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Key Chemical & Mineralogical Properties of Produced Solids: Part 2 (B-FSM020)

Effect of External Liquid Motion (Shear) on Oil Removal from Sand Particle

Key Chemical & Mineralogical Properties of Produced Solids: Part 2


In the previous article we discussed how produced solids are inert to most conditions and chemicals experienced in oil and gas production. Sand, while not reactive, does have a surface chemistry relationship interaction with oil that affects sand cleaning, oil agglomeration, and oily coating.

Contact Angle: Simple Analysis

Is sand water wet (hydrophilic) or oil wet (oleophilic)?

  • Contact angle is one method of estimating
  • May have been conducted by reservoir analysis, so check with that department

Static contact angle (Θc) measurement indicates wettability of a solid surface

  • Use sessile drop test with goniometer
  • Sand is preferentially oil wet at normal conditions (0° contact angle)
  • Previous water wetting will reduce oleophilicity
  • Important to clean sand early before it sets in oil

Isoelectric Point (IEP): Complex Analysis

Measurement of IEP give more exact answer than contact angle

Silica/sand IEP at 2-3 pH

  • Surface charge is negative “-” above 2 pH

Crude oil IEP at 5-7 pH

  • Surface charge positive “+” below 7 pH

At pH 2-7 sand is oil wet

At pH >7 sand is water wet

pH of several oilfield waters shown on table below

Spreading/Wetting Coefficients

Measurement of degree of surface wetting based on interfacial tension.

Spreading Coefficient (S) for Gas/Liquid/Sand system

  • Where γ is the interfacial tension (IFT) between respective phases
  • When S>0 the liquid wets surface completely

Wetting Coefficient (W) for Oil/Water/Sand system

  • When W>0 the oil wets the sand surface
  • For sand removal from oil system preference is for W<0

Oil Attachment to Sand Particle

Sand-oil interface a function of oil amount and contact angle.

How does external shear (liquid movement) affect shape? See header graphic for illustration.

In the next article we will wrap-up the discussion on produced sand properties with a comparison of macro vs. micro characteristics.


  1. Dubey, S.T., Doe. P.H., “Base number and wetting properties of crude oils”, SPE Reservoir Engineering paper SPE-22598-PA, August, 1993, pp. 195-200.

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