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Key Chemical & Mineralogical Properties of Produced Solids: Part 1 (B-FSM019)

Microbial Induced Corrosion on Piping

Key Chemical & Mineralogical Properties of Produced Solids: Part 1

 

The physical properties of produced sand, as covered in the previous seven articles, are the most important for designing a Facilities Sand Management system. The chemical and mineralogical properties of produced solids are of secondary importance, but can affect corrosion potential, sand cleaning, and oil coating of solids. These properties will be discussed in two articles so that the scope of sand properties is fully covered.

 

Produced Solids are Chemically Inert

Produced sand is inert (will not react or react only slightly) to most every condition experienced in oil and gas production

 

Silica/Quartz/Sand

  • Not degraded by temperature, hydrocarbon, salinity, pH, CO2/H2S, or dissolved solids experienced in normal oil & gas production
  • Negligibly affected by HCl and H2SO4 acids
  • Can be dissolved by HF acid and pH >12 (concentrated NaOH)

 

Clay/Carbonate

  • Not degraded by temperature, hydrocarbon, salinity, pH, CO2/H2S, or dissolved solids experienced in normal oil & gas production
  • Carbonate attacked by all acids to varying degree
  • Clay attacked by most acids to lesser degree and high pH

 

Corrosion Potential

One of the primary reasons for preventing solids build-up in production separators, is increased corrosion potential due to the presence of these solids.

  • Sand itself does not cause corrosion – silica is not part of the galvanic cell
  • However, settled solids form a stagnation zone beneath which pitting (crevice) corrosion is induced. Photo of pitting corrosion below (from here).
  • Also settled solids serve as a growth site for sulfate reducing bacteria (SRB) leading to microbial induced corrosion (MIC)
  • SRB reduce sulfate to sulfide, with resulting sulfide corroding iron (schematic below from Wikipedia)

Mineralogy of Natural Produced Solids

Analysis of mineralogy not critical, but is useful for estimating true density and potential chemical reactivity.

 

Common minerals in oil & gas operations:

  • Quartz: SiO2 or sand
  • Clay: hydrous aluminum silicates with metal cation (dozens of minerals)
  • Kaolinite – Al2SiO5(OH)4, Illite – (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)], Montmorillonite – (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·nH2O
  • Carbonate: metal cation with carbonate (CO32-) including Calcite (CaCO3) and Dolomite (CaMg(CO3)2)
  • Other: Feldspar: (K,Na,Ca)AlSi3O8 and Gypsum: CaSO4·2H2O

 

Analyze using X-Ray Diffraction (XRD).

 

 

We will continue the discussion of chemical and mineralogical properties of produced sand in the next article.

 
 
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