Note: Descriptions are shown in the official language in which they were submitted.
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RELATED APPLICATIONS
The present invention is related to the invention
of application Serial Number 385,414, filed September 8,
1981; for a system measuring the percent quantity o~ water
in a crude oil stream using microwave measurement.
BACKGROUND OF THE INVENTION
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Field of the Invention
The present invention relates to monitors in
general and, more particularly, to a water-in-crude monitor.
SU~MARY OF T~E INVENTION
A microwave-gamma ray water-in-crude monitoring
system measures the percent quantity of fresh water or salt
water in crude oil ~lowing in a pipe line. The system
includes a measuring cell arranged with the pipe line so
that the crude oil flows through the measuring cell. A
; microwave transmitter subsystem and a gamma ray source are
arranged with the measuring cell so that microwave energy
and gamma rays are transmitted through the measuring cell.
A microwave receivlng subsystem and a gamma ray detector
provide signals corresponding to received microwave energy
and to the received gamma rays, respectively. ~pparatus
connected to the microwave receiver and to the gamma ray
detector provides an indication of the percentage of water
in the crude oil.
The objects and advantages of the invention will
appear more ~ully hereina~ter from a consideration of the
detailed description which follows, taken together with the
accompanying drawings which follow, wherein one embodiment
of the invention is illustrated by way of e~ample. It is to
be expressly understood, however, that the drawings are for
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illustratlon purposes only and are not to be construed as
defining the limits o:E the invention.
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DESCRIPTION OF THE D~WINGS
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Figure 1 is a plot of relative loss factor versus
temperature at a particular wavelength.
Figure 2 is a simplified block diagram of a water-
in-crude monitor constructed in accordance with the present
invention.
Figure 3 is a detailed block diagram of the
monitor shown in Figure 2.
DESCRIPTION OF THE INVENTION
A method of determining the fresh water or salt
water content of flowing streams of gas free crude oil under
the conditions encountered in well flow lines utilizes the
measurement of microwave attenuation caused by water present
in the crude stream. Dielectric relaxation of the water
molecules at microwave frequencies causes severe attenuation
of electromagnetic waves of centimeter wavelength. Atte-
nuation of centimeter waves has been used to measure mois-
ture content in many materials such as concrete and core
slabs, see "Microwave Attenuation - A New Tool for Moni-
toring Saturations in Laboratory Flooding Experiments," by
R. W. Parsons, Marathon Oil Company, Society of Petroleum
Engineers Journal, August 1975, pp. 302-310.
The propagation of a plane-parallel electromag-
`~ netic wave can be represented by the following equations~
(1) E = Eoe ~x ~ ej2~(vt-~ x/2O
(2) H = HOe ~x , ej2~(vt-~ x/2~)
--2--
g ~ ~ .
where E and H are the electric and magnetic field vectors, x
and t the direction of propagation and propagation time in
space and v the frequency of the wave. Obviously the wave
has a time period T = l/v and a space period ,~ - 2Tr/~
(wavelength). Also the wave is attenuated by the factor
e ~ x as it proceeds along the x-direction. The attenuation
factor ~ is a function of dielectric and magnetic charac-
teristics of the propagating material at the frequency of
the wave and is of interest only to the water-in-crude
determination. Assuming no magnetic losses in the pro-
pagating materials which is certainly true for crude streams,
the attenuation factor is given by the following equation:
(3) G~ = ( 2 ~ '/2)~ ')z)
where ~O = wavelength in empty space (air),
k' = relative dielectric constant, and
k" - relative loss factor.
The parameters k' and k" are dependent on the
frequency o~ the wave, the temperature and the material
composition of the propagating material. The hydrocarbons
in crude oils have low values of k' and k" in comparison of
those of water and aqueous solutions of sodi~m chloride. As
an example k", the relative loss factor, for pure water and
for a 253 kppm aqueous NaCl solution is plotted versus
temperature ~or a wavelength of 1.267 cm (23.68 GHz) in
Figure 1. Data for the plot was obtained from "The Dielec-
tric Properties of Water in Solutions" by J. B. Hasted,
S.M.M. El Sabeh, Transaction of the Faraday Society, V. 49,
1953, London. Note that the loss factor has a maximum at
about 28C. This ma~imum shifts to lower temperatures at
lower ~requencies and to higher temperatures at higher
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frequencies. Also it should be noted that the values for
the almost saturated aqueous NaCl solution is only slightly
lower than that for the pure water. Values of k" for the
hydrocarbons in most crude oils are less than about 0.05 at
the above wavelength, as can be determined from "Tables of
Dielectric Dispersion Data for Pure Liquids and Dilute
Solutions" by Floyd Buckley et al, Nov. 1958, NTIS PB-
- 18829~.
The attenuation coefficients, CC for the pure
; 10 water and thP 253 kppm NaCl solution were computed for the
temperature range 0 to 60C (32 to 140F) at a wavelength
of 1.267 cm. The attenuation coefficient for the liquid
hydrocarbons in crude oils computes to less than 0.0013 cm 1
over the same temperature range.
The foregoing assumes that the crude oil does not
contain free gas. When the crude oil contains free gas the
free gas must be accounted for to determine a correct water
in crude content.
Let L be the total microwave beam path, then
microwave attenuation of initial value Io to the value I can
be expresse~ by the following equation:
(4) I = IO.exp ~ W~
where ~w = length of beam in water,. However, we have
(5) ~w = ~ ~ ~
where YL = length of beam in liquid (crude and water)
7:water/liquid fraction,
- and
( 6 ) '~ L 2,
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where y = fraction of length L which is filled with liquid.
We can now write equation (4) using equations (5)
and ~6) as follows:
(7) 1~ o ~ ~cp L-- ~ L ~ ~ ~ J
or
(7a) ~ (//~ L) eK~ /L) ~
~ is also the average void fraction in the measuring path.
This void fraction can be measured e.gO with a gamma ray
density gauge as follows.
A gamma ray beam traversing the measuring
section of length L is attenuated by the material (gas,
water, oil) within this section. This attenuation can
be described by equation (5).
(8) 1~ -lo~e~f-Lb~p~ f ~ ~ t ~ ";~
where~g, ~w' ~ oil are the gamma ray attenuation co-
; efficients per unit length for gas, water and oil, res-
pectively; ~gr ~w~ ~oil are the thicknesses of gas, water
and oil, respectively, within the path length; I~ is the
initial gamma ray intensity, Iy the attenuated gamma ray
intensity.
The following relationships between the above
parameters i (i.e. g, w, oil), L, q and ~ exist.
(9) L- ~ t Q,," t ~o;l
(10) ~L- ~w t ~ojl = L ~
(11) ~ ~L ~
(12) ~-L(~
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Using the relationships of (9) through (12) to
substitute for ~g~ ~w and oil in equation (8) the following
is obtained
(13) L~,= Ioy e~p ~ L L ht~8~{o
and
(14) ( I/L)~ Ioy/Iy )] ~ ~t~ ~[(~lc~ ~W ~;I)]~
or ( 15 ) ~--~ ( l /L ) ~ ro.~/ ~ Y ) ~ } / ~(4( o l t b~ w ~ 6; t
Substituting equation (15) into equation (7a) to
eliminate g and rearranging terms yields equation (16) for
determining ~ , the water/liquid ratio, from measured and
known parameters
(16) ~ L(l/KL)~ (~lr~ .)i?/~(l/L)~,fI /I )-,~ ?
~ L)(~W-~0,~ h~
In many cases ~W-~ojt~ may be
utilized without:making large errors,equation (16) then
; reduces to
~ (17) ~-E( ~ joCL) ~ of r)~/L(I/L) ~ ($~ ~9 ~? ~
Using again relationships of (9) through ~12) the
~: :
fractional water oil ratio can be calculated from the
: water/liquid ratio by equation (18)
(18) water/oil fraction = ~
'.
g ~ ~
Referring now to Figure 2, oil flowing from a well
head enters a measuring cell 1 by way of a pipe (not shown)
and leaves cell 1 by way of a pipe (not shown). Cell l
includes ceramic windows 7, 9 and steel windows 10, 11. A
conventional type klystron 12 provides microwave frequency
radiation through wave guides 14 to an isolator 16. Iso-
lator 16 stops reflected microwaves from entering klystron
12; a tuner 2~ provides a mechanical type tuning for mat-
ching the transmission subsystem when isolator 16 provides
microwaves to attenuator 28.
Attenuator 28 provides attenuated microwaves to a
conventional horn antenna 33 which propagates the microwaves
through window 7 and through window 9 to a second horn
antenna 38. Horn antenna 38 provides the recèived micro-
waves to a microwave detector 42 which in turn provides an
electrical signal El to an amplifier 46. The amplified
slgnal from ampllfier 46 is provided to an in~egrator 50
receiving pulse E2 from a clock 54 and provides an integrated
signal E3 to a monitor 60.
A gamma ray source 65, located in a shield col-
limator 67, provides a gamma ray beam through window lO
across measuring cell l and through window 11. Shield and
collimator 67 may be made of lead or tungsten.
A radiation detector 69, which may be a conven-
tional type sodium iodide (thallium activated) crystal
detector, detects the gamma radiation passing through window
11 and provides light pulses, corresponding in number and
amplitude to the detected gamma radiation, to a photo
multiplier tube 73. Detector 69 and photomultiplier
2~5
tube 73 are surrounded by a shield 75 which prevents the
gamma radiation passing through window ll Erom escaping from
the area. Photomultiplier tube 73 provides electrical
pulses on a one-for-one basis with the light pulses from
detector 69 to an amplifier 80 whare they are amplified and
provided to a gain stabilizer 83. Gain stabilizer 83 may be
a type manufactured by Hawshaw Chemical Co. as their part
No. NA-22AGC Amplifier. Gain stabilizer 83 provides
corresponding pulses to a conventional type discriminator
and count rate meter 88. Discriminator and count rate meter
88 provides a signal E5, corresponding to the detected
radiation, to monitor 60.
Referring now to Figure 3, signal E3 corresponding
to the term I in equation 16 is applied to a divider 100 in
monitor 60 where it is divided into a DC voltage corres-
ponding to a value o Io~ Divider 100 provides a signal to
a natural log function generator 104 which in turn provides
a signal corresponding to the term ln(Io/I) in e~uation 16.
A divider 108 divides a DC voltage corresponding
to a value for L, the distance from source 65 to detector
69, into a DC voltage corresponding to a value of 1.
Divider 108 divides a signal to another divider 110 where it
has a DC voltage corresponding to the attenuation constant
into it to provide a signal. The attenuation constant o~
may be determined prior to operation by determining Icwith
measuring cell l empty, then filling measuring cell l with
water and determining I and solving equation 4 for GC~
knowing the lPngth of the microwave beam in the water~ A
multiplier 114 multiplies the signals from natural log
function generator 104 and divider 110 to provide another
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signal to a multiplier 116~
Subtracting means 120 subtxacts a direct current
voltage corresponding to ~U g from a direct current voltage
corresponding to 1~ oil to provide a difference signal to
multiplier 116 where it is multiplied with the signal from
multiplier 114 to provide a product signal. The constants
,l~oil are determined in the same manner as the dielectric
constant by utilizing equation 4, using Iy for I and Ioy for
Ior and filling the measuring cell 1 with gas of the type
encountered in the producing well for the constant
and then filling measuring cell 1 with oil of the type
provided by the well to obtain the constant l~oil
Signal E5 is applied to a divider 125 where it is
divided into a DC voltage corresponding to the term I in
equation 16. The value of I~y is determined prior to ope-
ration by detecting the gamma radiation from source 65 while
measuring cell 1 is empty. An output signal from divider
125 is applied to a natural log Eunction generator 128 which
provides a signal corresponding to the term ln(I~y /Iy) in
equation 16. A multiplier 130 multiplies the signal pro-
vided by divider 108 with the signal from natural log
function generator 128 to provide a corresponding signal.
Subtracting means 131 subtracts the voltage corresponding to
~g from the signal provided by multiplier 130 to provide a
signal.
Subtracting means 134 subtracts the voltage cor-
responding to~ oil from the voltage corresponding to ~w
to provide a difference signal. A multiplier 137 multiplies
the signals from multiplier 114 and subtracting means 134 to
provide a product signal which is subtracted from the signal
_g_
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provided by subtracting means 131 by subtracting means 140.
A divider 144 divides the signal provided by subtracting
means 140 into the signal from multiplier 116 to provide a
signal corresponding to the term ~ to a divider 148 and to
subtracting means 149.
Subtracting means 149 subtracts the signal pro-
vided by divider 144 from the voltage corresponding to the
value of 1 to provide a signal which is divided into the
signal provided by divider 144 by a divider 148. Divider
148 provides a signal, corresponding to the water to oil
fraction, to a recorder 150 and to an analog to digital
converter 160. Converter 160 converts the analog signal
from divider 148 to digital signals which are provided to
readout means 164.
The present invention as hereinbefore described is
a water-in-crude monitor that determines the water to oil
fraction utilizing microwaves and gamma rays so that water-
in-crude oil that contains gas may be monitored.
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