Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-08-21
2004-03-16
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S617000, C324S639000
Reexamination Certificate
active
06707307
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the measurement of the dielectric constant of a fluid mixture and specifically the measurement of the amount of water contained in an oil/water mixture.
BACKGROUND OF THE INVENTION
It is very useful to know the water content of an oil/water mixture for a number of applications in the petroleum industry. Measuring the water content of the oil emerging from an oil well can give an indication of the general health of the well and whether or not the well is being pumped too fast. Measuring the water content of oil emerging from a treating facility provides feedback on the efficiency of the treating operation. And, measuring the water content of oil at the point of custody transfer assures the buyer and seller of the quantities of oil and water being transferred.
The prior art contains a number of instruments for producing such a measurement. A number of these devices rely on somehow measuring the dielectric constant of the oil/water mixture. Because the relative dielectric constant of oil is in the range of 2 to 3 and that of water is approximately 80 the presence of water in the oil has a significant effect on the dielectric constant of the mixture.
One such method for measuring the dielectric constant is the capacitance method. Devices covered by U.S. Pat. No. 3,200,312 to Callahan, U.S. Pat. No. 3,025,464 to Bond, U.S. Pat. No. 3,523,245 to Love et al, U.S. Pat. No. 5,929,342 to Thompson, and U.S. Pat. No. 4,774,680 to Agar are examples of this method applied to the measurement of water in oil/water mixtures. Other applications to which the capacitance method is applied to determine water content can be seen in U.S. Pat. No. 4,769,593 to Reed et al, U.S. Pat. No. 4,864,850 to Price, and U.S. Pat. No. 4,559,493 to Goldberg et al.
Another class of methods for determining the water content involves the use of microwaves. There are a few different ways that microwaves can be used.
U.S. Pat. No. 5,103,181 to Gaisford et al describes a device in which the oil/water mixture is made to flow through a section of pipe that has been modified to look like a resonant cavity. Microwave energy is introduced into the container and forms constructive and destructive interference at various positions within the cavity. Two microwave detectors are positioned at the side of the container at predetermined positions. The frequency of the microwave energy is adjusted until the phase of the signal at each receiver is exactly in phase or out of phase. The frequency at which this occurs is used to deduce the dielectric constant of the fluid within the resonant cavity.
U.S. Pat. No. 5,101,163 to Agar describes a form of microwave sensor similar to Gaisford et al. Agar places the microwave transmitter and two microwave receivers within a pipe containing the fluid to be measured. The pipe acts as a microwave waveguide instead of a resonant cavity. The receivers are positioned on either side of the transmitter at specified distances from the transmitter. The transmitter emits microwave energy into the waveguide. This energy is received by the receivers. The frequency of the microwave energy is adjusted until the signals at the receivers are in phase or out of phase. The frequency at which this occurs is used to deduce the dielectric constant of the fluid within the pipe.
U.S. Pat. Nos. 4,862,060; 4,996,490; 5,025,222; 5,157,339; and 5,748,002 to Scott et al describe the use of microwave load pulling to determine the dielectric constant of the oil/water mixture. The fluid to be tested flows through a resonant cavity. A microwave oscillator is electrically coupled to the resonant cavity. The dielectric constant of the fluid in the cavity alters the resonant characteristics of the cavity. The change in the frequency and amplitude of the microwave oscillations is used to deduce the dielectric constant of the fluid within the resonant cavity.
U.S. Pat. No. 5,926,024 to Blount et al describes a system similar to that of Scott et al that has been modified to work in down-hole applications.
U.S. Pat. No. 5,351,521 to Cracknell describes another method of using microwaves to deduce the dielectric constant of an oil/water mixture within a pipe. One or more pipe sections, each having a diameter smaller than the pipe containing the mixture, are inserted into the pipe. Microwave energy is transmitted along the pipe, through the smaller pipe sections, to a receiver. The pipe and pipe sections act as a waveguide. Thus, this geometry has an upper limit to the wavelength it will allow to propagate. The frequency of the microwave energy is lowered, increasing the wavelength until the receiver stops receiving the energy. This cutoff frequency is related to the geometry of the pipe and pipe sections and the dielectric constant of the fluid filling the pipe.
Another method of determining the water content involves the use of time domain reflectometry or TDF Generally, a TDR instrument consists of a signal source capable of supplying a voltage step with a very short rise time or voltage pulse with very short transition times, a transmission line, a probe that somehow interacts with the physical variable to be measured, and a timing circuit. The operation of the instrument consists of generating the signal propagating the signal along the transmission line to the probe, having the probe reflect the signal in some fashion, propagating the reflected signal back to the signal source, and measuring the interval of time between the generation of the signal and the return of the reflected signal. The probe can be fashioned to interact with one or more physical parameters. Two of these parameters are dielectric constant and fluid level.
If a known length of the probe is immersed in the material to be measured, the material not necessarily being an oil/water mixture, the measured time interval can be used to deduce the propagation velocity of the signal along the portion of the probe immersed in the material. This propagation velocity can, in turn, be used to deduce the dielectric constant of the material surrounding the probe. Examples of this kind of sensor are given in U.S. Pat. No. 3,965,416 to Friedman, U.S. Pat. No. 3,995,212 to Ross, U.S. Pat. No. 4,786,857 to Mohr et al, U.S. Pat. No. 5,459,403 to Kohler et al, U.S. Pat. No. 5,554,936 to Mohr, U.S. Pat. No. 5,723,979 to Mohr, U.S. Pat. No. 5,729,123 to Jandrasits et al, U.S. Pat. No. 5,818,241 to Kelly, and U.S. Pat. No. 5,898,308 to Champion.
U.S. Pat. No. 4,429,273 to Mazzagatti describes a probe geometry for an oil/water monitor. Mazzagatti briefly mentions two kinds of excitations that may be used with this geometry, but does not reveal the details of the monitoring means.
SUMMARY OF THE INVENTION
According to an aspect of the invention there is provided a method of determining a property of a fluid, such as water content of a hydrocarbon stream, that involves the use of time domain transmissometry or TDT. In TDT, the signal of interest enters the probe or sensor via one port, interacts with the fluid to be measured as it travels along the probe, and exits the probe via another port.
TDT has two main advantages over TDR. First, the signal only travels along the probe once in TDT whereas it makes two transits of the probe in TDR In cases where the bulk electrical conductivity of the fluid to be measured is high, the propagation losses of the signal while it travels along the probe will be high. In the case of TDR the signal must propagate a distance that is twice that of TDT so the losses will be at least a factor of 2 larger. Second, the receiver for a TDR instrument must distinguish the reflection of interest from a variety of other reflections caused by the system. When the amplitude of the reflected signal of interest is low this distinction can be difficult, even for a trained human observer. In the case of TDT, the first signal reaching the receiver is the signal of interest. Any subsequent reflected signals reaching the receiver are much less of a concern.
Therefore, there is provided a sensor for measuring the dielectri
Gabel Gail S.
McFarlane Ronald A.
Deb Anjan K.
ESI Environmental Sensors Inc.
Lambert Anthony R.
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