For every barrel of crude oil extracted, four barrels of water is also produced (Robertson & Jahsen, 2006). This water, known as produced water, is found within reservoirs alongside the oil, gas and sand. In all situations, the measurement of oil-in-water concentration is important. For discharge, the measurement of oil-in-water is governed by environmental regulations depending on the location of the field. With the global interest turning towards cleaner sources of energy and reducing environmental impact, regulations relating to crude oil discharge are becoming stricter. Due to the challenges with conventional sampling techniques, alternative methods to measure oil-in-water concentration for regulatory compliance need to be considered. The use of online techniques to replace laboratory analysis has been a growing trend throughout most industries, with the need to gather more data on a continuous basis. However, the use of online techniques for measuring oil-in-water comes with many challenges. Two are stated below:
• Being able to demonstrate that an online technique is capable of measuring oil-in-water concentration which is statistically equivalent or better than currently accepted reference methods.
• Lack of knowledge surrounding measurement uncertainty in both the offline reference techniques and the online methods.
To overcome these challenges, the research focuses on both online oil-in-water measurement techniques and the current laboratory reference methods. As an outcome of the research, the following contributions to knowledge in this topic are summarised.
• The design and construction of a novel facility at NEL, capable of simulating produced water conditions to allow testing of online measurement techniques, was successfully completed.
• Significant parameter effects on several oil-in-water continuous measurement techniques were determined, showing gaps in established measurement principles.
• The effect of droplet size on Laser Induced Fluorescence was characterised, allowing for an empirical based relationship based on droplet size, concentration and temperature to be developed. A reduction of uncertainty from up to ±80% to ±8.5% at ideal conditions was noted.
• Development of a novel method for calibrating and verifying online techniques using fluorescent tracers to reduce uncertainties and improve reliability of methods.
• Undertaken an uncertainty analysis of reference techniques and online measurements, demonstrating significant increase of uncertainty due to sampling. Several experiments were also conducted to determine the impact of various parameters on the overall uncertainty of offline oil-in-water concentration measurement due to sampling.
• Methodology for calibrating online methods using a dosing method to counteract issues with current techniques due to high uncertainties with reference methodology is proposed.
This thesis ultimately provides guidance for continuous online oil-in-water measurement as a method for regulatory reporting as current UK guidance is currently lacking several elements.
|Date of Award||Mar 2020|
|Sponsors||TUV SUD (NEL)|
|Supervisor||Elena Gaura (Supervisor)|