Oil-in-water concentration used to be measured by extracting the oil using Freon-113 (a solvent that was known to cause ozone depletion and damage to the environment) and then analysed using an infrared absorption-based instrument.
As OSPAR planned to introduce a new reference oil-in-water measurement method based on gas chromatography-flame ionisation dectector (GC-FID), there was a need to develop guidance on the implementation of such a method. GC-FID is a laboratory-based analytical method, which is not ideally suited for offshore operations for various reasons. It was therefore envisaged that alternative methods to GC-FID would be used by operators in the North Sea. However, alternative methods must be correlated to the GC-FID method or demonstrated to produce results that are equivalent to the GC-FID method.
A JIP was initiated, which was supported by both the UK and Dutch regulators, together with eight offshore operators. The objective of the JIP was to prepare both the regulators and the industry for a smooth transition from the use of an infrared based reference method to the new GC-FID based reference method. Specifically, the project aimed at the following:
- To identify the best practical means to implement the new reference method.
- To establish best practice guidelines for sample taking and handling.
- To develop a realistic set of acceptance criteria for alternative methods.
- To advise on how to relate data from the GC-FID method to the existing infrared based method.
The key outcome of the JIP was the development of the OSPAR1 and the UK DECC (Department of Energy and Climate Change, now Department of Business, Energy and Industrial Strategy – BEIS) guidelines on oil-in-water sampling and measurement.2 These guidelines are still being used today.
Produced water volume determination
As mentioned earlier, to calculate the total amount of oil being discharged into the sea via the discharge of produced water, accurate measurement of both oil in produced water concentration and discharge volume are required.
One of the company’s early surveys of North Sea installations indicated that produced water discharge volume was estimated using a variety of methods, from direct measurement with a flow meter to using information from well testing (a schematic of well testing arrangement is shown in Figure 1) or pressure differential data of a hydrocyclone. As a result, there was a huge variation in the uncertainty associated with the measurement of the produced water volume being discharged.
Figure 1. Schematic of flow circuit for well testing.
In 2005, the UK government introduced the Oil Pollution Prevention Control (OPPC) Regulation, which requires that the uncertainty in volume measurement of produced water be within ±10%. The UK Offshore Operators Association (now Oil and Gas UK) was also considering the introduction of a produced water trading scheme. Both of these initiatives emphasised the importance of the accurate determination of produced water discharge volume.
The produced water volume determination JIP was therefore initiated to improve the understanding of existing practices and to develop produced water volume verification procedures and guidelines. Ultimately, the project was aimed at helping the operators to improve produced water management and to assist the UK in meeting a 15% reduction target in discharge of oil via the discharge of produced water. The JIP was supported by the UK regulator together with five operators, and its outcome was a sponsor-wide best practice guidance on how to determine produced water volume.
Other joint industry projects
In addition to the oil-in-water measurement and produced water volume determination JIPs, TUV SUD NEL has instigated a number of other JIPs. Between 2009 and 2017, three JIPs were specifically conducted on behalf of operators that focused on the development of a subsea water quality measurement sensor for produced water. These projects not only helped advance water quality measurement technology for subsea applications, but also helped improve the reliability and accuracy of those technologies for surface applications. The advancements of these measurement technologies help improve the oil and gas production process, minimising the environmental impact through the use of fewer production chemicals, reduced produced water contamination levels, and fewer sampling and laboratory analyses.
The company has recently launched a new JIP aimed at making the use of online oil-in-water monitors for produced water discharge reporting a common practice. Specific objectives of the project include:
- To provide a status report on online oil-in-water monitoring technologies and also on the uses of online analysers for reporting purposes.
- To understand and establish uncertainties associated with oil-in-water sampling and measurements.
- To refine acceptance criteria for using online oil-in-water analysers for reporting purposes.
- To develop regulatory requirements for subsea discharges.
- To develop guidance for accepting online oil-in-water analysers for unmanned and subsea applications.
- To propose a set of changes to be made for the existing OSPAR, BEIS and Norsk Olje&Gas O85 guidance in relation to using online oil-in-water analysers.
The nine-month project is expected to start in July 2019.
An inevitable by product
Produced water is an inevitable by product of oil and gas production, but its discharge could potentially harm the environment. Good management and measurement practices are therefore crucially important in minimising this potential harm, and must involve an integrated, multi-disciplinary and holistic approach. With increasing water production from mature fields; and the move toward deepwater, chemical enhanced oil recovery (EOR), heavy oil, and unconventional oil and gas production, the oil and gas industry is facing a significant number of challenges to minimise the potential harm that can be caused by the discharge of produced water.
- OSPAR Agreement 2005 - 16 “Oil in produced water analysis – Guideline on criteria for alternative method acceptance and general guideline on sample taking and handling”, (2006).
- BEIS (formerly DECC), “Methodology for the sampling and analysis of produced water and other hydrocarbon discharges”, (2014).
This is part two of a two-part article. Part one is available to read here.
Written by Dr. Ming Yang, TUV SUD NEL.
Read the article online at: https://www.oilfieldtechnology.com/special-reports/17072019/rise-to-the-challenge--part-two/
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