Associated Minerals

Acid compatibility tests should be performed before acid treatments.

Mineral	Chemical Composition	Cautions
Anhydrite	CaSO₄	Gypsum precipitate upon contact with HCl acid.
Calcite (Limestone)	CaCO₃	Calcium Fluoride precipitate upon contact with HF acid.
Dolomite	CaMg(CO₃)₂
Chlorite	(Mg,Fe⁺²)₁OAl₂ (Si,Al)₈O₂(OH,F)₁ 6	Gelatinous ferric hydroxide will reprecipitate when acid has spent. Ferric hydroxide has large sized crystals that can block pore throats. This precipitate problem can be avoided if an oxygen scavengerand an iron chelating agent is added to the HCl acid.
Feldspar	(KAISi₂O₈) (NaAlSi₃O₈) (CaAl₂Si₂O₈) (BaAl₂Si₂O₈)	Silica precipitation upon contact with HCl Acid. Formation “Fines” such as quartz, chert, feldspar, etc. can dislodge and become mobile with high flow rates.
Glauconite	(K₁Na₁Ca)_0.5-1(Fe⁺³,Al,Fe⁺²,-Mg)₂ (Si,Al)₄O₁₀(OH₂) x nH₂O	Iron Hydroxide precipitate upon contact with HCl and HF acid or fresh water systems.
Hematite	Fe₂O₃	Iron Hydroxide precipitate upon contact with HCl and HF acid or fresh water systems.
Kaolinite	Al₂Si₂O₅(OH)₄	Mobile fines with high flow back rates.
Mixed Layer Illite/Smectite (Montmorillonite)	(½Ca,Na)_0.7(Al,Mg,Fe)₄(Si,Al)₈O₂₀(OH)₄7nH₂O	Swelling clays upon contact with fresh water systems.
Pyrite	FeS₂	Iron Hydroxide precipitate, Asphaltene sludging upon contact with HCl.
Siderite	Fe⁺²CO₃	Iron Hydroxide precipitate upon contact with HCl and HF acid or fresh water systems.

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Alphabetized collection of terms to assist our readers in understanding new or uncommon oil & gas terminology.