This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the described embodiments. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of prior art.
In the petroleum industry, viscosity is often a key characteristic used to understand a fluid environment. For example, the viscosity of crude oil can inform how difficult or easy it is going to be to pump the oil out of the ground. Other examples where viscosity is very frequently measured include monitoring chemical fluid injection in subsea oil wells, measuring downhole hydrocarbon viscosities, and sampling and blending applications of fluids. The petroleum industry is not the only industry that relies upon viscosity measurements to assure proper process controls. Other areas in which viscosity is often relied upon include monitoring the manufacturing of food products, for example, chocolate or tomato sauce production, paint products, cosmetic compositions, polymer coatings, consumer products, for example, detergents or lotions, or any other fluid for which flow is an important consideration. All of these areas would benefit from a simplified structure that effectively evaluates viscosity.
Industry currently uses ultrasonic meters to measure the flow rate of a fluid. It has been discovered that these ultrasonic flowmeters may be modified to further be viscometers. Typical ultrasonic flowmeter arrangements use two transducers at opposing ends of a pipe where one is upstream from the fluid flow and other is downstream from the fluid flow, both transducers transmit and receive signals. See, for example, U.S. Pat. No. 8,245,581 which is assigned to Cameron International Corporation. Each transducer generates plane waves into the fluid and surrounding pipe wall. The difference in transit times between the upstream signal and the downstream signal is used to calculate the flow rate. While current flowmeters can measure fluid flow rates, they cannot measure fluid density or fluid viscosity.
The present invention allows the measurement of fluid density in the same ultrasonic flowmeter used to measure the flow rate. With fluid density and fluid flow rate, viscosity may be calculated. To allow measurement of fluid density, an ultrasonic flowmeter is further equipped with either temperature or pressure sensors, or both. Temperature sensors measure upstream and downstream temperature and can be placed before or after one or more transducers. Pressure sensors may be disposed upstream and downstream, both or after transducers. According to one embodiment pressure sensors are disposed between the transducers.
The viscometer as described herein can be used in any process in which an ultrasonic flowmeter would currently be useful, as well as new areas where the ultrasonic flowmeter would not have been used heretofore because flow rate alone was not of interest. While, the invention will be described as it relates to oil wells, the invention is not so limited and is equally useful in other fluid systems where viscosity information is desired. The inclusion of pressure sensors in the ultrasonic flowmeter creates a simple and effective method for ascertaining viscosity that is more accurate than prior art methods.
In the accompanying drawings, the preferred embodiment of the invention and preferred methods of practicing the invention are illustrated in which:
The following discussion is directed to various embodiments of the invention. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.
Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function, unless specifically stated. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. In addition, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. The use of “top,” “bottom,” “above,” “below,” and variations of these terms is made for convenience, but does not require any particular orientation of the components.
As used herein, references to the “present invention” or “invention” relate to exemplary embodiments and not necessarily to every embodiment encompassed by the appended claims.
Fluid viscosity has often been measured by automated viscometers that are complex, expensive and unwieldy. Other viscometers such as glass capillary viscometers are common to the industry. These viscometers require the technician to sample the fluid offline in order to make a measurement. The present invention provides a simple solution to obtaining real time viscosity for fluids in the viscosity range of from about 1 to about 5,000 cst. The present invention provides an ultrasonic viscometer and a method for determining viscosity that is simple and cost effective using Poiseuille's equation.
Referring now to the drawings wherein like reference numerals refer to similar or identical parts throughout the several views, and more specifically to
The flowmeter 10 also comprises a controller (seen in
Pressure sensors are commercially available and selection of appropriate sensors would be readily apparent to the skilled artisan. Sensors for use in the method as described can be chosen from any art recognized sensor including but not limited to piezoresistive strain gauges, capacitive sensors, magnetic sensors, piezoelectric sensors, optical sensors, potentiometric sensors, resonant sensors, etc. According to one embodiment, the pressure sensor is selected to be a Rosemount 3051S differential pressure meter.
Temperature sensors are also commercially available and selection of appropriate temperature sensors would be readily apparent to the skilled artisan. Temperature sensors for use in the method as described can be electrical, for example a thermocouple or a thermistor or a resistance thermometer, or they can be mechanical sensors, for example, a thermometer.
While
Embodiments further relate to a method for measuring fluid density in a pipe 12 and ascertaining fluid viscosity. The method comprises flowing fluid through pipe 12, generating plane waves by an upstream transducer 16 in contact with the pipe 12 and positioned in alignment with the pipe so the plane waves propagate through the pipe and are received by a downstream transducer 18, which produces a downstream transducer 18 signal. Plane waves are also generated by the downstream transducer 18 in contact with the pipe 12 and positioned so the plane waves propagate through the pipe and are received by the upstream transducer 16, which produces an upstream transducer 16 signal. The upstream sensor 25 and the downstream sensor 30 measure at least one of temperature or pressure of the fluid flowing through the pipe and produce output signals indicative of the fluid condition measured. Finally, the transducer signals and sensor signals are sent to a controller, which uses the signals to calculate viscosity, density, and flow rate.
In operation, the ultrasonic flowmeter uses two wetted transducers at opposing ends of a pipe 12 where one is upstream from the fluid flow and the other is downstream from the fluid flow, both transducers transmit and receive signals (
For
V is velocity
C is speed of sound in liquid
t is time
tu is the upstream transit time
td is the downstream transit time
Δt is the transit time difference
L is the length of the pipe
In order to solve for the speed of sound in fluid and fluid velocity, the upstream and downstream transit times need to be measured via a controller. The controller computes the transit time differences between the upstream and downstream flow. The Δt is then used to calculate the fluid velocity for a given flowmeter length “L” for a calculated speed of sound “C”. Once the velocity “V” has been calculated then the Mass Flow Q can be determined since the area “A” of the fluid opening or pipe 12 is known.
For
λ=wavelength
Nd: focal length
r is the radius of the transducer
f is frequency
When sound diverges it diverges at angle φ. It then propagates into the wall of pipe 12, which is received by the opposing transducer as noise. This acoustic noise arrives at a time preceding the sound that travels in the liquid since sound velocities in the solid are higher than those in the fluid. According to one embodiment in the event the noise is significant and interferes with the accuracy of the flow measurements, the pipe 12 can be fitted with a dampening tube 14. The tube 14 with acoustically attenuative properties can be inserted within the pipe 12 (
Unlike prior art flowmeters, the flowmeter as described further comprises physical sensors 25, 30 to measure the density of the fluid. The density of the fluid can be calculated based on a speed of sound and temperature correlation or it can be measured by means of a pressure sensor. If calculating the density (ρ) of the fluid based upon the temperature (T) and the speed or sound, the following correlation may be used:
where K is the bulk modulus of the fluid and G is the shear modulus of the fluid.
The physical sensors 25, 30 can be either pressure sensors or temperature sensors or both. While only a single sensor is shown in
According to one embodiment fluid density is ascertained from the measurements taken by the differential pressure sensors 25 and 30. Once density and flow rate have been measured, the viscosity of the fluid may be calculated.
Using Poiseuille's equation, assuming the fluid flow is laminar viscous and incompressible, the fluid is passed through a cylindrical pipe where the length of the pipe is greater than its diameter.
Q is the volumetric flow rate
L is the length of the pipe
η is the dynamic viscosity
r is the pipe radius
π is the mathematical constant.
Since Q=Area×Velocity and r=D/2 then rearranging the equation and solving for dynamic viscosity yields:
D is the pipe diameter
V is the fluid velocity
Finally, the kinematic viscosity, V is:
The flowmeter/densitometer/viscometer described herein can be used in industrial processes where one wants to know or control the system viscosity, for example, when one wants to blend a variety of fluids and wants to control the final fluid viscosity.
Poiseuille's equation can theoretically be used to calculate dynamic viscosity given other physically measured parameters such as volume flow rate and pressure difference in pipes with flowing fluid. According to the following examples dynamic viscosity was calculated from a time of flight ultrasonic velocity measurement in a single path configuration using two opposing transducers in a small pipe (less than one inch diameter). Furthermore, the kinematic viscosity was calculated by dividing the dynamic viscosity by the density of the fluid, in this case propylene glycol. These examples were carried out to calculate the ΔP for a given flow rate Q in order to establish that it is realistic to make such viscosity measurements on hydrocarbons.
Using Poiseuille's equation and solving for ΔP yields:
Propylene glycol was selected as the test fluid having a dynamic viscosity of 0.404 Poise @ 25° C., a density of 1.036 g/cm3, and a kinematic viscosity of 39 cst. Based on the following information: r=0.5″=1.27 cm; L=12″=30.48 cm; η=0.404 Poise @ 25° C.; the ΔP was calculated for various flow rates. Note: 1 mmHg=1333 dynes/cm2.
For a flow rate of Q=1600 L/hr=4444 cm3/s, the ΔP was 53566 dynes/cm2 which equals 40.18 mmHg. The Reynolds number (Re) was 5,715.20.
For a flow rate of Q=600 BPH=95 m3/hr=26,388 cm3/s, the ΔP was 318,073 dynes/cm2 which equals 238 mmHg. The Reynolds number was 33,941.
For a flow rate of Q=150 L/hr=41 cm3/s, the ΔP was 494 dynes/cm2 which equals 0.37 mmHg. The Reynolds number was 53.
Based upon the flow rate Q and the pressure drop, the Reynolds Number was calculated for each system. The Reynolds number can be calculated using the following equation:
Based on the calculations above, only example 3 has a Re<2300. Accordingly, Example 3 is the only example that maintained a laminar flow pattern. Measurements made using the pressure differential across sensors are, like known ultrasonic flowmeters, Reynolds number dependent. Flowmeters according to the instant disclosure will vary in size and configuration depending upon the particular application and fluid to be measured. As is well understood by the skilled artisan, less turbulence will be present at lower flow rates or in smaller pipes. So, in order to use the 12″ by 1″ pipe flowmeter to measure the viscosity of propylene glycol, the flow rate of the system Q has to be 1788 cm3/s or less to maintain laminar flow, i.e., a Reynolds number below 2300.
Based upon the foregoing discussion, the skilled artisan would understand how to modify the flowmeter or calculate the maximum flow rate so as to maintain laminar flow and thereby ascertain the fluid viscosity. When Re>2300 then flow conditioners would have to be used or other mathematical adaptations of Poiseuille's equation based on fluid dynamics.
A variety of flow conditioner options can be seen in
A cross section view of one tube arrangement according to the embodiment depicted in
Although the invention has been described in detail in the foregoing embodiments for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be described by the following claims.
Other embodiments of the present invention can include alternative variations. These and other variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.