PEFTEC 2019 - Abstract

Abstract Title: The chronology and importance of on-site chemistry
Abstract Type: Poster
Session Choice: Other
Presenter Name: Mr Matt Bower
Co-authors:Mr Matt Kirby
Company/Organisation: Qa3 Limited
Country: United Kingdom

Abstract Information :

Natural gas, condensate and oil produced from an underground reservoir will always contain certain non-hydrocarbon components and trace elements. These constituents may be considered as impurities or contamination of the hydrocarbons and must be quantified accurately prior to field development.

Some constituents are non-combustible and of no economic value, while others are corrosive, resulting in a requirement for special design and materials in processing and transportation systems. Others may be environmentally unfriendly, poisonous, or simply dilute the hydrocarbon fraction thereby reducing the calorific value. Even at trace concentrations the non-hydrocarbon components can cause significant implications.

The most important non-hydrocarbon constituents in petroleum fluids are:

  • Volatile sulphur compounds (hydrogen sulphide, mercaptans, carbonyl sulphide etc.)
  • Non-combustible gases (nitrogen, carbon dioxide, helium, argon etc.)
  • Mercury
  • Other heavy metals
  • Radionuclides
  • Moisture (in gas phase)
  • Oxygen
  • Formation water
  • Chemical compounds arising from chemical injection (methanol, glycol, scale inhibitors etc).
The quality of the oil and gas, defined in terms of the concentrations of the natural impurities can have a strong influence on the market price.

Obtaining reliable, accurate data for non-hydrocarbons requires a detailed knowledge of the chemistry of the species of interest. Many components have a tendency to adsorb onto surfaces (e.g. sampling lines and sample containers) resulting in erroneously low concentrations in the samples. Other components, such as radionuclides, water pH and bicarbonate may be affected by delays in the analysis and must therefore be determined either on site or be preserved for off-site analysis. In addition, sampling regimens and procedures often need to be tailored on site to suit the analyte concentrations found, which may vary significantly from one geographical location to another or even from field to field in the same vicinity.

For the above reasons, often the most appropriate approach to analysis (or even the only suitable approach to analysis) is to perform the works on site. Where on site analysis is not practical eg. due to non-portable equipment, consideration must be given to the most appropriate sampling and preservation technique to ensure that when the sample is finally analysed, the sample is, as far as possible, representative of the fluid in system.