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Liquid Desander – Effects of Chemicals (B-FSM073)

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This article addresses the effects of chemicals on the operation of a liquid desander – albeit qualitatively.

Oil and gas operations have many natural and artificial chemicals present. Under the natural realm these include waxes, paraffins, hydrates, organic acids, resins, etc. The world of artificial chemicals is vast and just some of those that may be present include glycol, methanol, diluent, corrosion inhibitor, hydrate inhibitor, oxygen scavenger, demulsifier, gels and associated breakers, etc. The result is a complex mixture of which one chemical intended for a positive benefit may combine with another downstream to create an unintended negative consequence.

My goal is to provide very simple guidelines for effects of these chemicals on operation of the liquid desander. All these chemicals are grouped into the two uncomplicated categories of Bad and Good. The only advice is to avoid the Bad and promote the Good.

Bad Chemicals

  • Anything that increases viscosity, stabilizes emulsions, or allows oil to wet solids
  • The main concern is viscosity – as increased viscosity degrades desander performance (see post B-FSM-058 from 23-Oct-18).
  • Oil-wetting of solids also decreases desander performance by reducing the net density difference between the solids and water (see post B-FSM-058 and B-FSM-025 of 30-Jan-18)

Good Chemicals

  • Anything that decreases viscosity, breaks emulsions, or removes oil wetting from solids
  • Heat helps in all these categories – so putting the desander closest to the outlet of the production separator (before heat loss in downstream piping) will assist in operation

Flocculants

One of the more common questions when trying to remove very fine solids from produced water is – “Will a flocculant or coagulant chemical improve the desander performance?”. Both flocculant and coagulants work to chemically aggregate very small solids in a water stream and “grow” the particle size. As the practical limit for desander operation in produced water is 10-micron separation size, the desire is to gather all the smaller particles (i.e. 1, 2, 3, etc. micron) and make a larger particle that can be separated.

This is an amiable goal, but the operation of a desander (hydrocyclone) that allow for such efficient separation are a hindrance in this case. The hydrocyclone has such strong shear forces within the vortex flow pattern that any flocs formed by the chemical addition are destroyed within the desander. Many types of flocculants or coagulants have been tried, with occasional reported improvement – but the results are inconclusive or repeatable. In summary these chemicals will not improve the separation performance of a desander.

The next article will briefly discuss the main components of liquid desanders.

References:

  1. Svarovsky, L. 1984. Hydrocyclones. Technomic Publishing Co., Inc. Lancaster, PA, USA. 

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