Operators are required to conduct analytical testing for a variety of reasons, including reservoir monitoring, flowmeter calibration, developing an injection chemical concentration profile, or determining local contamination. Clearly what is sampled and how the sample is collected are dictated by these requirements.  Additionally, sampling method and the sampling operation itself will have a direct impact on the integrity of the sample, and by effect, how representative the sample is of the production fluid. And the significance of the sampling stage cannot be overstated.

If the sample is not representative of the original production fluid from which it is collected, analysis and data garnered from the analysis will not be representative of the fluid no matter how good the analytical method is or how carefully the analysis is performed.

The benefit of sampling is, therefore, to obtain data for which an opinion can be derived through enhanced understanding of the chemistry at source. For subsea samples, the insight obtained can stand to provide a range of benefits including:

• Chemical optimization
• Reservoir management
• Allocation and metering
• Leak rate determination
• Scale squeeze and pigging

Operationally, subsea sampling removes the requirement for shutting-in wells which in-turn means production efficiency can be enhanced as the downtime for collecting samples is greatly reduced.

The ability to safely capture and contain samples from subsea is a testament to advances in engineering. Subsea sampling technologies comprise the use of an interface (Diver or ROV), and a specifically designed and certified subsea sampling system.

There are many different styles of System available in the marketplace with the main systems and benefits highlighted in Table 1.

Subsea sampling from a production system requires the extraction of fluids from a live process and the equipment need include a suitably qualified storage module for the collected fluid, slops containment, and back-flushing. This storage module should have the capability of maintaining the integrity of the sample temperature and pressure at the well operating conditions. This ensures the samples are maintained (as captured) during their transfer to the surface and onwards to the onshore laboratory for analysis.

Furthermore, where the subsea interface is already being deployed for other maintenance, inspection and / or intervention projects, the high-cost assumption placed with subsea sampling is dramatically reduced.