Subsea separation and produced water re-injection (PWRI) or discharge has long been considered as an enabling technology for developing deepwater / ultra deepwater and marginal fields. It is an integral part of the subsea processing strategy which brings many economical, operational and environmental benefits for the offshore Oil & Gas industry. However, one of the key technology gaps remaining is in relation to water quality measurement for subsea separated produced water. This review is based on JIPs that NEL has conducted and its recent involvement in a RPSEA project. The review also includes progress made by operators and vendors.

Existing practice for subsea water quality measurement involves in sending an ROV (Remotely Operated Vehicle) to take a produced water sample and then bring it to surface for analysis. This practice is extremely expensive, time consuming and not good for operations. The technology gap has in many ways prevented the widespread of using subsea separation and produced water re-injection systems.

Good progress has been made in developing a subsea water quality measurement device in recent years. This has been achieved through a combination of efforts by operators, government bodies, vendors and independent organizations. Technologies that have the best potential for subsea applications include:

  • Light scattering;

  • Microscopy imaging;

  • Laser Induced Fluorescence;

  • Ultrasonic acoustic.

Most of the above-mentioned technologies are currently surface proven. They are of Technology Readiness Level (TRL) of 3 in relation to subsea applications, which means that they are prototype developed, function and performance assessed. Some of the key progresses to date are resulted from the use of LED as a light source, better fouling mitigation approaches, purposefully conducted lab and surface field trials. Further progresses are anticipated in which some of the mentioned technologies will be developed to TRL 4 (environmental tested) and TRL 5 (system integrated).

There are currently very few references in the literature on the subject. This paper will add valuable information to the public domain regarding the status of the development of subsea produced water quality measurement sensors.

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