U.S. patent application number 11/729563 was filed with the patent office on 2008-10-02 for system and method for separating, monitoring and sampling coiled tubing flow back returns.
This patent application is currently assigned to Tetra Technologies, Inc.. Invention is credited to David Odum, Henry C. Reeves.
Application Number | 20080236822 11/729563 |
Document ID | / |
Family ID | 39792277 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080236822 |
Kind Code |
A1 |
Reeves; Henry C. ; et
al. |
October 2, 2008 |
System and method for separating, monitoring and sampling coiled
tubing flow back returns
Abstract
The invention relates to a system and method for separating, and
safely monitoring and sampling flow back fluid returns from coiled
tubing operations in oil and natural gas wells. The system
comprises a flow back tank; one or more gas diffusers; one or more
shale shakers; and a chute, which diverts flow from the gas
diffusers to a sampling site positioned near the perimeter of the
flow back tank. The system also has a volume level indicator on or
near the perimeter of the flow back tank. The method comprises
piping fluid returns from a wellbore, separating the trapped gases
from the fluid returns, directing the degassed fluids to a shale
shaker to separate the solids and directing the separated solids
and liquids into separate tanks for analysis and reconditioning, if
necessary. Cleaned liquids may be recirculated back to the
wellbore.
Inventors: |
Reeves; Henry C.; (Sandia,
TX) ; Odum; David; (Corpus Christi, TX) |
Correspondence
Address: |
D'AMBROSIO & ASSOCIATES, P.L.L.C.
10260 WESTHEIMER, SUITE 465
HOUSTON
TX
77042
US
|
Assignee: |
Tetra Technologies, Inc.
|
Family ID: |
39792277 |
Appl. No.: |
11/729563 |
Filed: |
March 29, 2007 |
Current U.S.
Class: |
166/267 |
Current CPC
Class: |
E21B 49/08 20130101;
E21B 21/063 20130101; E21B 19/22 20130101 |
Class at
Publication: |
166/267 |
International
Class: |
E21B 43/00 20060101
E21B043/00 |
Claims
1. A system for separating, monitoring and sampling flow back fluid
returns in coil tubing operations for an oil and natural gas well
comprising a wellbore, the fluid returns comprising gases, liquids
and solids, the system comprising: one or more gas diffusers for
removing gases from the fluid returns; means adapted to connect the
wellbore to the one or more gas diffusers; a flow back tank for
receiving liquids and solids from each gas diffuser, the flow back
tank comprising a perimeter; a chute adjacent to each gas diffuser
for collecting the fluid returns after the gases are removed, the
chute slanted towards the perimeter of the flow back tank; a
sampling site positioned adjacent the perimeter of flow back tank
for monitoring flow back fluids within the flow back tank; and
means for analyzing samples of flow back fluid returns to determine
conditions down the wellbore.
2. The system of claim 1 wherein each gas diffuser is rigidly and
removably attached to the flow back tank.
3. The system of claim 2 wherein each gas diffuser is rigidly and
removably attached to the flow back tank with quick disconnects,
the disconnects positioned adjacent ground level.
4. The system of claim 1 further comprising a means for ascending
the flow back tank, the means for ascending the flow back tank is a
stairway, a ramp, or a ladder.
5. The system of claim 4 wherein the means for ascending the flow
back tank further comprises a personnel access platform, the
platform positioned adjacent the area of the perimeter approximate
the chute.
6. The system of claim 1 further comprising means for sampling the
flow back fluids within the flow back tank, the sampling site for
the means for sampling positioned adjacent the perimeter
approximate the chute.
7. The system of claim 1 further comprising a volume level
indicator to determine the volume of fluid within the flow back
tank.
8. The system of claim 7 wherein the volume level indicator
comprises an external sight glass, the external sight glass
comprises a U-shaped cylinder, the cylinder comprising two
contiguous columns, a first column positioned internal to the flow
back tank, the second column positioned external to the flow back
tank.
9. The system of claim 1 further comprising one or more shale
shakers for separating the liquids and solids discharged from each
gas diffuser, each shale shaker positioned to receive the liquids
and solids discharged from the gas diffuser.
10. The system of claim 9 wherein each shale shaker comprises a
liquid discharge channel so that the liquids are directed to the
flow back tank and a solids discharge channel so that the solids
are directed to a collection bin.
11. The system of claim 10 further comprising a liquid sampling
site positioned between the shale shaker and the flow back tank for
observing and sampling liquids leaving the shale shaker.
12. The system of claim 10 further comprising a solids sampling
site positioned between the shale shaker and the collection bin for
observing and sampling solids leaving the shale shaker.
13. The system of claim 10 further comprising a liquid treatment
and makeup tank for reconditioning the liquids prior to returning
the liquids to the wellbore.
14. A system for separating, monitoring and analyzing flow back
fluid returns in coil tubing operations for an oil and natural gas
well comprising a wellbore, the fluid returns comprising gases,
liquids and solids, the system comprising: one or more gas
diffusers for removing gases from the fluid returns; a means
adapted to connect the wellbore to the one or more gas diffusers; a
flow back tank for receiving liquids from the gas diffuser, the
liquids comprising particulate matter, the flow back tank
comprising a perimeter; the one or more gas diffusers rigidly and
removably attached to the flow back tank; a chute fixedly attached
to the one or more gas diffusers for collecting the fluid returns
after the gases are removed, the chute slanted towards the
perimeter of the flow back tank; a sampling site positioned
adjacent the perimeter of the flow back tank for monitoring and
sampling liquids within the flow back tank; a means for ascending
the flow back tank, the means for ascending positioned adjacent the
perimeter of the flow back tank in the area of the chute; a means
for sampling the liquids within the flow back tank, the means for
sampling positioned adjacent the perimeter approximate the chute; a
volume level indicator positioned on or near the perimeter of the
flow back tank; one or more shale shakers for separating the
liquids from the solids discharged from the gas diffuser, the
solids directed to a collection bin and the liquids directed to the
flow back tank; means for sampling the solids directed to the
collection bin; and means for analyzing the liquids and solids to
determine conditions down the wellbore.
15. A method for separating, monitoring and sampling flow back
fluid returns in oil and natural gas wells, the method comprising:
a. piping fluids from a wellbore to one or more gas diffusers, the
fluids comprising gases, liquids and solids, the one or more gas
diffusers rigidly and removably attached to a flow back tank; b.
separating the gases from the fluid returns within each gas
diffuser and releasing the gases to the atmosphere; c. discharging
the remaining liquids and solids from each gas diffuser by
directing the liquids and solids down a chute leading from each gas
diffuser to one or more shale shakers; d. separating the liquids
from the solids as they pass through each shale shaker; e.
directing the liquids down a liquid discharge channel to the flow
back tank and sending the solids down a solids discharge channel to
a collection bin; f. monitoring and sampling the liquids as the
liquids flow down the liquid discharge channel; and g. monitoring
and sampling the solids as the solids flow down the solids
discharge channel.
16. The method of claim 15 further comprising positioning a
platform adjacent a perimeter of the flow back tank to facilitate
monitoring and sampling of the liquids within the flow back
tank.
17. The method of claim 15 further comprising analyzing the liquids
after they are sampled to determine composition of liquids.
18. The method of claim 17 further comprising the step of
reconditioning the liquids prior to returning the liquids to the
wellbore.
19. The method of claim 15 further comprising visually inspecting
the solids at a solids sampling site positioned between the shale
shaker and the collection bin.
20. The method of claim 19 further comprising analyzing the solids
to determine conditions down the wellbore.
21. The method of claim 15 further comprising positioning a volume
level indicator on the perimeter of the flow back tank.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a system and method for
separating and real time monitoring of high pressure flow back
returns during coiled tubing drilling and other oil and gas well
operations, more particularly inspecting and sampling the returns
and analyzing the samples to monitor downhole operational
performance.
BACKGROUND OF THE INVENTION
[0002] In coiled tubing oil and gas operations, it is critically
important to monitor the effectiveness of the downhole operations,
particularly the condition of downhole tools and their work
performance. This is especially important in coiled tubing
operations, which circulate fluids and completion fluids under
extremely high pressures. Conditions are encountered downhole that
adversely affect the coiled tubing downhole operations. Tubulars
can fail; tools break; debris from the formation mixes with return
fluids; formations fracture; and other detrimental events can
occur. Knowing what is happening downhole is important. Monitoring
downhole activities, however, is difficult. Aside from using costly
and lengthy fiber optics, it is not practical to physically view,
in real time, what is occurring down a wellbore that may be
thousands of feet in depth. Because of this predicament, there are
two primary methods for monitoring the effectiveness of any
on-going coiled tubing operation.
[0003] The first method is to measure the penetration rate and the
coiled tubing string pressure. If the penetration rate or string
pressure changes drastically, the operator will know that either
the drill bit has been damaged, or the drill bit has encountered a
different medium. However, by just measuring the penetration rate
and string pressure, the operator cannot determine which of the
aforementioned problems exist. Therefore, the operator must stop
drilling and pull the coiled tubing string out of the wellbore to
check the condition of the drill bit. Depending on the depth of the
well, this can be extremely time-consuming, resulting in
unnecessary delays, and further increasing costs.
[0004] The second method to monitor the effectiveness of the
operation is to analyze the oil and gas fluids when they are
circulated from the bottom of the well. The purpose of circulating
the fluids back to the surface is to aid in the removal of all
types of debris, which can include pieces of metal broken-off from
downhole tools. Sand and earth, along with other debris, are also
picked up by the fluid returns. The fluids are constantly
circulated back up the annulus to a surface containment unit
whereby debris gathered downhole are observed, monitored and
removed. These circulated oil and gas fluids are often referred to
as flow back fluid returns.
[0005] Under current methods, high pressure flow back fluid returns
are piped from the well head into a gas diffuser to remove gases,
and reduce the dangerously high pressures, which can sometimes
exceed 12,000 psi. During this stage, the gas diffuser discharges
gases into the atmosphere, and the remaining fluids fall down into
a collection tank.
[0006] In order to measure the effectiveness of any downhole
operation using this second method, an operator must collect grab
samples from underneath the gas diffuser, also known as a gas
buster, by precariously leaning over the tank rim and placing a
collection container underneath the hot, circulating fluid that is
being released to the atmosphere in great volumes. The operator
then visually examines the grab sample to evaluate: the type of
material being drilled, the physical properties of the fluid
returns after circulation downhole to determine if additives are
necessary, and the presence of any other unexpected substances
circulated from the bottom of the well. Additionally, the operator
can check the grab sample for metal shavings that might indicate
any degradation of the downhole tool. This is especially useful
because it allows the operator to stop the operation and bring the
tool to the surface before more serious damage is done, which, if
left unchecked, would result in even more down time and
consequently, lost revenues.
[0007] However, this technique poses a serious safety hazard for
the operator because of the fluid's high temperatures, often over
250.degree. F., and high pressures. Also, depending on the
circulating fluid's composition, the operator could encounter
exposure to dangerous chemicals, resulting in various chemical
burns or reactions.
[0008] Additionally, the circulating fluids used in hydrocarbon
well operations are often re-circulated back down the well.
Downhole, the wellbore fluids often pick up solid cuttings and
debris, which must be removed if the fluid is to be reused. Using
cleaner recirculated fluids allows for lower circulating pressures,
and also results in less wear and tear on the tools and equipment
that come in contact with the circulating fluid.
[0009] Collection tanks used in these operations are opaque, and
therefore, the operator must walk up to the tank and lean over the
rim in order to detect the volume level of the recirculated fluids
inside the tank; posing another danger for the operator. The
operator may be forced to walk out to the tank and either lean over
the tank or climb a platform to periodically check the fluid level.
These actions expose the operator to additional field hazards.
[0010] Consequently, in order to minimize the risk to the operator
and increase efficiency when monitoring and analyzing flow back
fluids, there exists a need for a system and a method that enables
the operator to quickly and efficiently monitor the characteristics
of the flow back fluids and volume of the collection tank without
being subjected to any unnecessarily dangerous conditions.
SUMMARY OF THE INVENTION
[0011] The present method and system of separating, monitoring and
sampling high pressure coiled tubing flow back fluid returns from
oil and natural gas wells allows an operator to quickly and safely
identify the physical characteristics of the flow back return
fluids by minimizing the hazards facing the operator. The greatest
danger lies in the need for the operator to monitor and sample the
returns to understand what is happening down the wellbore,
especially deep drilling and offshore wellbores where the returns
are under pressures as high as 12,000 psi to 14,000 psi and
greater.
[0012] In one embodiment of the system for separating, monitoring
and sampling flow back fluid returns, the flow back fluids
returning from the wellbore are fluids that contain gases, liquids
having particulate matter and larger solids. The solids may include
pieces of well cuttings and/or metal shavings from drilling tools
and formation debris.
[0013] High pressure flowline piping is used to connect the
wellbore to one or more gas diffusers, which are rigidly and
removably attached to a flow back tank. A choke manifold, installed
between the wellbore and gas diffuser, can be used to reduce the
dangerously high pressures, which can sometimes exceed 12,000 psi.
Advantageously, the connection between the wellbore and the gas
diffusers has a means for a quick disconnect so that the gas
diffusers can be installed rapidly. The gas diffusers remove the
trapped gases from the fluid mixture, releasing them to the
atmosphere with the rest of the fluid mixture exiting from portals
positioned on the underside of the gas diffusers.
[0014] Preferably, a chute is fixedly attached to each gas diffuser
to collect depressurized and decelerated fluid mixture. As a safety
feature, the chute is positioned so that it directs the fluid
towards the perimeter of the flow back tank. In one embodiment, a
sampling site is located adjacent to the perimeter of the flow back
tank and the chute is positioned for easier and safer monitoring
and sampling of the fluid mixture leaving the gas diffuser. In
another embodiment, a means for ascending the flow back tank is
utilized to reach the top of the flow back tank. The means for
ascending the flow back tank can include a stairway, a ramp, a
ladder or a motorized stairway. Preferably, it is positioned
adjacent the perimeter of the flow back tank and the chute in order
to provide better access to the sampling site. In an alternate
embodiment, a means for sampling the fluid mixture within the flow
back tank, such as a sampling carousel, is used, and it is also
positioned adjacent to the chute.
[0015] In another aspect of this invention, a volume level
indicator is used to determine the volume of the liquid within the
flow back tank. Preferably, the volume level indicator is visible
up to at least 30 feet from the flow back tank and is positioned on
or near the perimeter of the flow back tank so that an operator may
determine the level of the flow back tank without having to
precariously look over the edge.
[0016] In an alternate embodiment, after discharging the gases to
the atmosphere, one or more shale shakers are used to separate the
solids from the liquids as the fluids leave the gas diffuser.
Preferably, the shale shaker is positioned adjacent the gas
diffuser so that the fluid is discharged from the gas diffuser and
directed into the shale shaker. The shale shaker separates the
larger solids from the liquids within the fluid and sends the
solids to a collection bin, while the liquids, which may contain
some particulates, are directed to the flow back tank. In an
alternative embodiment, a centrifuge may be used to separate the
solid particulates from the liquids discharged from the underflow
of the shale shaker. The system of this invention further comprises
a liquids discharge channel to direct the liquids from the shale
shaker to the flow back tank and a solids discharge channel to
direct the solids to a collection bin. A safe means is also
provided for sampling the liquids and solids after they leave the
shale shaker in order to observe and analyze them to determine the
conditions down the wellbore.
[0017] In another embodiment, a method for monitoring and sampling
the flow back fluid returns of oil and natural gas wells begins
with pumping fluid returns, brought up from the wellbore, to one or
more gas diffusers. The fluid returns comprise gases, liquids and
solids. The gas diffusers are rigidly and removably attached to a
flow back tank. The gases are then separated from the fluid returns
by one or more gas diffusers and released to the atmosphere. Next,
the liquids and solids remaining within the degassed fluid are
discharged from the one or more gas diffusers into a chute that
directs the liquids and solids into a shale shaker, wherein the
solids are separated from the liquids. The solids are sent to a
collection bin via a solids discharge channel, and may be monitored
and sampled as the solids travel down the solids discharge channel
for analysis at a solids sampling site. The liquids are then
directed into the flow back tank via a liquids discharge channel,
where they may be monitored and sampled for analysis while en route
to the flow back tank at a liquid sampling site. In another
embodiment of the method of this invention illustrating a second
safety factor, the operator can safely monitor the liquids and
solids in real time by positioning a platform and means for
ascending the platform adjacent the flow back tank to observe the
liquids or solids coming out of the gas buster or shale shaker and
take samples of the materials for further analysis. Either the
liquids or the solids, preferably both, can be analyzed to
determine changes in downhole conditions.
[0018] The liquids separated from the solids are often returned
back down the wellbore to be reused in the oil and gas operations.
A reconditioning tank can be used to treat the liquids leaving the
shale shaker to refurbish the liquids prior to sending back to the
well. In still another embodiment for additional safety, the
operator reads a volume level indicator to determine the volume
within the flow back tank at a distance from the flow back
tank.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic of the invention
[0020] FIG. 2 is a side view of the system of the invention
DETAILED DESCRIPTION OF THE INVENTION
[0021] Separating, monitoring, sampling and analyzing flow back
return fluids are necessary steps in controlling the process of
coiled tubing operations. Failing to perform these steps can result
in catastrophic tool failure as well as degradation of fluids,
thereby rendering the operation ineffective. The result is
increased down time and escalated costs. However, current methods
and systems used to monitor and sample flow back fluids can pose
serious safety hazards for an operator, including burns caused by
high temperatures and/or chemical compositions of the flow back
fluid.
[0022] The present invention provides a method and system for
safely separating, monitoring and sampling flow back returns in
coiled tubing operations. Referring to FIG. 1, in one embodiment of
this invention, coiled tubing 12, preferred in well interventions
including subsea and horizontal wells, is inserted into a wellbore
17. The fluid is pumped into the well via coiled tubing 12, where
it lubricates and provides power to the drill bit. The fluid also
removes well cuttings from the bottom of the well before returning
to the surface 11. The fluid, combined with any debris and gas that
it has picked up in the wellbore 17, is known as flowback fluid
returns 15. The flow back fluid returns are a combination of
solids, dirty liquids, i.e., liquids comprising particulate matter,
and gases. The fluid returns 15 travel from the wellbore 17 to one
or more gas diffusers 20 using piping 19, 26. The piping 19 from
the wellbore 17 is joined to the piping 26 leading to the gas
diffuser 20 by a means adapted to connect 22 the piping 19, 26. In
the preferred embodiment, a quick connect such as a hammer union 22
is used as the means to connect 22 the piping 19 from the wellbore
17 to the piping 26 leading to the gas diffusers 20.
[0023] As shown in FIGS. 1 and 2, the one or more gas diffusers 20
release substantially all of the gases 16 trapped in the flow back
fluid returns 15 into the atmosphere, resulting in a significant
reduction in pressure. The remaining degassed fluids descend from
the one or more gas diffusers 20 into a chute 24 (illustrated by
FIG. 2), where they are decelerated. This is an important safety
measure since the decelerated and depressurized gases are less of a
hazard to the operator. In embodiments in which the fluid is mostly
liquid, FIG. 2, the liquid flows from the gas diffuser directly
into the flow back tank 30. Alternatively, the fluids having a high
solid content 33 are directed to an alternate gas diffuser and
shale shaker unit where they are discharged from the gas diffuser
20 down into the shale shaker 40, FIG. 1. The one or more shale
shakers 40 separate the degassed fluid into two separate streams: a
solids stream 42 and a liquids stream 32. Gases discharged into the
atmosphere may be sent to a scrubber to remove hazardous or odorous
materials before leaving the system.
[0024] The solids stream 42 is directed into a collection bin 46
via a solids discharge channel 44, and the liquids stream 32 flows
through a liquid discharge channel 37 into the flow back tank 30.
The solids stream 42 may be observed and/or collected at the solids
sampling site 48, which is positioned between the one or more shale
shakers 40 and the collection bin 46. The liquids stream 32 may be
observed and/or collected at a liquid sampling site located
adjacent the liquid discharge channel 37. Alternatively, as seen in
FIG. 2, a sampling point 36 may be used to collect a liquid sample
from the flow back tank 30. In another aspect, a centrifuge can be
used to remove particulates from the liquid stream 32. A means for
analyzing 38 the liquids stream 32 in the flow back tank 30 is used
in order to determine the physical and chemical properties of the
liquids in the flow back tank 30, before recycling them back into
the wellbore 17.
[0025] Careful monitoring by the operator of the liquid and solid
stream 32, 42 in real time is critical in maintaining efficient oil
and gas operations. By observing the types of solids that make-up
the solids stream, the operator can quickly assess the types of
materials that were in the bottom of the wellbore 17 as well as the
physical characteristics of the fluids such as composition,
viscosity, and the presence of undesirable materials, metal
shavings or pieces of tools and equipment. One method for analyzing
the materials for the presence of iron is the use of magnets
positioned in or near the collection bin 46. Other analysis
procedures for determining the physical and chemical
characteristics of the fluids, including both liquid and solid
content, are well known in the art. These procedures can be
automated or manual. With this knowledge, the operator will be able
to understand the chemical and physical events occurring downhole.
For example, if metal pieces are found in the solids discharged
from the shale shaker, and the metal pieces are determined to be
from a drill bit, the operator will know that the drill bit has
become degraded. This knowledge permits the operator to shut down
the well operation before any additional damage can be done.
[0026] As illustrated in FIG. 1, the system 10 of this invention
further comprises a system and method for monitoring in real time,
sampling, testing and reconditioning the liquids so that they can
be recirculated back to the well. The system of this invention
comprises the step of observing and/or collecting a sample from the
liquids stream 32 at the liquid sampling site 37. Problems downhole
such as damaged tools and excessive wellbore debris can be
discovered by simply looking at the fluids flowing into the flow
back tank 30. Samples of the liquids stream 32 can also be sent to
a means for analyzing and testing 64 the liquids stream 32 either
as it is discharged from the shale shaker or once it is within the
flow back tank 30. After the physical and chemical characteristics
of the liquids are determined, the liquids are sent to a liquid
makeup tank 38 for reconditioning the liquids. Careful monitoring
of the liquids stream 32 is also important for successful well
operations because, as mentioned above, an operator must know the
composition of the liquids in the flow back tank 30 so that he can
adjust the properties accordingly. The liquids 32 leaving the shale
shaker may not have the composition and physical characteristics,
such as viscosity, required for downhole operations. This is
corrected in the liquid makeup tank 38 so that any liquids returned
to the wellbore are reconditioned and corrected as to the fluids
specification. The reconditioned liquids are then recirculated to
the wellbore 17. Without this monitoring step, the resulting
recirculated fluids might not have the correct fluid properties
necessary to perform their downhole functions, for example: density
and lubricating qualities. The problems associated with obtaining
the samples such as injury to the operator are overcome by the
safety mechanisms of this invention.
[0027] Referring to FIGS. 1 and 2, one safety characteristic
comprises the rigidity of the attachment of the one or more gas
diffusers 20 connected to the tank 30. In one aspect, piping from
the wellbore is connected to piping 26 entering the gas diffuser 20
via quick disconnects 22, which are positioned adjacent ground
level and allow the gas diffusers to be quickly hooked up or
removed. The quick disconnects 22 allow the operator to efficiently
get the process of recirculating downhole fluids up and running in
a brief period of time. Another safety feature of this invention
comprises a chute 24 that slopes slightly downward towards the
perimeter 34 of the flow back tank 30 to a sampling site 36, which
is positioned adjacent the perimeter 34 of the flow back tank 30.
By using a chute 24 and directing the liquids stream 32 to the
perimeter 34, the operator does not have to lean into the tank or
be exposed to the high pressure fluids leaving the gas diffuser.
The sampling site 36 is now an easily accessible area that allows
an operator to gather samples in order to analyze the contents and
properties of the liquids exiting the one or more gas diffusers 20.
To further assist the operator in monitoring, sampling, and
analyzing the liquids and solids coming from the wellbore 17, this
invention also comprises a means to ascend 50 the flow back tank
30. Possible means for ascending 50 the flow back tank 30 include a
stairway, a ramp, or a ladder. The means for ascending 50 the flow
back tank further comprises a personnel access platform 54, which
is positioned adjacent the area of the perimeter 34 approximate the
chute 24. In one embodiment, the means for ascending 50 and the
platform 54 are movable around the perimeter 34 of the flow tank
30.
[0028] Operators must keep track of the volume of fluids within the
flow back tank. An additional safety feature is a volume level
indicator 60 that is used to alert the operator to the volume level
in the flow back tank 30 without the operator having to look over
the side of the flow back tank 30. In the preferred embodiment, the
volume level indicator 60 is made up of an external sight glass,
which comprises substantially of a U-shaped cylinder that has two
contiguous columns, where the first column is positioned internal
to the flow back tank 30, and the second column is positioned
external to the flow back tank 30.
[0029] The foregoing description of the preferred embodiments of
the invention is presented for purposes of illustration and
description, and is not intended to be exhaustive or to limit the
invention to the precise form or embodiment disclosed. The
description was selected to best explain the principles of the
invention and their practical application to enable others skilled
in the art to best utilize the invention in various embodiments.
Various modifications as are best suited to the particular use are
contemplated. It is intended that the scope of the invention is not
to be limited by the specification, but to be defined by the claims
set forth below.
* * * * *