What is a subsea control fluid anyway? We'll tell you...but let's start with calling them SCFs for short - carpal tunnel is no joke.
Full disclosure, we sell several subsea control fluids - like Castrol's Transaqua and Brayco Micronic lines and MacDermid's Oceanic line.
These are some highly technical and sensitive products.
Essentially SCFs are most often used as a hydraulic fluid of sorts. Think of a fluid being used as a medium to control all sorts of things - only under water. They help to make subsea equipment function and can be found on the drilling side of oil & gas applications (like BOP fluids) and on the production side. Drill rigs and offshore production platforms use these fluids to control and operate subsea equipment.
You can start quickly with a broad & loose definition of "a fluid to hydraulically control subsea equipment". And then you can divide them into two primary roles - the drilling side (like BOPs) and the production side (Subsea Production Control Fluids).
SCFs typically consist of lubricating properties with corrosion and bacterial protection. These fluids often stay inside the system for the lifetime of the field - sometimes up to 30 years! So bacteria control, product stability, pH balance, and other factors are critical. Especially at the SCSSV (surface-controlled subsea safety valve) as fluid replacement is not an option.
Fluid cleanliness is typically ISO 4406 17/15/12 / NAS 1639 Class 6. Prevention of contamination from product manufacturing & packaging to rig use and implementation must be paramount in the process.
Most subsea control fluids are water based, some are oil based. Oil based have increased lubrication; however, most are not environmentally acceptable - therefore water based is more dominant.
Water based subsea control fluids are typically comprised of Di-mineralised water and mono ethylene glycol (MEG). Concentrations of each will depend on the product, climate/environment, and application. Additives are also added for lubrication, biocides, dyes, corrosion inhibitors, surfactants, extreme pressure additives, etc.
On the lubrication side of SCFs, you're looking for anti-wear characteristics suitable for the goals of the system. For instance, your equipment may need superior rotational/torque force reductions, or increased wear protection. Often measured in standard testing formats like 4-ball wear/mean wear & scar diameters.
For corrosion protection you can imagine a long life being required, within highly specialized equipment, in often extreme temperatures; with variations in metallurgy, seal composition and materials, and so forth. Compatibility with the equipment is critical, hence the OEM's vital role in fluid selection. Vapor phase protection should also be important for your fluids.
Environmental concerns vary depending on system types (i.e. closed loop systems and vent-to-sea & open loop systems) along with regional requirements such as OSPAR, bioaccumulation rates, and leak detection capabilities (UV dyes/tracers, etc.).
Suitability and stability when exposed to brines and seawater contaminants, miscibility & compatibility with other fluids, OEM qualifications and approvals, global availability, supply chain security, and pressure/viscosity/temperature data should all be considered as well.
The future of subsea control fluids is exciting. The oil & gas sector is moving further offshore, deeper into the ocean, and experiencing higher pressures and temperature ranges. This may call for a shift from the more popular (and less expensive) water-based SCFs into the higher performance, higher cost oil-based subsea control fluids.