Fiscal metering -its importance in the East African pipeline considerations

lng-metering-e1408549410314-307x175
Courtesy of Alderley

Last month, Kenya announced it is eyeing to start producing by March 2017 and is looking to have its crude oil pipeline operational by 2021. The same goes for Uganda whose timelines are 2018 and 2020 for production and pipeline operation respectively. The envisioned 24-inch Hoima – Tanga pipeline is to cover 1,403 kilometres and  is expected to convey 200,000 barrels of crude oil per day for exports. The Uganda – Tanzania pipeline project is expected to create 15,000 jobs during its execution after which upon completion, in 2020, it will employ about between 1,000 and 2,000 people.

The pipeline is envisaged not only to be of benefit to Uganda and Tanzania but also to other countries in the region such as Kenya, South Sudan, Rwanda, Burundi and the Democratic Republic of Congo (DRC). DRC have expressed interests in the Uganda-Tanzania pipeline.

On the other hand Tanzania have started their gas production and are in the process of laying pipelines to transport the gas.

Definition of Fiscal metering

The element of sharing pipelines in the East African region brings to the fore the important consideration of fiscal metering. Fiscal metering is a general term comprising of allocation and custody transfer flow measurement of hydrocarbons (oil  and gas).

  • ·         Allocation is defined as the numerical distribution of products between parties according to their equity share.
  • ·         Custody transfer on the other hand is contract driven: meaning that there is a contractual duty between buyer and seller which may require adherence to accuracy, repeatability, linearity or uncertainty standards as defined by measurement standards such as API, GOST (Russian equivalent to API), International Standards Organization (ISO), American Gas Association (AGA), Petroleum Measurement Standards, OIML standards, American society of Mechanical Engineers (ASME), American National Standard Institute (ANSI), API Manual of petroleum Measurement (API MPMS), etc. are some of the standards followed by industries.

Custody transfer need not imply change of ownership.

Fiscal metering is thus an essential tool for the profitable operation of offshore platforms.

custody_img1
Courtesy of eximinengineering

 

Fiscal metering system

A Fiscal metering system is therefore a supervisory system for liquid and gas flow measurement. The system may communicate with flow computers.

There are a range of flow meters that may be employed in the flow measurement of air, gas and fluids . These include Orifice Plate,Venturi, V-Cone (which measure by pressure differentials (ΔP)),Turbine, coriolis, multiphase flow meters( which measure Mass flow) and ultrasonic, vortex (which measure velocity).

The Flow meters are mostly used to deduce mass flow through calculations made by them in conjunction with flow monitoring instruments, that is after taking a variety of flow measurements such as absolute pressure, differential pressure, viscosity and temperature.

Most flow meters consist of three parts, namely

a)                  the primary device,

b)                  the transducer

c)                  the transmitter, all combined into one instrument.

Functions of fiscal metering systems

The fiscal metering functions include;

  1. Flow computer communication.
  2. Computation of totals and average values.
  3. Providing the main operator interface to the metering system.
  4. Handling batch set-up and reporting.
  5. Flow scheduling between individual metering lines.
  6. Proving set-up and termination, including proving report, and acceptance of computed K-factors.
  7. Control sampling of produced oil.
  8. Setting of manual base density value.
  9. Printing reports.
  10. Indicating fixed values.

Oil and gas custody transfer flow measurement can take place anywhere along the process value chain from the wellhead to delivery or sale location, however the underlying forces may be influenced by several factors although the two key ones are regulation and commercial arrangements.

The flowmeters are usually placed on locations which would provide the favourable conditions such that flow measurement devices can operate predictably and repeatability.  These locations include platform/production exit location, pipeline entry/exit, terminal entry etc.). These points are considered to have the lowest uncertainty, stable, predictable single phase locations.

The importance of fiscal metering arises due to stronger variations in compositions of crude oil and gas around the globe and the scarcity of this resource. Fiscal metering therefore facilitates fair trade of liquid and gas and safeguarding against large financial differences due to small measurement errors.

References

  1. Emerson process, white paper FSG-WP-0012, published on February 2014
  2. IDC Technologies
  3. Alderley metering systems

 

Stay tuned for the next installation on the various fiscal metering systems

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