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Claims  |
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What is claimed is:
1. A method for hydrating a polymer comprising the steps of:
(a) providing a polymer slurry;
(b) providing a base liquid;
(c) mixing said polymer slurry with said base liquid;
(d) introducing the mixture of said polymer slurry and said base liquid
into a first compartment;
(e) removing said mixture from said first compartment after an initial
residence time and introducing same into a recycle compartment;
(f) withdrawing a first portion of said mixture from said recycle
compartment, applying high shear energy to said first portion and
recycling said first portion into said recycle compartment; and
(g) withdrawing a second portion of said mixture from said recycle
compartment wherein said mixture comprises said first portion, applying a
high shear energy to said second portion and introducing said second
portion into an exit chamber, wherein said first and second high shear
energies are sufficient to substantially fully hydrate said polymer.
2. The method of claim 1 wherein said applications of high shear energy are
provided at least in part by centrifugal pumps, in-line static mixing
devices, paddle mixers or combinations thereof.
3. The method of claim 1 wherein said applications of high shear energy are
provided by a plurality of pumps, each having a flow rate of greater than
50 gallons per minute and providing a pressure of greater than 60 psi, in
combination with in-line static mixing devices.
4. The method of claim 1 wherein the total high shear energy provided to
said mixture is equal to at least two hydraulic horsepower for every
barrel/minute of mixture withdrawn from said exit chamber.
5. The method of claim 1 wherein the total high shear energy provided to
said mixture is from about 3 to about 4 hydraulic horsepower for every
barrel/minute of mixture withdrawn from said exit chamber.
6. The method of claim wherein said first compartment comprises a plurality
of chambers separated by baffles.
7. The method of claim 1 wherein the time interval between the mixing of
said polymer slurry with said base liquid and the application of shear to
said first portion of said mixture is at least about 45 seconds.
8. The method of claim 1 wherein the flow of said mixture through said
first compartment is essentially plug flow.
9. The method of claim 1 wherein the polymer is slurried into a
hydrocarbon-based fluid.
10. The method of claim 1 wherein the polymer is slurried into an
aqueous-based fluid.
11. The method of claim 1 wherein the polymer is selected from the group
consisting of xanthan gum, guar gum, hydroxypropyl guar,
carboxymethylhydroxypropyl guar, hydroxyethylcellulose and combinations
thereof.
12. The method of claim 1 wherein said base liquid comprises water.
13. The method of claim 1 wherein said base liquid comprises water and a
buffer.
14. The method of claim 1 wherein said base liquid comprises water and a
salt selected from the group consisting of KCl, NH.sub.4 Cl, CaCl.sub.2
and NaCl.
15. The method of claim 1 wherein the pH of the mixture is monitored
continuously.
16. The method of claim 1 wherein the temperature of the mixture is
monitored continuously.
17. The method of claim 1 wherein the viscosity of the mixture is monitored
continuously.
18. The method of claim 1 wherein the polymer slurry further comprises a
surfactant and a suspension agent.
19. The method of claim 1 wherein the polymer slurry is substantially fully
hydrated in less than about 3 minutes from the time of initial mixing.
20. The method of claim 1 wherein the pH of the mixture is between about
6.5 and 7.5 and the temperature is greater than about 55.degree. F.
21. The method of claim 1 wherein the fluid is pumped down a well-head.
22. The method of claim 1 wherein said mixing step comprises:
(a) introducing a stream of said polymer slurry into a stream of said base
liquid, and
(b) dispersing said polymer slurry in said base liquid.
23. The method as claimed in claim 22 wherein the dispersion is
accomplished using a pump and in-line static mixing device.
24. A method for hydrating a polymer comprising the steps of:
(a) providing a polymer slurry comprising a hydratable polymer dispersed in
a hydrocarbon liquid;
(b) providing an aqueous base liquid;
(c) mixing said polymer slurry with said aqueous base liquid;
(d) dispersing said polymer slurry in said aqueous base liquid using an
in-line static mixing device;
(e) introducing said mixture into a first compartment which comprises a
plurality of chambers separated by baffles, each chamber except the first
in fluid communication with a preceding chamber;
(f) introducing said mixture after at least about 45 seconds from the time
of initial mixing into a recycle compartment which is in fluid
communication with an exit compartment;
(g) withdrawing a first portion of said mixture from said recycle
compartment, applying high shear energy to said first portion with a
centrifugal pump and a mixer element, and recycling said first portion
into said recycle compartment;
(h) withdrawing a second portion of said mixture from said recycle
compartment wherein said mixture comprises said first portion, applying a
high shear energy to said second portion with a centrifugal pump and a
mixer element, and a introducing said second portion into said exit
compartment, wherein the combined first and second high shear energies are
at least two hydraulic horsepower for every barrel/minute of mixture
withdrawn from said exit chamber;
(i) removing said mixture from said exit compartment; and
(j) adding proppants to said mixture and pumping it into a well.
25. A method for the fracturing of a subterranean formation comprising the
steps of:
(a) providing a polymer slurry;
(b) providing a base liquid;
(c) combining said polymer slurry with said base liquid;
(d) dispersing the polymer slurry in the base liquid;
(e) maintaining the mixture in a first compartment for from about 45 to
about 90 seconds;
(f) introducing liquid from said first compartment into a recycle
compartment;
(g) removing a first portion of the mixture from the recycle compartment
with a high shear pump;
(h) pumping the mixture back into the recycle compartment;
(i) removing a second portion of the mixture from said recycle compartment
with a high shear pump;
(j) pumping the second portion of the mixture into an exit compartment;
(k) removing substantially fully hydrated mixture from said exit
compartment;
(l) adding proppants to the substantially fully hydrated mixture; and
(m) injecting said hydrated mixture into a subterranean formation under
hydraulic pressure.
26. The method of claim 25 wherein the polymer is slurried into a
hydrocarbon-based fluid.
27. The method of claim 25 wherein the polymer is selected from the group
consisting of guar, hydroxypropyl guar, carboxymethylhydroxypropyl guar,
and hydroxyethylcellulose and combinations thereof.
28. The method of claim 25 wherein the base liquid is selected from the
group consisting of water, water and KCl, water and NH.sub.4 Cl, and water
and NaCl.
29. The method of claim 25 wherein the dispersion in step (d) is imparted
by a static mixing device.
30. The method of claim 25 wherein high shear energy is imparted to the
mixture at least in part by a centrifugal pump and mixer element.
31. The method of claim 25 wherein the polymer mixture is substantially
fully hydrated in less than about 3 minutes.
32. An apparatus effective for the hydration of polymer gels comprising:
(a) a first vessel for containing a polymer slurry;
(b) a second vessel for containing a base liquid;
(c) means to combine said polymer slurry with base liquid to form a
mixture;
(d) a first compartment having a residence time of greater than about 45
seconds;
(e) a recycle compartment in fluid communication with said first
compartment;
(f) means to withdraw a first portion of a fluid from said recycle
compartment, impart high shear energy to the first portion and return the
first portion to said recycle compartment;
(g) an exit compartment;
(h) means to withdraw a second portion of a fluid from said recycle
compartment, impart high shear energy to the second portion and to
introduce the second portion into said exit compartment, and
(i) means for withdrawing fluid from said exit compartment.
33. The apparatus of claim 32 further comprising an in-line static mixing
device to disperse said polymer slurry within said base liquid.
34. The apparatus of claim 32 further comprising a plurality of baffled
chambers within said first compartment which impart essentially plug flow
to the mixture.
35. The apparatus of claim 32 wherein the high shear is imparted by a
plurality of centrifugal pumps.
36. The apparatus of claim 32 wherein the high shear is imparted by a
plurality of centrifugal pumps in combination with a plurality of in-line
static mixing devices.
37. An apparatus effective for the hydration of polymer-based fracturing
fluids comprising:
(a) a first vessel for containing a polymer slurry;
(b) a second vessel for containing an aqueous base liquid;
(c) means to combine said polymer slurry with said aqueous base liquid to
form a mixture;
(d) an in-line static mixing device to disperse said mixture;
(e) a first compartment comprising a plurality of chambers in fluid
communication with each other, said first compartment having a residence
time of at least about 45 seconds;
(f) a recycle compartment in fluid communication with said first
compartment;
(g) means to withdraw a first portion of fluid from said recycle
compartment and return the first portion to said recycle compartment,
comprising a high shear pump in fluid communication with an in-line static
mixing device;
(h) an exit compartment;
(i) means to withdraw a second portion of fluid from said recycle
compartment and to introduce the second portion into said exit
compartment, comprising a high shear pump and an in-line static mixing
device, and
(j) a means for withdrawing fluid from said exit compartment. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention generally relates to fracturing fluids useful for
fracturing subterranean formations to facilitate the recovery of resources
such as oil and natural gas, and in particular, the present invention
relates to a method and apparatus useful for providing the rapid and
continuous hydration of polymer-based fracturing fluids.
BACKGROUND OF THE INVENTION
The use of fracturing fluids for well stimulation is well-known. Fracturing
fluids are pumped down a well into a subterranean formation under
hydraulic pressure until fracture of the formation is achieved. As a
result, production of the well can be improved.
Proppants are typically added to the fracturing fluid before injection into
the well. The proppants are useful in propping open the fractures produced
during the process to maintain channels in the subterranean formation
through which oil or other fluids can flow. It is beneficial if the
fracturing fluid has a high viscosity, as this permits a large amount of
proppant to be carried by the fracturing fluid.
One type of fracturing fluid comprises a polymer and a base liquid, e.g. an
aqueous solution. The polymer is combined with the aqueous solution and
hydrates, or gels, over a period of time, causing the fluid mixture to
become more viscous. Proppants and other desired additives can be mixed
with the hydrated, viscous fluid, which is then pumped into a well under
hydraulic pressure.
One problem encountered with polymer-based fracturing fluids is the length
of time required for hydration. Typically, ten minutes or more are
required for the polymer to achieve full hydration, and hence, for the
fluid to achieve full viscosity. As a result, large tanks are typically
utilized to produce batches of hydrated fracturing fluids at the job site.
Wasted fluids often result due to hydrating more polymer than is necessary
to complete a particular fracture job.
Therefore, a need has arisen for methods to conduct continuous or
"on-the-fly" fracturing fluid hydration. On-the-fly hydration is
accomplished by continuously hydrating a sufficient amount of polymer for
injecting into the well as required during the fracture job, as opposed to
batch hydration, where the entire amount of fluid which is estimated to be
necessary is hydrated in one batch prior to the job. On-the-fly fluid
hydration provides a number of advantages including: ability to vary the
amount of polymer added during the fracture process; losses due to unused
fluid left in batch tanks are reduced; disposal costs for unused fluid are
reduced; tank cleaning costs are reduced; on-site time is reduced; the
need for bactericides and buffers is reduced; job sites are left cleaner
since there are fewer spills of fluids and materials; and overall job
efficiency and safety is improved by reducing the labor and efforts
required by equipment operators prior to the actual pumping of the job.
A previous technique for on-the-fly fracture fluid hydration utilizes
chemicals to eliminate the storage tank for holding the fluid during
hydration. Anderson et al. U.S. Pat. No. 4,635,727, discloses a method for
the formation of a hydrated gel from a guar gum by utilizing cross-linking
agents which allow the gel to continue to hydrate in their presence. The
disclosed cross-linking agents include zirconium lactate and aluminum
chlorohydrate. The gel is pumped into the well before complete hydration
is achieved and continues to hydrate in the well until full viscosity is
reached. However, it is desirable that hydration be substantially complete
before the fluid is pumped into the well in order to permit the addition
of large amounts of proppants.
Adams, Jr., U.S. Pat. No. 4,716,932, discloses an apparatus for the
gelation of a polymer fracturing fluid. Dry polymer is mixed with water in
a storage tank. The mixture is then pumped through a long manifold to
achieve hydration. The disclosed manifold is a 115-foot long section of
14-inch diameter pipe. However, a pipe of this size presents even greater
cleaning problems and waste disposal problems than a batch tank. In other
words, once the fracture job is complete, the fluid remaining in the pipe
would require disposal, and the pipe itself would require cleaning.
Constien, et al., U.S. Pat. No. 4,828,034, discloses a method for
continuously producing a hydrated fracture fluid from a slurried polymer
during the fracturing of a subterranean formation. This method utilizes a
high shear pump followed by a plug flow tank followed by another high
shear pump and another plug flow tank. It is disclosed that substantially
full hydration can be achieved in less than 5 minutes during this
operation.
Although the method taught by Constien et al. provides a number of benefits
over methods disclosed in the prior art, it also suffers from a number of
disadvantages. For example, the high shear pumps employed in the method of
Constien et al. are not efficiently located in the process. Also, a
separate pump must be employed for each application of shear.
Therefore, it would be advantageous to have a continuous hydration method
and apparatus that permitted hydration prior to introduction of the fluid
into a well. It would also be advantageous if clean-up after the fracture
job could be simplified and left-over fluid could be reduced to a minimum.
Additionally, it would be advantageous if a method and apparatus could be
provided for producing a continuously-hydrated fracturing fluid in an
efficient and rapid manner.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and apparatus for
continuously and rapidly hydrating a polymer contained in a polymer-based
fracturing fluid is provided.
A preferred embodiment of the method in accordance with the present
invention includes a step of mixing a polymer slurry and a base liquid.
The intensity of the initial mixing of the two components does not have to
be very high, just enough mixing to disperse the polymer slurry in the
base liquid is sufficient. Preferably, the base liquid is an aqueous
solution. The polymer slurry and base liquid mixture is introduced into a
first compartment. The purpose of this first compartment is to provide an
initial time lag between the mixing of the polymer and base liquid and
subsequent high shear steps. The mixture flows through the first
compartment, preferably in a plug flow manner, and enters a recycle
compartment, preferably after a residence time in the first compartment of
at least 45 seconds. A first portion of the mixture in the recycle
compartment is withdrawn, subjected to high shear and then returned to the
recycle compartment. A second portion of the mixture in the recycle
compartment is withdrawn, subjected to high shear and introduced into an
exit compartment. Substantially fully hydrated fluid can be withdrawn from
the exit compartment and employed in a well fracture job. As used herein,
the term "substantially fully hydrated fluid" will be understood to mean a
fluid which contains a polymer which is at least 90 percent, and
preferably 95 percent, hydrated. Preferably additives, e.g. proppants, are
introduced into the hydrated fracture fluid prior to its being pumped into
the well.
A preferred embodiment of an apparatus for continuously hydrating a
polymer-based fracturing fluid is also provided in accordance with the
present invention. The apparatus includes a first vessel for containing a
polymer slurry and a second vessel for containing a base liquid. A device
is provided to combine the polymer slurry with the base liquid to form a
mixture. Preferably, the device for mixing the two components includes a
pump and an in-line static mixing device. A first compartment for
receiving the mixture is also provided. At flow rates employed in the
practice of the present invention, the first compartment preferably has a
residence time of at least about 45 seconds. A recycle and an exit
compartment are also provided. In fluid communication with the recycle
compartment is a device for: a) withdrawing fluid from the recycle
compartment; b) imparting high shear energy to the fluid; and c) returning
the fluid to the recycle compartment. Preferably, this device includes,
piping, a centrifugal pump, and an in-line static mixing device, for
providing high shear energy to a fluid. Similar devices are also provided
for: a) withdrawing a second portion of a fluid from the recycle
compartment; b) imparting high shear energy to the fluid; and c)
introducing the fluid into the exit compartment. Mechanisms can also be
provided for incorporating additives, such as proppants, into the fluid
prior to its introduction to a well.
The apparatus of the present invention provides a number of advantages over
the prior art. For example, it has been discovered that the application of
shear during the initial dispersion of the polymer slurry into the base
liquid is a highly inefficient way to increase the rate of hydration. This
unexpected discovery is contrary to the teachings of Constien et al. in
U.S. Pat. No. 4,828,034. Constien et al. disclose that: "The slow initial
increase in viscosity is related to the method of introduction of slurried
polymer into the water and the intensity of mixing which is occurring at
that point. By introducing the slurry directly into a flow stream (rather
than into the top of an open mixing vessel) the dispersion time can be
reduced. Intense mixing of the fluid at this time is also very helpful".
In other words, according to the teachings of Constien et al., the
hydration rate can be increased by applying high shear energy during the
initial dispersion. Unexpectedly, the present inventor has discovered that
this is not the case. Therefore, in the present invention high shear
energy is preferably not applied until the mixture reaches the recycle
stage. This provides a more efficient apparatus and method.
Additionally, it has been discovered that recycling the fracturing fluid
improves the efficiency and speed of hydration. In this way, the present
invention is capable of continuously producing substantially fully
hydrated fracturing fluids in as little as 3 minutes or less. This is an
important advantage.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic view of a preferred embodiment of an
apparatus in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed toward a method and apparatus for the
hydration of a polymer dispersed within a base liquid. Rapid, effective
hydration is achieved by the timely application of an effective amount of
shear energy.
Hydratable polymers are typically used in fracturing fluids due to the
large increase in viscosity of the fluid as the polymer hydrates. The rate
of hydration is affected by a number of factors. An important factor is
the amount of mixing that the polymer/base liquid mixture is subjected to.
It was previously thought that in order to increase the hydration rate,
one need merely increase the intensity of mixing, i.e., the shear energy
to which the mixture is subjected. However, the present inventor has
discovered that not only is the amount of shear energy which is applied
important, but also the timing of the application and the manner in which
the shear energy is applied to the fluid.
The present invention will be described with reference to FIG. 1. A
prefered embodiment of the apparatus 10 of the present invention is
illustrated in FIG. 1. The apparatus includes a slurry tank 12 having a
mixing paddle 14. The slurry tank 12 contains a hydratable polymer
dispersed in a liquid phase.
Any of a large number of hydratable polymers known to those skilled in the
polymer-based fracturing fluid art are suitable for use in the present
invention. Examples of suitable polymers include xanthan gum, guar gum,
guar gum derivatives (e.g. hydroxypropyl guar and
carboxymethylhydroxypropyl guar), and cellulose derivatives (e.g.
hydroxyethylcellulose). Typically, the polymer slurry comprises about 4
pounds of polymer per gallon of liquid. However, this amount will vary
with changing conditions such as desired final viscosity, temperature, and
pH of the system. Preferably, the temperature of the mixture immediately
after mixing is greater than about 55.degree. F. and the pH is from about
pH 6.5 to about pH 7.5, and most preferably from about pH 6.8 to about pH
7.2. Viscosity, temperature and pH are preferably monitored continuously
and adjusted as necessary.
The liquid phase preferably is diesel oil. However, other hydrocarbons and
water-based liquids can be utilized, including but not limited to crude
oil, crude oil distillates, vegetable oils, silicone oils, animal oils and
treated water. Further, chemical additives can be blended into the polymer
slurry. These chemical additives preferably include, but are not limited
to, surfactants and suspension agents.
In a preferred embodiment, the polymer slurry tank 12 is 41/2 feet.times.5
feet.times.8 feet with a volume of about 1,350 gallons. An outlet 15 is
provided at or near the bottom of the tank 12. Preferably, the tank 12 is
equipped with a device to measure volume (not shown), such as a marked
strap on the side to permit visual measurement of the slurry volume. The
bottom of the tank 12 can be sloped to aid in the drainage of the polymer
slurry to the outlet 15. A baffle (not shown) can also be provided across
the tank 12 to prevent fluid shift during transportion of the device 10.
To provide ease of transportation, the entire device 10 can be mounted on
a truck or trailer.
An entry port (not shown), for example a 16 inch hatch with a 10 inch
opening, for adding polymer prior to or during the fracture operation can
be provided. To insure that the polymer slurry remains homogeneous, the
polymer slurry tank 12 can be agitated by one or more paddles 14. These
paddles can, for example, be operated hydraulically. Agitation may also be
accomplished by circulating the polymer slurry through pipes (not shown)
located in the tank 12.
The polymer slurry is pumped via a slurry pump 16, for example a
hydraulically driven centrifugal pump. Examples of suitable slurry pumps
include a 11/2 inch.times.3 inch.times.10 inch centrifugal pump or an SB
11/2 H "Sand Piper" pump manufactured by the Warren-Rupp Company. The flow
rate from the pump can be controlled by a hydraulic valve. Preferably, the
flow rate is measured using a mass flow rate meter 18.
The base liquid is preferably water and more preferably is a buffered
aqueous solution containing, for example, about 2% KCl. Other salts can
also be employed as buffering agents, for example, NH.sub.4 Cl, NaCl or
CaCl.sub.2. The base liquid is held in one or more tanks 20 until it is
combined with the polymer slurry. The mixture of polymer slurry and base
liquid passes from suction pump and manifold 22 through flow meter 24 and
fluid level control 26. The mixture pH can be adjusted at this point. The
mixture is further dispersed by an in-line static mixing device 28 before
entering into a first compartment 30. The intensity of mixing provided by
the pump and manifold 22 and the in-line static mixing device 28 does not
have to be very great. The purpose of the pump and manifold 22 and in-line
mixer 28 is merely to disperse the polymer slurry in the base fluid.
The first compartment 30 comprises three chambers 32, 34 and 36. The three
chambers 32, 34 and 36 are separated by baffles 33 and 35. The mixture
passes through the three chambers 32, 34 and 36 of the first compartment
30 in essentially plug flow. The purpose of the first compartment is to
provide a time interval between the time the polymer slurry and base
liquid are combined at pump and manifold 22 and the time that the mixture
enters into a recycle compartment 38. Preferably this time interval is
equal to at least 45 seconds and more preferably is between about 45 and
about 90 seconds.
The mixture of the polymer slurry and base liquid which is present in the
recycle compartment 38 is subjected to high shear energy. A first portion
of the mixture is withdrawn from recycle compartment 38 through inlet 52
of pipe 58 by centrifugal pump 50. After passing through centrifugal pump
50, the mixture continues through pipe 58, around in-line static mixing
device 54 and discharges from outlet 56 into recycle compartment 38. The
combination of the centrifugal pump 50, the in-line static mixing device
54 and the pipe 58 itself impart a high shear energy to the mixture
passing therethrough.
A second portion of the mixture in recycle compartment 38 is withdrawn
through pipes 60 and 62. Pipes 60 and 62 contain centrifugal pumps 64 and
66 and in-line mixers 68 and 70, respectively. These elements combine to
impart a high shear to the second portion of the mixture withdrawn from
recycle compartment 38. This second portion of the mixture is introduced
into exit compartment 40. A substantially fully hydrated fracturing fluid
can be withdrawn from exit compartment 40 through outlet 72.
In a preferred embodiment of the present invention, the centrifugal pumps
50, 64 and 66 are 8 inch.times.10 inch Crane-Deming centrifugal pumps or
similar type pumps. These particular pumps are rated at 60 barrels per
minute at 85% efficiency. While the rating is reduced at higher
elevations, preferably the volumetric flow rate never falls below 50
barrels per minute. The pipes 58, 60 and 62 are preferably 8" diameter
pipes that contain in-line static mixing devices 54, 68 and 70 that are
approximately 2 feet long. In-line static mixing devices are available
from, for example, Chemix and Lightnin.
In order to achieve substantially full hydration, a certain minimum shear
energy must be supplied to the mixture. Preferably, the energy is at least
2, and more preferably from about 3 to 4 hydraulic horsepower for every
barrel per minute of fracturing fluid exiting compartment 40 through
outlet 72. As used herein, the term hydraulic horsepower shall be
calculated according to the equation:
##EQU1##
In a preferred embodiment of the present apparatus the centrifugal pumps
50, 64 and 66 have a flow rate of from about 50 to about 70 barrels per
minute and a pressure of from about 60 to 80 psi. Preferably, the flow
rate of the fracturing fluid which is withdrawn from exit chamber 40
through outlet 72 is from about 60 to about 90 barrels per minute, and
more preferably about 75 to about 85 barrels per minute. The total volume
of the first compartment 30, the recycle compartment 38 and the exit
compartment 40 is preferably from about 200 to about 250 barrels.
Minimum shear energy imparted to the mixture by the combination of pipes
58, 60 and 62; centrifugal pumps 50, 64 and 66 and static mixing devices
54, 68 and 70, is equal to at least about 2 hydraulic horsepower for each
barrel per minute of fluid withdrawn from chamber 40 through outlet 72.
Preferably the shear energy input rate is from 3 to 4 hydraulic horsepower
per barrel per minute. At rates of less than two hydraulic horsepower per
minute, the energy is typically insufficient to achieve substantially full
hydration. As the energy increases, the hydration rate increases. However,
at rates over 5 hydraulic horsepower per barrel per minute, the excess
energy required to drive the centrifugal pumps is typically not worth the
relatively small increases in hydration rate.
Alternatively, the shear energy can be applied to the mixture by devices
other, than centrifugal pumps and in-line static mixing devices. For
example, paddle mixers can be employed. As used herein, the term "paddle
mixers" will include blade type blenders, dispersators, propeller mixers,
etc.
Compartment 40 includes an outlet 72 for the removal of the substantially
fully hydrated fracturing fluid. With two pumps pumping fluid into
compartment 40 at the rate of 55 barrels per minute each, it is possible
to withdraw fluid from compartment 40 at a rate of 110 barrels per minute.
However, the fracturing fluid is typically drawn off at a rate of
approximately 85 barrels per minute or less. Excess fluid can flow over
wall 37 into recycle compartment 38. After removal from exit compartment
40, additional items can be blended into the fluid, such as proppants and
cross-linking agents, before it is pumped into a well.
It is contemplated that the hydration of the fluid is substantially
complete upon the removal from exit compartment 40. The time necessary to
substantially fully hydrate the polymer is preferably less than 3.5
minutes, more preferably less than 3 minutes and most preferably less than
2.5 minutes.
The invention has been described in detail with particular reference to
preferred embodiments thereof, but it would be understood that variations
and modifications can be effected within the spirit and scope of the
invention as described hereinabove and as defined in the appended claims.
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