as lower alcohols, acetone, dioxane, dimethyl sulfoxide and
mixtures thereof, and others in which the lignosulfonate and the acrylate
monomer are sufficiently soluble to effect the reaction may be employed.
Preferably a mixture of water and one of the other solvents may be used
when derivatives of acrylic acid having limited water solubility are used
as one of the monomers for the formation of the acrylate polymer.
Lignosulfonates obtained from any source may be used for the polymerization
with the acrylate polymer. Lignins are polymeric substances composed of
substituted aromatics found in plant and vegetable tissue associated with
cellulose and other plant constituents. In the pulp and paper industry,
lignin-containing materials such as wood, straw, corn stalks, bagasse, and
other vegetable and plant tissues are processed to recover the cellulose
or pulp. The residual pulping liquors containing the lignin as by-products
are thus one of the main sources of lignins. While there is some
variations in the chemical structure of lignin, depending upon the plant
from which lignin is obtained, place where the plant is grown, and also
upon the method used in recovery or isolation of the lignin from the plant
tissue, the basic structure and properties of the lignins are similar, all
containing an aromatic nucleus through which the reaction may possibly be
affected. Thus, lignins obtained by any method or from any source may be
used in this reaction as long as the lignin is in a form which may at
least be partially soluble in a solvent in which it may be polymerized
with the acrylate polymer to form water-soluble copolymers.
Since the lignins separated from the plant may be chemically altered
somewhat from that found in the plant, the term "lignins", as used herein,
means the lignin products which are obtained upon separation from the
cellulose or recovered from the plant. In the sulfite pulping process, the
lignocellulosic material is digested with a sulfurous acid-metal bisulfite
solution resulting in the sulfonation of the lignins. In other methods of
the recovery or separation of the lignins from the plant, the lignins may
not be sulfonated but may be chemically altered somewhat in some other
manner. For example, in residual pulping liquors obtained in the sulfate
and other alkaline pulping processes, the lignins are present as alkaline
metal salts dissolved in the alkaline aqueous liquor. "Hydrolysis lignin"
is obtained from the hydrolysis of lignocellulosic materials found in the
plant. The lignin obtained by hydrolysis or by an alkaline pulping process
as well as spent sulfite lignin may be sulfonated as well. Also, the
lignin products such as a residual pulping liquor may be subjected to
various treatments such as, for example, acid, alkaline or heat treatment
or reacted with the other chemicals which may further alter somewhat the
lignin constituents. The lignins remain operative as long as the treatment
is not so severe as to destroy the basic aromatic polymeric structure.
The residual pulping liquors, or the lignin-containing product obtained in
the separation or recovery of lignins from the plant, will generally
contain lignins of various molecular weights varying from less than 1,000
to over 100,000. These liquors also may contain other constituents besides
the lignins. For example, in the sulfite pulping process, the spent
sulfite liquor contains lignosulfonates which may be present as salts or
cations, such as magnesium, calcium, ammonium, sodium and other cations
which may have been present during the sulfonation of the lignin. The
spent sulfite liquor generally contains only about 40 to 60 weight percent
on an oven-dried basis of lignosulfonates with the remainder being
carbohydrates and other organic and inorganic constituents dissolved in
the liquor. Lignin products obtained by other pulping processes may
likewise contain other materials such as carbohydrates, degradation
products of carbohydrates, and resinous materials which are separated from
the lignocellulosic materials with the lignin. Lignin obtained by
hydrolysis of lignocellulosic materials may not contain the carbohydrates
but may contain resinous-type materials as well as other materials which
are not removed by the hydrolysis. It is not necessary to separate the
lignin-containing constituents from the other constituents. The lignin
product as obtained containing all of the constituents may be used as such
or subjected to different treatments such as alkaline, acid, or heat
treatments as well as reacted with chemicals to modify or remove some of
the non-lignin constituents prior to the polymerization reactions. Some
reaction of the polyacrylate with the non-lignin constituents may be
obtained, but the presence of the products of reaction of these
constituents is not necessarily detrimental and may be somewhat
beneficial. They are generally of lower molecular weight materials and can
be easily removed from the final lignosulfonate-polyacrylate copolymer
after reaction if desired, using methods, such as dialysis, gel permeation
chromatography, chemical precipitation and extracting, or other methods
well known in the art for the fractionation and recovery of high molecular
weight organic water-soluble polymers from lower molecular weight
materials. The lignin materials may also be separated from the non-lignin
constituents and fractionated in fractions of various molecular weights
prior to reaction with the acrylate monomer.
The acrylate monomer which is preferably used for the preparation of the
polyacrylate is acrylic acid, since water soluble polyacrylates are
obtained. Derivatives of acrylic acid such as methacrylic acid,
acrylamide, alkyl esters of 1 to 2 carbon atoms of acrylic acid, and alkyl
esters of 1 to 2 carbon atoms of methacrylic acid may also be used in
mixtures with acrylic acid. Polymerization of these polyacrylates with
lignosulfonate is obtained. The copolymers are water soluble or if not,
most may be converted to water soluble products upon hydrolysis in an
alkaline medium. The low-solid drilling fluids in which the additives are
used are generally alkaline, at a pH usually in a range of 8 to 10.5. When
a mixture of acrylic acid and a derivative of acrylic acid is used in
preparation of the polyacrylate, the amount of the acrylic acid derivative
employed generally is from about 10 to 90%, preferably 20 to 40%, but may
be widely varied as long as the polyacrylate when grafted upon the
lignosulfonate is water soluble or upon alkaline hydrolysis becomes water
soluble. Lignosulfonate is hydrophilic and influences to a considerable
extent the solubility of the lignosulfonate-polyacrylate copolymer
obtained.
In the reaction of the lignin with polyacrylate using free radial
initiators, it is preferred to carry out the reaction in an aqueous
medium. However, when reactants or monomers are employed which have
limited solubility in an aqueous medium other solvents such as alkanols
having from 1 to 4 carbon atoms, acetone, dioxane, ethylene glycol,
formamide, dimethylformamide, dimethylsulfoxide, and others may be used.
Preferably the solvents which are water miscible and which can be used in
mixture with water are preferred. In some of the reactions, the presence
of an alcohol such as methanol may enhance the polymerization of the
polyacrylate to the lignin molecule. However, it is not necessary to use
an aqueous medium. The copolymerization of the lignosulfonate with the
acrylate may be carried out in other mediums in which the reactants are at
least partially soluble. For example, the medium used may be such that the
lignin is only partially soluble swelling in the medium or a medium in
which the lignosulfonate-polyacrylate will precipitate upon formation. The
products obtained will vary somewhat depending upon the particular
reaction employed for the polymerization of the lignin with the
polyacrylate. For example the number and molecular weight of the
polyacrylate side chains polymerized to the lignosufonate backbone
presumably may differ when the reaction is carried out using a peroxide or
chemical free radical initiator in place of radiation as well as when
particular acrylic acid derivatives are polymerized in the formation of
the polyacrylate. The weight ratio of the acrylate monomer to
lignosulfonate used may be widely varied from a ratio of 2 to 1 to 1 to 5.
Larger amounts of acrylate polymer may also be used. In the reaction in
the formation of the polyacrylate copolymer with the lignin not all of the
polyacrylate becomes grafted or associated with the lignin. Generally some
homopolymer or copolymer of acrylic acid and the acrylic acid derivative
is obtained. With large excesses of the acrylate monomer, the portion of
the polyacrylate which is unassociated with the lignin increases.
Generally it is preferred to use the reaction product as obtained which
will usually have an intrinsic viscosity of at least 1.0 dlg.sup..sup.-1
preferably in the range of 1.2 to 3 dlg.sup..sup.-1 with the
lignosulfonate-acrylate copolymer having an average molecular weight of at
least 100,000. Often, the solubility characteristic of the
lignosulfonate-polyacrylate copolymer and that of the polyacrylate itself
may not differ sufficiently to effect a separation by solubility
differences.
In using the lignosulfonate-polyacrylate copolymer, the methods and
procedures normally used for low-solids muds are employed. The copolymer
is added to the drilling fluid in a sufficient amount to beneficiate or
increase the yield of the bentonite or bentonitic clay present in the
drilling fluid which may vary widely depending upon the formation being
drilled and the particular situation involved. Generally the additive is
used in an amount from about 0.01 to 1 pound per barrel but may be
decreased or increased in particular situations. The additives may be used
with weighting materials, water loss agents, and also with other additives
normally used with low-solids drilling fluids. The drilling fluids
containing the lignosulfonate-polyacrylate copolymer are effective in
presence of contaminants normally encountered in drilling operations such
as sodium chloride or gypsum.
EXAMPLE I
A fermented calcium base spent sulfite liquor in an amount of 100 grams of
20% solution was mixed with 16 grams of acrylic acid. The reaction mixture
was stirred and 4 milliliters of 30% hydrogen peroxide were slowly added.
Upon addition of the hydrogen peroxide, an exothermic reaction occurred
after which the solution was heated for 16 hours at 62.degree. C with the
reaction mixture gelling. The resulting gel was neutralized with 17 grams
of 50% sodium hydroxide solution and then diluted with water to a
concentration of about 5% solids and spray dried. The reaction mixture or
product was a high molecular weight material containing less than 1% of
acrylic acid as determined by gas chromatographic analysis. In
determination of molecular weight by the agar gel diffusion method as
described by J. Moacanin, H. Nelson, E. Back, V. F. Felicetta and J. L.
McCarthy in the Journal of the American Chemical Society 81, 2054 (1959),
only 90% of the reaction product diffused in the gel with about 10% being
too large for diffusion. Of the portion which diffused into the gel the
weight average molecular weight was 110,000. In the diffusion method, the
analysis is based upon ultra-violet absorption of lignosulfonate which
indicated that the lignosulfonate was present as a high molecular weight
material. Intermixing a sodium polyacrylate with the unreacted calcium
base, fermented liquor had no effect on the diffusion coefficient of the
lignosulfonate. Also, when the reaction of the spent sulfite liquor was
repeated except that the acrylic acid is omitted the weight average
molecular weight obtained is about 37,000. The reaction mixture of the
lignosulfonate and polyacrylate polymer had an intrinsic viscosity of 1.4
dlg.sup..sup.-1 in 0.1 molar sodium chloride solution at 25.degree. C. A
similar product was also obtained when the reaction of the lignosulfonate
with the acrylate acid was repeated except that in addition to the 80%
acrylic acid added, acrylamide was also added in an amount of 20% of the
spent sulfite liquor solids.
The spray dried lignosulfonate-polyacrylate product was tested in low
solids drilling fluids using AP1 RP 13B, April, 1969, standard test
procedures for drilling fluids. The mud system was prepared by intermixing
bentonite in an amount of 12 pounds per barrel with water to which about
1/2 pound per barrel of sodium carbonate was added. The drilling fluid
thus prepared was mixed for 3 hours to hydrate the clay prior to testing.
A series of tests were made. To one portion of the fluid no additive was
added, while various amounts of the lignosulfonate-polyacrylate copolymer
were added to other portions of the drilling fluid. The results obtained
with these samples were compared to comparative control samples containing
a copolymer of maleic anhydride and vinyl acetate commercially sold for
low solids drilling fluids. The results obtained with unweighted mud are
shown in the following table:
__________________________________________________________________________
24 Hour Cold Roll 20 Hour Hot Roll at 96.degree.F
10 10
lbs/ Min. Min.
Additive
bbl IG 600 300 PV Y Gel pH IG 600 300 PV Y Gel
WL
__________________________________________________________________________
Base 0 1.0
11.0
7.0
4.0 3.0
8.0
10.3
1.0
10.5
7.0
3.5
3.5
8.0
15.6
Fluid
Lignin
0.025 5.5
21.5
19.0
2.5 16.5
22.0
10.3
2.5
24.5
17.5
7.0
10.5
22.0
15.4
Poly-
0.050 19.5
42.0
33.5
8.5 25.0
36.0
10.3
12.5
36.0
28.0
8.0
20.0
38.0
17.0
acrylate
Control
0.025 10.0
36.0
27.5
8.5 19.0
22.0
10.3
10.0
33.0
25.0
8.0
17.0
26.0
14.8
0.050 21.5
48.5
40.5
8.0 32.5
41.0
10.3
20.0
44.5
36.0
8.5
27.5
45.0
15.4
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In addition to the runs above, the lignosulfonate-polyacrylate copolymer
was likewise tested with the drilling fluid which contained barium sulfate
in the amount of 250 pounds per barrel. The results obtained after rolling
for 16 hours at room temperature are shown in the following table.
______________________________________
10
Additive Min.
lbs/bbl pH IG 600 300 PV Y Gel WL
______________________________________
0 9.7 1.0 24.0 13.5 10.5 3.0 12 18.8
0.05 9.6 2.0 30.0 18.0 12.0 6.0 28 18.0
0.10 9.7 22.5 60.0 45.0 15.0 30.0 51 17.3
0.15 9.7 40.0 77.5 63.5 14.0 49.5 81 16.5
0.20 9.8 43.0 78.5 64.5 14.0 50.5 124 16.0
0.25 9.7 26.0 70.0 51.5 18.5 33.0 103 15.0
______________________________________
A test was also made with drilling fluids contaminated with salt and
gypsum. The drilling fluid was prepared by mixing 12 pounds per barrel of
bentonite to which about one pound of sodium carbonate per barrel was
added. The clay was hydrated by mixing for 3 hours after which runs were
made to which various amounts of sodium chloride and gypsum as
contaminants were added. The lignosulfonate-polyacrylate copolymer
additive was added to the drilling fluid in an amount of 0.050 pounds per
barrel and compared to a control sample containing an equal amount of the
maleic anhydride-vinyl acetate commercial additive. The results obtained
after 16 hours cold roll are shown in the following table.
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Concentration 10
of Contaminants Min.
Additive
Contaminants
lb/bbl pH IG 600 300 PV Y Gel WL
__________________________________________________________________________
Base Fluid
-- -- 10.2
6.0
17.0
11.5
5.5 6.0
12.0
16.2
Lignin -- -- 10.2
21.0
39.5
33.0
6.5 26.5
23.0
18.2
Poly- NaCl 1 10.3
17.5
37.0
31.5
5.5 26.0
17.0
19.0
acrylate
NaCl 4 10.3
14.0
31.5
25.5
6.0 19.5
13.5
20.6
Gypsum
1 10.0
17.5
39.5
33.5
6.0 27.5
15.5
17.8
Gypsum
5 7.9
9.0
17.5
14.0
3.5 10.5
10.0
29.0
Control -- -- 10.5
18.0
39.5
32.0
7.5 24.5
16.0
16.6
NaCl 1 10.2
16.5
34.5
27.5
7.0 20.5
13.0
18.6
NaCl 4 9.9
13.5
30.0
24.0
6.0 18.0
7.0
20.2
Gypsum
1 10.2
19.0
42.5
35.0
7.5 27.5
17.0
17.0
Gypsum
5 7.7
8.0
19.0
14.5
4.5 10.0
10.0
30.2
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The product was also tested as a flocculant for a low yield clay. A slurry
containing 4% of Panther Creek clay was prepared and the
lignosulfonate-polyacrylate was added in various amounts and the time in
seconds to settle to 50% of the volume in a 100 ml graduated cylinder was
noted. The clay slurry was at a pH of 9. It contained in addition to the
Panther Creek clay sodium chloride in amount of 1,000 parts per million
and had a settling time of about 600 seconds without the additive.
The amounts of the additive used and the settling times obtained are shown
in the table below:
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Additive Added, Time to Settle,
ppm Seconds
______________________________________
2 95
5 70
10 44
200 43
______________________________________
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Description |
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