Key Chemical & Mineralogical Properties of Produced Solids: Part 2 (B-FSM020)
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
- Measure zeta potential
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.
In the next article we will wrap-up the discussion on produced sand properties with a comparison of macro vs. micro characteristics.
References:
- 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.
