Midstream Oil and Gas, Production Storage & Measurement
Metering and Measurement of Oil and Gas and How It Works
July 30, 2019 Welcome
Oil and gas metering or measurement is the phase along the hydrocarbon supply value chain where exploration and production (E&P) efforts turn into profits for operators, investors, and other relevant stakeholders. Hydrocarbon metering is carried out using specialized and high-precision equipment to ensure accuracy.
This article will discuss the process of crude and natural gas measurement, some technologies involved, and where to find metering solutions for your oil and gas products.
Oil and Gas Measurement
Oil and gas measurement is the process of quantifying the mass or volume of hydrocarbons produced as the oil & gas is sold to a buyer along the supply chain. In the United States, oil and gas metering usually begins at the wellsite, as mandated by law.
Before custody transfer, the operator will separate oil or natural gas. Entrained solids, water vapor, and other impurities are removed from crude oil before it is quantified and sold. Similarly, water vapor, sulfur, and other contaminants are extracted from natural gas. After cleanup, the oil and gas must meet a certain specification in order to qualify to be sold.
How Is Oil Measured in the Field?
Crude oil is an unrefined mix of hydrocarbon fluid that has been obtained from an oil well. This liquid is primarily what is sold as a commodity. The unit of sale is barrels of crude (BBL) which is equivalent to 42 US gallons. After separating water molecules and sediment from crude, the volume can be ascertained using one of two methods:
For small volumes (1-100 barrels of oil per day), oil measurement is carried out directly from storage tanks in runs. A run is the process of drawing oil drawn from a lease location and transporting it off-site for treatment.
First, we take a sample of crude and place it in a centrifuge for a ‘shake-out’ test which separates the water molecules and sediments from the mixture. Afterward, the volume of a run is measured by lowering a measuring strap into the storage tank. This device is weighted on one end and contains an outlet valve which opens to discharge fluid into a pipeline or truck nearby. When the storage tank is almost empty, a second measuring strap reading is taken (and the volumes compared) to find the exact volume of oil drawn.
For large volumes (100-100,000 barrels of oil per day), operators typically use an automated measurement system called a LACT unit, which we will be discussing shortly.
Measurement of Natural Gas
Natural gas measurement can be carried out using Orifice meters. Orifice meters help to determine the volumetric flow of natural gas by finding the differential pressure between the upstream and downstream sections of a pipe (orifice) which is partially impeded. The unit of sale for natural gas is thousands of cubic feet (MCF) or British Thermal Units (MMBTU).
Commonly Used Oil and Gas Metering Technology
A wide range of equipment for oil and gas flow measurement is available on the market. Selecting the right equipment will depend on the type of fluid to be metered. Some common examples are:
Lease Automatic Custody Transfer (LACT) units measure the net volume and quality of hydrocarbons during product transfer in midstream oil and gas operations. LACT units are automated systems for measurement, sampling, and transfer of liquid hydrocarbons with volumes ranging from 100 – 1000 barrels/hour between a stock tank and feed line.
A metering skid is an automated system for measuring crude or natural gas comprising several measurement instruments assembled on a steel frame. They are used to determine financial estimates during custody transfer metering. Metering skids usually consist of several flow meters for metering fluid flow, proving system and a gas chromatograph for analyzing and metering gaseous hydrocarbons.
LACT units and Metering skids from IFS can accurately measure and sample hydrocarbon liquids with viscosities ranging from 2 – 5000 centistokes.
Some ancillary instruments that may be found on a metering skid include Coriolis flow meters, turbine or positive displacement flow meters, densitometer, back pressure and thermal relief valves, air eliminator, prover connections, and PLC control systems.
Let’s take a brief look at the two flow meters listed:
A Coriolis flowmeter is a special type of flow meter that measures a mass of fluid based on inertia. The ‘Coriolis effect’ is a physical phenomenon where inertia created by a mass of fluid flowing through an oscillating tube cause the tube to twist proportionally to mass flowrate. In practice, hydrocarbon liquid or natural gas flows through the inlet tube on a Coriolis flowmeter is vibrated with an actuator that causes turbulence in the fluid to be measured.
Coriolis flowmeters are widely regarded as some of the most accurate metering instruments in the industry. However, these instruments can have a margin of error when the fluid under test contains bubbles.
Turbine or Positive Displacement Flowmeters
Other oil and gas flowmeter types include turbine or positive displacement (PD) flowmeters. These are special oil and gas measurement instruments that determine the volume of fluid flowing through them by repeatedly trapping a quantity of the fluid and releasing it.
Positive displacement flowmeters utilize multiple rotating parts that ‘mesh’ together like a pair of gears. PD flowmeters can measure the volumetric flow through pipelines for a variety of fluids including water, hydrocarbons, corrosive liquids, etc.
IFS Is a Trusted Partner for All O&G Process Needs
Integrated Flow Solutions is an industry-leading oil and gas skid manufacturer of modular and custom process metering equipment. We offer a range of modular and engineered-to-order LACT units and metering systems for high-precision oil or natural gas measurement.
For more information about our services or to speak with a professional, please contact us online today or call us at 1-800-795-4068.