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Oil and Gas Fundamentals

For US O&G companies it is important to improve the speed and efficiency of drilling and completions and optimize the well spacing. Companies also have to optimize the spud-to-spud rate to less then 30 days. All wells have to perform at or above expectations with ultimate goal of accessing higher oil and gas recovery and growing value.

Houston provides excellent opportunities to enter the oil and gas play, with 6 of the top 10 companies based in Houston offers a good job market.

What are Hydrocarbons

Hydrocarbons are formed by the decomposition of bio material over a period of millions of years. They include Methane, Ethane, Propane, Pentane in gas form and Heptane, Ocatane, noname, decame in Liquid form and C20, C30, C40, C50  in Semi Solid form.

During a drilling process a well can produce Wet gas, dry gas, Liquid Oil and water, some oil sands wells produce Semi Solid material.  Sulfur content lowers the value of crude, Sweet crude has less than .5% sulfur. Sour crude has more than 1% sulfur. Gas with high sulfur is also called sour gas.  After the crude has been extracted from the well, it will be sent to refinery for processing, heat and catalysts are used to separate hydrocarbon molecules. The output can be Methane, Gas, NGL, Gasoline, Kerosene, Jet Fuel, Heating Oil, Diesel, Lubricants, Fuel oil, coke and asphalt.

Oil and gas business process can be broken into Upstream, Midstream, and Downstream.

Upstream can be broken down into:

  • identity prospective areas
  • Obtain O&G rights and partners,
  • Acquire data and identify properties,
  • Drill and Appraise,
  • develop wells and facilities,
  • operate and produce.

Midstream can be broken down into:

  • Gather Crude and process
  • Market Transport and storage

Downstream can be broken down into:

  • Refining
  • Distribution and retail marketing

Companies that produce oil and refine are called integrated such as Exxon, if companies are in exploration only they are called E&P companies such as Anadarko.

Terms and Terminology used in Oil and Gas

Atmospheric Pressure is the pressure exerted by the atmosphere usually expressed in psia. Although this pressure varies with altitude, barometric pressure, and humidity, the atmospheric pressure can be defined in custody transfer contracts or by state or federal authorities.

Automatic Custody Transfer is an acronym for an arrangement of equipment designed for unattended transfer of transmission quality natural gas (finished product).

Automatic Line Sampling is withdrawing a fluid (dense phase or gas phase) sample by equipment to obtain a representative sample from a flowing stream. Automatic line sampling involves several pieces of equipment: a sample probe, sample extractor, sample controller, inline mixing system (if applicable), and sample container.

Automatic Sampler is a device that, when installed in a flowing pipe and actuated by automatic equipment, obtains a representative sample from the flowing stream.

Base Pressure – Standard used for determining natural gas volumes. Volumes are measured at operating pressures and then converted to the appropriate base pressure volume as defined by the State in which the gas is produced. For example, Base Pressure is 14.65 psia for Texas and Oklahoma and 15.025 psia for Louisiana and Mississippi.

Base Temperature – Standard used for determination of natural gas volumes. Volumes are measured at operating temperatures and then converted to the appropriate base temperature volume as defined by the State in which the gas is produced. Base Temperature is normally 60oF.

BTU – British Thermal Unit: A unit of heat equal to the amount of heat required to raise one pound of water 1oF at 14.73 psia. Used to describe the amount of heat generated during combustion of the gas.

Bubble Point Curve is the curve separating single-phase liquid from the two-phase region. The bubble point curve starts at the critical point and extends down to atmospheric pressure.

Calibration is the process of testing and adjusting EGM system components to conform to traceable reference standards to provide accurate values over the EGM prescribed operating range (static differential pressure and temperature transmitters, online water analyzers, online densitometers, ADC and DAC, and so forth). The final step in calibration confirms whether the secondary device, tertiary device, and its data transmission methodology are operating within the specified tolerance over a minimum of three points across the range of operation. Calibration involves adjusting the device to meet the accuracy requirements (i.e., transmitters, readout devices, etc.), or for flowmeters, applying a correction factor.

Calibration Repeatability is the ability of the flowmeter and the calibration system to repeat the flowmeter’s performance during a series of runs under the same operating conditions

Calorimeter is a device that measures the gas heating value.

Closing Data are the measurement information (static or dynamic) taken at the end of a flowmeter ticket period.

Commingled is a term that defines a mixture of natural gases that, while originating from multiple sources, are similar enough in makeup to be combined into a single stream for transport, storage, and handling (Gulf Coast, Amarillo, etc.).

Common Carrier is a transportation system available for hire by the public for transporting material (pipelines, railroads, trucks, and so forth).

Composition is the components and their respective concentrations of a natural gas sample.

Compressibility, gas defines the correction for deviation from the ideal gas law. The compressibility term is required to calculate the mass density of a gas.

Condensate refers to pipeline condensate, retrograde condensate, and injected condensate.

Contaminants are foreign substances that make a fluid unsuitable for use or sale.

Continuous Sample is a pipeline tap sample, which is withdrawn in uniform mass (or base volume) increments over the period of a batch.

Contract is a legal agreement between two or more parties.

Corrosion is the deterioration of a material, usually a metal, because of a reaction with its environment.

Counter is a counting device, electrical or mechanical, to register the indicated volume passed through the flowmeter.

Cricondenbar is the maximum pressure at which gas and liquid may coexist in equilibrium.

Cricondentherm is the maximum temperature at which gas and liquid may coexist in equilibrium.

Critical Point is the pressure  and temperature at which the properties of the liquid and gas phases become identical. The critical point is also defined as the intersection of the bubble point and hydrocarbon dew point curves.

Cubic Foot – A unit of measurement for volume of 12 inches by 12 inches by 12 inches or 1,728 cubic inches.

Custody Transfer is a change in ownership or responsibility of fluids.

Custody Transfer Measurement  is a measurement that furnishes quantity and quality information for use as the basis for a change in ownership or responsibility of fluids.

DAC is the acronym for digital-to-analog converter.

Dead Leg is a section of piping designed to not have flow through the section in normal operations.

Deadweight Tester is pressure reference standard used to verify and calibrate static pressure sensors.

Decade Box is a precision resistance device that can be set to precise electrical resistance values. A certified decade box may be used to verify and calibrate the input to a temperature transmitter (simulates an resistor temperature device sensor).

Dehydration is a water vapor removal process for gas and dense-phase fluids. Dehydration usually is accomplished using desiccants: glycols, silica gel, mole sieve, alumina, or calcium chloride.

Dekatherm (Dh)is a quantity of energy content equivalent to 1 million Btu (MM Btu).

Delivery is the quantity delivered or movement out of the pipeline system to a connecting party.

Delivery Point is a measurement facility that exits a pipeline system to a connecting party.

Dense Phase Region (or supercritical region) has no definite volume or shape. The dense phase fluid will completely fill the container in which it is placed. The dense phase region is in the single phase and exhibits high fluid compressibility and high mass density values. These values vary as a function of the fluid’s pressure and temperature values. The dense phase region is defined as the region whose pressure exceeds the critical value.

Densitometer is a device that measures the fluid’s mass density at flowing conditions. Operating personnel sometimes refer this device as a density meter.

Deviation is any departure from the true value.

Dew Point is the temperature, for a given pressure and composition, when liquid condenses from a gas.

Dew Point Curve, hydrocarbon, is the curve separating the dense and gas phases from the two-phase region. The hydrocarbon dew point curve starts at the critical point and continues to atmospheric pressure.

Dew Point Curve, water, is the curve designating the ability of a gas to suspend water vapor. If the operating temperature and pressure are to the left (or below) the water dew point curve, then free water is present in the fluid. If the operating temperature and pressure is to the right of the water dew point curve, then free water is not present in the fluid.

Diameter Ratio is the ratio of the diameter of the constriction (orifice plate) to the pipe internal diameter. This is commonly referred to as the Beta Ratio.

Diaphragm Flowmeter is an energy extractive, discrete flowmeter that employs a diaphragm as the known volume or “bucket.”

Differential Pressure – The difference between the pressure upstream and downstream of the orifice, in inches of water (27.68 inches of water = 1 psi).

Digital is a term describing the output of a device that transmits data numerically using a communications protocol.

Diluents are components of natural gas that have no heating value such as nitrogen, oxygen, carbon dioxide, helium, and argon.

Discrete Flowmeter is a flowmeter that measures flow rate by filling and emptying a known volume or “bucket” (rotary displacement, diaphragm).

Discrimination (or resolution) is used to describe how finely an instrument can indicate a measure. We commonly refer to this as resolution. Discrimination describes how many decimal places you can read to; it does not tell you how many decimal places you can rely on to be accurate. A flowmeter cannot be more accurate than the calibration standard or the discrimination of the flow meter’s output.

Displacement Flow Meter is an energy extractive, discrete flow meter that measures flow by mechanically separating the fluid into discrete quantities of a known or fixed volume. As the element rotates, the flow meter’s register totalizes the volume passed through the device.

DOT is the acronym for U.S. Department of Transportation, the federal agency authorized to regulate aspects of the pipeline industry to protect the general public.

Drift is to move slowly out of tolerance.

Dry Gas – Natural gas whose water content has been reduced by a dehydration process.

Dynamic Measurement refers to the measurement of fluids in motion (flowmeters).

Electromechanical refers to equipment comprising both mechanical and electrical components.

End User is the consumer of natural gas. Categories of end users are industrial, commercial, and residential.

Energy Content is the amount of heat released by a given volume of a gas at reference pressure and temperature

when completely burned in an excess of air at the same pressure and temperature as the gas. The higher heating value (HHV,) stated in base volume units at 14.73 psia and 60°F on a “dry” basis is used exclusively for commercial transactions in the United Sates.

Environmental Protection Agency (EPA) coordinates a government action on behalf of the environment. The EPA endeavors to abate and control pollution.

Equation of State (EOS) is a mathematical equation used to calculate transport (density, viscosity, speed of sound) and thermodynamic (phase envelope, enthalpy, entropy, etc.) properties of fluids. An equation of state for pure fluids, such as polymer-grade ethylene, is a function of pressure and temperature. For a fluid composed of multiple components, such as natural gas, the equation of state is a function of composition, pressure, and temperature.

Event Log is a electronic document that notes and records all exceptions and changes to the flow parameters contained within the configuration log that occur and have an impact on a quantity transaction record.

Expansion Factor is the correction for the change in density for differential pressure sensing flow meters.

Extractor is a device on a sample probe that physically captures a representative sample of fluid from a flowing stream, also referred to as a sampler.

Filter, particulate, is a device designed to remove fine particles from the fluid to ensure proper performance of the flow meter and associated equipment.

Finished Product is a fluid that has been completely processed for industrial and commercial applications (transmission quality natural gas).

Flow Computer is a tertiary device in compliance with the API EGM standards that handles all calculations and processing of electronic data from a flow meter. A flow computer is an arithmetic processing unit and associated memory device that accepts electronic signals (analog or digital) representing input variables from a gas measurement system and performs calculations for flow rate and total quantity data.

Flowing Conditions are the flowing temperature pressure and density of the fluid.

Flowmeter is a device used to measure fluid flow. The major classes of flowmeters are energy additive and energy extractive. The subclasses are discrete and inferential.

Flowmeter Assembly consists of the flowmeter, upstream piping sections with a high-performance flow conditioner (if applicable), downstream piping section, and auxiliary equipment.

Flowmeter Capacity (qmax) is the maximum flow rate specified by the manufacturer.

Flowmeter Linearity is the difference between its calibration curve and a best-fit straight line over a specified flow range.

Flowmeter Range is that range of flow rates over which the flowmeter meets a specified linearity, repeatability, and accuracy. The ratio of the maximum flow (qmax) to the minimum flow (qmin) for a specified range is commonly referred to as the Turn Down Ratio.

Flow Proportional Sample is a sample taken by an automatic sampler from a pipeline at a rate proportional to the rate of flow in the pipeline.

Flow Rate is the mass, volume (actual and standard), or energy content of the fluid per unit of time.

Fluids are substances that flow and have four technical classifications: liquid, gas, dense phase, and two phase.

Frequency is the number of cycles of a periodic signal, such as pulses, alternating current, or voltage, occurring in 1 –second intervals and expressed as Hertz (1 pulse per second).

Fungible describes fluids or commingled streams assigned a designation such as “Gulf Coast” or “Amarillo”.

Gas Chromatograph is a device that determines the composition of a gas stream. A small, precisely measured volume of

multiple-component gas is injected into an analytical column. This multiple-component gas stream is swept through the column by an inert carrier gas. Absorption by partitioning agents in the column retards carryover of the various components of the sample by varying amounts so that they emerge from the column at different times. The segregated components pass through a detector that gives an electrical signal proportional to their concentration in the carrier gas.

Gas Distribution Pipeline is a gas pipeline other than a gas gathering or transmission line.

Gas gathering pipeline is a pipeline that transports gas from a production facility to a gas processing plant or transmission pipeline.

Gas Phase Region (or vapor phase region) has no definite volume or shape. A gas will completely fill a container. The gas phase region exhibits high fluid compressibility and low mass density values.

Gas Transmission Pipeline is a gas pipeline other than a gas gathering or distribution pipeline. A transmission pipeline transports gas from a gas gathering pipeline, gas processing plant, or storage facility to another gas transmission pipeline, storage facility, industrial end user, commercial end user, or gas distribution pipeline.

Gate Valve is a device used to block the flow of fluids in pipelines using a sliding plate of steel.

Gauge Pressure is pressure measured relative to atmospheric pressure, taken as zero, usually expressed in units of psig.

GPA is the acronym for Gas Processors Association, which is a trade association of operating and producing companies

which are engaged in the processing of natural gas.

GPSA is the acronym for Gas Processors Suppliers Association, which is an organization catering to the supply and service needs of the gas process industry.

Gross Heating Value  is the amount of energy released by burning one standard cubic foot of natural gas. The amount of

heat released, measured in Btu units, and includes the heat released by condensing the water formed as a combustion product.

Homogeneous indicates that the fluid has a constant composition and mass density across the pipe or storage vessel.

Hydrate is a crystalline compound formed by the combination of gaseous hydrocarbons with water. Hydrates are quasi-solid or solid hydrocarbon-water mixtures similar to snow, slush, or ice.

Hydrocarbon is a fluid classification that indicates the presence of hydrogen and carbon atoms. Subclasses of hydrocarbons are paraffinics, aromatics, and alcohols.

Hydrogen Sulfide (H,S) is a highly poisonous acid gas that may be present in natural gas. If H2S is present, the gas is toxic when inhaled or fumes contact moist areas of the human body: skin, eyes, and the like.

Indicating Instrument is a sensing device in which the measured value is visually displayed but not recorded.

Inferential Flowmeter is a flowmeter that infers the flow rate from a variable measured in the flowing stream.

Inspection is defined as the process of visual and audible observations for proper operation and condition of measurement equipment that may affect the accuracy of the fiscal flowmetering facilities. Inspection assures that the equipment is in proper working condition but does not verify, calibrate, or certify the device. Generally, inspection involves visual observation of the equipment instrumentation tubing leaks, dP manifold leaks, wires, seals, configuration and behavior of field sensors based on their readout, configuration and behavior of flow computers, and so forth. The term describes the act of looking and listening, if appropriate, for obvious defects in equipment, such as broken thermometers, separated mercury columns, and flowmeter bearing wear. Inspections are performed on all equipment

before each use, verification, or calibration, as well as a normal routine during operations.

Internal Diameter (ID) is the measured, or calculated, internal diameter of the containment vessel (pipe, ultrasonic flowmeter body, orifice flowmeter, or tank). For precise applications, such as orifice and ultrasonic flowmeters, the measured internal diameter (D,) is determined by multiple measurements (or  mikings”). For less precise applications, the internal diameter (ID) is calculated from the following formula: ID = OD – (2 X wall thickness).

International Temperature Scale is an internationally defined relative scale of temperature that is referenced to known physical points (freezing point of water, boiling point of water, and so forth).

K Factor is a term that defines the number of pulses per unit of actual volume for a flowmeter determined from a calibration of the flowmeter.

Kinetic Energy is the energy that a body has because of its movement.

LACT is an acronym for Lease Automatic Custody Transfer – an arrangement of equipment designed for unattended transfer of hydrocarbons from producing leases to a transporting carrier.

Laminar Flow is flow in which forces due to viscosity are more significant than forces due to inertia. Pipe flow is defined as laminar, transitional, or turbulent based on the Reynolds number and the pipe wall roughness.

Linearity is a measure of an instrument’s ability to deviate from its predicted performance.

LPG is the acronym for liquefied petroleum gas, such as butane or propane.

Measuring Chamber is the portion of a displacement flowmeter that contains the “bucket volume.”

Measuring Element is the portion of a displacement flowmeter that moves within the measuring chamber to divide the fluid into discrete segments as it passes through the flowmeter.

MAOP is the acronym for Maximum Allowable Operating gauge Pressure.

Mercaptan is a hydrocarbon chain containing a sulfur-hydrogen group used for odorization of gas distribution systems.

Meter Calibration is the procedure required to calibrate a flowmeter.

Meter Case is the outer portion of a displacement flowmeter that encloses the measuring chamber and other moving parts.

Meter Factor which corrects for any flowmeter error is obtained by dividing the true mass of fluid passed through the calibration system by the indicated mass of the flowmeter.

Meter Factor Curve, linearity based, is a graph showing the performance of a flowmeter as a function of flow rate. Flowmeter linearity is expressed as the total range of deviation of the accuracy curve from such a straight line between the minimum and maximum recommended flow rates.

Meter Performance is a general expression used to describe the relationship between the volume registered by a flowmeter and the actual volume that passed through the flowmeter. Meter performance can refer to flowmeter errors, MF, and other criteria.

Meter Proof is a term that refers to the series of calibrations performed to determine a meter factor (MF).

Meter Readings are the instantaneous display of the fluid quantity read directly from a flowmeter counter (non reset totalizer).

Meter Registration is the indicated volume metered for a period. The final flowmeter reading minus the initial flowmeter reading is the indicated volume for the custody transfer.

Meter Run is the upstream (usually including a high-performance flow conditioner) and downstream sections of straight pipe for inferential flowmeters. The upstream and downstream sections of straight pipe should conform to the appropriate standards with respect to length, circularity, internal surface finish, and freedom from obstructions that may disturb the flow through the primary device.

Meter Slippage is the volume of fluid at a given flow rate that passes through the displacement flowmeter without causing registration.

Off-Spec is a term denoting that the fluid does not meet the stated quality parameters of the stream and, therefore, may require special handling.

On-Spec is a term denoting that the fluid does meet the stated quality parameters of the stream.

Orifice Flowmeter is an energy extractive, inferential flowmeter that infers the flow rate by measuring the differential pressure (dP) across a restriction (orifice plate) placed in the flowing stream. For custody transfer, the flange-tapped, concentric square-edged orifice flowmeter shall comply with the specifications and tolerances stated in A.G.A. Report No. 3 (API MPMS C14.3).

Orifice Plate, concentric, is a circular plate with a center hole that is inserted in a flowing stream to create a known resistance to flow (or pressure drop). The difference in pressure (dP) on either side of the orifice plate is used to infer the flow rate.

Outside Diameter (OD) is the pipe outside diameter. For an API 5L line pipe, the outside diameter conforms to certain requirements as a function of nominal line size.

Overranging is a term that, when applied to flowmeters, indicates that the device exceeded the maximum recommended flow rate by the manufacturer.

Pacing is a term in automatic sampling that defines how often the sample controller instructs the sample extractor to grab a sample from a stream. Stated another way, pacing is the frequency of sampling.

Partial Immersion Thermometer is a thermometer that is immersed up to the immersion line inscribed on the back of the thermometer, leaving the scale above the surface for ease of reading.

Physical Properties are characteristics that pertain to nonchemical aspects of a material. Physical properties include color, odor, shape, size, phase (gas, liquid, supercritical, or two-phase), molecular weight, mass density, relative density, viscosity, isentropic exponent, freezing point, boiling point, dew point, heating value, and vapor pressure.

Potential Energy  is energy due to the position of an object (related to the differential height of the fluid between two points).

Pressure – Force per unit area and expressed as psi (pounds per square inch; lbs/in2)

Pressure Drop is the permanent or temporary reduction in line pressure caused by a resistance to flow.

Pressure Sensor is a device that senses the pressure. A pressure sensor is part of a pressure transmitter and part of a pressure gauge.

Pressure Tap, static, is a tap on a pipe or vessel used to sense the internal pressure.

Pressure Taps, differential, are taps used to sense differential pressure (dP) across “head class” flowmeters or strainers.

Pressure Transmitter is an electronic device that senses and transmits pressure readings to a register or flow computer. Transmitter may be “dumb” or “smart,” depending on the sophistication of the electronic device. Smart transmitters are more accurate than dumb transmitters.

Primary Device is a flowmeter.

Product Specifications defines the normal specifications of the fluid.

Pulsating flow is flow in which the flow rate or static pressure varies significantly over short time periods.

Pulsation dampener is a device used to reduce the pressure pulsations in a flowing stream.

Pulse Generator is a device designed to produce a series of electrical pulses whose number is proportional to the quantity measured and whose frequency is proportional to the flow rate.

Quality is the characteristic of a fluid that represents it conformance to the specifications.

Quantity is the amount of fluid that changes custody or the amount of fluid (mass, volume, or energy) determined by the static or dynamic measurement method for allocation.

Random Error is the scatter of data (or a sensor’s output) that deviates from a mean value in accordance with the laws of chance. Random errors are errors that drift in an unbiased manner and whose mean measurement approximates the mean value.

Rangeability of an instrument is defined as the range over which it meets the stated performance specifications. The rangeability of a flowmeter, stated by the manufacturer, is limited by the linearity and repeatability specifications as well as the upper limit of the device due to mechanical damage.

Real Relative Density for a gas is the ratio of the density of gas to that of air at the same conditions of pressure and temperature.

Recording Instrument is a measuring device that records the value of the measured variable by marking or printing on a chart, paper, tape, or other recording material.

Register, meter, is a device that accumulates and displays the quantity passed through a flowmeter.

Repeatability  is an indication of an instrument’s ability to produce the same results when it is used to measure the same variable in succession. Repeatability is often confused with accuracy. If an instrument has poor repeatability, it is bound to have poor accuracy; but, if it has good repeatability, this does not necessarily mean it is accurate (although it could be), since it could be indicating the same wrong answer every time.

Representative Sample is a small amount of fluid extracted from a flowing stream (or stored fluid) that contains the same proportions of the various constituents as the total quantity of fluid.

Reproducibility is an instrument’s ability to “stick to the same story” over a long time or over variable conditions and between operating personnel. Reproducibility is often confused with accuracy. If an instrument has poor reproducibility, it is bound to have poor accuracy; but, if it has good reproducibility, this does not necessarily mean it is accurate (although it could be), since it could be indicating the same wrong answer every time. Simply stated, reproducibility is the ability of the instrument to tell the same story over a long time period with changing variables (pressure, temperature, flow rate, density, viscosity, and so forth).

Resistance Temperature Device  is a temperature sensor that exhibits a decreasing electrical resistance as a function of increasing temperature.

Reynolds Number is the ratio of inertial to viscous forces in a fluid.

Rich Gas is natural gas with a relatively high gross heating value.

Rotary displacement Flowmeter is an energy extractive, inferential flowmeter that infers the flow rate by the speed (or revolutions) of the rotors placed in the flowing stream.

Rotor is a device inside a flowmeter attached to a shaft. The rotors rotate when fluid flows past (rotary displacement flowmeter).

RTU is the acronym for remote terminal unit.

Sample is a small portion of a larger quantity that may or may not be representative of the total quantity of the fluid. The selected sampling method must be applicable to ensure that the portion taken is representative of the total fluid stream.

Sample Container is a receptacle used for fluids’ sample storage or transport. This sample container is a pressure vessel that operates at elevated pressures. This sample container operates at elevated pressures to ensure a single-phase fluid and collects a flow-weighted average representative sample for the transfer.

Sample Extractor is a device on a sample probe that physically captures a representative sample of fluid from a flowing stream, also referred to as a sampler.

Sample Grab is the fluid volume taken from the pipeline by a single actuation of the sample extractor.

Sample Receiver is a container that is part of an automatic sample system to collect the flow-weighted average representative sample.

Sampler Probe is part of a sampling system that extends into the pipe to allow extraction of a representative sample.

Sampling Frequency is the number per unit of time that an input variable is retrieved for monitoring, accumulation, or calculation purposes.

Sampling period is the time in seconds between the retrieval of flow parameters for accumulation and calculation purposes.

Sampling Point is the location where the sample is obtained (center one-third of pipe).

SCADA is the acronym for Supervisory Control And Data Acquisition.

Secondary Device may include, but is not limited to a device that measures pressure temperature composition, or other parameters.

Security Seal is a wire-and-lead or plastic device placed on fiscal system components to prevent or indicate tampering. A boxcar, wire-and-lead, or plastic device that closes off any point in a pipeline, tank, or associated equipment where a sample of fluid is collected or its volume can be determined; it is used to prevent or indicate tampering.

Sensor is a device that responds to a physical stimulus such as light, temperature, pressure, chemical reaction, or motion and provides a usable output signal for indication, recording, or transmission.

Slippage, flowmeter, is the volume of fluid that passes through a flowmeter without increasing the quantity of the flowmeter. Flowmeter slippage varies with the flow rate, viscosity, and dimensional changes in the flowmeter due to temperature and pressure.

Spot Sample is a manual sample taken from a flowing stream.

Standard Cubic Foot – The amount of natural gas occupying a cubic foot of volume at standard temperature and pressure (60oF and 14.73 psi)

Static Measurement refers to the measurement of fluids at rest (not moving).

Static Pressure is the pressure in a fluid that is exerted normal to the surface. In a moving fluid, the static pressure is measured at right angles to the direction of flow. A pressure tap is required to measure static pressure, expressed in absolute or gauge pressure units.

Steady-State Flow is a flow rate does not vary significantly over short time periods.

Strainer is a device designed to remove foreign material from the stream to ensure proper operation of flowmeters, compressors, control valves, samplers, and other secondary instrumentation.

Stream Conditioning is the process of generating a homogeneous fluid for manual and automatic sampling of flowing streams.

Sweet Gas is a gas that contains no appreciable amount of H2S.

Tap is a hole or opening in a containment vessel (pipe, tank) where a thermowell, instrumentation valve, or sampling probe can be inserted or attached.

Tariff is a legal contract between a transporter and shipper or the governmental tax associated with importing or exporting material.

Temperature – A measure of the internal energy in a substance or environment. This degree of “hotness” or “coldness” is typically measured on a thermometer.

Temperature Sensor is a device that senses the temperature. A temperature sensor is part of a temperature transmitter or gauge.

TemperatureTransmitter is an electronic device that senses and transmits temperature readings to a register or flow computer. The transmitter may be “dumb” or “smart” depending on the sophistication of the electronic device. Smart transmitters are more accurate than dumb transmitters.

Tertiary Device is an electronic device, programmed to calculate flow within specified limits, that receives information from primary and secondary devices (flow computer).

Thermistor is a semiconductor composed of a metallic oxide; its electrical resistance is a function of temperature.

Thermometer is a device that senses and indicates temperature.

Thermowell  is a protective metal socket installed in the wall of a containment vessel into which a temperature sensing element and heat conducting medium is placed (or inserted).

 Time-Proportional Sample is a sample taken from a pipeline at regular time intervals.

Transitional Flow is flow between laminar and turbulent flow. Generally, pipe flow is thought to be in transition from a pipe Reynolds number of 2,000 to 10,000.

Transmitter is a secondary device that converts a sensor’s input and sends a signal (analog or digital) to a tertiary device (flow computer).

Turbine Flowmeter is an energy extractive, inferential flowmeter that infers the flow rate from the speed (frequency) of the rotor inserted in the flowing stream.

Turbulent Flow is flow in which forces due to inertia are more significant than forces due to viscosity. Fluid particles are chaotic and random in their creation and destruction of vortices in the flowing medium.

Ultrasonic Flowmeter is an inferential flowmeter that infers the flow rate from the difference in transit times of high-frequency sound waves along individual chordal path(s).

Units of Measurement – The standard unit of measurement for natural gas is “Mcf” (one thousand cubic feet).

Gas is typically sold on the basis of its heating value or energy content per cubic foot. This “heating value” is expressed in MMBtu’s or million British Thermal Units. (“M”= roman numeral for 1,000; “MM”= roman numerals for 1,000,000)


An MMBtu is calculated by multiplying the volume of natural gas expressed in cubic feet (ft3) by its corresponding Btu per cubic foot (Btu/ ft3).

Example calculation of MMBtu:


1,000 Mcf = 1,000,000 ft3

Btu per cubic foot = 1,250 Btu/ ft


(1,000,000 cubic feet) x (1,250 Btu/ft3) = 1,250,000,000 Btu’s

1,250,000,000 Btu’s ÷ 1,000,000 = 1,250 MMBtu

(Shortcut Method)

1,000 Mcf x 1.250 (Btu factor) = 1,250 MMBtu.

Velocity is the speed of the flowing fluid.

Venturi Flowmeter is an energy extractive, inferential flowmeter that measures flow as a function of the differential pressure across a contoured restriction.

Viscosity is a physical and transport fluid property that is a measure of the fluid’s resistance to flow (shear stress). Viscosity is generally expressed in centipoise (cP) or centistokes (cSt) units.

Volatility is the tendency of a liquid to become gaseous.

Volume – The amount of 3-dimensional space occupied by a solid, liquid, gas or plasma. Typically measured in cubic feet; ft3.

Wall Thickness (wt) is the wall thickness of the containment vessel (pipe or tank).

Water Vapor Content is the amount of water vapor held in the gas. The amount of water vapor that a fluid can suspend depends on the pressure and temperature of the stream.

Wet Gas is gas having a high water vapor content or free water present in the stream.

Witness is anyone who witnesses the measurement activities.


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