A very large Facilities Sand Management system may have a two-stage dewatering station. In that case the first stage is called Bulk Dewatering, while the last stage is Final Dewatering. A two-stage dewatering system is not very common, but both steps are discussed here for completeness.

Bulk Dewatering

Also called 1^st Stage Dewatering

• Not often required
• Only with large volume or semi-continuous systems
• Removes 75-90% of the liquid volume to simplify and shrink final stage dewatering and transport
• Bulk fluids sent to open or closed drains (offshore) or to capture pit (onshore)

Bulk dewatering methods

• Urethane cyclones (similar to that used for drill cuttings)
• Settling tank with liquid overflow
• Spiral classifier (onshore)

Process Design

• Slurry flow rate/pressure/duration/cycle, concentration and total mass amount of solids, and oil-on-sand concentration, particle size analysis

Final Dewatering – The primary purpose of dewatering

Minimize disposal volume and weight of sand/slurry for transport

• Up to 95% of volume removed
• Final slurry is <3 vol. % liquid – sand castle building material
• Wet sand is ~1700 kg/m³ bulk density

Remove free hydrocarbon liquid

• Most oil flows freely with drainage water
• Flushing with clean water during dewatering provides basic cleaning

Capture liquid and vapor for containment in closed systems

• Enclosed dewatering captures all free liquid and vapor for HSE

Process Design

• Slurry flow rate/pressure/duration/cycle, concentration and total mass amount of solids, and oil-on-sand concentration, particle size analysis

References:

1. Rawlins, C.H. and Wang, I. 2001. “Design and Installation of a Sand-Separation and -Handling System for a Gulf of Mexico Oil Production Facility”. SPE Production and Facilities, August, pp. 134-140. https://doi.org/10.2118/72999-PA
2. Rawlins, C.H. 2019. “Enhanced Production Through Surface Facilities Sand Management.” SPE Distinguished Lecturer presentation. Link here
3. Rawlins, C.H. “What to do with Produced Solids after Separation: Dewatering, Transport, and Disposal.”. White Paper Publication, eProcess Technologies. Link here

Next week I will cover open and closed dewatering.