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Solids Handling for Upstream Oil & Gas Industry: Step 4 - Dewatering (B-FSM038)

Photograph filtrate water from dewatering bag used to treat wellhead desander slurry

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
  1. 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.

References

  1. Rawlins, C.H., “Sand Management Methodologies for Sustained Facilities Operations,” paper 164645-MS, North Africa Technical Conference & Exhibition, Cairo, Egypt, Apr. 15-17, 2013.
  2. Rawlins, C.H., and Wang, I. I., “Design and Installation of a Sand Separation and Handling System for a Gulf of Mexico Oil Production Facility,” SPE Production and Facilities, paper 72999, Vol. 16, No. 3, 2001, pp. 134-140.

The next article will detail Step 4 on Dewatering. 

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