Note: Descriptions are shown in the official language in which they were submitted.
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WO 96/09880 - PCT/GB95102294
A tdIXER AND APPARATUS FOR ANALY~IP3G FLUID FLOW
The invention relates to a mixer and apparatus for
analysing fluid flow.
Mixers are widely used in a number of industries. One
such industry is the oil industry. Oil wells produce
a mixture of oil, water and gas and homogenisation of
these components is desirable for accurate flow
measurement.
EP 0395635 discloses a number of static miner devices.
One sucl-~ device has a plate arranged normal to the
flow through the pipe. The plate has two apertures
and two curved vanes ofsheet material lie directly
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behind these apertures. Fluids flowing in the pipe
will pass through one or other of the apertures to be
divided into two streams and will be deflected by the
r.
vanes to rotate in opposite senses about axes parallel
to the direction of flow of the fluid and will thus be
homogenised.
1'
According to one aspect of the present invention there
' is provided a static mixer far one or more fluids
flowing in a pipe, the mixer comprising an element to
divide the f lowing fluids ir~to at least two strearc~s
within the pipe and to deflect two of the resulting
WO 96/09880 PCTlGB95/02294
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2
streams so that those streams rotate in opposite
senses about axes parallel to the direction of flow of
the fluid, the element being shaped so as to maintain ,
movement of the flow in a substantially smooth manner.
In this way, effective homogenisation can be obtained
without introducing unnecessary turbulence ar
otherwise unduly disturbing the flow.
The mixer of the invention. provides adequate mixing
over a wide range of flow conditions thus allowing
accurate measurements to be made of phase fraction and
velocity at points downstream of the mixer using
single narrow gamra or X-ray beams or other
established techniques.
Without adequate mixing the phases are rot
homogeneously distributed across the pipe section,
witr~ the result that a singly narrow beam may give an
erroneous indication of tree phase contents due to norm-
uniformity and the exponential nature of the photon
absorption. Furthermore, without adequate nixing the
phases move at different velocities and a single
velocity measurement does not give an accurate measure ,
of the flow rates but must be corrected by the use of
theoretical models or correlatior~s to account for the
relative velocities of the phases. This inver~tior~
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WO 96/09880 PCT/GB95/02294
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avoids the need far such corrections and their
associated uncertainty.
Further, the characteristics of the mixer of the
invention are such that the differential pressure
across the mixer, when combined with phase fraction
information, will provide an accurate measurement of
velocity of the flowing fluids over a wide range of
flow conditions, including slug flow.
Preferably, the element includes a smoothly contoured
surface leading to the part of the element which
divides the flowing fluids. Preferably further, the
element includes a smoothly contoured surface which
leads away from the part of the element which deflects
two of the resulting streams so that those streams
rotate in opposite senses.
Preferably, the part of the element which divides the
flowing fluids into at least two streams within the
pipe extends over a significant axial distance which
may be about a half to three-quarters of a diameter of
the pipe and preferably is about five-eighths of the
' diameter of the pipe. As the separation of the flows
takes place over a significant distance, undue
turbulence and disturbance are avoided. Preferably,
the part of the element which deflects two of the
WO 96/09880 PCT/GB95/02294
,22011~~
4
resulting streams so that those streams rotate in
opposite senses extends over a significant axial
distance which may be a half to three-quarters of a
diameter of the pipe and preferably is about five-
eighths~of a diamEter of the pipe.
Preferably, the surface of the element wl-~ich faces
downstream defines a substantial absence of cavities
facing downstream. Preferably, the surface of the
element which faces upstream defines a substantial
absence of cavities facing upstream.
Preferably further, substantially the entire
impingement surface of the element is at ar~ angle of no
greater than 85°, preferably 80°, most preferably 'C°
to the flow direction. Preferably, substantially the
entire past impingement surface Of the 8lement is at an
angle of ro greater than 85° to the flow direction,
preferably 75°, most preferably EO°. Preferably the
maximum angle of direction change of the flaw surface
of the element is 9C°, most preferably ~0°.
The most upstream part of the element may comprise a
part which presents a rising slope from an inner wall
of the pipe to a ridge andl~ay then present a
descer~ding slope back to the inner wall of the pipe.
The element iiiay comprise a central wall part which
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WO 96/09880 PCT/GB95/02294
divides the pipe into two. The element may comprise a
pair of handed curved parts which direct the flow
through an angle of 60° to 120°, preferably 80° to
100°, most preferably about 90°.
5
The element may be made in any suitable fashion and
preferably is produced in one or two pieces, for
example, by casting or moulding.
According to another aspect of the invention, there is
provided apparatus for monitoring flow comprising a
mixer according to the first aspect of the invention
and means for measuring the pressure drop across the
mixer.
By means of the measurement of the pressure drop, flow
rate calculations can be carried out.
Preferably, in particular when used for metering
mixtures of liquid and gas, the apparatus further
includes means for measuring liquid hold-up after the
mixer. By measuring the pressure drop and the liquid
hold-up, the total velocity of the fluid in the pipe
' and the liquid flow rate can be calculated.
The means far measuring liquid hold-up may take any
suitable farm and may comprise phase fraction or
WO 96/09880 PCT/GB95/02294
9 22A~ ~1.
6
liquid fraction measurement instruments. Tree or each
measuring means may comprise at least one radiation
source such as an x-ray or preferably gamma radiation
source and at Ieast one radiation sensor. The smooth
through flow enabled by the mixer of the invention
enables consistent and accurate calculations to be
carried out of total mixture velocity and mean flow
rates. This is particularly important, for example,
where oil is produced from one or a group of oil
wells. The total homogenised mixture velocity
together with phase fraction information can be used
to calculate the proportions arid quantities of oil,
gas and water being produced. Indeed an accuracy of
better than 5% carp be achieved with this technique
over a wide range of flow conditions which represents
a considerable improvement over prior techniques.
Freferably the radiation source or sources are
arranged to emit radiation at least at two different
energies and at least one radiation detector is
provided positioned to receive from t3-~e source or
sour Ces r ad I at 5. 'vn W h 3. Ch has gassed th rough the f i OW ,
the source or source's emitting radiation at least at
two different energies, tree or each detector providing
a signal to processing means, the processing means
being arranged to process the signal to provide a
series of chronological values and to group the values
WO 96109880 PCT/GB95/02294
7
by magnitude far analysis by analysis means.
' One situation in which fluid flow analysis is
important is in the production of oil from an oil
well, or group of oil wells. OiI is commonly found
mixed with water and gas thus providing a three phase
fluid flow. Clearly, it is important to be able to
determine how much of the fluid flow is constituted by
each of the three phases.
Known apparatus for phase fraction analysis comprises
two gamma radiation sources with associated detectors,
which are spaced apart along a pipe in the flow
direction. The sources emit radiation at different
energies. The signals fron the detectors are
proportional to the gamma radiation. received and hence
indicate the radiation absorption. from the flow. This
information enables the phase fractions of the flow to
be determined. The phase fractions of the flow may
vary widely with time as the flow passes the detectors
due the occurrence of slug flow, for example, and the
analysis is consequently subject to inaccuracy,
particularly as the relationship between radiation
absorption and the amount of fluid intercepting the
beam is exponential.
According to another aspect of the invention there is
WO 96/09880 s ~ PCT/GB95/02294
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provided apparatus for analysing fluid flow in a pipe
compris..ing at least one radiation source to direct
radiation through the flow, and at least one radiation
detector positioned to receive from the source or
sources~radiation which has passed through the flow,
the source or sources emitting radiation at least at
two different energies, the or each detector providing
a signal to processing means, the processing means
being arranged to process the signal to provide a
series of chronological values and to group the values
by magnitude for analysis by analysis means.
As the signal becomes a series of values which are
grouped, the analysis means car conduct a more
sophisticated analysis than simple averaging and a
more accurate analysis can be conducted. Preferably,
the analysis means is arranged to determine the phase
fractions in the flow. Alternatively, or in addition,
the analysis means may be arranged to determine the
type of flow e.g. slug flow or stratified flow. In
addition the analysis of the signals by grouping
provides information on the variation of composition
of the mixture with time. For example in slug flow
the oil/water ratios in the slug and in the thin film
between slugs can be individually determined.
Preferably, radiation from the or each source will be
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WO 96/09880 PCT/GB95/02294
9
measured over a series of'short time intervals. In
one embodiment, a single detector is provided. In
that case, two sources may be provided, each emitting
radiation at a different energy. In the prior system,
necessary separation of the two sources lead to errors
as the radiation beams did not "see" the same section
of flow. Because of the processing and analysis which
is carried out by the apparatus of the invention, this
necessary separation is possible without incurring
errors.
As an alternative to two sources, a single source can
be used which is arranged to emit radiation of at
least two different energies, e.g. a caesium source
emitting radiation at 32 keV and 661 keV.
The apparatus is principally intended for use with
three phase flow and so preferably radiation at only
two different energies is emitted by the source or
sources.
The radiation may be X-ray and/or gamma radiation.
The apparatus may include a nixer and means for
sensing pressure drop across the mixer. This enables
f
velocity calculations to be carried out when combined
with means for sensing liquid hold-up. The sensing
WO 96/09880 PCT/GB95/02294
means are preferably associated with the analysis
means which is arranged to determine flow rate. The
means for sensing the liquid hold-up may camgrise at ,
least one radiation source to direct radiation through
5 the flow to at least one radiation detector positioned
to receive radiation which has passed through the flow
from the or each source.
In one embodiment, the apparatus includes only two
10 sources and only two detectors and the ar~alysis means
is arranged to determine both phase faction and flow
rate. Phase fraction is determined using two energies
from one of the sources and velocity is dEterz~ined by
corpar ison of the dynamic radial.lVr1 slgrtals received
by the two detectors spaced axially along the pipe.
This arrangement uses the minimum number of compor~enis
arid is thus particularly simple and cost advantageous.
One embOdlZent Of the inventlOn wiii nOw be described
by way of example arid with reference to the
accompanying drawings, ir~ which:
Fig. 1 is a side elevation in partial cross-
section of the apparatus of the embodiment; ,
Fig. 2 is a perspective view of the mixer of the
embodiment;
Fig. 3 is a side elevation of the mixer of the
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WO 96/09880 PCT/GB95/02294
11
embodiment; and,
Fi..g. 4 is a plan view of the mixer of the
embodiment.
The apparatus 10 comprises two gamma radiation units
12,14, two pressure transducers 16,18 and a central
processing unit 20.
The pressure transducers 16,18 are provided on either
side of a static flow mixer 22 within the pipe 24.
The pressure transducers 16,18 are connected to the
central processing unit 20. Downstream of the mixer
22 is provided a temperature sensor 26 which is also
connected to the central processing unit 20. Just
downstream of the temperature sensor 26 is provided
the first gamma radiation unit 12. The first gamma
radiation unit 12 comprises a caesium source of
energies 32 keV and 661 keV. The source directs its
radiation through the pipe 24 to a single detector to
the other side of the pipe 24. The detector is
connected to an amplifier and analyzer 28 which has
high and Iow outputs to the central processing unit
20. The amplifier and channel analyzer 28. is powered
' by a DC power supply 30 adjacent the central
processing unit 20. Downstream of the first radiation
unit 12 is provided the second radiation unit 14.
This includes a single 661 keV caesium source a
d
n
a
WO 96/09880 ~ PCT/GB95l02294
12
thick crystal detector which is connected to a second
amplifier and analyzer 32 which is also powered by the
power supply 30 and is also connected to the central
processing unit 20.
In use, a three pr~ase fluid flow of oil, water and gas
flows through the pipe 24 and through the mixer 22.
The temperature sensor 26 senses its temperature and
the pressure transducers 16,18 upstream arid downstream
of the mixer 22 provide pressure information to the
central processing unit 20 to enable to pressure drop
across the mixer 22 to be determined. High and Iow
energy radiation from the source of the first
radiation unit 12 is detected by the single detector
of the first radiation unit 12 after absorption
through the fluid and is processed and analyzed by the
central processing unit 20 together with the signals
from the second radiation unit 14. The signals from
the first radiation unit 12 are chronologically
divided and grouped into bands by magnitude far
statistical analysis by the central processing unit 20
(whicl-~ constitutes the aforesaid "processing means"
and "analyzing means"~ to enable an accurate
determination of phase fraction to be made. Second
radiation unit 1~ in combination with tl-~e signal from
the first radiation unit 12 enables velocity to be
calculated and this information together with the
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calculation of pressure 'drop enables the total and
phase flow rates to be determined. The temperature
sensor information is needed to take account of the
fact that t1-.e gas constitutes a compressible phase.
Alternatively, or in addition, velocity may be derived
from pressure drop across the mixer such that the
second radiation unit 14 may be omitted.
Figs. 2 to 4 show the mixer 22 in more detail. The
mixer 22 of the embodiment is cast as a single piece,
but can be considered to comprise two parts 1.2,114.
The mixer 22 is provided in a cylindrical pipe 108.
The first part 112 rises from the floor of the pipe
108 presenting a flat surface 116 to the oncoming flow
of fluid through the pipe 108 at an ar~gle of about 20°
to the longitudinal axis of the pipe 108. The surface
116 rises to a smoothly curved ridge 118 of height W
from which it descends again as a flat surface 120 at
an angle of about 40° to the axis of the pipe 108, the
angle of descent decreasing close to the floor of the
pipe 108 so that the surface 120 smoothly curves to
meet the floor of the pipe 108.
The second part 114 is formed to its upstream side as
an upright wall 124 of constant thickness and with a
rounded front edge 126 against which incoming flow
WO 96!09880 PCT/GB95/02294
14
will impinge. The wall 124 intersects the rising
surface.116 of the first part 112. Just past the
ridge 118, the shape of the second part 114 changes.
The lower edge of this central section 128 of the
second part 114 continues at the height of the ridge
118, and at the same thickness as the wall 124. The
upper part of the central section 128 broadens
increasingly in a smoothly curved manner. The degree
of broadening of the central section 128 increases
along the axis of the pipe until the second part 114
intersects the wall of the pipe 108 at the level of
the ridge 118 at which point the angle of the curved
surface to the axis of the pipe is about 70°. The
downstream section 130 of the second part 114 smoothly
curves back towards the wall of tree pipe 108 at an
increasing angle to the axis of the pipe 108 the
greatest angle being about 60° just before
intersection with the pipe 108.
In use, flow, for example, of oil, gas and water,
passes along the pipe 108 and first impinges upon the
ascending surface 116 of the first part which
restricts the flow area of the pipe 108. Once the
flow reaches the wall 124 it is divided into two and
continues to be further restricted until reaching the
ridge 118. As the central section 128 of the second
part 114 broadens, each flow is subjected to induced
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WO 96/09880 PCT/GB95/02294
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rotation, the flows being rotated in different
directions. The downstream section 130 of the second
part 114 and the descending slope 120 of the first
part then slope away from the axis of the pipe 108 and
the flew area thus broadens out and the homogenised
mixed fluid passes further through the pipe 108. It
is thus seen that fluid is smoothly guided through the
mixer 22.
The distance A from the upstream edge of the surface
116 to intersection with the upstream edge 126 of the
wall 124 may be about seven-eighths of the diameter B
of the pipe 108. The distance C from the upstream
edge 126 of the wall 124 to the ridge 118 may be about
five-eighths of the diameter B of the pipe 108. The
distance D from the ridge 118 to the end of the
central section 128 of the second part 114 may be
five-eighths of the diameter B of the pipe 108. The
distance E from t1-~e end of the central section 128 to
the downstream edge of the downstream section 130 of
the second part 114, which is further downstream than
the downstream edge of the first part 112, may be
about nine-sixteenths of the diameter of the pipe.
The diameter of the pipe may be about 80-180mm arid in
a particular embcdimer~t is 80mm.
Gamma or X-ray sources arid sensors or other means may
WO 96/09880 PCT/GB95/02294
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16
be provided after the mixer 22 to enable the liquid
hold-up..to be measured and transducers may be provided
to measure pressure drop across tree mixer 22 to
thereby enable calculation of the total mixture
velocity. It has been established experimentally tat
r
tree pressure drop DQ is linearly related to the product
of total and superficial liquid velocities Vt, V~ .
Dp = a + b Vt VL
The I i qu i d ho 1 d-up EL i s g i ven by E~ - VL /Vt .
Thus . Vt = ( (DF-a}/(bE~} ~~
where a and b are calibration factors dependent mainly
upon the properties of the flow components. Because
of the nature of tl-~e mixer in producing good
1-~omogenisation without undue flow disturbance, tl-~e
factors a and b are relatively insensitive to the
ratio of components in particular water, oil and gas.
This is unlike the prior static mixers of EP 0395635
for example which produce conditions under which the
relevant equations do not hold true with sufficient
accuracy. By means of the invention multiphase total
velocities and superficial liquid velocities can be .
measured with an accuracy of better than 5~.
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WU 96/09880 PCT/GB95/02294
17
The first radiation unit 12 may include two distinct
caesium.sources, or a single caesium source capable of
. radiating at both energies. Clearly, other types of
radiation source may be used.
In a further etr~bodiment, the first radiation unit 12
and second radiation unit 14 use different energies
and source of only a single energy is provided in the
first radiation unit.
Clearly the dimensions of the mixer may be varied in
different embodiments. The height W of the ridge 118
may be increased to provide a smaller restriction for
the flow to pass through, or may be decreased. The
length D of the central section 128 which rotates the
two streams may be increased to further smooth the
flow, or may be decreased. The differential pressure
across the mixer can be adjusted in this way to suit
the particular installation.
r
.v. . . . . . ; . .:
