Naturally occurring and added chemicals can have an effect on efficiency of sand cleaning. The common chemicals present in oil & gas system are identified below along with their effect on sand cleaning.

pH: increase to >7 promotes oil-sand separation (FSM-M2)

• Silica i.e.p. ~2-3, oil i.e.p. 5-7, ∴ pH>7 changes surface potential of both to “-” thus promoting oil-sand repulsion, increase pH lowers crude-brine IFT

Oil Viscosity: reducing promotes oil-sand separation

• Lower viscosity facilitates deformation and break-up of oil film by shear forces
• Temperature or solvent additions

Chemicals: reducing crude-brine IFT promotes oil-sand separation

• Ionic surfactants best in crude/brine system for cleaning
• Would like to reduce oil-brine IFT to < 1 mN/m (1 dyn/cm)
• Increasing napthenic acid, and oil acid number decrease IFT, decreasing n-C7 asphaltenes, oil base number, and viscosity all decrease IFT (pH dependent)
• Biocide, corrosion inhibitor, defoamer, hydrate inhibitors, and demulsifier all lower crude-brine IFT

Salinity: decreasing may promote oil-sand separation

• Decreasing salinity slightly promotes oil-sand separation

References:

1. Rawlins, C.H. and Wang, I. 2001. “Design and Installation of a Sand-Separation and -Handling System for a Gulf of Mexico Oil Production Facility”. SPE Production and Facilities, August, pp. 134-140. https://doi.org/10.2118/72999-PA
2. Rawlins, C.H. 2019. “Enhanced Production Through Surface Facilities Sand Management.” SPE Distinguished Lecturer presentation. Link here

Next week I will cover physical and process effects on sand cleaning.