Note: Descriptions are shown in the official language in which they were submitted.
,\
1 BACKGROL;2tD OF THE INVENTION
2
3 1. Field of the Invention:
4
The present invention relates to methods and
6 compositions for controlling the gellation rate in an
7 aqueous well fracturing fluid. It particularly Yelates to a
8 novel lia_uid complexor used to obtain controlled delayed
9 gellation of borated polysaccharides.
to
11 2. Description of the Frior Art:
12
33 . During.hydraulic fracturing, a sand laden fluid is
14 injected into a well bore under high pressure. Once the
natural reservoir pressures are exceeded, the fracturing
16 fluid initiates a fracture in the formation whic:: generally
17 conta.nues to grow during pumping. The treatment design
18 generally reauires t::e f't:id to reach maximum triscosity as
19 it enters the fracture which affects the fracture length and
width. This viscosit_~ is normally obtained by td:e gellation
21 of suitable polymers, sue:: as a suitable polysaccaride. In
22 recent years, gellation has been achieved by cress-linking
23 these polymers with metal ions~including aluminum, antimony,
24 zirconium and titanium containing compounds including the
so-called organotitanates. See, for instance, L'.S. Patent
26 No. 4,514,309, issued April 30.,1985, and assigned to the
27 assignee of the present invention.
28
29 The viscous fracturing fluid being pumped usually
encounters high shear in the pipe string during pumping from
31, the surface to the fracture and after entering the fracture,
32 flows at low shear. Recent investigations indicate that the
33 high shear encountered in the pipe string causes extensive
- 2 -
1 degradation of the cross-linked fracturing fluid. Also,
2 high fluid viscosities cause excessive back or friction
3 pressures, limiting the pumping rate, which also affects
4 fracture geometry. These investigations have shown that by
delaying the gellation for several minutes during most of
6 the high shear, higher pump rates can be obtained and the
7 fluid generally exhibits better stability. In the case of
8 the metal ion cross-linking systems, the delay in gellation
9 is normally achieved with a delaying additive that binds or
chelates the metal ions in solution.
11
12 Recently, guar and guar derivaties cross-linked- with
13 borate ions have again become popular. In alkaline water
14 having a pH greater than about 7.8, cross-linking of the
guar polymer is essentially instantaneous. This action is
16 probably due to the 'act that borates easily and readily
17 esterify with 1,2-cissoidial dialcohols or palyhedric
18 alcohols, such as those found on the guar polymer. This
19 esterification is readily reversible, especially at the
elevated temperatures found in the well bore, so that free
21 borate ion is altaays available. As a result, the delay of
22 borate ion cross-linking sysuems is difficult to achieve.
23
24 Certain of the prior art borated guar systems have
employed either slow dissolving metal .oxides which slowly
26 increase the fluid alkalinity, which in turn promotes cross-
27 linking, or by using calcium borate salts having poor water
28 solubility, relying upon the slaw dissolution of borate ions
29 for delay. xn both cases, the delay action was based
primarily on the slow dissolution of a solid in the aqueous
31 fracturing fluid, resulting in poor control of the delay
32 time and ultimate viscosity of the fluid. U.S. Patent No.
33 4,619,776, issued October 28, 1986, to Mondshine, is typical
3
1 of the prior art in teacing the use of a sparingly soluble
2 borate to achieve some degree of control over the cross-
3 linking reaction.
4
A need exists for a composition and method for
6 providing more precise control over the cross-linking
7 reaction of a borated ac~,~eous fracturing fluid.
8
9 A need also exists for such a composition and method
which does not rely upc~ the slow dissolution of a solid as
11 the basis of the delay Wechanism.
12
13 A need also exists for such a method and composition
14 which allows selective adjustment of the delay rate at a
well site quickly and conveniently.
is
17 A need also exists for such a method and composition
18 which provides a reverse °eaction to reduce the viscosity of
19 the fracturing fluid wi4:: time to facilitate the cleanup of
the treatment from the taell bore.
q,
1 SLIM~IARY OF TFi~ INV~NTICa
2
3 The cross-linking system of the invention utilizes a
4 novel complexor solution to control the gellation rate of an
aqueous fracturing fluid containing a hydrated
6 polysaccharide polymer. The complexor solution comprises a
7 cross-linking additive and a delay additive which controls
8 the rate at which the cross-linking additive promotes
9 gellation of the hydrated polymer, the control rate being a
function of the pH of the complexor solution. Preferably,
11 the cross-linking additive is a material ~ahich supplies free
12 borate ions in solution and the delay additive is a material
13 which attempts to bind chemically to ~e borate ions in
14 solution, whereby the hydrated polymer is forced to comuete
with the delay additive far the free borate ions. Mast
16 preferably, the delay additive is selected from the group
17 consisting of dialdehydes having about 1 to 4 carbon atoms,
18 keto aldehydes having about 1 to 4 car: on atoms, hydroxyl
19 aldehydes having about 1-4 carbon atoms, ortho substituted
aromatic dialdehydes and ortho substituted aromatic hydroxyl
21 aldehydes.
22
23 Tn the method of the invention, a hydratable polymer
24 capable of gelling in the presence of borate ions is blended
with an aqueous fluid to form a base fluid and the polymer
26 is allowed to hydrate. A complexor solution is formed for
27 the base fluid by combining a cross-linki.~.g additive capable
28 of furnishing borate ions in solution wit:: a delay additive,
29 to chemically bond with both boric acid and the free borate
ions produced by the cross-linking additive to thereby limit
31 the number of borate ions available in solution for
32 subsequent cross-linking of the hydrated polymer. The pH of
33 the complexor solution is adjusted in order to control the
- 5 -
CA 02037974 2000-11-30
rate of the subsequent cross-linking of the hydratable
polymer. The complexor solution is then added to the base
fluid to cross-link the hydrated polymer.
In one preferred embodiment of the invention there is
provided a method of controlling the cross-linking reaction
of an aqueous fracturing fluid in fracturing a subterranean
formation, comprising the steps of: blending together an
aqueous fluid and a hydratable polymer capable of gelling in
the presence of borate ions; allowing the polymer to hydrate
to form a hydrated polymer sol; adding an alkaline buffer to
thereby adjust the pH of the hydrated polymer sol in the
range from about 8.0 to 11.5; forming a complexor solution
for said hydrated polymer gel by combining a cross-linking
additive capable of furnishing borate ions in solution with
a delay additive selected from the group consisting of
dialdehydes having about 2-4 carbon atoms, keto aldehydes
having about 3-4 carbon atoms hydroxyl aldehydes having 2-4
carbon atoms, ortho substituted aromatic dialdehydes and
ortho substituted aromatic hydroxyl aldehydes, the delay
additive being effective, to chemically bond with the borate
ions and boric acid produced by the cross-linking additive
to thereby limit the number of borate ions available in
solution for subsequent cross-linking of the hydrated
polymer sol; adjusting the pH of the complexor solution to
achieve a desired delay in the cross-linking reaction of the
hydrated polymer gel, the delay achieved being a function of
the complexor solution pH, wherein upward adjustment of the
pH of the complexor solution serves to retard the rate of
the subsequent cross-linking of the hydrated polymer sol
while downward adjustment of the pH of the complexor
solution serves to accelerate the rate of subsequent cross-
linking; and adding the complexor solution to the hydrated
polymer sol to cross-link the hydrated polymer sol.
In another preferred embodiment of the invention there
is provided a method of fracturing a subterranean formation
comprising the steps of: blending together an aqueous fluid
- 6 -
CA 02037974 2000-11-30
- and a hydratable polymer capable of gelling in the presence
of borate ions; allowing the polymer to hydrate to form a
hydrated base fluid; adjusting the pH of the base fluid to
above about 7.8; forming a complexor solution for the base
fluid by combining a cross-linking additive capable of
furnishing borate ions in solution with a liquid delay
additive, the delay additive being added in an amount
effective to chemically bond in the alkaline pH base fluid
with the borate ions produced by the cross-linking additive
to thereby limit the number of borate ions available in
solution for subsequent cross-linking of the base fluid; and
while maintaining an alkaline pH in the base fluid adding
the complexor solution to the base fluid to cross-link the
fluid.
In a further preferred embodiment there is provided a
complexor solution when used to initiate a time controlled
cross-linking reaction with an aqueous hydrated
polysaccharide fracturing fluid, the complexor comprising: a
mixture of cross-linking compound which supplies borate ions
in solution and a liquid delay additive which controls the
rate at which said cross-linking compound promotes cross-
linking of said polysaccharide, the control rate being a
function of the pH of the complexor solution, said liquid
delay additive being selected from dialdehydes having 2-4
carbon atoms, keto aldehydes having 3-4 carbon atoms,
hydroxyl aldehydes having 2-4 carbon atoms in the carbon
chains, ortho substituted aromatic dialdehydes and ortho
substituted aromatic hydroxyl aldehydes.
Additional objects, features, and advantages will be
apparent in the written description which follows.
- 6a-
DETAILED DESCRI?TION OF THE IPd'VENTION
2
3 The present invention provides a method for controlling
4 the cross-linking reaction of an aqueous fracturing fluid in
fracturing a subterranean formation. In order to practice
6 the method, an aqueous (water ar brine) based fracturing
7 fluid is first prepared by blending a hydratable polymer
8 into the base fluid. Any suitable mixing apparatus may be
9 used for this procedure. _Tn the case of batch mixing, the
hydratable polymer and aaueous fluid are blended for a
11 period of time which is sufficient to form a hydrated sol.
12 Once the hydration of the polymer is complete, a
13 predetermined quanity of complexor solution is added to the
14 base fluid sufficient to achieve a desired cross-linking
reaction time. The mixture is pumped into the well bore as
16 the cross-linking reaction takes place.
17
18 Propping agents are typically added to the base fluid
Z9 prior to the addition of the complexor. Propping agents
include, for instance, quartz sand grains, glass and ceramic
21 beads, walnut shell fragments, aluminum pellets, nylon
22 pellets, and the like. The propping agents are normally
23 used in concentrations between about 1 to 8 pounds per
24 gallon of fracturing fluid composition, but higher or lower
cancentrations can be used as required. The base fluid can
26 also contain other conventional additives common to the well
27 services industry such as surfactants, corrosion inhibitors,
28 buffers, and the like.
29
The hydratable polymer useful in the present invention
31 can be any of the hydratable polysaccharides familiar to
32 those in the well service industry which is capable of
33 gelling in the presence of borate ions to form a gelled base
1 fluid, for instance, suitable hydratable polysaccharides are
2 the galactomannan gums, glucomannan gums, guars, derived
3 guars and cellulose derivatives. Specific examples are guar
4 gum, guar gum derivatives, locust bean gum, karaya gum,
carboxymethyl cellulose, carboxymethylhydroxyethyl
6 cellulose, and hydroxyethyl cellulose. The preferred
7 gelling agents are guar gum, hydroxypropyl guar,
8 carboxymethylhydroxypropyl guar, and carboxymethyl-
9 hydroxyethyl cellulose. A suitable synthetic polymer is
7.0 polyvinyl alcohol. The most preferred hydratable polymers
11 for the present invention are guar gum and hydroxypropyl
12 guar.
13
14 The hydratable polymer is added to the aa_ueous base
fluid in concentrations ranging from about 0.10% to 5.0% by
16 weight of the aqueous fluid. The most preferred range for
17 the present invention is about 0.24% to 0.72% by Weight.
18
19 The cross-linking system of the invention utilizes a
novel complexor solution to control the cross-linking rate
21 of the base fluid ccntaining the hydrated polymer. The
22 complexor solution comprises a cross-linking additive and a
23 delay additive which controls the rate at which the cross-
24 linking additive promotes gellation of the hydrated polymer,
the control rate being a function of the pH of the complexor
26 solution. Preferably, the cross-linking additive is a
27 material which supplies borate ions in solutian. Thus, the
28 cross-linking additive can be any convenient source of
29 borate ions, for instance the alkali metal and the alkaline
earth metal borates arid boric acid. A preferred cross-
31 linking additive is sodium borate decahydrate. The cross-
32 linking additive is preferably present in the range from
g -
1 about 5 to 25 % by weight, most preferably about l0 to 15
2 by weight of the complexor solution.
3
4 The delay additive used in the complexor solution is a
material which attempts to bind chemically to the borate
6 ions produced by the cross-linking additive in solution,
7 whereby the hydrated polymer is forced to compete with the
8 delay additive for 'the borate ions. As will be explained,
9 the effectiveness of the delay additive in chemically
bonding to the borate ions in the complexor solution is pFi
11 dependent. Thus, unlike the prior art systems which
12 utilized slow dissolving metal oxides or calcium borate
13 salts having poor water solubility, the present complexor
14 does not rely upon the slow dissolution of solids.
16 Preferably, the delay additive is selected from the
17 group consisting of dialdehydes having about 1-4 carbon
18 atoms, keto aldehydes having about 1-4 carbon atoms, hydroxy
19 aldehydes having about 1 to 4 carbon atoms, ortho
substituted aromatic dialdehydes and ortho substituted
21 aromatic hydroxyl aldehydes. Preferred delay additives
22 include, for instance, glyoxal, propane dialdehyde, 2-keto
23 propanal, 1.4-butanedial, 2-keto butanal, 2.3-di keto
24 dibutanal, phthaldehyde, salicaldehyde, etc. The preferred
delay additive is gly~xal due to its ready availability from
26 a number of commercial sources. Preferably, the delay
27 additive is present in the range from about 5 to 40 % by
28 weight, most preferably about 15 to 30 % by weight of the
29 compleaeor solution. The preferred ratio of glyoxal to sodium
borate is from about 1:0.1 to 1:1, and most preferably is
31 about 1:0.516.
32
g
~~~'~~"~~~
1 Glyoxal, a 1.2- dialdehyde, hydrates to form 1.1.2.2-
2 tetrahydroxyethane which favorably binds to the borate ions
3 provided by the cross-linking additive of the complexor. As
4 the pH of the complexor solution increases, the rate of
gellation declines. As the pH of the camplexor solution
6 decreases, the rate of gellation increases. Thus, by
7 adausting the ,pH of the complexor solution within a
8 preselected range, extremely accurate control of the cross-
9 linking delay time can be achieved. Experimental delay
times have ranged from 10 to 300 seconds by varying the pH
11 of the complexor solution from about 5.0 to 11.50,
12 respecti~rely.
13
14 The complexor can also contain a stabilizer which
increases the shelf life of the complexor and can serve to
16 enhance the delay time. Suitable stabilizers include, for
17 instance, polyhedric alcohols such as pentaerythritol
18 glycerin, lanolin, mono and oligosaccharides having multiple
19 hydroxyl groups, and the like. The preferred stabilizer is
sorbitol, a reduced sugar. Ths stabilizer is preferably
21 present in the range from about 5 to 20 % by weigh, most
22 preferably about 8 to 10% by weight of the complexor
23 solution.
24
The complexor mixture is heated to a temperature
26 ranging from ambient to 105°C for 1 to 5 hours. Most
27 preferably heating should range from 65-80'C for 2 to 4
28 hours.
29
The complexor of the invention can be used to control
31 the delay time of a cross-linked fracturing fluid being
32 pumped into a well bore traversing the subterranean
33 formation to be fractured. The fracturing fluid is pumped
- 10
1 at a rate sufficient to fracture the formation and to place
2 propping agents into the fracture. A typical fracturing
3 treatment would be conducted by hydrating a 0.24 to 0.72%
4 galactomannan based polymer, such as a guar, in a 2%
(wt/vol) KC1 solution at a pH ranging from about 5.0 to 8.5.
6 The pH of the complexor would be adjusted with caustic prior
7 to the treatment to provide the desired delay time. During
8 actual pumping, a buffer would be added to increase the
9 hydrated polymer pH to above 8.0, followed by addition of
the complexor, and typically a breaker and proppant. During
11 the treatment, the area close to the well bore will
12 typically begin cooling gradually, resulting in a decreasing
13 gellation rate. The delay tine can be easily readjusted to
14 accommodate the cooling by acidifying the complexor.
15 In addition to a precisely controlled delay, the novel
17 complexor of the invention provides another useful junction.
18 After the fracture is formed and the pumping is terminated,
19 the viscosity of the fluid must be reduced below about 10
centipoise. At this viscosity, the fluid can be recovered
21 while leaving the proppant in the fracture. As previously
22 discussed, borate cross-linked galactomannans are pH
23 dependent, requiring an alkaline base fluid having a pH
24 above about 7.8. Glyoxol, in alkaline water, slowly
converts to alpha-hydrnxy acetic acid, a strong acid, which
26 decreases the pH of the hydrated polymer gel with time.
27 This in turn reduces tre amount of available borate ion,
28 since the borate ion is converted to boric acid which does
2~ not cross-link, and thus reduces the viscosity of the
fracturing fluid.
31
32 The following examples of the cross-linked fracturing
33 fluid of the present invention embodying the novel complexor
- 11 -
'~ H
1 discussed above are intended to serve primarily for the
2 purpose of illustration. The invention, in its broader
3 aspects, is not to be construed as limited thereto.
4 Included are examples of glyoxol/borate formulation, data
relating gellation times to complexor pH and gellation
6 stability after cross-linking.
7
8 Example 1
9
Complexor Preparation:
11
12 rnto 300 parts of 40% aaueous glyoxal are added, with
13 stirring, 130 parts of sodium borate decahydrate yielding a
14 milky white suspension. Then, 65 parts of 25% aqueous
sodium hydroxide are slowly added resulting in a clear, pale
16 yellow solution. The solution pH can range from 4.90 to
17 6.50. Afterward, 71.4 carts of 70% aqueous sorbitol are
18 added to the solution followed by heating to 95°C far 3
19 hours. During heating, the solution color changes from pale
yellow to amber. After cooling to ambient, the solution pH
21 ranges between 4.50 and 5.00.
22
23 Example 2
24
Gellation Rate:
26
27 The base sol used to determine the gellation rate is
28 prepared by adding, with vigorous stirring, 2.4 parts of a
29 0.4 D.S. hydroxypropyl guar gum and 0.18 parts of sodium
bicarbonate to 500 parts of 2% aqueous potassium chloride
31 solution. After the addition, the stirring rate is reduced
32 to provide mild agitation to the sot for 2 hr. Then, 3.2
- 12 -
1
1 parts of 30~ aqueous potassium carbonate are added which
2 buffers the sol to about pF3 10Ø
3
4 Meanwhile, the complexor prepared in Example 1 is
blended with 0,4,8 and 12 parts of 25% aq sodium hydroxide
6 per 100 parts of complexor. The pHs of the treated
7 complexors are shown in Table 1.
8
Then, 250 parts of hydrated sol are transferred to a
one liter blaring blender jar and sheared at a rate
11 sufficient to create a vortex exposing the hub nut on the
12 blender blades. Next, 0.98 parts of the treated complexors
13 are added to the sol vortex. The time required for the
14 fluid to viscosity and cover the hub nut is defined as the
vortex closure time. These data are also shown in Table 1.
16
17 TABLE 1
18
19 Parts of 25% as NaOH Vortex Closure Complexor
per 100 warts comnlexor Ti~ae (sec.)
21
22 0 22 4.92
23 4 44
5.80
24 8 121 6.09
12 275 8.28
26
27 Example 3
28
29 Shear and thermal stability of borated galactomannans:
31 The preparation of the base sol used in this example is
32 mixed as described in Example 2. After hydrating for 2
33 hears, the 500 parts of base sol are treated with 4.5 parts
- 13 -
7 L
1 of 30$ aqueous potassium carbonate which buffers the sol to
2 about pH 10.3. Afterward, 2.28 parts of complexor
3 containing 0.17 parts of 25~ aqueous sodium hydroxide are
4 added to the vigorously stirring sol. After 100 seconds, 42
parts of gel are syringed into a Fann 50~ cup. The sample
6 is sheared at 102 sec-1, using an R1B1 cup and bob
7 combination, while heating to 190°F in a preset bath and
8 pressuring to 110 psi with nitrogen. The sample is heated
9 and sheared fox 20 minutes followed by a rate sweep using
170, 128, 85 and 42 sec-1 while recording stress. These
11 sweeps are repeated about every 30 minutes and the interim
12 rate between sweeps is 102 sec-1. After 359 minutes; the
13 shearing is stopped while heating continues overnight. A
14 final sweep is made after 22 hours and 21 minutes. The
rates and stresses are used to calculate the Power Law
16 indices, n° and K, described in the API bulletin RP-39.
17 From the calculated indices, the viscosity of the gel at
18 various shear rates can be calculated and are shown in Table
19 2 at 170 and 85 sec-1 over time.
- 14 -
~~~'.~~'~~
1 TABLE 2
2
Time Temp n K V9.scos~ty(cp)
i ~t
(m ~
n) lbm/ft2 170 s 85 s
F
6 20 183 0.7005 0.0497 512 630
7 51 191 0.7090 0.0420 451 552
8 81 191 0.6631 0.0456 387 489
9 112 1.92 0.8411 0.0144 306 341
141 192 1.0?62 0.0040 286 271
11 172 190 1.1220 0.0028 252 231
12 202 191 1.1981 0.0016 210 183
13 232 191 1.1293 0.0020 185 169
14 262 192 1.1020 0.0022 181 169
292 192 1.0589 0.0025 160 155
16 359 193 0.9811 0.0020 86 87
17 1341 192 0.5486 0.0034 16 20
18
19 Example 4
21 Shear and thermal stability
of borated galactomannans:
22
23 The experiment in Example
3 is repeated using
4.0 parts
24 30% aqueous potassium onate and 1.62 parts of untreated
carb
complexor prepared in
Example 1. After 60
secands, 42 parts
26 of gel are syringed intothe Farm 50C cup. The fluid
is
' 27 sheared at 102 sec1 whileheating to 160F in a preset
bath
28 and pressuring to 110 with nitrogen. The rate sweeps
psi
29 are conducted as describedin Example 3. After 233 minutes
of heating and shearing,the shearing is stopped while
31 heating overnight continues.
A final sweep is made
after
32 heating for l9 hours
and 40 minutes. These
data_are shown
33 in Table 3.
34
_ 15 _
20"'l~"l4
1
2 TABLE 3
3
4 Time Temp n' K Viscos~ty(c ) t
(mln) °F lbm/ft2 170 sr~- 85ps°~
6
7 20 160 0.4708 0.1844 583 841
8 51 164 0.4824 0.1530 513 ?35
9 80 163 0.5501 0.1038 493 674
111 163 0.5143 0.1143 452 632
11 141 164 0.5275 0.1047 443 614
12 171 163 0.5224 0.1044 430 599
13 203 163 0.6097 0.0625 403 529
14 233 162 0.6572 0.0419 345 437
1180 163 0.7992 0.0011 19 21
is
17 Example 5
18
19 Shear and thermal stability of borated galactomannans:
21 The polymer used in Examples 3 and 4 is a hydroxypropyl
22 guar gum. The polymer used in this example is 3.0 parts of
23 a nonderivatized guar gum in 500 parts of 2~ aqueous
24 potassium chloride solution mixed as described in Example 2.
The sol is stirred for 2 hours prior to adding 4.5 parts of
26 30~ aqueous potassium carbonate and 1.12 parts of
27 triethanolamine, a temperature stabilizer. Then with
28 vigorous stirring, 1.30 parts of untreated complexor
29 prepared in~Example 1 are added. After 60 sec~l of shear,
42 parts of gel are syringed into a Fann 50C cup. The gel
31 is then sheared at 102 sec°1 while heating to 245°F in a
32 preset bath and pressuring to 110 psi with nitrogen. The
33 rate sweeps are routinely made as described in Example 3.
_ 16 _
~~~"l~'~j~
1 The final sweep is made after shearing and heating for 149
2 minutes. These data are shown in Table 4.
3
4 TABLB 4
6 Time Temp n' K Viscos~.ty(cp) t
7 (min) 'F lbm/ft2 17o s-1 8s s-~
s
9 20 239 0.4516 0.1763 505 738
50 244 0.7736 0.0298 446 521
11 83 . 245 1.1109 0.0046 389 . 360
12 119 245 1.3101 0.0008 194 157
13 149 245 1.3858 0.0003 102 78
14
An invention has beer, shown with several advantages.
16 The cross-linking system of the present invention provides
17 an increase in viscosity in an aqueous well fracturing fluid
18 by a method which is si:~ple and economical. The cross-
19 linking system provides a fracturing fluid which is shear
stable at normal fractur'_::g pump rates. The delayed borate
21 cross-linking of the hydrated polymer occurs without the use
22 of suspended solids. Because the delay mechanism does not
23 rely upon the dissolution of solids in solution, the delay
24 time can be precisely ad;usted. Since the rate of cross-
linking is a function of the pH of the complexor, the rate
26 can be adjusted while the fob is running at the well site by
27 the addition of caustic or acid to the complexar solution.
28 Because glyoxol, in alkaline water, slowly converts to an
29 acid, it serves to decrease the pH of the polymer gel with
time, thereby decreasing the viscosity of the fluid for
31 easier cleanup.
32
33 While the invention has been shown in only one of its
34 forms, it is not thus limited but is susceptible to various
17 -
1 changes and modifications without departing from the spirit
2 thereof.
0 18
