Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Apparatus to Recover Sample Gases from Fluids
Field of the Invention
This invention relates to a system for the collection and extraction of gases
entrained in a fluid, and more particularly, hydrocarbon gases in the return
flow
drilling mud material of an oil or gas exploration well.
Background of the Invention
There is a demand for apparatus to collect gases emitted from and extract
gases
entrained in fluid and slurry materials. For example, gases entrained in the
return
flow material discharged from an oil or gas exploration well. This return flow
material is generally in the form of a mud stream and is usually referred to
as
drilling mud. Collection, extraction and analysis of drilling mud gases can be
used to indicate the hydrocarbon content in the well return flow material
which, in
turn, provides the basis for an assessment of the formation and any
indications
that the well drilling has hit a producing zone. In an oil and gas well,
generally
the primary hydrocarbon gas of interest is methane gas. Thus, information
relating to the methane gas content of the well return flow material is the
information that is usually of most interest. Although, under certain drilling
conditions, there is also interest in information relating to some of the
other
hydrocarbons that may be present in the well return flow material.
The gases obtained from the return flow material discharged from the oil or
gas
exploration well are sampled for analysis. A gas collection, extraction device
provided for this purpose is generally referred to as a gas trap. The gas trap
apparatus is typically positioned in a "Shaker Box" or "Possum Belly" of a
"Shaker
Tank" into which the well return material is directed when it exits the well
bore.
Generally, the gas trap provides the collected, extracted gases to a sample
tube
extending from the gas trap to the sample analysis equipment. The sample tube
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typically has a small diameter and the collected gas sample is transported in
the
sample tube to sample analysis equipment on a continuous basis.
The current state of the art drilling mud gas sample collection, extraction
systems
have several problems that cause such systems to require high maintenance
costs and attention. Current gas trap apparatus provides a canister with an
electric motor mounted on top, which drives a centrifugal impeller housed
centrally within the canister. The canister has a plate on the bottom with a
small
hole in the centre that acts as an inlet for the drilling mud. Another hole is
provided in the side of the canister that forms an outlet for the driiling mud
to be
expelled from. This arrangement is designed both to pump mud through the gas
trap sample canister and to agitate the mud contained within the sample
canister
sufficiently to permit entrained gases to be released. The gases are released
from the return drilling fluid well mud stream as gas bubbles and are
evacuated
from the sample canister via a sample outlet, which couples to a sample tube.
Current gas traps are quite heavy, usually weighing 70 lbs. or more making the
devices relatively heavy and, consequently, onerous to install, operate and
maintain. Generally, the gas traps are attached to the shaker box and disposed
inside of the shaker box, positioned at a particular depth in the drilling mud
flowing through the shaker box. Typically, the apparatus for attaching the gas
trap to the shaker box includes a bracket that permits up and down adjustment
of
the gas trap to allow the gas trap to be positioned at the correct depth in
the
drilling fluid. Positioning the gas trap at the prescribed or optimum depth in
the
drilling fluid is very important with the current design of gas traps. Any
variation
from the optimum depth causes the gas trap to change the amount of driiling
mud
it will pass in a given period of time as well as causing it to liberate more
or less
entrained gases from the drilling mud in that same given period of time.
Furthermore, if the level of the drilling mud rises too high, drilling mud
will be
drawn into and through the sample tube by the sample pump toward the sample
analyzer causing contamination of the equipment. Depending on the amount of
drilling mud drawn into the sample tube, the sample handling, conditioning and
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analysis systems can all become contaminated with the drilling mud. At a
minimum, drawing drilling mud into the sample tube will cause contamination
that
will require maintenance intervention and may necessitate replacement of the
sample tube. In operation, most shaker boxes will experience a change in
drilling
mud level as the mass flow quantity of drilling mud changes or as the density
and
viscosity of the drilling mud changes. Drilling mud level changes in the
shaker
box can also occur as a result of the rig crew making adjustments to the
shaker
box itself.
Current oil and gas well drilling gas traps require operational maintenance
and
attention to operate in harsh winter environments. For example, the collected
gas sample is typically delivered to analysis equipment that often is
distances of
hundreds of feet from the gas trap. A sample tube effects delivery of the
sample,
which is subject to freezing in the winter. Consequently, the sample is
dehumidified to avoid freeze-up in the sample tube. Dehumidification apparatus
typically includes a glycol dryer that the sample is bubbled through. The
moisture
removed from the sample causes the vessel holding the glycol to become full,
requiring replacement of the glycol to rejuvenate the apparatus. Another,
dryer
apparatus generally found is a solid desiccant, for example calcium chloride,
to
further dry the sample. The solid desiccant will require replacement, often
several times per day, to maintain operation of the dehumidifier systems. An
example of such type of systems is described in US patent 4,565,086 to Orr.
U.S. Patent No. 5,199,509 to Wright for a controlled gas trap system provides
a
gas trap forming a sample chamber having an inlet and outlet both submersed in
the fluid to be sampled. Disposed within the gas trap is a rotating agitator
and a
vent to admit substantially gas-free air into the housing and a means to draw
off
the gas evolved from the mud. To provide for varying mud levels, the apparatus
of Wright relies on the rotation of agitator to maintain a constant mud level
within
the sample chamber.
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U.S. Patent No. 5,648,603 to Hansen describes a method and apparatus for
stabilizing a quantitative measurement gas trap used in a drilling operation.
The
method involves providing a known quantity of standard gas for injection to
the
trap in which the gas stream is evolved, for example Ethylene, Isobutylene and
Nitrous Oxide.
It is desirable to have a drilling mud gas sample collection, extraction
system that
is operable over a range of drilling mud levels within the sampled flow
stream, for
example, in a shaker box.
It is desirable to have a drilling mud gas sample collection, extraction
system that
operates consistently over a wide range of ambient temperatures, including
freezing winter temperatures.
It is desirable to have a drilling mud gas sample collection, extraction
system that
operates consistently over a wide range of drilling mud viscosity.
It is desirable to have a drilling mud gas sample collection, extraction
system that
operates with little or no frequent operator maintenance or intervention.
Summary of the Invention
The invention provides a gas trap assembly to recover sample gases from fluids
having pneumatic motor driven agitator blade rotatably disposed within a gas
sample collection canister. To enable operation of the pneumatic motor in
winter
conditions, the pneumatic motor compressed air supply has an air dryer to dry
the air supply to a dew point below minus 40 degrees Celsius. The compressed
air treatment system is housed in a heated environment to prevent the water
extracted from the air from freezing up.
For operation in winter environments, a heater heats the motor compressed air
supply. The heated compressed air is delivered to the gas trap to power the
gas
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trap pneumatic motor. Before going to the motor at the gas trap, the heated
compressed air is passed through a heat exchanger on the gas trap to warm the
gas trap apparatus to ensure the sample gas is maintained at a temperature
above its dew point and prevent freezing. Sample gas recovered from the fluid
is
supplied to a sample tube for transport to analysis equipment. In the
preferred
embodiment, the sample tube is bundled together with the air supply tube
inside
an insulated jacket. This arrangement transfers heat from the heated
compressed air supply tube to the sample tube to keep the sample gas warm
until it arrives at the analyzer equipment.
Within the gas trap, changing mud levels in the fluid flow in which the gas
trap is
disposed are controlled to a set or predetermined level using compressed air.
To
maintain the drilling fluid mud level at a consistent level within the gas
trap, a two-
chamber configuration is employed comprising a sample canister forming the
first
chamber and a bubbler enclosure or canister forming a second chamber.
Compressed air is supplied in common to both chambers, consequently, the
bubbler enclosure regulates the pressure within the sample canister to keep
the
mud level within it constant. The bubbler enclosure is sealed at the top and
has
an air exit port opening at the bottom at the level or point where the mud
level in
the sample canister is desired to be. The exit port opening at the bottom of
the
bubbler enclosure may be provided by cutting off the bubbler enclosure at the
desired length. In operation of the gas trap, pressurized air is supplied to
bubbler
enclosure. The chamber formed by the bubbler enclosure is in common air
communication with the sample chamber of sample canister through a
passageway equalizing the pressure in the two chambers.
To operate the gas trap, the amount of air supplied to the bubbler enclosure
is
slightly greater than the amount of sample gas drawn from the chamber formed
by the sample canister. Therefore, the bubbler enclosure will always be
bubbling
air out of the bottom as long as it is under the surface of the mud. The
cavities
formed by the bubbler enclosure and the sample canister are in communication
with each other, consequently, the mud level maintained by the air pressure
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within the bubbler enclosure causes the mud level inside the sample canister
to
be at the same level. Variations in the drilling mud level exterior to the gas
trap in
the shaker box can rise a great deal without having any effect on the level of
the
drilling mud within the sample chamber of the gas trap. With this arrangement,
the gas trap is prevented from "flooding", that is, the condition where
drilling mud
is sucked up into the sample tube. In the event that main air pressure is
lost, it
would be possible for the gas sample extraction pump to suck the drilling mud
into the sample tube following main air pressure loss.
In a preferred embodiment, the sample canister provides baffles projecting
into
the sample cavity formed by the sample canister. The baffles prevent or reduce
mud fluids from entering into the sample tube.
To prevent or reduce contamination of the sample tube and to remove
condensed moisture that may be collected in the sample tube, the sample tube
can be purged when the flow of sample gas through the sample tube falls below
a lower threshold. To purge the sample tube, pressurized air is supplied to
the
sample tube causing a gas flow through the sample tube that is the reverse of
the
sample gas flow. Preferably, the reverse flow pressurized air is supplied at
higher flow rates and pressures than that of the sample gas.
In one of its aspects, the invention provides an apparatus to recover gases
from a
fluid that includes a sample canister submersible in a fluid. The sample
canister
forms a sample cavity and has a fluid ingress port and a fluid egress port to
provide a path for the flow of fluid through the sample cavity of the
canister. A
sample extraction port is exterior to the sample canister and in communication
with the sample cavity. A bubbler enclosure is attached to the sample canister
and has an exit port at a predetermined location in relation to the sample
container and a supply port adapted to receive a supply of pressurized gas. A
passage extends between the sample canister and the bubbler enclosure to
provide a path for communication of pressurized gas from the supply port to
the
sample cavity of the sample canister. When the sample canister is submersed in
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a fluid, a supply of pressurized gas to the inlet port of the bubbler
enclosure will
result in a level of fluid within the sample cavity of the sample canister
that is
correspondingly set by the exit port location of the bubbler enclosure.
In another of its aspects, the invention provides an apparatus to recover
gases
from a fluid that has a sample container adapted for submersion in a fluid.
The
sample container forms sample cavity therein and includes a fluid ingress port
and a fluid egress port to provide a path for the flow of fluid through the
sample
cavity of the container. A sample extraction port is exterior to the sample
container and in communication with the sample cavity. Agitator means is
rotatably disposed within the sample cavity of the sample canister and a motor
drives the agitator. A bubbler enclosure is attached to the sample container
and
has an exit port at a predetermined location in relation to the sample
container. A
supply port is adapted to receive a supply of pressurized gas into the bubbler
enclosure and a passage extends between the bubbler enclosure and sample
container to provide a path for communication of pressurized gas from the
supply
port to the sample cavity of the sample container.
In yet another of its aspects, the invention provides apparatus to recover
gases
from a fluid operable in freezing conditions including a sample container
adapted
for submersion in a fluid. The sample container forms a sample cavity therein
and a fluid ingress port and a fluid egress port to provide a path for the
flow of
fluid through the sample cavity. A sample extraction port is exterior to the
sample
container and in communication with the sample cavity. An agitator is
rotatably
disposed within the sample cavity of the sample canister and motor means is
provided to drive the agitator. A bubbler enclosure is attached to the sample
container and has an exit port at a predetermined location in relation to the
sample container. A supply port is adapted to receive a supply of pressurized
gas and a passage extending between the sample container and the bubbler
enclosure provides a path for communication of pressurized gas from the supply
port to the sample cavity and the bubbler enclosure. The apparatus also
includes
a source of pressurized air and a heater to heat the pressurized air. A heat
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exchanger block is disposed on a frame supporting the sample canister and the
bubbler enclosure to recover heat from the pressurized air.
And in yet another of its aspects, the invention provides apparatus operable
in
freezing conditions to warm a gas recovered from a well drilling return flow
fluid.
A sample tube receives a gas recovered from a well drilling return flow fluid
and a
second tube is adapted to receive a source of heated air that axially
coextends
with said sample tube to facilitate heat exchange between them.
In another aspect, the invention provides apparatus to facilitate transport in
freezing conditions of a sample gas recovered from a fluid that includes at
least
two longitudinal co-extending hoses forming a common surface there along. The
hoses are adapted to facilitate heat exchange between them. One hose is for
transport of a sample gas and the other hose is for transport of heated air. A
sheath surrounds the co-extending hoses providing the capability to transfer
heat
energy is from the heated air hose to the sample gas hose.
In yet another of its aspects, the invention provides apparatus to indicate
the
relative viscosity of a fluid including an agitator adapted for rotatable
placement in
a viscose fluid. A pneumatic motor is provided to effect rotation of the
agitator. A
variable valve controls the supply of compressed air to the pneumatic motor
means in response to a control signal produced by a controller. A sensor
produces rotation signalling representative of the rotation of the agitator
for the
controller. The controller operates to maintain a substantially constant rate
of
rotation of said agitator by varying the control signal with relative changes
in fluid
viscosity.
In another of its aspects, the invention provides a self cleaning apparatus to
recover gases from a fluid including a sample container submersible in a
fluid.
The sample container forms a sample cavity and has a fluid ingress port and a
fluid egress port to provide a path for the flow of fluid through the sample
cavity of
the sample container. A sample extraction port is exterior to the sample
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container and in communication with said sample cavity. A means to draw a flow
of gas through the sample extraction port causes a flow of gas through the
sample extraction port in a supply direction. The invention has a flow valve
operable to connect a source of compressed air to the sample extraction port
to
effect a flow of compressed air through the sample extraction port in a
direction
reversed to the supply direction. Activation means effects operation of the
flow
valve. The activation means operates the flow valve when the flow of gas
through the sample extraction port is too low or periodically.
The preferred embodiments of the invention will now be described with
reference
to the attached drawings, which are briefly described as follows:
Brief Description of the Drawings
Figure 1 shows a functional block diagram of a preferred embodiment of a
sample gas extraction apparatus in accordance with the invention and a
supply air system.
Figure 2 is a cross-section view of the air tubes of Figure 1.
Figure 3 is a partial cross-sectional view of the gas trap of Figure 1.
Figure 4 is a bottom plan view of the gas trap frame of Figure 1.
Figure 5 is a top cross-sectional view of the heat exchanger of Figure 1.
Figure 6 is an exploded schematic view of the gas trap of Figure 1.
Figure 7 is a functional block diagram of a controller apparatus to operate
the
sample gas extraction apparatus.
Figure 8 is a flow chart representation of a relative viscosity measurement
process control loop performed by the controller of Figure 7.
Detailed description of the Preferred Embodiment
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In the drawings and this detailed description, the same reference numbers are
used to denote like features of the invention throughout the various figures.
Reference is made to Figure 1, which shows a functional block diagram of a
preferred embodiment of the sample gas extraction apparatus and a compressed
air supply system. A rig compressor 10 provides a source of compressed air,
which is supplied via compressed air supply hose or tube 12 to a heated
enclosure housing 14, shown in dotted outline form, that contains equipment to
extract moisture from the air supplied in compressed air supply tube 12.
Heated
enclosure housing 14 is provided to prevent water extracted from the
compressed air from freezing when the system is in operation in winter
conditions. A valve 16 controls the ingress of air to the dryer equipment. A
separate filter 18 is provided to remove particulate matter or oils from the
compressed air. A coalescing filter 20 provides a first dryer apparatus to
remove
moisture from the air. A membrane dryer 22 is provided to further remove
humidity from the air and is capable of reducing humidity in the air to a
dewpoint
of -40 C. A regulator 24 controls the pressure of the air leaving the heated
enclosure 14. The dried air is supplied to analyzer apparatus 26, generally
shown by box 26. A pressure sensor 28 provides an indication of the pressure
of
the air supplied from rig compressor 10. A temperature sensor 30 is provided
to
measure the temperature within heated enclosure housing 14. The pressure and
temperature signalling are supplied to analyzer 26 on a dryer signalling line
32.
Apparatus to recover gases from a fluid, or gas trap, constructed in
accordance
with the invention, generally depicted by reference numeral 34, is positioned
within a fluid 36, for example, a well drilling mud return flow. The gas trap
34 is
positioned in the fluid so as to place the lower portion of the gas trap below
the
surface level of the fluid mud level 38 to facilitate extraction of a gas
sample by
the gas trap from the fluid well return flow 36. The gas trap 34 is connected
to
analyzer equipment 26 by an insulated sheath 40, which houses air supply tubes
running between the analyzer 26 and gas trap 34. A primary air supply tube 42
is
used to supply air to drive the pneumatic motor 44 of the gas trap. A bubbler
air
supply tube 46 supplies air to a bubbler enclosure 48 of the gas trap 34. The
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sample gas recovered by the gas trap 34 from the fluid 36 is collected within
the
gas trap 34 for transport to the analyzer 26 via sample supply tube 50.
Preferably, transducers monitor the operation of gas trap 34 provided in the
gas
trap to measure the gas trap temperature and the gas trap pneumatic motor 44
rpm. Signalling from these transducers is supplied to analyzer 26 by trap
signalling line 52.
Figure 2 is a cross-section view of the air hoses or tubes of Figure 1. The
primary air supply hose or tube 42 is disposed within sheath 40 along with the
bubbler tube 46 and the sample tube 50. The three hoses are disposed inside
sheath 40, which provides protection for the tubing and is preferably
insulated to
reduce heat loss to the exterior of sheath 40. The tubes 42, 46 and 50 are
preferably in contact with each other to facilitate heat exchange
therebetween.
Figure 3 shows a partial cross-sectional view of the gas trap 34 of Figure 1.
The
gas trap has a main frame 54 to provide a mounting structure for the
components
of the gas trap. A bubbler enclosure 48 extends downwardly from frame 54.
Bubbler enclosure 48 forms a cavity to receive the bubbler air supplied by
bubbler supply tube which couples to a fitting 56, which supplies the bubbler
air
to the bubbler enclosure 48 via a bubbler air passage 58 in main frame 54. The
bubbler air passage 58 can be drilled through main frame 54. Fitting 56
includes
a conventional coupling nipple that can be mounted on frame 54, for example,
by
threading engagement with main frame 54, to provide a mount for the sleeve
coupling of the bubbler tube 46 to mate with. A common passage 64 extends
through frame 54 to openings provided in bubbler cavity 49 and sample cavity
62.
In this embodiment, only one opening of common passage 64 is required in the
bubbler cavity 49, which is for the common passage 64 and also serves as the
supply port for bubbler air received at the gas trap via the bubbler air
supply tube
46.
The gas recovered from the fluid 36 is collected in a sample canister 60,
which
extends down from frame 54 to form an interior sample collection cavity 62.
The
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sample collection cavity 62 is in communication with the cavity 49 formed by
the
bubbler enclosure 48 via passage 64 extending therebetween. To use the gas
trap, the lower portion of the gas trap is submersed within a fluid 36. A
supply of
compressed air is provided to the gas trap via the bubbler air supply tube 46.
The compressed air is contained within the bubbler enclosure 48 that becomes
pressurized with the compressed air supplied to cavity 49. When cavity 49
fills
with compressed air, bubbles 66 escape from the lower extremity of bubbler
enclosure 48 into the fluid 36 that the gas trap has been positioned in, for
example, well drilling mud return flow. The compressed air causing
pressurization of the cavity 49 of the bubbler enclosure 48 is applied also to
the
sample collection cavity 62 of the sample canister 60 as the cavities 49 and
62
are in communication via passage 64. The common pressurization of cavities 49
and 62 causes the fluid level within cavity 62 of the sample tube to be at the
same level as the fluid within cavity 49 of the bubbler enclosure 48.
The bubbles 66 will not exit the bubbler enclosure 48 until the cavity mud
level 68
reaches a level where the compressed air supply can exit the cavity 49 of the
bubbler enclosure 48. The preferred manner of controlling the bubbler cavity
compressed air exit level, and therefore the fluid level in the bubbler cavity
49, is
simply to cut the bubbler enclosure 48 at the desired length. This manner of
construction leaves a relatively large exit opening from bubbler enclosure 48
which avoids fouling and plugging of the exit opening by the mud 36. The lower
extremity of bubbler enclosure 48 is positioned or disposed relation to the
sample
canister 60 to select or locate the desired fluid mud level within sample
canister
60.
The quantity of compressed air supplied to bubbler enclosure 48 via the
bubbler
air supply tube 46 is set, for example at the analyzer 26, to supply a
quantity of
air that is slightly more than the gas sample which is extracted from sample
cavity
62. In this manner, the excess air supplied to cavities 49 and 62 will be
sufficient
to cause bubbles 66 to exit bubbler enclosure 48 at the exit opening, for
example,
at the foot thereof. Consequently, irrespective of the mud level 38 exterior
to the
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gas trap, the cavity mud level 68 will always be located at the foot of the
bubbler
enclosure 48. Because bubbler cavity 49 is in communication with sample cavity
62 via passage 64, the average mud level within cavity 62 will be at the same
level as the cavity mud level 68.
In the interior of sample canister 60 is an agitator 70 that is driven in
rotation by
pneumatic motor 44. In operation, agitator 70 will rotate at an angular
velocity of
approximately 1700 rpm. The rotation of agitator 70 within the fluid 72, for
example well drilling mud, contained within the sample canister 60 will cause
the
well drilling mud to be agitated or whipped and to develop an inclined conical
surface 74.
Sample canister 60 has an egress port 76 formed in the lower portion thereof
at a
position such that the upper portion of conical surface 74 will extend toward
egress port 76. While agitator 70 is rotating, a continuing portion of the
well
drilling mud agitated by agitator 70 will reach upward toward egress port 76
where it will overflow into egress port 76 to exit sample canister 60 for
return to
the well drilling mud main fluid flow 36. To prevent exchange of gases between
the interior and exterior of sample canister 60 through egress port 76, a
baffle 78
is provided. Baffle 78 forms an opening 79 that is below both the surface 38
of
the well drilling mud fluid 36 and below the mud level 68 of the cavity in the
bubbler enclosure 48. The opening 79 is below the mud level 68 in the bubbler
enclosure 48 to ensure that the excess compressed bubbler air exits only out
of
the bubbler cavity via bubbles 66 and does not flow through the sample cavity
62.
Replenishment fluid, for example drilling mud, enters the chamber or sample
cavity 62 of the sample canister 60 in the direction of arrow 80 through
ingress
port 82. Naturally, ingress port 82 is below the fluid level 68 set by the
bubbler
enclosure 48. Agitation of the sampled well drilling mud fluid 72 within
sample
canister 60 by agitator 70 assists to release gases into sample cavity 62 that
are
entrained in the well drilling mud mixture.
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Collected sample gases are evacuated or extracted from sample cavity 62 via
port 84. The gas sample extraction port 84 is in communication with sample
outlet coupling 86 to permit coupling of a sample transport tubing to the gas
trap
to permit the extracted gas sample to be transported to analysis equipment. To
prevent contamination of the sample gas pathways, baffles 63 extend from the
sample canister wall and agitator shaft 91 and act to block splashing mud from
reaching and fouling the sample port 84.
Because the extracted gas sample is recovered from a fluid flow, the recovered
gas sample will be high in humidity. To prevent the humid sample gas from
freezing in transport to the analysis equipment during winter conditions, it
is
preferable to heat the gas sample. In the preferred embodiment, the gas trap
apparatus and gas sample is heated by a heat exchanger block 88. The heat
exchanger block 88 imparts heat to the gas trap apparatus, in particular to
frame
54 on which it is mounted, from the heated air supply provided to the gas trap
to
operate pneumatic motor 44. Any suitable heat exchanger may be used, for
example, a maze heat exchanger as shown in cross section in Figure 5. The
heat exchanger has a sample inlet 90, in Figure 5, that is in communication
with
the sample outlet coupling 86. A sample inlet 90 provides the source of sample
gas to the heat exchanger block 88. The primary air supply tube 42 is coupled
to
supply coupling 92 to provide a supply of heated air to heat the gas trap and
to
heat the sample gases that are passing through the heat exchanger, when
ambient temperatures warrant heating. The supplied air then exits the heat
exchanger block 88 at main air supply exit 94 where it is transported to the
pneumatic motor 44 by motor supply tube 96.
Pneumatic motor 44 is coupled to agitator 70 via a coupling 98. A seal 100 is
provided on the cavity side of frame 54 to keep debris and moisture from
escaping the sample cavity 62 and fouling the bearings 101 disposed between
agitator shaft 91 and frame 54. A rotational sensor 102 is provided to produce
signalling representative of the revolutions per minute (rpm) of agitator
shaft 91.
The RPM signalling is output on line 104 for use by monitoring equipment, for
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example, by analyzer 26. The temperature of the sample gas leaving the gas
trap is measured by a gas trap sample temperature sensor 106, which provides
sample temperature signalling on line 108 for use by monitoring equipment, for
example, by analyzer 26.
Figure 4 is a bottom plan view of the frame of Figure 1. For clarity, the
frame 54
is shown without the other apparatus of the gas trap attached. The left
portion of
the frame forms the upper side of the sample chamber side. The gas sample
extraction port 84 is in communication with the heat exchanger gas inlet 90.
Gas
inlet 90 is on the reverse side of the frame 54 and, therefore, is shown in
hidden
dotted outline form in the drawing. An opening 65 for passage 64 is shown
disposed within the sample chamber. The right side of the frame forms the
upper
side of the bubbler chamber shown with the opening for passage 64 depicted.
Figure 6 is an exploded schematic view of the gas trap apparatus of Figure 1.
The sample canister 60 has a removable bottom 110, which forms the fluid
ingress port 82 for the sample canister. A coupling 98 couples motor 44 to the
agitator shaft 91. An exhaust muffler 112 is provided for exhaust air
discharged
from pneumatic motor 44. A mounting bracket 114 is attachable to a main frame
54 and includes arm 116 which couples to a mounting bracket on the shaker box
to which the gas trap will be mounted. The trap signalling line 52 contains
the
sensor signalling lines 104 and 108 therein.
Figure 7 is a functional block diagram of an embodiment of controller
apparatus
to operate of the sample gas extraction apparatus of Figure 1. Analyser 26 has
a
controller 120 which is a computer that receives signalling from the elements
of
the sample gas extraction apparatus and produce control signalling. The
controller 120 controls the operation of the analyser and gas trap apparatus
in the
manner described in more detail hereafter.
The pressure and temperature signalling from the sensors 28 and 30 located in
the heated enclosure 14 is supplied to the analyser 26 on the dryer signalling
line
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32. The compressed air is supplied to the analyser via supply hose 25, which
is
coupled to the analyzer at fitting 25'.
The gas trap 34 has a trap signalling line 52, two air tubes 42 and 46, and a
sample tube 50 running between it and the analyser 26. The trap signalling
line
52 connects two sensors to the analyser, that is, a proximity or rotational
sensor
102 which measures the RPM of the pneumatic motor 44 and a temperature
sensor 106 to measure the temperature at a suitable location of the gas trap,
for
example, the heat exchanger block 88. The analyser controller 120 controls
both
the motor RPM and the temperature of the gas trap as described in more detail
subsequently. The tubes are in contact along their length in the run from the
analyser 26 to the gas trap 36 to provide a counter flow heat exchange to
facilitate heat flow between the air tubes 42, 46 and the sample tube 50. The
tubes are surrounded by insulated sheath 40 which impedes heat loss through
sheath 40.
The compressed air supplied to the gas trap 34 from the analyser 26 in the
main
air supply hose 42 can be heated but is not cooled. Consequently, the
temperature of the gas trap 34 is controlled for low outside temperatures. The
temperature sensor 106 in the gas trap heat exchanger block 88 provides a
temperature feedback. The heat exchanger block 88 in turn heats the humid
sample gas recovered from the drilling mud fluid to avoid sample freezing or
condensation in the gas trap during winter conditions. The co-located tubes
42,
46 and 50 within sheath 40 provide a heat exchange surface along their length,
principally between the main air supply hose 42 and the sample supply tube 50
to
provide heating to the sample gas when it leaves the gas trap 34. The heated
air supplied to the gas trap 34 exits the heat exchanger block 88 where it is
supplied to power and warm the air-motor 44, promoting prolonged motor life
expectancy in winter operation.
Heater 122, the activation of which is under the control of controller 120,
heats
the compressed air supplied to analyzer 26. Controller 120 activates heater
122
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based on temperature data supplied on signalling line 52. A set point
temperature can be input to controller 120 using suitable input means such as
keypad 124. When the gas trap falls below a set point temperature, for
example,
32 C, heater 122 is activated to heat the compressed air supplied to the gas
trap,
the main flow of which will be the air supplied to operate pneumatic motor 44
via
coupling 42'. Conversely, when the temperature of the gas trap exceeds a set
point temperature, for example 34 C, controller 120 turns off heater 122 to
cease
the supply of further heat to the gas trap.
The main air supply hose 42 that carries air from the analyser 26 carries the
air
supplied at a controlled variable pressure and temperature. As noted, the
compressed air is heated when the ambient temperature of the gas trap falls
below a specified set point.
The analyser 26 operates to control the operation of gas trap 34. The bubbler
air
supply tube 46 couples to fitting 46' and the primary motor air supply tube 42
couples to coupling 42'. The gas sample recovered from the gas trap is
supplied
to the analyzer 26 via sample tube 50, which couples to sample tube coupling
50'. A pressure control valve 126 controls the pressure of the flow of air
therethrough under the control of controller 120. The speed of rotation of the
gas
trap motor 44 is provided to controller 120, via the trap signalling line 52.
In operation, the gas trap 34 may become fouled by mud clogging the sample
tube gas sample extraction port 84 or by water forming in the gas sample tube
50. These conditions will interfere with the operation of the analysis system,
for
example, cause a reduction in the sample gas flow rate. To effect self
cleaning,
gas sample variable control valve 136 is closed and a reverse flow of
compressed air to the gas sample supply tube 50 is effected by opening
reversing valve 138 to supply compressed air to the sample supply tube 50 via
coupling 50'. In this manner, analyzer 26 operates to effect a cleaning
process of
the gas trap.
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The gas trap cleaning process may be carried out periodically during the
operation of the gas trap. For example, controller 120 can initiate the self
cleaning process periodically every few hours, such as every 4 hours. For
further
refinement of the self cleaning process, the controller 120 can monitor the
sample
gas flow rate and initiate a self cleaning process when the sample gas flow
rate
falls below a predetermined threshold. To initiate self cleaning based on
sample
gas flow rates, controller 120 monitors the sample gas flow rate by using the
sample flow sensor 132. When a reduction in sample gas flow rates below the
threshold amount occurs, controller 120 reconfigures the apparatus to effect a
self-cleaning process.
Figure 8 shows a flow chart representation of a relative fluid viscosity
measurement process loop carried out by the gas trap controller 120. The
process loop serves to operate the pressure flow control valve 126 based on
rotational feed back received from rotational sensor 102. A the start of the
speed
control process, indicated by 140, a set point speed, for example 1700 RPM and
an initial pressure amount, which will effect an initial compressed air flow
rate, is
established. The compressed air pressure amount setting value is output to
pressure control valve 126 as indicated by process box 142. The actual RPM
reading is then obtained from the rotational sensor as indicated by input box
144.
The RPM reading and pressure amount to effect the target flow rate can be
output to a suitable output device such as a display or logged to a file or
sent
over a communications link to a remote computer, as indicated by output box
146. The actual RPM speed of the motor is compared to a lower threshold at
decision box 148. If the speed is below the lower threshold amount, the "Y"
exit
of the decision box is taken and the compressed air rate amount setting value
is
increased as indicated by process box 150. The process loop will continue with
the changed compressed air rate amount setting value being output to the
pressure control valve 126 as indicated by process box 142. If the result of
the
comparison of decision box 148 is that the air motor 44 speed is not below the
lower threshold amount, then the "N" exit of the decision box is taken and air
motor speed is next compared to an upper threshold limit as indicated by
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decision box 152. If the result of the comparison at decision box 152 is that
the
air motor 44 speed is above the upper threshold amount, the "Y" exit of the
decision box is taken and the compressed air pressure rate amount setting
value
is decreased as indicated by process box 154. The process loop will continue
with the changed compressed air pressure rate amount setting value being
output to the pressure control valve 126 as indicated by process box 142.
Thus, when the rotational speed of the motor 44 decreases, controller 120
operates to open valve 126 to increase the pressure and consequently the flow
of
compressed air to the gas trap motor. Opening valve 126 effects an increase in
the pressure and flow of compressed air, and therefore the power, supplied to
the
motor 44 to assist in maintaining a constant motor RPM. Similarly, when the
rotational speed of motor 44 increases, controller 120 operates to close the
variable control valve 126 to reduce the flow of compressed air therethrough.
Consequently, the flow of compressed air or the amount of power supplied to
the
gas trap motor 44 will decrease to assist in maintaining a constant motor RPM.
In this manner, the rate of supply of compressed air is varied to control the
RPM
of the air motor 44 to maintain a pre-set speed, for example, 1700 RPM. The
rotational speed of air motor 44 is fed back to the controller 120 from the
rotational sensor 102.
This allows for constant speed agitation of the mud in the sample canister of
the
gas trap and results in gas readings that are consistent even with variable
mud
viscosity. Controller initiated variation in the rate of compressed air supply
to
maintain constant speed of the air motor 44 provides a relative indication of
mud
viscosity and can be monitored by controller and output on an output means
such
as display 125. Display 125 is preferably remote from analyser 26, as for
example, at a remote computer system.
Restrictor 130 sets the constant rate of supply of the bubbler air supplied to
the
gas trap 26. The sample received from the gas trap arrives at the analyzer 26
at
coupling 50' which couples to the gas sample supply tube 50. The flow rate of
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the gas sample is monitored by flow meter 132. The sample is drawn into
analyzer 26 by means of a pump 134 and the rate of flow of the gas sample into
the analyzer 26 is controlled by the sample variable flow control valve 136 to
a
constant rate, for example, 500 ml. per minute. Restrictor 128 sets the
bubbler
air supply rate flow to the gas trap 34 and the bubbler air supply rate is
greater
than the sample gas supply rate. In this manner, analyzer 26 sets the bubbler
gas supply rate corresponding to the gas sample supply rate to ensure that
excess bubbler air is supplied to the gas trap 34 over the sample gas flow
rate
which is supplied to the analyser. The excess bubbler air is provided to
ensure
that the bubbler enclosure 48 is bubbling excess air when the gas trap is in
operation. In this way, flooding of the trap is prevented irrespective of an
increase in the mud level that the trap is positioned in.
Further, to prevent flooding the gas trap, the gas trap motor speed signalling
arriving on gas trap signalling line 52 can be used as a fail safe. When the
supply air pressure is too low or not present, the gas trap motor 44 will not
be
able to maintain the target speed. Controller 120 deactivates sample pump 34
to
prevent the analyzer from continuing to operate when the main air pressure
supply is too low or not present.
Now that the invention has been explained, numerous substitutions and
mechanical equivalents will occur to those skilled in the art without
departing from
the spirit and scope of the invention, which is defined in the claims appended
hereto.
40138108.4
