Mineral Scale

Mineral scales (subsequently referred to as scales) are inorganic solids precipitated from water and subsequently deposited. Scales are a common form of formation damage and blockages or restrictions to perforations, screens, liner or tubing.
Like most production chemistry problems, they pose a safety issue through loss of operability of check valves, safety valves or, in severe cases, tree valves. To predict the scaling potential of reservoir aquifer water, a representative water sample is required.
This requires that an appraisal or exploration well deliberately produces water, and that any contaminants such as completion or drilling fluids are also analyzed so that interference is backed out.
The water chemistry of hydrocarbon bearing reservoirs is highly variable, ranging from very low ion strength to high salinity brines containing a wide range of various ions.
Prevention and mitigation:
1.Mitigate or prevent scale in formation by using formation water instead of seawater,
2.Scale Inhibitor
Scales:
Hard inorganic crystals (~ 3 –4 mhos)
1-Slightly less than steel (5 mhos)
2-Diamond, 9 mhos
3-Variable crystal size
4-Microns to centimeters
5-Produced form aqueous solutions
6-Soluble in specially formulated solutions

Scale Types

The equilibrium that existed for so long is then upset on a geologically diminutive timescale during the production phase of the field development.
Production creates pressure and temperature reduction or introduces new fluids (muds, completion fluids or water injection).
The main types of scales are:
1-Carbonates–mainly calcium carbonate, but also iron carbonate
2-Sulphates–barium, strontium and calcium
3-Sulphide–less frequently encountered scales, but include lead, zinc and iron
4-Salts–mainly sodium chloride;
Most Common Types of Scales
1-Calcite (CaCO3)
–Formed due to the presence of calcium ions and bicarbonate ions in the produced water
–Pressure changes may cause precipitation

2-Barite (BaSO4)
–Generally formed when there is co-production of formation water (Ba2+) and injection water (SO4-)