Production Chemistry

WAX FORMATION

Mechanism:
Pressure and temperature drop causes solid paraffin waxes to drop out of oil, partly or completely blocking pores.

Occurrence:
Crude oil with high wax cloud point temperature.

Impact:
Potentially severe with susceptible crude oil.

Possible Remedy:

  • Minimise pressure drawdown during production.
  • Intermittent stimulation during production using carefully selected wax dissolver, or removal by heat treatment (hot oil/steam).

    • SCALE FORMATION (DUE TO P/T REDUCTION)

    Mechanism:
    Solid precipitates from reservoir fluids due to pressure and/or temperature reduction. Damage from pore blocking/plugging. Possible scales are calcium carbonate, iron carbonate, iron sulphide.

    Occurrence:
    Relatively common where pore fluids are of high salinity. More frequent than scale due to fluid mixing. Common where bottom hole pressure is below bubble point and carbon dioxide is released.

    Impact:
    Potentially serious and self aggravating, as once formed scale will cause additional pressure drop. Scale can also be a major problem in pipework and surface equipment.

    Possible Remedy:

  • Squeezing of carefully selected inhibitor chemicals into reservoir prior to production.
  • Some scales may be removed by dissolution.

    • SCALE FORMATION (DUE TO FLUID MIXING)

    Occurrence:
    Solid precipitates formed due to mixing of native and invading aqueous fluids. Possible scales: calcium sulphate, barium sulphate, strontium sulphate and iron oxide.

    Impact:

  • Limited mixing in near wellbore zone so potential for damage limited. Significant mixing and scaling will occur in watered-out zones with little production potential.
  • Mixing of reservoir and injected (secondary recovery) waters can be a significant cause of scale.
  • Can be very damaging in tubulars.

    Possible Remedy:

  • When pore water chemistry is known, invading fluids can be customised to prevent scaling.
  • Some scales may be removed by dissolution.

    • ASPHALTENE DEPOSITION

    Mechanism:
    High molecular weight components of crude oil drop out if pressure and/or temperature changed.

    Damage by:

  • Physical pore size reduction.
  • Asphaltenes can cause wettability change.

    Occurrence:
    Some oil types susceptible and may even occur in gas - condensate systems. Controlled by oil type and pressure/temperature change involved.

    Impact:
    Serious where it occurs.

    Possible Remedy:

  • Minimise downdraw.
  • Apply carefully selected solvent wash.
  • Squeezing of carefully selected inhibitor chemicals into reservoir prior to production.
  • Thermal recovery e.g. steamflooding.

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