FLOW METERS IN OIL & GAS

WHAT ARE FLOW METERS?

Flow meters are devices designed to measure the rate at which a fluid or gas moves through a conduit or pipeline.

These instruments are pivotal in various industries, including water treatment, chemical processing, and particularly in the oil and gas sector, for ensuring precise control and measurement of fluid dynamics.  Gases, liquids, and fluids are measured in terms of mass flow rate and volumetric flow rate, thanks to flow meters.

Flow meters quantify the flow in terms of volume or mass per unit of time (e.g., liters per minute or kilograms per second), facilitating accurate monitoring, process control, and billing for consumption or trade.

They come in numerous types, each suited to specific applications, fluid characteristics, and accuracy requirements. Common types include turbine, ultrasonic, electromagnetic, Coriolis, and differential pressure flow meters (details for each type are given below). The choice of flow meter depends on several factors, including the fluid type, presence of particulates, temperature, pressure conditions, and the required flow range. By providing essential data on flow rates and totals, flow meters play a crucial role in optimizing processes, enhancing efficiency, and ensuring safety and compliance in fluid handling and transfer operations.

Over the years, people who are involved in the oil and gas industry have been innovating and creating ways to get accurate measurements. From extracting to delivering these raw materials, everyone in the business has been deeply invested in getting the most accurate measurements possible.

Thus, scientists and engineers have been working long and hard to discover new ways and technologies to make more efficient metering systems. Because of their hard work, the creation of different flow meters materialized, and because of that, the oil and gas industry is still going strong today.

FLOW METERS APPLICATION IN THE OIL & GAS INDUSTRY

Flow meters in the oil and gas industry are used for:

• Custody transfer: Accurate measurement of volumes being bought, sold, or transferred.
• Process control: Regulating processes by measuring fluid flow within the system.
• Leak detection: Identifying leaks in pipelines and systems by monitoring flow rates.
• Regulatory compliance: Ensuring adherence to environmental and safety regulations by accurately measuring emissions and discharges.

WHAT MEANS CUSTODY TRANSFER?

Custody transfer, in the context of the oil and gas industry as well as other sectors dealing with bulk commodities, refers to the physical transfer of substances from one party to another. It is a critical process where ownership of the product (such as crude oil, natural gas, water, or chemicals) changes hands. This transfer is not just physical but also legal and commercial, necessitating precise measurement to determine the exact amount of product being exchanged.

Accuracy in measuring the volume, mass, or energy content during custody transfer is paramount because these values directly impact the financial transactions between the buying and selling parties. Discrepancies can lead to significant financial losses or disputes. Therefore, standardized procedures, calibrated measurement equipment (like flow meters and quality analyzers), and often third-party verification are employed to ensure fairness and accuracy.

Custody transfer also involves documentation that details the quantity and quality of the product transferred, the time and place of the transfer, and the conditions agreed upon by both parties. This documentation is crucial for regulatory compliance, taxation, and in case of any disputes. In summary, custody transfer is a critical point in the commodity supply chain, where precise measurement and documentation are essential for legal and financial accountability.

THE 7 TYPES OF FLOW METERS IN THE OIL & GAS INDUSTRY

CORIOLIS FLOW METERS

ULTRASONIC FLOW METERS

Ultrasonic flow meters are sophisticated devices used to measure the velocity of a fluid flow through a pipe, which can then be used to calculate the flow rate. They employ ultrasonic sound waves to determine the flow rate and are highly favored for their non-intrusive nature, meaning they do not require any physical insertion into the fluid flow, thus avoiding any disruption to the flow or pressure drop.

Ultrasonic flow meters are versatile and can be used across a wide range of liquid and gas flow measurements in various industries. There are two primary types of ultrasonic flow meters, based on their operational principles: Transit-Time and Doppler flow meters.

Transit-Time Ultrasonic Flow Meters

Transit-time flow meters work on the principle that sound waves traveling against the fluid flow take longer to traverse the path than those traveling with the flow. The meter sends ultrasonic pulses alternately in the direction of and against the fluid flow. By measuring the time difference between the pulses traveling downstream and those traveling upstream, the meter can calculate the velocity of the fluid. This method is highly accurate for clean, particulate-free liquids because impurities can scatter and absorb the ultrasonic waves, affecting accuracy.

Doppler Ultrasonic Flow Meters

Doppler flow meters utilize the Doppler effect, where the frequency shift of the ultrasonic signal reflects off suspended particles or gas bubbles in the fluid, is measured. When the fluid is in motion, the frequency of the reflected wave changes in proportion to the velocity of the fluid. This method is suitable for liquids that are not perfectly clear, containing suspended solids or aeration, as these characteristics are necessary for the Doppler effect to occur.

Key Features and Applications

• Non-intrusive Measurement: Ultrasonic flow meters do not contact the fluid directly, making them suitable for applications where hygiene or corrosion is a concern.
• Versatility: They can measure various types of fluids, including water, chemicals, and gases, over a wide range of flow rates and pressures.
• Maintenance and Installation: With no moving parts and an external mounting capability, ultrasonic flow meters are relatively easy to install and maintain.
• Applications: These meters are widely used in water and wastewater management, oil and gas industries, chemical processing, power generation, and many more sectors for process control, monitoring, and custody transfer applications.

Conclusion

Ultrasonic flow meters offer a non-intrusive, accurate, and versatile solution for flow measurement across a broad spectrum of applications. Whether for clean or dirty fluids, their ability to provide reliable flow data without affecting the fluid dynamics makes them an invaluable tool in modern industrial and environmental monitoring systems.

THERMAL FLOW METERS

Thermal flow meters, also known as thermal mass flow meters, are devices used to measure the mass flow rate of a gas or, less commonly, a liquid, based on the principle of heat transfer. Unlike other types of flow meters that measure the volume of the fluid passing through, thermal flow meters directly determine the mass flow rate, offering a unique advantage in applications where the density of the flowing medium can vary with temperature or pressure. These meters are particularly useful for measuring the flow of gases in various industrial processes.

Operating Principle

The fundamental principle behind thermal flow meters involves heating a portion of the fluid and measuring the rate of heat transfer. This can be achieved through one of two primary methods:

• Constant Temperature Differential: This method maintains a constant temperature difference between two sensors—a heated sensor and a temperature sensor placed downstream. As the flow rate increases, more heat is carried away from the heated sensor, and the energy required to maintain the temperature difference is proportional to the mass flow rate of the gas.

• Constant Power (Hot-Wire Anemometer): In this method, a constant amount of power is applied to a heated sensor, and the temperature difference between this sensor and the fluid is measured. The temperature difference decreases as the flow rate increases, due to increased cooling of the heated element. The flow rate is then determined based on the cooling effect.

Key Features

• Direct Mass Flow Measurement: Thermal flow meters measure the mass flow rate directly, without the need for separate temperature or pressure measurements to calculate density.
• Accuracy and Sensitivity: They are highly accurate for gas flow measurements and capable of detecting very low flow rates due to the sensitivity of the thermal sensing element to changes in heat transfer.
• No Moving Parts: The absence of moving parts in the flow path reduces maintenance requirements and improves meter longevity.
• Wide Application Range: Suitable for various gases, including clean, dry gases and, in some designs, slightly moist or dirty gases.

Applications

Thermal flow meters are widely used in industries and applications where gas flow measurement is critical, such as:

• Environmental Monitoring: Measuring emissions, vent gas, and flare gas.
• Chemical and Pharmaceutical Industries: Process gas measurements, chemical reactions monitoring, and gas distribution systems.
• HVAC: Monitoring and controlling airflow in ventilation systems.
• Semiconductor Manufacturing: Controlling and monitoring specialty gas flows used in fabrication processes.
• Energy and Power: Measurement of natural gas for fuel consumption, combustion airflow, and biogas applications.

Conclusion

Thermal flow meters offer a reliable and accurate solution for measuring the mass flow rate of gases across a wide range of industrial and environmental applications. Their direct measurement capability, sensitivity to low flow rates, and low maintenance requirements make them an attractive option for many scenarios where precise gas flow measurement is essential.

TURBINE FLOW METERS

Turbine flow meters are velocity measurement devices used for the quantification of the flow rate of fluids—liquids or gases—within a pipeline. They operate on the principle that the flow rate of the fluid is directly proportional to the rotational velocity of the turbine rotor placed in the fluid stream. As the fluid moves through the meter’s body, it impinges on turbine blades that are mounted on a freely rotating rotor. The fluid’s velocity turns the rotor, with the rate of rotation being proportional to the velocity of the fluid.

Operating Principle

The fundamental components of a turbine flow meter include the turbine rotor, which is equipped with blades or vanes; a housing that directs the fluid flow onto the rotor; and a pickup assembly (often magnetic) that detects the rotor blade’s passage, converting it into an electrical signal. Each rotation of the rotor corresponds to a specific volume of fluid passing through the meter, allowing the flow rate to be calculated based on the frequency of the electrical pulses generated by the rotor’s motion.

Key Features

• High Accuracy and Precision: Turbine flow meters are known for their high accuracy, particularly in steady, clean fluid flow conditions. They can achieve accuracy levels within ±0.5% of the flow rate under optimal conditions.
• Wide Flow Range: They can measure very low flow rates up to very high flow rates, making them versatile across a range of applications.
• Rapid Response: The turbine design allows for a quick response to changes in flow rate, which is advantageous in dynamic flow conditions.
• Linear Output: The relationship between the flow rate and the frequency of the generated electrical signal is linear, simplifying the process of flow measurement and calculation.

Applications

Turbine flow meters are used across various sectors where precise fluid flow measurement is critical, including:

• Oil and Gas Industry: For the measurement of petroleum products, natural gas, and other hydrocarbons.
• Water and Wastewater Management: For monitoring water flow in treatment plants and distribution systems.
• Chemical and Pharmaceutical Manufacturing: For dosing and process control in the production of chemicals and pharmaceuticals.
• Food and Beverage: In applications requiring sanitary flow measurement, such as in the production of beverages and liquid food products.
• Energy and Utilities: For measuring the flow of steam, gas, and water in power generation and utility applications.

Considerations

While turbine flow meters are highly effective in many situations, their performance can be affected by the fluid’s viscosity, particulate content, and flow profile. High-viscosity fluids can dampen the rotor’s rotation, while particulates can cause wear and tear on the turbine blades, affecting accuracy over time. Proper installation and maintenance are crucial to ensure the longevity and reliability of turbine flow meters.

Conclusion

Turbine flow meters offer a reliable and accurate means for measuring fluid flow velocities in a wide array of applications. Their ability to provide precise flow rate measurements across a broad range of conditions makes them invaluable in many industrial, commercial, and utility settings.

DIFFERENTIAL FLOW METERS

Differential pressure (DP) flow meters, also known as differential flow meters, are devices that measure the flow rate of a fluid by interpreting the pressure drop across a flow restriction inserted in the flow path. This method is one of the oldest and most widely used techniques for flow measurement, valued for its simplicity, reliability, and versatility. DP flow meters work on the principle that the flow rate of a fluid through a pipe is directly related to the square root of the pressure difference created by placing an obstruction within the flow.

Operating Principle

The core component of a differential pressure flow meter is the primary flow element—typically an orifice plate, venturi tube, flow nozzle, or pitot tube—that creates a constriction within the pipeline. As fluid flows through this constriction, a pressure drop occurs between the upstream and downstream sides of the obstruction. This pressure drop is measured using a differential pressure transmitter.

The relationship between the flow rate and the pressure drop is defined by Bernoulli’s principle, which states that an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. The greater the flow rate, the larger the pressure drop, allowing the flow rate to be calculated based on the measured differential pressure.

Key Features

• Versatility: Suitable for measuring the flow of liquids, gases, and steam over a wide range of pressures and temperatures.
• Standardization: The dimensions and installation procedures for primary flow elements like orifice plates are well-standardized, facilitating accurate and reliable measurements.
• Simplicity and Reliability: With no moving parts in the primary flow element, DP flow meters are simple and robust, ensuring long service life with minimal maintenance.

Applications

Differential pressure flow meters are used in a variety of industrial settings, including:

• Chemical and Petrochemical Industries: For controlling and monitoring process flows.
• Oil and Gas: In upstream, midstream, and downstream operations for measurement of crude oil, natural gas, and byproducts.
• Water and Wastewater Treatment: For measuring the flow of water, wastewater, and treatment chemicals.
• Power Generation: To measure steam flow as well as cooling water.

Considerations

While differential pressure flow meters are highly effective, their performance can be influenced by several factors:

• Installation Requirements: Proper installation and placement are critical to ensure accurate measurements.
• Fluid Characteristics: Changes in the fluid’s density, viscosity, and temperature can affect the pressure drop and, therefore, the accuracy of the flow measurement.
• Energy Loss: The constriction in the flow path introduces a permanent loss of pressure and, consequently, energy within the system, which may be a consideration in the overall system design.

Conclusion

Differential pressure flow meters are a cornerstone in the field of flow measurement, offering a reliable and time-tested method for quantifying fluid flow across a broad spectrum of applications. Their adaptability to different fluids and conditions, combined with the comprehensive standardization of primary elements, makes them a staple in many industrial processes.

POSITIVE DISPLACEMENT FLOW METERS

Positive displacement (PD) flow meters, also known as volumetric flow meters, are precision instruments designed to measure the actual volume of fluid that passes through the meter. Unlike other flow measurement technologies that infer flow rate based on fluid dynamics principles, PD flow meters directly measure flow by trapping a fixed amount of fluid and counting the number of times the volume is filled and transferred. This direct measurement approach allows PD flow meters to achieve high accuracy and repeatability, even at low flow rates and with viscous fluids.

Operating Principle

The fundamental mechanism of a PD flow meter involves dividing the fluid flow into separate, measurable volumes. The meter consists of a chamber that traps a predetermined volume of fluid. Rotors, gears, pistons, or vanes within the chamber move in a specific sequence, driven by the flow of fluid. Each rotation or cycle of the mechanism represents a discrete volume of fluid passing through the meter. By counting these cycles, the total volume of fluid measured over time can be accurately determined.

Key Features

• High Accuracy and Precision: PD flow meters are renowned for their ability to provide highly accurate and repeatable measurements, making them ideal for applications requiring precise flow control and for custody transfer purposes.
• Wide Viscosity Range: They perform well across a broad range of viscosities, from light gases to heavy oils, without significant impact on accuracy.
• Low Flow Measurement: Effective at measuring very low flow rates, where other types of flow meters might struggle to maintain accuracy.
• Direct Volume Measurement: By measuring volume directly, PD flow meters eliminate the need for compensations based on temperature or pressure variations.

Applications

PD flow meters are used in diverse applications across various industries, including:

• Oil and Gas: For the accurate measurement of crude oil, refined petroleum products, and natural gas, especially in custody transfer and fiscal metering.
• Chemical and Pharmaceutical: For dosing, blending, and batch control processes where precise volume measurement is critical.
• Food and Beverage: In applications requiring sanitary conditions for measuring volumes of ingredients and final products.
• Utilities: For water and wastewater measurement, including residential water meters.

Types of Positive Displacement Flow Meters

Several types of PD flow meters are tailored to specific applications, including:

• Rotary Vane: Utilizes rotating vanes in a chamber to measure discrete volumes of fluid.
• Oval Gear: Features two oval-shaped gears that rotate synchronously to meter the flow.
• Piston: Employs a piston that moves back and forth, trapping and transferring a known volume with each stroke.
• Diaphragm: Uses a flexible diaphragm that expands and contracts, capturing and releasing measured volumes of gas or liquid.

Considerations

While PD flow meters offer several advantages, there are considerations to keep in mind:

• Wear and Tear: Moving parts are subject to wear over time, which can affect accuracy. Regular maintenance and calibration are necessary.
• Fluid Compatibility: The construction materials must be compatible with the fluid being measured to avoid corrosion or degradation.
• Pressure Drop: The mechanical nature of the flow measurement can introduce a pressure drop across the meter, which may be a concern in certain applications.

Conclusion

Positive displacement flow meters provide a reliable and accurate solution for direct volume measurement of fluid flow. Their versatility and precision make them a favored choice in applications requiring meticulous flow measurement, from the oil field to the pharmaceutical lab.

VORTEX FLOW METERS

Vortex flow meters are a type of flow measuring device that exploits the von Kármán Vortex Street principle to determine the flow rate of a fluid—liquid, gas, or steam—within a pipe. These meters are especially valued for their versatility, lack of moving parts, and ability to measure high flow rates with reasonable accuracy and minimal pressure drop.

Operating Principle

The principle behind vortex flow meters involves shedding vortices from a bluff body (a non-streamlined obstruction) placed in the path of the fluid flow. As the fluid flows past this bluff body, it creates alternating vortices on either side of the obstruction. This phenomenon is known as a von Kármán Vortex Street. The frequency of these shed vortices is directly proportional to the velocity of the fluid flow. By measuring this vortex shedding frequency, the flow meter can accurately determine the flow rate.

A sensor positioned downstream from the bluff body detects these vortices, typically using ultrasonic, piezoelectric, or capacitive means, and converts the frequency of the vortex shedding into an electronic signal that can be processed to calculate the flow rate.

Key Features

• Broad Applicability: Can measure the flow of liquids, gases, and steam over a wide range of temperatures and pressures.
• No Moving Parts: Results in lower maintenance requirements and a longer operational life compared to meters with mechanical components.
• High Accuracy and Reliability: Offers good accuracy for volumetric flow and mass flow measurements when the operating conditions are stable.
• Minimal Pressure Drop: The design of vortex flow meters generally results in a minimal pressure drop across the meter, making them efficient for use in various applications.

Applications

Vortex flow meters are used across a diverse array of industries due to their robustness and versatility:

• Chemical and Petrochemical Industries: For measuring the flow of chemicals, process fluids, and hydrocarbons.
• Energy and Power Generation: Steam flow measurement is crucial in power generation processes.
• Oil and Gas: Utilized in both upstream and downstream processes for measuring the flow of natural gas and other petroleum products.
• Water and Wastewater Treatment: For monitoring water flow in treatment plants and large distribution systems.
• Food and Beverage: Employed in applications requiring sanitary conditions and the measurement of various liquid flows.

Considerations

While vortex flow meters are highly adaptable and efficient, there are some considerations to keep in mind:

• Flow Profile and Disturbances: The accuracy of vortex flow meters can be affected by flow disturbances caused by upstream and downstream piping configurations. Proper installation and sometimes straightening vanes are required to ensure an undisturbed flow profile.
• Fluid Properties: The fluid’s viscosity, density, and conductivity (for liquids) can influence the meter’s performance. Vortex meters are best suited for relatively clean and steady flows.
• Temperature and Pressure Conditions: Extreme temperatures and pressures can affect the measurement accuracy. However, many vortex meters are designed to operate effectively under a wide range of conditions.

Conclusion

Vortex flow meters provide a reliable and efficient means for measuring fluid flow, capitalizing on the natural phenomenon of vortex shedding. Their ability to deliver accurate flow measurements across a variety of conditions, coupled with low maintenance requirements, makes them a favored choice for industrial flow measurement applications.

FLOWMETER CALIBRATION: A MUST

Calibration is a critical process for ensuring the accuracy and reliability of flow meters across various applications. It involves comparing the flow meter’s readings with a known standard or reference and then adjusting the meter’s output to match the reference accurately. Regular calibration is essential for maintaining the optimal performance of flow meters, whether they measure gas, liquid, or steam flows. Here’s an overview of the calibration needs for flow meters:

WHY CALIBRATION IS NECESSARY

• Accuracy Maintenance: Over time, the accuracy of flow meters can drift due to wear and tear, changes in the fluid’s properties, or environmental factors. Calibration ensures they continue to provide precise measurements.
• Compliance with Regulations: Many industries are governed by regulations that mandate the accuracy of flow measurements, especially in applications like custody transfer, environmental monitoring, and healthcare.
• Quality Control: In manufacturing and processing industries, accurate flow measurements are crucial for product quality. Calibration ensures that flow meters are performing within the required specifications.
• Safety: In applications involving hazardous materials, accurate flow measurement is essential for safety. Calibration helps prevent accidents caused by incorrect flow readings.

CALIBRATION FREQUENCY

The frequency of calibration depends on several factors:

• Manufacturer’s Recommendations: Manufacturers provide guidelines on how often their flow meters should be calibrated.
• Regulatory Requirements: Some industries have specific regulations that dictate calibration frequency.
• Usage Conditions: Flow meters used in harsh conditions or with corrosive, abrasive, or high-temperature fluids may require more frequent calibration.
• Criticality of Measurement: Flow meters used in critical applications where accuracy is paramount may need more frequent checks and calibrations.

CALIBRATION METHODS

• In-Situ Calibration: Some flow meters can be calibrated in place, without removing them from the pipeline. This is less disruptive but may not be as precise as off-site calibration.
• Off-Site Calibration: This involves removing the flow meter from its installation site and sending it to a laboratory for calibration. This method is usually more accurate but can be more costly and time-consuming.
• Use of Calibration Standards: Calibration often involves comparison against a known standard or master meter. These standards themselves must be traceable to national or international standards to ensure the accuracy of the calibration process.

CALIBRATION PROCESS

1. Pre-Testing: Assessing the flow meter’s performance before calibration to identify any issues.
2. Adjustment: The flow meter’s readings are compared to a reference, and adjustments are made until the meter’s readings align with the reference values.
3. Verification: After adjustment, the flow meter is tested again to ensure it meets the required accuracy levels.
4. Documentation: Calibration results are documented, providing a record of the meter’s performance over time.

Regular calibration of flow meters is essential for ensuring measurement accuracy, complying with regulations, maintaining quality control, and ensuring safety in various industrial applications. By adhering to recommended calibration frequencies and methods, organizations can ensure their flow measurement systems remain reliable and accurate, supporting efficient and safe operations.

DIFFERENCES FLOWMETERS FOR GAS VS. OIL