Flowmeter moisture correction device and method

Abstract

A method for improving the precision of a flow meter is provided. The flow meter includes at least one flow tube, at least one pickup sensor attached to the flow tube, at least one driver attached to the flow tube, and meter electronics in communication with the at least one pickup sensor and the driver. The method includes the steps of vibrating at least one flow tube in a drive mode using at least one driver, and receiving a sensor signal based on a vibration response to the drive mode vibration from at least one pickup sensor. And obtaining the uncorrected density by using the flowmeter. And obtaining the uncorrected mass flow rate by utilizing the flow meter. And the flow meter is used for obtaining extended driving gain. At least one traffic variable is received. And calculating the density ratio. A plurality of moisture coefficients are provided. A dry gas mass flow rate is calculated using the density ratio and at least one moisture coefficient of the plurality of moisture coefficients.

Description

Technical Field

[0001] The present invention relates to flow meters and, more particularly, to Coriolis-based measurement methods and related apparatus that provide increased accuracy of multiphase fluid flow. Background Art

[0002] Vibrating conduit sensors such as Coriolis mass flow meters and vibrating densitometers typically operate by detecting the motion of a vibrating conduit containing a flowing material. Properties associated with the material in the conduit (e.g., mass flow, density, etc.) can be determined by processing measurement signals received from a motion transducer associated with the conduit. The vibration modes of a vibrating material-filled system are typically affected by the combined mass, stiffness, and damping characteristics of the containing conduit and the material contained in the conduit.

[0003] A typical Coriolis mass flowmeter includes one or more conduits (also referred to as flow tubes) connected in series in a pipeline or other transmission system and delivering materials, such as fluids, slurries, emulsions, etc., in the system. Each conduit can be considered to have a set of natural vibration modes, including, for example, simple bending, torsion, radial and coupled modes. In a typical Coriolis mass flow measurement application, when the material flows through the conduit, the conduit is excited with one or more vibration modes, and the movement of the conduit is measured at points spaced apart along the conduit. The excitation is usually provided by a driver, such as an electromechanical device that perturbs the conduit in a periodic manner, such as a voice coil type actuator. The mass flow rate can be determined by measuring the time delay or phase difference between the motions at the transducer position. Two or more such transducers (or pick-off sensors) are usually adopted to measure the vibration response of the flow tube or conduit, and are usually located at positions upstream and downstream of the driver. The instrument receives signals from the pick-off sensors and processes the signals to obtain mass flow rate measurements.

[0004] Flow meters are used to perform mass flow rate measurements on a wide variety of fluid flows. For example, one area where Coriolis flow meters may be used is in the metering of oil and gas wells. The product of such a well may include a multiphase flow that includes, for example, oil or gas, but also other components such as water and / or solids. Of course, even for such a multiphase flow, it is highly desirable that the resulting metering be as accurate as possible.

[0005] Coriolis meters provide high accuracy for single-phase flows. However, when Coriolis flow meters are used to measure aerated fluids, i.e., fluids that include entrained gas, or for measuring gas flows with a liquid component (i.e., "wet gas"), the meter's accuracy may be reduced. The same is true for flows with entrained solids and for mixed-phase fluid flows, such as when a hydrocarbon fluid contains water.

[0006] In the past, Coriolis meters were designed to measure single-phase processes. The Coriolis technology is unique in that it measures both the mass flow rate and density of the process fluid simultaneously and independently. If only two phases (i.e., liquid and gas) needed to be measured independently in the process and the densities of these two phases at process conditions were known, this information would be sufficient to provide the total mass flow rate as well as the phase fraction. When multiple phases are present, some of the basic assumptions made in the Coriolis measurement fail. In particular, the fluid no longer vibrates synchronously with the flow tube, resulting in measurement errors.

[0007] In general, when a Coriolis meter experiences the onset of multiphase flow, the vibration of the sensor tube is damped, resulting in a reduction in the amplitude of the flow tube vibration. Typically, the meter electronics compensates for this reduced amplitude by increasing the drive energy or drive gain to restore the amplitude. However, there is an upper limit because the maximum drive energy is limited for safety reasons and other reasons. Therefore, when the multiphase flow becomes more significant, the relatively measurable drive amplitude decreases and cannot be increased anymore because the driver is already running at 100% drive gain. At this point, the meter electronics will continue to drive the tube vibration at a reduced amplitude. In even more severe cases of multiphase flow, the amplitude of the vibration becomes up to an order of magnitude smaller than that of single-phase flow, or even smaller. In addition to these challenges, the presence of bubbles or droplets with a different density from the main carrier phase can cause the droplets to decouple from the surrounding fluid. The degree of decoupling depends on many flowmeter and process fluid conditions, such as viscosity, droplet or bubble size, and flowmeter vibration frequency. This decoupling phenomenon results in measurements of both density and mass flow rate that are less than the actual value. The reduction in tube amplitude also affects the quality measurement of the Coriolis meter. A similar effect on accuracy exists for the case of wet gas. Conventional guidelines and best practices often state that Coriolis meters are not optimized for two-phase performance with small amounts of liquid entrained in the gas and often conclude that Coriolis meters may have unpredictable behavior in wet gas conditions.

[0008] For example, for measuring well performance in oil and gas well testing, separators are often used to separate liquids from gases, or oil from water and gas. In either case, separate flow meters are used to measure each phase separately. These separators are usually large, heavy pressure vessels that have many level controllers, safety valves, level sensors, control valves, piping, flow meters, and internal devices to facilitate efficient separation. Such separators are often very expensive, so that multiple wells must share one separator for well testing. Manifolds are usually provided to allow testing of one well at a time, generally for 24 hours.

[0009] What is needed is a flow meter that operates accurately without compositional fluid analysis or other inputs other than readily available process measurements. The present embodiments provide apparatus and methods for improved measurement accuracy for wet gas applications. The embodiments can be made directly to wellhead measurements, but can also be employed in any flow meter application. Thus, an advance in the art is achieved. Summary of the invention

[0010] According to one aspect, a method for improving flow meter accuracy includes a flow meter, the flow meter also including at least one flow tube, at least one pickoff sensor attached to the flow tube, at least one driver attached to the flow tube, and meter electronics in communication with the at least one pickoff sensor and the driver. The method includes the steps of: vibrating the at least one flow tube in a drive mode vibration using the at least one driver; and receiving a sensor signal based on a vibration response to the drive mode vibration from the at least one pickoff sensor. Deriving an uncorrected density using the flow meter. Deriving an uncorrected mass flow using the flow meter. Deriving an extended drive gain using the flow meter. Receiving at least one flow variable. Calculating a density ratio. Providing a plurality of moisture coefficients. Calculating a dry gas mass flow rate using the density ratio and at least one moisture coefficient of the plurality of moisture coefficients.

[0011] According to one aspect, a meter electronics device for a flow meter is provided, the meter electronics device being configured to improve measurement accuracy. The flow meter includes at least one flow tube, at least one pickoff sensor attached to the at least one flow tube, and at least one driver attached to the flow tube. The meter electronics device is in communication with the at least one pickoff sensor and the at least one driver, and the meter electronics device is configured to: vibrate the at least one flow tube in a drive mode vibration using the at least one driver, and receive a sensor signal based on a vibration response to the drive mode vibration from the at least one pickoff sensor. The meter electronics device is also configured to: derive an uncorrected density using the flow meter, derive an uncorrected mass flow using the flow meter, and derive an extended drive gain using the flow meter. Receive at least one flow variable. Calculate a density ratio. Provide a plurality of moisture coefficients; and calculate a dry gas mass flow rate using the density ratio and at least one moisture coefficient of the plurality of moisture coefficients.

[0012] All aspects

[0013] According to an embodiment, a method for improving the accuracy of a flow meter is provided. The flow meter includes at least one flow tube, at least one pickoff sensor attached to the flow tube, at least one driver attached to the flow tube, and meter electronics in communication with the at least one pickoff sensor and the driver. The method includes the steps of: vibrating the at least one flow tube in a drive mode vibration using at least one driver; and receiving a sensor signal based on a vibration response to the drive mode vibration from at least one pickoff sensor. Deriving an uncorrected density using the flow meter. Deriving an uncorrected mass flow using the flow meter. Deriving an extended drive gain using the flow meter. Receiving at least one flow variable. Calculating a density ratio. Providing a plurality of moisture coefficients. Calculating a dry gas mass flow rate using the density ratio and at least one of the plurality of moisture coefficients.

[0014] Preferably, the flow variable comprises pressure, and wherein pressure is one of a measured input and a user input.

[0015] Preferably, the flow variable comprises water cut.

[0016] Preferably, the moisture content is measured using a moisture content analyzer in communication with the meter electronics.

[0017] Preferably, the flow variable comprises temperature.

[0018] Preferably, the method includes the step of deriving an extended drive gain using a flow meter.

[0019] Preferably, calculating the density ratio comprises dividing the uncorrected density by the dry reference density.

[0020] Preferably, the method comprises retrieving a dry reference density from the meter electronics.

[0021] Preferably, the dry reference density retrieved from the meter electronics is determined by at least one of temperature, pressure and gas composition.

[0022] Preferably, the method includes the step of deriving the liquid mass flow rate by subtracting the dry gas mass flow rate from the corrected mass flow rate.

[0023] Preferably, the corrected mass flow rate is derived from the uncorrected mass flow rate and a meter factor.

[0024] Preferably, the meter factor is derived from an extended drive gain and a plurality of moisture coefficients.

[0025] Preferably, the moisture coefficient is a function of a plurality of flow variables.

[0026] Preferably, the moisture coefficient is a function of pressure, gas velocity, drive gain and water cut.

[0027] Preferably, the step of calculating the dry gas mass flow rate using the density ratio and at least one moisture coefficient among a plurality of moisture coefficients comprises: using a gas mass ratio derived from the density ratio and the plurality of moisture coefficients.

[0028] Preferably, the gas mass ratio is obtained using a quadratic fit with density ratio calibration and moisture coefficient.

[0029] Preferably, the meter factor is obtained using a quadratic fit from extending the drive gain and multiple moisture coefficients.

[0030] According to an embodiment, a meter electronics device for a flow meter is provided, the meter electronics device being configured to improve measurement accuracy. The flow meter includes at least one flow tube, at least one pickoff sensor attached to the at least one flow tube, and at least one driver attached to the flow tube. The meter electronics device communicates with the at least one pickoff sensor and the at least one driver, and the meter electronics device is configured to: vibrate the at least one flow tube in a drive mode vibration using the at least one driver, and receive a sensor signal based on a vibration response to the drive mode vibration from the at least one pickoff sensor. The meter electronics device is also configured to: derive an uncorrected density using the flow meter, derive an uncorrected mass flow using the flow meter, and derive an extended drive gain using the flow meter. Receive at least one flow variable. Calculate a density ratio. Provide multiple moisture coefficients; and calculate a dry gas mass flow rate using the density ratio and at least one of the multiple moisture coefficients.

[0031] Preferably, the flow variable comprises pressure, and wherein pressure is one of a measured input and a user input.

[0032] Preferably, the flow variable comprises water cut.

[0033] Preferably, the moisture content is measured using a moisture content analyzer in communication with the meter electronics.

[0034] Preferably, the flow variable comprises temperature.

[0035] Preferably, the meter electronics is further configured to derive an extended drive gain.

[0036] Preferably, calculating the density ratio comprises dividing the uncorrected density by the dry reference density.

[0037] Preferably, the meter electronics comprises: retrieving the dry reference density from the meter electronics.

[0038] Preferably, the dry reference density retrieved from the meter electronics is determined by at least one of temperature, pressure and gas composition.

[0039] Preferably, the meter electronics is further configured to derive the liquid mass flow rate by subtracting the dry gas mass flow rate from the corrected mass flow rate.

[0040] Preferably, the corrected mass flow rate is derived from the uncorrected mass flow rate and a meter factor.

[0041] Preferably, the meter factor is derived from an extended drive gain and a plurality of moisture coefficients.

[0042] Preferably, the moisture coefficient is a function of a plurality of flow variables.

[0043] Preferably, the moisture coefficient is a function of pressure, gas velocity and water content.

[0044] Preferably, calculating the dry gas mass flow rate using the density ratio and at least one moisture coefficient from among a plurality of moisture coefficients comprises: using a gas mass ratio derived from the density ratio and the plurality of moisture coefficients.

[0045] Preferably, the gas mass ratio is obtained using a quadratic fit with density ratio calibration and moisture coefficient.

[0046] Preferably, the meter factor is obtained using a quadratic fit from extending the drive gain and multiple moisture coefficients. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A flow meter including a meter assembly and meter electronics is shown;

[0048] Figure 2 shows a block diagram of a meter electronics device according to an embodiment;

[0049] Figure 3 is a graph showing the variation of the gas mass ratio of oil with the density ratio (apparent / dry gas) (the water curve is not shown);

[0050] Figure 4 is a graph showing a meter factor curve for oil as a function of extended drive gain;

[0051] Figure 5 An embodiment of a process for determining both the gas mass flow rate and the liquid mass flow rate of a wet gas flow is shown;

[0052] Figure 6 The concept of extended drive gain is shown;

[0053] Figure 7 The improvement in flow meter accuracy as a result of implementing the present embodiment is shown. DETAILED DESCRIPTION

[0054] Figures 1 to 7The following description depicts specific examples to teach those skilled in the art how to make and use the best mode of the present invention. For the purpose of teaching the principles of the invention, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the present invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the present invention. Therefore, the present invention is not limited to the specific examples described below, but is only limited to the claims and their equivalents.

[0055] Figure 1 A vibrating flow meter 5 according to an embodiment is shown. The flow meter 5 includes a sensor assembly 10 and a meter electronics 20 coupled to the sensor assembly 10. The sensor assembly 10 is responsive to at least the mass flow rate and density of the process material. The meter electronics 20 is connected to the sensor assembly 10 via leads 100 to provide density, mass flow rate, and temperature information, as well as other information, via a communication link 26. Although a Coriolis flow meter configuration is described, it will be apparent to one skilled in the art that the present invention may also be used as a vibrating tube densitometer.

[0056] The sensor assembly 10 includes: manifolds 150 and 150', flanges 103 and 103' having flange necks 110 and 110', parallel flow tubes 130 and 130', first and second drivers 180L and 180R, and first and second pickoff sensors 170L and 170R (for simplicity, the drivers and pickoff sensors may be collectively referred to as "transducers" herein). The first and second drivers 180L and 180R are spaced apart on one or more flow tubes 130 and 130'. In some embodiments, there is only a single driver. In addition, in some embodiments, the sensor assembly 10 may include a temperature sensor 190. The flow tubes 130 and 130' have two substantially straight inlet branches 131 and 131' and outlet branches 134 and 134', which converge toward each other at the flow tube mounting blocks 120 and 120'. The flow tubes 130 and 130' are bent at two symmetrical locations along their lengths and are substantially parallel throughout their lengths. The support rods 140 and 140' are used to define an axis W and a substantially parallel axis W' about which each flow tube oscillates. It should be noted that in embodiments, the first driver 180L can be juxtaposed with the first pickoff sensor 170L and the second driver 180R can be juxtaposed with the second pickoff sensor 170R.

[0057] The side branches 131 , 131 ′, 134 , 134 ′ of the flow tubes 130 and 130 ′ are fixedly attached to the flow tube mounting blocks 120 and 120 ′, and these blocks are in turn fixedly attached to the manifolds 150 and 150 ′. This provides a continuous closed material path through the sensor assembly 10 .

[0058] When flanges 103 and 103' having holes 102 and 102' are connected to a process pipeline (not shown) carrying the process material being measured via inlet port 104 and outlet port 104', the material enters the inlet port 104 of the flow meter 5 through the orifice 101 in flange 103 and is directed to the flow tube mounting block 120 through manifold 150. Within manifold 150, the material is separated and conveyed through flow tubes 130 and 130'. Upon exiting flow tubes 130 and 130', the process material recombines into a single stream within manifold 150' and is thereafter conveyed to outlet port 104', which is connected to a process pipeline (not shown) via orifice 101' through flange 103' having bolt holes 102'. The flowing fluid may include a liquid. The flowing fluid may include a gas. The flowing fluid may include a multiphase fluid, such as a liquid including entrained gas and / or entrained solids; or a gas including entrained liquid.

[0059] The flow tubes 130 and 130' are selected and appropriately mounted to the flow tube mounting blocks 120 and 120' so as to have substantially the same mass distribution, moment of inertia, and Young's modulus about bending axes W--W and W'--W', respectively. These bending axes pass through support rods 140 and 140'. Since the Young's modulus of the flow tubes varies with temperature, and this variation affects the calculation of flow and density, a temperature sensor 190 (which may be a resistance temperature detector (RTD)) is mounted to the flow tubes 130, 130' to continuously measure the temperature of the flow tubes 130, 130'. The temperature-dependent voltage appearing across the temperature sensor 190 can be used by the meter electronics 20 to compensate for changes in the elastic modulus of the flow tubes 130 and 130' due to any changes in the flow tube temperature. The temperature sensor 190 is connected to the meter electronics 20 by leads 195.

[0060] The flow tubes 130, 130' are typically driven by drivers 180L, 180R in opposite directions about respective bending axes W and W' and in what is referred to as a first out-of-phase bending mode of the vibrating flow meter 5. The drivers 180L, 180R may include one of many well-known arrangements, such as a magnet mounted to the flow tube 130 and an opposing coil mounted to the adjacent flow tube 130'. An alternating current is passed through the opposing coils to cause the two flow tubes 130 and 130' to oscillate. The meter electronics 20 applies appropriate drive signals to the drivers 180L, 180R. Other driver arrangements are also contemplated and are within the scope of the specification and claims.

[0061] Meter electronics 20 receives the sensor signal from sensor assembly 10 and also generates a drive signal that causes drivers 180L, 180R to oscillate flow tubes 130, 130'. Other sensor arrangements are contemplated and within the scope of the description and claims.

[0062] The meter electronics 20 processes the left and right velocity signals from the pick-off sensors 170L, 170R to calculate flow rate, etc. The communication link 26 provides input and output means that allow the meter electronics 20 to interface with an operator or with other electronic systems.

[0063] In one embodiment, as shown, the flow tubes 130, 130' comprise generally U-shaped flow tubes. Alternatively, in other embodiments, the flow meter 5 may comprise substantially straight flow tubes 130, 130'. Other flow meter shapes and / or configurations may be used and are within the scope of the description and claims.

[0064] Figure 1 The description is provided merely as an example of the operation of a flow metering device and is not intended to limit the teachings of the present invention.

[0065] Figure 2 The meter electronics 20 of the flow meter 5 according to an embodiment of the present invention is shown. The meter electronics 20 may include an interface 201 and a processing system 203. The meter electronics 20 receives transducer signals from the sensor assembly 10, such as but not limited to pick-off sensor 170L, 170R signals. The meter electronics 20 processes the sensor signals to obtain flow characteristics of the flowing material flowing through the sensor assembly 10. For example, the meter electronics 20 may determine one or more of phase difference, frequency, time difference (Δt), density, mass flow rate, strain, and volume flow rate based on the sensor signals. In addition, in some embodiments, other flow characteristics may be determined.

[0066] Interface 201 via Figure 1The leads 100 shown in FIG. 1 receive sensor signals from the transducer. The interface 201 may perform any necessary or desired signal conditioning, such as any manner of formatting, amplification, buffering, etc. Alternatively, some or all of the signal conditioning may be performed in the processing system 203 .

[0067] Additionally, for example, interface 201 may enable communication between meter electronics 20 and an external device, such as via communication link 26. Interface 201 may enable any manner of electronic, optical, or wireless communication.

[0068] The interface 201 in one embodiment includes a digitizer 202, wherein the sensor signal includes an analog sensor signal. The digitizer 202 samples and digitizes the analog sensor signal and generates a digital sensor signal. The interface 201 / digitizer 202 may also perform any required decimation, wherein the digital sensor signal is decimated to reduce the amount of signal processing required and to reduce processing time.

[0069] The processing system 203 performs operations of the meter electronics 20 and processes flow measurements from the sensor assembly 10. The processing system 203 executes one or more processing routines and thereby processes the flow measurements to produce one or more flow characteristics.

[0070] Processing system 203 may include a general purpose computer, a microprocessing system, a logic circuit, or some other general or custom processing device. Processing system 203 may be distributed among multiple processing devices. Processing system 203 may include any form of integrated or independent electronic storage media, such as storage system 204.

[0071] The processing system 203 is configured to retrieve and execute stored routines to operate the flow meter 5. The storage system 204 can store routines including a general flow meter routine 205, a wet gas flow routine 220, a gain routine 224, and a correction routine 226. The processing system 203 can determine at least the amplitude, phase difference, time difference, and frequency of the transducer signal. Other measurement / processing routines are also contemplated and are within the scope of the specification and claims. The storage system 204 can store measurements, received values, working values, and other information. In some embodiments, the storage system can store, for example, but not limited to, mass flow 210, density (ρ) 212, viscosity (μ) 214, temperature (T) 216, any one or more of other values ​​known in the art and their products. The flow meter routine 205 can generate and store fluid and flow measurements. These values ​​can include substantially instantaneous measurements, or can include total values ​​or cumulative values, and can also include databases and lookup tables. For example, the flow meter routine 205 can generate mass flow measurements and store such measurements in the storage system 204. The flow meter routine 205 can generate density measurements and store them in the storage system 204. As will be understood by those skilled in the art, it is contemplated that other measurements are similarly generated and stored in the storage system. As previously discussed and as known in the art, the mass flow 210 value and the density 212 value are determined based on the transducer response. The mass flow 210 may include substantially instantaneous mass flow rate values, may include mass flow rate samples, may include average mass flow rate over a time interval, or may include cumulative mass flow rate over a time interval. The time interval may be selected to correspond to a period of time during which a particular fluid condition is detected, such as a fluid state containing only liquid, or alternatively a fluid state including liquid and entrained gas. In addition, other mass flow quantifications are also contemplated and within the scope of the specification and claims.

[0072] In an embodiment, flow is sensed by directly measuring the relative motion of the outlet 134, 134' (or inlet 131, 131') side of the flow tube 130, 130' relative to the inlet 131, 131' (or outlet 134, 134') side of the same flow tube 130, 130'. During fluid flow, the signal output generally has an amplitude and phase as a function of the flow rate. In a related embodiment, a combined signal from one or more transducers on the inlet side of the meter and a combined signal from one or more transducers on the outlet side of the meter are input into the meter electronics. A measurement of phase can be derived from the inlet signal and the outlet signal.

[0073] In an embodiment, the sensor assembly 10 can measure the amplitude of the flow tubes 130, 130' via a pickoff sensor 170L closest to the inlet of the flow meter 5. When the signal of the pickoff sensor drops below a certain threshold, the uncertainty in the mass flow rate and the uncertainty in the density of the mixture are generally too large to be considered a reliable measurement result. For example, the threshold at which the signal is considered unreliable may be different for the mass rate measurement result and the density measurement result. When a multiphase flow is generated, such as from an oil and gas well, through a Coriolis sensor, there are generally periods of unmeasurable flow and periods of measurable uniform flow. The measurable period is typically characterized by low gas void fraction (GVF) flow in liquid-dominated flow and low Lockhart-Martinelli (LM) parameters in wet gas flow. LM is a dimensionless number used in two-phase flow calculations and represents the liquid fraction of the flowing fluid. See the following: Lockhart, RW, Martinelli, RC, "Proposed Correlation of Data for Isothermal Two Phase Flow, Two Component Flow in Pipes", Progress in Chemical Engineering (Chem. Eng. Prog.), Vol. 45, 1949, pp. 39-48, which is incorporated herein by reference. During these periods of relatively uniform flow, mass flow and density errors may be low enough to be acceptable for generating reliable measurements. The embodiments provided herein improve upon prior art methods for wet gas flow measurement.

[0074] For some embodiments provided herein, and in particular for the wet gas flow routine 220 described further below, it will be assumed that the flow through the flow meter includes three main components. The first is a gas core flow. The second is a liquid film flow, which includes liquid attached to the walls of the flow tube. The third is a liquid mist flow, which includes droplets entrained in the gas core. As an example, for oilfield applications, the liquid entrained in the natural gas may be primarily water, primarily condensate (or crude oil), or a mixture of the two.

[0075] The gas mass ratio is defined as the gas mass flow rate divided by the total mass flow rate, as shown in equation (1):

[0076]

[0077] in:

[0078]

[0079] It is assumed that the flow regime of interest is annular mist in most cases. In this case, the liquid entrainment factor E is defined as the mass rate of liquid mist entrained (in the gas core) relative to the total liquid mass rate, as shown in equation (2):

[0080]

[0081] in:

[0082]

[0083] The slip factor S is the gas superficial velocity U SG and the apparent velocity of the liquid film U SL The ratio of , and can be described by formula (3):

[0084]

[0085] For most cases, S>1 means that for longitudinal flow, the liquid mist entrained in the gas flow travels at approximately the same speed as the gas core flow, but the liquid film attached to the tube wall travels at a different (lower) speed than the gas core. This method assumes that the multiphase flow is steady, and the calibration implicitly takes into account the slip factor.

[0086] For the purpose of flow meter 5 operation, it will be assumed that the resonant frequency response depends only on the gas core and liquid film, and that the liquid mist contributes only to the damping coefficient. This approach shows that the resonant frequency is independent of damping, although damping will broaden the frequency response around resonance.

[0087] Furthermore, it will be clear that the frequency response will depend on the flow rate, as some liquid in the form of droplets will be extracted from the wall film and entrained in the core gas flow.For operation of the flow meter 5, calculations that are independent of flow rate may be performed in some embodiments.

[0088] The natural vibration frequency of the flow tube 130, 130' is determined by its stiffness and mass. Since the volume of the fluid in the flow tube 130, 130' is constant, changes in the density of the fluid will result in changes in the mass within the flow tube 130, 130'. When the mass inside the flow tube 130, 130' changes, the natural frequency of the tube will also change, and this change is detected by the pick-off sensors 170L, 170R. The natural frequency is directly related to the density of the fluid inside the tube. In an embodiment, as will be understood by those skilled in the art, the temperature is measured to compensate for slight changes in the tube stiffness (Young's modulus) with temperature.

[0089] In an embodiment, the density ratio is defined as the ratio of the measured density to the dry gas density, as shown in equation (4):

[0090]

[0091] in:

[0092] ρ a = the apparent (uncorrected) density measured by the Coriolis meter

[0093] ρ g = Gas density at pipeline conditions (dry reference)

[0094] Based on the above relationships, if the liquid density and gas density at flow conditions are known, and the measured densities are known, the gas mass ratio (also referred to as "gas quality") can be expressed as a function of liquid entrainment. In an embodiment, a lookup table can be used to obtain the liquid density and gas density at pipeline conditions. It should be noted that in this embodiment, the E factor is not calculated, but is used as a theoretical framework for establishing the use of the density ratio to obtain the gas mass ratio.

[0095] Based on the theoretical decoupling model, it is expected that the measured apparent density will vary with gas velocity at a constant mass ratio. For example, for very high velocities (assuming theoretical values, e.g., E is about 0.9), most of the liquid is mist entrained in the gas core, so the measured density will be very close to the dry gas density (expected density ratio from 1.002 to 1.025). As the gas velocity decreases (e.g., medium gas velocity, E is about 0.5), the density ratio will increase from 1.01 to 1.3 (depending on pressure and gas mass ratio). For low gas velocities (assuming, e.g., E is about 0.1), there is almost no entrainment of liquid mist, and the expected density ratio will increase from 1.3 to 1.6 or more. It is clear that the measured density has a strong dependence on the gas mass ratio.

[0096] In an embodiment, a corrected gas mass flow rate is obtained according to the corrected total mass flow rate and the gas mass ratio. The corrected gas mass flow rate is a function of pressure, gas superficial velocity and water content.

[0097] As shown in Equation 4, the density ratio Expressed as the Coriolis meter density measurement (uncorrected) divided by the dry gas density at pipeline conditions. A table of reference dry gas densities at various temperatures and pressures can be retrieved from the meter electronics 20. The table reference values ​​may be based on measured inputs or user inputs. The inputs may include one or more of temperature, pressure, and gas composition.

[0098] In an embodiment, the density ratio is used to correlate the gas mass ratio. In particular, the data is segmented or filtered by pressure range, gas superficial velocity, and / or water content. Since the data is filtered by these characteristic flow parameters, a quadratic equation with lower residual error can be obtained. The gas mass ratio (at a specific pressure, velocity, and water content) is then obtained by calibrating the density ratio using a quadratic fit, such as Figure 3 As shown and described by equation (5):

[0099]

[0100] in:

[0101] GMR P，Vel，WC = the mass ratio of gases at a specific pressure, velocity and water content; and

[0102] A, B, C = Moisture coefficients based on pressure, velocity and water cut stored in a lookup table in the meter electronics.

[0103] A closer look Figure 3 , Figure 3 is an example of the gas mass ratio of oil (water not shown) as the density ratio varies. It should be noted that this is an example, and the actual curve and the resulting curve fit / equation will be different depending on the specific flow meter and process conditions. Where the gas mass ratio is known and controlled under laboratory conditions, E (not shown) can be expressed. Since E depends on the flow velocity, it is expected that the measured apparent density will vary with the gas velocity given a constant mass. At very high velocities, most of the liquid is a mist entrained in the gas core, and the measured density is closer to the gas density value. Looking at the points within the rectangle (gas mass ratio of approximately 0.8), it can be observed that the lowest gas velocity (at approximately 33 ft / s) has the highest density ratio, and as the velocity increases at a constant gas mass ratio, it is clear that the gas ratio is inversely proportional to the gas velocity.

[0104] The meter factor is used to compensate for the decoupling error of the total mass flow rate and is obtained by extending the drive gain, but has a discrete calibration curve as a function of pressure, velocity and water content. If the extended drive gain is allowed to exceed 100%, then the extended drive gain is the drive gain. This is expressed by equation (6):

[0105] MF P,Vel,WC =F*ExtDG 2 +G*ExtDG+H (6)

[0106] in:

[0107] MF P,Vel,WC = meter factor at a specific pressure, velocity and water content;

[0108] ExtDG = Extended drive gain; and

[0109] F, G, H = Moisture coefficients based on pressure, velocity and water cut stored in a lookup table in the meter electronics.

[0110] Figure 4An example of a calibration curve is shown which is used to obtain a meter factor to compensate for decoupling errors in the total mass flow measurement. It should be noted that this is an example and the actual curves and resulting curve fits / equations will differ depending on the specific flow meter and process conditions. The effect of water content is shown by the curve for oil being lower than the curve for water. The drive gain is related to the flow tube damping and provides an estimate for the meter factor correction. Liquid entrainment is a function of pressure, gas velocity, and water content (which is related in part to the surface tension of the liquid). For the same drive gain, the decoupling of oil is expected to be higher because water is a polar molecule and oil is not, and the polarity of water gives it a higher surface tension, making it more difficult for water droplets to separate from the liquid film attached to the flow tube wall.

[0111] Applying the meter factor according to equation (6) to the uncorrected mass flow rate:

[0112]

[0113] in:

[0114] RemFlow P,Vel,WC = Corrected mass flow rate at a specific pressure, velocity and water cut.

[0115] Calculate the dry gas flow rate, given the corrected total mass flow rate and gas mass ratio, with an indication of liquid content:

[0116] GasFlow P,Vel,WC =(RemFlow*GMR) P,Vel,WC (8)

[0117] in:

[0118] GasFlow P,Vel,WC = dry gas mass flow rate at a specific pressure, velocity and moisture content.

[0119] The liquid flow rate is simply calculated by subtracting the corrected gas mass flow rate from the corrected total mass flow rate:

[0120] LiqFlow P,Vel,WC =RemFlow P,Vel,WC -GasFlow P,Vel,WC (9)

[0121] in:

[0122] LiqFlow P,Vel,WC = mass flow rate of a liquid at a specific pressure, velocity and water content.

[0123] Figure 5An embodiment of a correction process 300 for wet gas flowing through a flow meter 5 is shown. In a first step, the fluid flow is measured by the flow meter 5, and an uncorrected density 302 and an uncorrected mass flow 304 are measured. The temperature 306 is measured by a measuring device such as a thermistor, thermocouple, or resistance temperature detector (RTD), which may be associated with the flow meter 5, or may be external to the meter. There may be multiple temperature measuring devices, and an average or weighted average may be utilized to determine the temperature 306.

[0124] An extended drive gain 308 is also calculated by the flow meter 5. The term "drive gain" itself refers to the amount of current available to keep the flow tube oscillating at the design amplitude. The drive gain is measured as a percentage, so if the sensor is operating under normal conditions, the sensor only requires a small portion of the total current available, such as a 5% drive gain. However, if the sensor detects a decrease in tube amplitude, the sensor may use more current to restore the amplitude to the design value, but the drive gain will be increased to, for example, 10%. During wet gas flow, the flow tube is significantly damped and the meter will attempt to keep the tube oscillating at the design amplitude by using more energy until the drive gain reaches 100%, at which point no more current can be delivered to the coil and magnet. The extended drive gain 308 is a calculated value that represents the amount of energy required to keep the tube oscillating at the design amplitude if the sensor had no restrictions on how much current it could use. Figure 6 The concept of extended drive gain 308 is shown in FIG.

[0125] The pressure 310 may be measured by a pressure gauge, or may be manually input into the meter electronics 20, such as by an end user. There may be multiple pressure measuring devices, and an average or weighted average may be utilized to determine the pressure 310.

[0126] The moisture content 312 may be measured by a moisture content analyzer, or may be manually input into the meter electronics 20, for example, by an end user. In an embodiment, the moisture content analyzer is configured to measure the moisture content in the mist phase of the humid gas stream.

[0127] The gas composition 314 may be measured by a gas analyzer, or may be manually input into the meter electronics 20, for example, by an end user. In an embodiment, a list of gas compositions may be provided for selection by a user via an interface in communication with the meter electronics 20.

[0128] Gas velocity 316 is calculated by flow meter 5. In an embodiment, if the process stream experiences intermittent periods of dry gas (indicated by low dry gain, etc.), the "dry gas" density at line conditions is stored in a memory variable and used in the calculation of the density ratio. The volume flow rate is calculated by dividing the mass flow rate 304 by the density 302. The gas velocity is calculated by dividing the volume flow rate by the area of ​​the flow tube 130, 130'.

[0129] The dry gas density table 318 is stored in the meter electronics 20. The dry gas density table 318 uses one or more of the temperature 306, pressure 310, and gas composition 314 as inputs and outputs a dry reference density p based on these inputs. g .

[0130] As described above by equation (4), the uncorrected density 302 is divided by the dry reference density p g , to obtain a density ratio of 320.

[0131] Density ratio 320 is used to determine gas mass ratio 322. As described above, Figure 3 As shown in the example of and as described by equation (5), the gas mass ratio is determined by using a coefficient group 324 determined according to a specific pressure, velocity, and water content, and the gas mass ratio is obtained by density ratio calibration using a quadratic fit.

[0132] like Figure 4 As shown in the example of and as described by equation (6), the meter factor 326 utilizes the extended drive gain 308 and a coefficient set 324 determined based on a specific pressure, velocity, and water cut.

[0133] The meter factor 326 and the uncorrected mass flow rate 304 are then used to determine a corrected mass flow rate 328 as described by equation (7).

[0134] The dry gas mass flow rate 330 is then determined using the gas mass ratio 322 and the corrected flow rate 328 as described by equation (8).

[0135] The liquid mass flow rate 332 is then calculated by subtracting the dry gas mass flow rate 330 from the corrected flow rate 328 as described by equation (9).

[0136] In an embodiment, the flow meter 5 provided can measure the performance of the well at the wellhead, thereby significantly reducing costs, related manpower and overall complexity. By monitoring each site separately, there are considerable benefits, the most obvious of which is the elimination of separators and the maintenance that comes with them. Another advantage is that all wells in the oil field can be monitored simultaneously, so that real-time decisions can be made about strategies and tactics for efficient production and enhanced oil recovery (EOR). EOR involves the injection of water, CO2, natural gas, surfactants or steam; this can be expensive and must be applied at the right time using the right amount of media. Having real-time production data for the entire oil field, for example but not limited to, will provide production and reservoir engineers with valuable information about how to fine-tune their EOR. Operators will also have the following advantages, detecting wells with problems earlier and being able to take quick action to remedy the problem. Another advantage is that in new oil fields, the flow line collection system can include a main line and branch line design, rather than setting up a separate flow line leading to a test separator for each well. This saves capital costs on required pipes, welding, trenching and land.

[0137] The embodiments provided herein improve upon current wet gas metering by adding density and water cut inputs to better account for multiphase measurement issues. Additionally, multiple calibration curves available based on coefficient set 324 can reduce residual errors from curve fitting, enabling better prediction of liquid loading. This is due in part to the use of pressure, gas superficial velocity, and water cut. Prior art wet gas metering results in higher errors (for gas, the current specification is 7% when the liquid loading is less than 20% by mass). The improvement in liquid accuracy is dramatic: 10% accuracy over most of the operating range, while under some operating conditions, the error in current metering can exceed 100%. Figure 7 A comparison of a flow meter of the prior art and a flow meter using an embodiment provided herein is shown. The diamonds represent post-processed data using the new method and show accuracy within 2% for most points. In contrast, the flow meter of the prior art shows accuracy within 7% for most points, and the accuracy deteriorates greatly at higher liquid loads, showing an error of nearly 25% when the gas mass ratio is below 0.7. This is an example under a specific set of process conditions.

[0138] This specification describes specific examples to teach those skilled in the art how to make and use the best mode of the present invention. For the purpose of teaching the principles of the invention, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the present invention.

[0139] The detailed description of the above embodiments is not an exhaustive description of all embodiments contemplated by the inventors within the scope of the present invention. In fact, those skilled in the art will recognize that certain elements of the above embodiments may be combined or removed in various ways to produce additional embodiments, and such additional embodiments fall within the scope and teachings of the present invention. It is obvious to those of ordinary skill in the art that the above embodiments may be combined in whole or in part to produce additional embodiments within the scope and teachings of the present invention.

[0140] Therefore, although the specific embodiments and examples of the present invention are described herein for illustrative purposes, various equivalent modifications within the scope of the present invention are possible as will be appreciated by those skilled in the relevant art. The teachings provided herein may be applied to other embodiments in addition to the embodiments described above and shown in the accompanying drawings. Therefore, the scope of the present invention is determined according to the appended claims.

Claims

1. A method for improving the accuracy of a flow meter, wherein: The flow meter includes at least one flow tube, at least one pickoff sensor attached to the flow tube, at least one driver attached to the flow tube, and meter electronics in communication with the at least one pickoff sensor and the at least one driver, the method comprising the steps of: vibrating at least one flow tube in a driven mode using the at least one driver; receiving a sensor signal based on a vibration response to the drive mode vibration from the at least one pickoff sensor; deriving an uncorrected density using the flow meter; deriving an uncorrected mass flow rate using the flow meter; deriving an extended drive gain using the flow meter; receiving at least one flow variable; Calculate density ratio; Provide multiple moisture coefficients; A dry gas mass flow rate is calculated using the density ratio and at least one moisture coefficient of the plurality of moisture coefficients.

2. The method according to claim 1, wherein: The flow variable comprises pressure, and wherein the pressure is one of a measured input and a user input.

3. The method according to claim 1, wherein: The flow variables include water cut.

4. The method according to claim 3, wherein: The moisture content is measured using a moisture content analyzer in communication with the meter electronics.

5. The method according to claim 1, wherein: The flow variables include temperature.

6. The method of claim 1 including the step of deriving an extended drive gain using the flow meter.

7. The method according to claim 1, wherein: Calculating the density ratio includes dividing the uncorrected density by the dry reference density.

8. The method according to claim 7, comprising: The dry reference density is retrieved from the meter electronics.

9. The method according to claim 8, wherein: A dry reference density retrieved from the meter electronics is determined by at least one of temperature, pressure, and gas composition.

10. The method of claim 1 including the step of deriving the liquid mass flow rate by subtracting the dry gas mass flow rate from the corrected mass flow rate.

11. The method according to claim 10, wherein: The corrected mass flow rate is derived from the uncorrected mass flow rate and a meter factor.

12. The method according to claim 11, wherein: A meter factor is derived based on the extended drive gain and the plurality of moisture coefficients.

13. The method according to claim 1, wherein: The moisture coefficient is a function of multiple flow variables.

14. The method according to claim 1, wherein: The moisture coefficient is a function of pressure, gas velocity, drive gain, and water cut.

15. The method according to claim 1, wherein: The step of calculating the dry gas mass flow rate using the density ratio and at least one moisture coefficient among the plurality of moisture coefficients includes using a gas mass ratio derived from the density ratio and the plurality of moisture coefficients.

16. The method according to claim 15, wherein: The gas mass ratios were obtained using a quadratic fit, utilizing density ratio calibration and moisture coefficients.

17. The method according to claim 12, wherein: The meter factor is obtained by expanding the drive gain and the plurality of moisture coefficients using a quadratic fit.

18. A meter electronics device (20) for a flow meter (5), the meter electronics device (20) being configured to improve measurement accuracy, wherein: The flow meter (5) comprises: at least one flow tube (130, 130'); at least one pick-off sensor (170L, 170R) attached to the at least one flow tube (130, 130'); and at least one driver (180L, 180R) attached to the flow tube (130, 130'); wherein the meter electronics (20) is in communication with the at least one pick-off sensor (170L, 170R) and the at least one driver (180L, 180R), and the meter electronics (20) is configured to: Vibrating the at least one flow tube (130, 130') in a driven mode using the at least one driver (180L, 180R); receiving a sensor signal based on a vibration response to the drive mode vibration from the at least one pick-off sensor (170L, 170R); Wherein, the meter electronic device (20) is further configured to: deriving an uncorrected density using the flow meter; deriving an uncorrected mass flow rate using the flow meter; deriving an extended drive gain using the flow meter; receiving at least one flow variable; Calculate density ratio; Providing multiple moisture coefficients; and A dry gas mass flow rate is calculated using the density ratio and at least one moisture coefficient of the plurality of moisture coefficients.

19. The meter electronics (20) of claim 18, wherein: The flow variable comprises pressure, and wherein the pressure is one of a measured input and a user input.

20. The meter electronics (20) of claim 18, wherein: The flow variables include water cut.

21. The meter electronics (20) of claim 20, wherein: The moisture content is measured using a moisture content analyzer in communication with the meter electronics.

22. The meter electronics (20) of claim 18, wherein: The flow variables include temperature.

23. The meter electronics (20) of claim 18, wherein: The meter electronics is also configured to derive an extended drive gain.

24. The meter electronics (20) of claim 18, wherein: Calculating the density ratio includes dividing the uncorrected density by the dry reference density.

25. The meter electronics (20) of claim 24, comprising retrieving the dry reference density from the meter electronics.

26. The meter electronics (20) of claim 25, wherein: The dry reference density retrieved from the meter electronics is determined by at least one of temperature, pressure, and gas composition.

27. The meter electronics (20) of claim 18, wherein: The meter electronics is further configured to derive a liquid mass flow rate by subtracting the dry gas mass flow rate from the corrected mass flow rate.

28. The meter electronics (20) of claim 27, wherein: The corrected mass flow rate is derived from the uncorrected mass flow rate and a meter factor.

29. The meter electronics (20) of claim 28, wherein: The meter factor is derived from an extended drive gain and the plurality of moisture coefficients.

30. The meter electronics (20) of claim 18, wherein: The moisture coefficient is a function of multiple flow variables.

31. The meter electronics (20) of claim 18, wherein: The moisture coefficient is a function of pressure, gas velocity and water content.

32. The meter electronics (20) of claim 18, wherein: Calculating the dry gas mass flow rate using the density ratio and at least one moisture coefficient among the plurality of moisture coefficients includes using a gas mass ratio derived from the density ratio and the plurality of moisture coefficients.

33. The meter electronics (20) of claim 32, wherein: The gas mass ratios were obtained using a quadratic fit, utilizing density ratio calibration and moisture coefficients.

34. The meter electronics (20) of claim 29, wherein: The meter factor is obtained from the extended drive gain and the plurality of moisture coefficients using a quadratic fit.

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