The fourth step of solids handling in the upstream oil & gas industry is Dewatering. This step is used to remove free liquids (mainly water) from sand slurry to minimize disposal volume (covered in detail in FSM-M9).

• Reduce the disposal volume by 90% and produce sand “cake”
• Will remove hydrocarbon liquids (aids cleaning) and other liquid contaminants

There are two types of dewatering systems – open (non-hazardous) or closed (hazardous)

• Open – liquids returned to open drain, sand/vapors open to atmosphere
• Closed – liquids captured to closed drain, vapors captured to vent system, and solids not exposed to atmosphere or personnel

Water removal using gravity drain is relatively fast (10-15 minutes)

• Dewatering rate reduced by increased liquid viscosity, clay/silt content, total particle specific surface area, and particle packing density

Unit Processes for Dewatering

1. Use gravity or enhanced forces

• Gravity drain most common – simple/inexpensive
• Pressure filtration – more complex but faster
• Cyclonic – 1st stage in two-step process (followed by gravity), removes bulk liquid from dilute slurry

2. Open hanging filter-bag or closed bin-bag

• Both use rapid-weep, oleophobic dewatering bag
• Dewatering bag or bin serve as transport device (combined step)

Dewatering is detailed in module M9 and will be covered further in a future post.

Dewatering Examples

Three unit-process examples below show dewatering system employed in the upstream oil & gas industry. The first (left) shows a two-stage open dewatering system using desilter cyclones for bulk liquid removal and open-frame dewatering bag for final removal. The middle system shows an open system with a cabinet-trolley enclosure used to treat slurry from a produced water desander. The system on the right shows a fully enclosed dewatering bin with transport cage for hazardous environment containment.