Note: Descriptions are shown in the official language in which they were submitted.
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CONTROLLED REMOVAL OF LIQUIDS
Field of the Invention
Management of stratified liquids or one or more liquids having vertical
gradients in a
container and, more particularly, controlling the removal of liquids to limit
removal to a selected
liquid or liquids or the removal of a portion of a liquid within a range of
selected gradients.
Background of the Invention
Liquids having different specific gravities and immiscibility naturally
stratify in a
container. Also, a liquid in a container that has temperature variances in the
vertical direction
will have gradients in the specific gravity at various levels. Other physical,
chemical or
electrical characteristics may vary in a liquid and may be sensed to aid in
the management of the
liquid. A particular problem arises with the stratified liquids from natural
gas wells (NGLs) in
storage tanks and the removal of the liquids from the tanks. The liquids
stratify with the heavy
material, termed bottom sediment and water, at the bottom of the tank. On top
of the BS&W is
water, waste oil or interface, dirty oil, clean oil. On top of the liquid is
air and any gases that
may be present.
The storage tanks at well sites typically have a drain port near the bottom of
the tank and
a load-out port a selected distance above the bottom of the tank. This
distance typically being
16" for storage tanks used in the gas fields. When it is desired to remove
clean oil from a storage
tank, the bottom liquids must be removed first, in gravitational order,
according to their relative
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density, starting with the BS&W at the bottom, then water and so on. The
operators of water
trucks that are called in to remove the lower liquids often mistakenly, or
intentionally, take oil
with the water. Sometimes many barrels of oil are taken with the water and at
$60.00 or more a
barrel, this is a very expensive mistake. Additionally, there is not an
efficient cost effective way
to determine the amount of water, waste oil, dirty oil and clean oil in a
storage tank for liquid
management and to aid in scheduling trucking to minimize truck traffic to and
from the well
sites. A major consideration in issuing drilling permits for gas wells and oil
wells is the impact
on the environment. Limiting trucks to full loads only, whenever possible,
significantly reduces
truck traffic. It is desired to control the removal of the liquids in storage
tanks at gas wells and at
oil wells to: 1) limit water truck operators to the removal of water only, 2)
to have full loads
when possible for the various types of trucks that visit well sites to reduce
truck traffic, and 3) to
control the removal of one or more selected liquids or layers of a liquid from
a tank.
The apparatus and method of managing liquids in tanks has general application
but will
be disclosed in the context of liquids from gas wells. Such disclosure is not
a limitation on the
use of the apparatus and method of this invention. The invention is broadly a
system of
mechanical and electronic devices designed to secure oil and gas liquid tanks,
particularly those
in remote areas, allowing only selective removal of certain liquids. At gas
wells it is desired to
permit removal of BS&W, water and interface layers, while restricting the
removal of oil, except
under certain defined circumstances.
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Summary of the Invention
The removal of liquids from a tank is controlled by sensing one or more of the
electrical,
physical or chemical characteristics of the liquids. The system of this
invention senses the
change in the dielectric coefficient of the liquids and limits the flow of
only authorized liquids
through the outlet of the tank. If, for example, only water is to be removed
and the sensed
coefficient corresponds to that of water, the removal is permitted. However,
when the sensed
coefficient of the liquid changes from the coefficient of an approved liquid
for removal to that of
a non-approved liquid, a signal is generated. This signal is applied to an
alarm to alert the person
withdrawing the liquid that a non-approved liquid is being or is about to be
withdrawn. This
alarm alerts the person to close the valve to discontinue the removal of
liquids from the tank. As
an incentive and as a record, the signal may also activate a camera mounted to
record
information concerning the identity of the person removing the liquids and the
identification of
the truck used for offloading the liquids from the tank. A more secure system
to prevent the
removal of unauthorized liquids includes an controlled valve that is activated
by a controller in
response to the generated signal. Further, the system requires proof of
authorization to remove a
liquid from the tank. This may be done in the form of a magnetic card
activated at a control
station, such as a water plant, for removal of liquids from an identified
tank. For further
management of the liquids, such as the water recovered from the gas well and
stored in a tank at
the well site, the water truck operator is required to use the same form of
identification and
memory to record the quantity of water delivered to the water plant. This also
includes the
identification of the operator of the truck or the trucking company, the date
and time. This
system fulfills the desire to track all liquids removed from gas wells.
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The dielectric coefficient of each liquid in a tank is sensed by a capacitive
sensor. The
sensor includes capacitor plates that are in contact with the liquids in the
tank. The capacitor
plates may be parallel plates having a size and spacing appropriate for the
environment of use.
When used in a storage tank with NGLs, the plates may be rectangular in shape,
with a width of
1 centimeter and length of 8 centimeters and a spacing between the parallel
flat faces of the
plates of 1 1/2 centimeters. Other configurations of the capacitor plates and
sizes and spacing
may be used. For example, a pair of coaxial cylindrical plates may be used or
a single plate
extending into liquids with the housing of the capacitive probe or tank being
the second plate.
It is preferable that all of the circuitry necessary to convert the dielectric
to a digital
signal is within the housing of the probe that is placed inside the tank.
Alternatively, some of the
circuitry may be located outside the housing for the probe and outside the
tank. The capacitor
plates have a coating of insulating material that is resistant to corrosion
and the caustic materials
in a tank such as a tank containing NGLs. Further, the housing is made of a
material such as
polyethylene that will withstand the corrosive and caustic liquids from gas
wells that are stored
in storage tanks.
The NGLs include layers of liquids designated clean oil, dirty oil, waste oil
(interface),
water and bottom sediment and water (BS&W). These liquids are identified and
defined in the
BLM brochure "Onshore Oil and Gas Operations; Federal and Indian Oil & Gas
Leases; Onshore
Oil and Gas Order No. 4; Measurement of Oil" issued under 43 CFR 3160 and
published in the
Federal Register at Volume 54, No. 36, February 24, 1989 and effective August
23, 1989. As
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the liquids in the tank pass between the plates of the capacitive sensor, they
function as a
dielectric with a certain dielectric coefficient. In this description of the
capacitive sensor and
capacitive probe the characteristic of the liquid sensed will be termed
dielectric and/or
coefficient, with the terms being used interchangeably. The circuitry and
capacitor plates of the
probe function to convert the dielectric to a digital signal indicative of the
coefficient of the
liquid between the capacitor plates.
Many of the storage tanks for NGLs have a capacity of 400 barrels or 500
barrels and an
internal height of 20 feet. These tanks typically have two 4" openings on the
top, one of which
may be used for installing a capacitive sensor. A capacitive sensor may be
installed in tanks that
are already in use and contain volatile explosive and corrosive liquids from
gas wells or may be
installed in new tanks that have not yet been placed in service. In new tanks,
the capacitive
sensor may be attached directly to a wall at a selected distance from the
bottom of the tank. The
placement of the capacitive sensor will be at a distance with respect to the
outlet port from which
is liquids are removed to sense the coefficient of the liquid approaching the
outlet. In this way, as
the coefficient changes from that of water to that of oil, for example, a
warning or control signal
will be generated. This warning or control signal may also be generated (for
the change in)
coefficients of different liquids other than just oil and water.
In retrofit applications, the capacitive sensor is attached to a rod of
sufficient length to
hold the capacitive probe in place inside the tank. The support rod and
capacitive probe are
inserted in the tank through one of the 4" openings on top of the tank. The
capacitive probe may
be attached to the support pole to be located a fixed distance relative to the
bottom of the tank
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and relative to one or more of the outlets of the tank. Alternatively, the
capacitive probe may be
mounted on a lead screw and guided on a support pole that are inserted through
an opening in the
top of the tank. The lead screw is rotated to position the capacitive sensor
at the desired height
inside the tank. A lead screw and support pole may also be used in original
installation in a new
tank as well as in a retrofit situation. In either case, the lead screw may
have threads over
essentially the complete length of the lead screw so that the capacitive
sensor may be moved
vertically through each of the liquids in the tank to survey the liquids and
to provide information
as to the contents of the tank as well as the location of each liquid or
gradients in a liquid in the
tank.
The ability to survey and the use of the information are described in greater
detail in the
patent application entitled Apparatus and Method for Content Discrimination
having the docket
number G13:1068 and filed concurrently with this application.
Additionally, the content discrimination probe may be set at any selected
level to monitor
the removal of a selected liquid from a tank. For example, if the interface
layer is to be removed,
the content discrimination sensor or capacitive sensor is set at the bottom of
the interface layer or
in the interface layer at the same level as the orifice of the variable height
inlet/outlet orifice to
sense when the interface layer has been removed and the next liquid layer is
approaching the
outlet orifice of the variable height inlet/outlet orifice tool. Any of the
variable height inlet/outlet
orifice tools of the PCT Application Serial Number US2006/004479 filed
February 8, 2006 may
be used with the content discrimination sensor. Reference is also made to the
disclosure in the
Provisional Patent Application Serial Number 60/810,013 filed May 31, 2006.
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Brief Description of the Drawines
Additional features and advantages of the invention will be apparent from the
detailed
description which follows, taken in conjunction with the accompanying
drawings, which
together illustrate, by way of example, features of the invention; and
wherein:
Fig. 1 is a block diagram of a capacitive sensor, including a dielectric to
digital converter,
in accordance with the present invention;
Fig. 2 is a functional block diagram of a capacitance to digital converter
used in the
capacitive probe, in accordance with the present invention;
Fig. 3 is a block diagram of an alternative circuit for a dielectric to
digital converter, in
accordance with the present invention;
Fig. 4 is an illustrative diagram of a storage tank including a capacitive
sensor, in
accordance with the present invention;
Fig. 5 is an illustrative diagram of a storage tank containing natural gas
liquids with a
moveable capacitive probe, in accordance with the present invention;
Fig. 6 is a top-plan view of the capacitive probe in place in the tank along
the section
lines 7-7 of Fig. 6, in accordance with the present invention;
Fig. 7 is a front-elevation view of the capacitive probe and carrier on a lead
screw, in
accordance with the present invention;
Fig. 8 is a top-plan view of the carrier and the capacitive probe, in
accordance with the
present invention; and
Fig. 9 is a schematic diagram of the capacitive probe in a tank attached to a
variable
height inlet/outlet orifice, in accordance with the present invention.
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Detailed Description of the Invention
Reference will now be made to the exemplary embodiments illustrated in the
drawings,
and specific language will be used herein to describe the same. It will
nevertheless be understood
that no limitation of the scope of the invention is thereby intended.
Alterations and further
modifications of the inventive features illustrated herein, and additional
applications of the
principles of the inventions as illustrated herein, which would occur to one
skilled in the relevant
art and having possession of this disclosure, are to be considered within the
scope of the
invention.
Different physical, chemical and/or electrical characteristics of liquids in a
tank can be
sensed to determine the contents of the tank and when coupled with means for
determining the
position in the tank, the transitions from one liquid to another can also be
determined. The
different dielectric coefficients of liquids in a tank may be used to
discriminate and identify the
various liquids in a tank. Further, by sensing the dielectric coefficient of
liquids that are being
removed from a tank, it is possible to tell when the removal of one liquid has
been completed
and the removal of a different liquid is beginning.
A capacitive probe is used to detect the coefficients of the liquids between
the capacitor
plates of the probe and creates an output signal indicative of the coefficient
and therefore the
type of liquid between the capacitor plates of the probe. The liquid or
dielectric is identified and
converted to a digital signal. A dielectric to digital converter creates a
digital signal out which
may be called the converted coefficient of the dielectric (liquid) in contact
with the capacitor
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plates. Such a dielectric to digital converter 1 is shown in block form in
Fig. 1. A pair of
capacitor plates 3 and 4 are electrically connected to the dielectric to
digital converter 1. The
digital signal or converted coefficient that is the output of the converter 1
is applied as an input to
a communication protocol converter 5 as shown in Fig. 1. Power is provided to
both converters
by a cable 6 that combines with a data output cable 7 from converter 5 as a
power and data cable
8. The two converters 1 and 5 may advantageously be housed in the housing for
the capacitance
probe with the power and data cable communicating with circuitry outside of
the tank in which
the capacitive probe is located. The dielectric to digital 1 may also have an
input from a
temperature sensor such as an RTD, thermistor or diode. In this way, the
temperature of the
liquid or dielectric between the capacitor plates 3 and 4 may also monitored.
Additionally, the
converter 5 may have an input from a pressure sensor 11 that is useful in
determining the volume
of the liquid above the capacitor plates 3 and 4 when there is only one type
of liquid above the
pressure transducer 11 in the tank.
A housing 12 for the capacitive probe is shown in block form in Figs. 4-7. The
capacitor
plates 3 and 4 extend from the housing 12 and are in electrical contact with
the electronics in the
housing 12.
The functional block diagram of dielectric to digital converter is shown in
Fig. 2. The
particular capacitance to digital converter or dielectric to digital converter
shown in Fig. 2 is an
AD7745-24 bit, 1 channel Capacitance to Digital Converter available from
Analog Devices
(www.analog.com).
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An alternative dielectric to digital converter is shown in block form in Fig.
3. This
dielectric to digital converter employs an astable oscillator 15 coupled to
parallel capacitor plates
3 and 4. The frequency of the astable oscillator is initially set by a
variable resistor in a
frequency setting block 16. With air between the capacitor plates 3 and 4, the
frequency of the
oscillator 15 is set at 200 kilohertz. Thereafter, the frequency of the
oscillator 15 varies as the
dielectric or liquid between the capacitor plates 3 and 4. The variable
frequency, at the output of
the oscillator 15, is converted to a digital signal representative of the
coefficients of the various
liquids that pass between the capacitor plates 3 and 4. The converted
coefficient digital signal
from the output of the microprocessor 18 is applied to a communications
protocol converter 19
for communication with the selected communication network outside the tank. A
temperature
sensor 13 is coupled as an input to the microprocessor 18 to monitor the
temperature of the
liquids that pass between the capacitor plates 3 and 4. The pressure of the a
single liquid above
the capacitive probe may be sensed by a pressure transducer 14 that provides
an output that may
be used to determine the volume of the single liquid above the pressure
transducer 14.
For new tank installation, the capacitive probe may be attached to the wall
inside the tank
as shown in Fig. 4. A tank 20 diagrammatically shown in Fig 4 represents a 400-
barrel or 500-
barrel tank that is commonly used to store liquids at gas well sites. Tank 20
has two outlets that
are common in such tanks, the lower one 21 being a drain port and the higher
one 22 being the
load-out port. Typically the drain port 21 is used to remove water and other
liquids to bring the
lower surface of the clean oil to a point just above the drain port 21. In
this way, the lower
surface of the oil is below the load-out port 22 to satisfy a requirement that
is common in the gas
fields; which is that the lower surface of the clean oil must be 8" below the
center of the load-out
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port 22. A controller 24 may be attached to the outside of the tank 20 to
communicate directly
through the wall to the capacitive probe 10. Alternatively, the controller 24
may be placed in a
box that is mounted on a pole removed from the tank 20. When the controller is
mounted on the
outside of the tank, near the capacitive probe inside the tank, the power and
data cable 8 is
connected directly through the wall of the tank. Alternatively, the power and
data cable 8
extends out through the top of the tank 20 to the controller 24.
At most gas well sites the power for instrumentation and other devices is
provided by a
solar panel 25 and a battery 26. The controller 24 is powered by the solar
panel 25. A speaker
28 is coupled to the controller 24 to provide an audible alarm when a liquid
that is not authorized
for removal is sensed by the capacitance probe 10. A camera 30 may also be
mounted on the
side of the tank 20 or in some other position to observe and record or take
pictures of the truck
removing the liquids from the tank 20 and the operator of the truck. The
operation of the camera
30 is controlled by the controller 24 and thus the capacitance probe 10 inside
the tank 20.
For a further secure operation to limit the removal of only authorized liquids
from the
tank 20, an automatic valve 31 is provided in the output line from the tank
20. Application
software in the controller 24 requires that the operator of the truck that
connects to the drain port
21 of the tank 20 must first provide authorization and identification to the
controller 24 before
the controller 24 will open the valve 31. A water truck may service a
plurality of tanks in a
given area and, in the interest of the economy, the automated valve 31 may be
located on a water
truck rather than at each tank that is serviced by a water truck. In any
event, the automatic valve
will only be activated by the individual controller 24 present at each of the
tank sites from which
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water is to be taken. Another placement for the capacitive sensor (not shown)
is in the output
line between the valve 31 and drain port 21.
An alternative placement of the capacitive probe 10 is also shown in Fig. 4.
For tanks
that have been in use or are in use, it is generally not possible to enter the
tank 20 to attach the
capacitive probe 10 to the inside wall of the tank. Consequently, the
capacitive probe 10 is
attached to a support pole 33 and inserted through a hole 35 at the top of the
tank. Tanks in
general use as storage tanks in gas fields have one or more 4" couplings
welded to the top of the
tank for access to the inside of the tank. The hole 35 is such a coupling at
the top of the tank 20.
The capacitive probe 10 is attached to the support pole 33 in a position so
that it will be at the
desired height relative to the bottom of the tank 20 and the outlet ports 21
and 22 of the tank 20.
The support pole 33, with capacitive probe 10, is inserted through the 4"
opening 35 at the top of
the tank so that the bottom of the support pole 33 touches the bottom of the
tank 20. In this way
the capacitive probe 10 is fixed in place inside the tank 20. The bottom of
the pole 33 may carry
a magnet 36 to position and secure the bottom end of the pole in place.
Alternatively, as shown in Figs. 5-8, the capacitive probe 10 may be attached
to a housing
37 that is moveable vertically in the tank 40. The carriage 37 has an internal
bushing 38 that
functions as a nut on a lead screw 39. The lead screw 39 may be threaded only
near the bottom
end of the lead screw and the carriage 37 moveable only in the bottom portion
of the tank 40 so
that the capacitive probe 10 may be positioned in the area of the bottom of
the tank relative to
outlet ports 41 and 42 of the tank 40. Alternatively, the lead screw 39 may be
threaded for
nearly its entire length so that the capacitive probe 10 may be moved
vertically to cover
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essentially the full height of the tank 40 to identify and discriminate
between the contents of the
tank 40. Additionally, the position of the carriage 37 to which the capacitive
probe 10 is
attached is monitored by an encoder, not shown, that tracks the rotations of
the lead screw 39 and
the position of the carriage 37. The carriage 37 on the lead screw 39 is
guided in its vertical
movement inside the tank 40 by a support pole 44. The support pole 44 may have
any
configuration but is shown as having a square cross-section in Figs. 6 and 8.
Although the capacitive sensor 10 is advantageously used to monitor the
removal of
liquids from storage tanks at gas wells to prevent the removal of oil, it may
also advantageously
be used to monitor the removal of any other liquid level from a storage tank.
For example, it
may be attached to the carriage for a vertically adjustable inlet/outlet
orifice 51 as shown in Fig.
9 and more fully described in the concurrently filed application, docket
number G13:1068.
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