Salt Contamination

Salt, NaCl, contamination may be a result of salty makeup water, drilling salt stringers, or saltwater flows. Saltwater-based drilling fluids are used when salt is drilled in large quantities or where salty makeup water is used. In saltwater muds, salt is not a problem; however, in freshwater muds salt becomes a contaminant.

Salt contamination is usually easy to detect. It will be accompanied by an increase in the chlorides content of the filtrate. Other possible indications are: an increase in rheology, specifically the yield point, an increase in fluid loss, and a possible decrease in pH and alkalinities. If the salt source is a saltwater flow, there may also be a decrease in mud density (see Figure 1).

Figure 1

Effects of Contaminants on Drilling Fluid Properties

Figure 1

Effects of Contaminants on Drilling Fluid Properties

Contaminant

Funnel Vis

PV

YP

Gels

pH

Fluid Loss

Pf/Mf

PM

Cl-

Ca++

Solids

MBT

Solids

y

î

y

y

-

y

y

y*

Cement

Î

y

î

î

î

y

î

î

y

Gypsum

Î

y

î

î

1

î

1

1

î

Salt

Î

î

î

1

î

1

1

î

/

Temperature

/

î

î

1

î

1

/

Carbonates

î

î

î

-

î

  • No Change A May Change or T Will Increase I Will Decrease
  • Slight Change I *
  • No Change A May Change or T Will Increase I Will Decrease
  • Slight Change I *

Salt contamination cannot be removed from a drilling fluid by chemical treatment. Salt concentration can only be decreased through dilution. The harmful effect of salt on a drilling mud is due to the increased ionic concentration which changes the charge distribution at the clay surfaces. The resulting flocculation causes an increase in rheological properties and fluid loss. Further exposure to high salt concentration will dehydrate the reactive solids in the mud and cause decreased viscosity and a continued increase in fluid loss.

The choice of reconditioning agents for salt contamination in freshwater muds depends on the severity of contamination. Lightly deflocculated drilling fluid systems can tolerate up to 10,000 mg/L chlorides as long as the colloidal reactive solids are at a reasonable level for the mud density being used. As the chloride content increases above 10,000 mg/L, rheological and fluid loss properties become difficult to control and an increase in deflocculant treatment is necessary. When salt is encountered, the high concentration of Na+ ions tends to replace some of the H+ ions at the clay surfaces and may slightly reduce the pH. The alkalinity of the system should therefore be slightly higher in salt contaminated drilling fluids to improve deflocculant performance. Calcium or magnesium are commonly associated with salt contamination and may magnify the effect of the salt on the drilling fluid.

Treatment - If the salt contamination is minimal (Cl- <20,000 mg/L) or can be tolerated for a brief period such as to TD the well or set pipe within a few days, the mud should be treated with water to dilute the chlorides to an acceptable concentration level. This level will vary depending on the mud weight, active solids concentration, temperature, etc. The fluid should simultaneously be treated with causticizing agents and deflocculants to restore flow properties. Finally, control fluid loss with PAC or other additives which are salt tolerant, and pre-hydrated bentonite.

If the existing salt contamination level cannot be tolerated or if continued contamination is expected, such as drilling massive salt sections, the fluid should be either converted to a saturated salt system or displaced with an oil-based system. The mud can be converted to a salt-saturated mud by addition of NaCl to saturate the system (±125 lb/bbl) coupled with large quantities of deflocculant for viscosity control, caustic soda or lime for pH and PF control, PAC materials and pre-hydrated bentonite for fluid loss control.

Was this article helpful?

+4 0
Waste Management And Control

Waste Management And Control

Get All The Support And Guidance You Need To Be A Success At Understanding Waste Management. This Book Is One Of The Most Valuable Resources In The World When It Comes To The Truth about Environment, Waste and Landfills.

Get My Free Ebook


Responses

  • saare
    Does gypsum cause decrease in drilling mud density?
    8 years ago
  • FABIOLA
    Why salt contamination happens in drilling fluids?
    4 years ago
  • belba
    Does salt water thicken my drilling fluid?
    3 years ago
  • Adam
    How can drilling fluid get contaminated by salt?
    3 years ago
  • Grossman
    How does salt affect drilling fluid?
    3 years ago
  • harri
    What is the effect of contaminants on the mud?
    3 years ago
  • jenni
    Why salt influences the viscosity of waterbased mud?
    3 years ago
  • israel
    How salt affects mud ph?
    3 years ago
  • calan maclean
    How does sodium chloride contaminates driliing mud?
    3 years ago
  • GENOVEFFA
    Why does nacl increased in density during the drilling od fliud pd?
    2 years ago
  • Ronnie
    When salt is added to the drilling fluid, does it increase or decrease the fluid loss?
    2 years ago
  • kayden
    How can salt as a contaminant affects drilling fluid?
    2 years ago
  • ilmari
    What is the effect of chloride in a mud system?
    1 year ago
  • Mikaela
    How to treat salt contamination in drilling mud?
    1 year ago
  • Eoghan McGregor
    How to treat redbed with drilling mud?
    12 months ago
  • helena
    How to treat high chloride in drilling fluid?
    11 months ago
  • MACARIA
    How do chlorides affect oilfield fluid systems?
    9 months ago
  • Gilda
    How to resolve contamination drilling mud?
    5 months ago
  • Joseph Cottle
    How does salt water affect drilling mud?
    4 months ago
  • melanie
    How to prepare salt contmination 3.3μg/cm2?
    4 months ago
  • mantissa
    What salts are in water contaminatnts?
    4 months ago
  • zewdi
    What concentration of chloride inhibits bentonite?
    3 months ago
  • KIMBERLY
    How to treat mud contaminated with salt?
    2 months ago
  • martina abendroth
    What is level of contamination in drilling mud?
    2 months ago
  • Einojuhani
    What happens to rxo and rt if the drilling fluid has the same level of salinity as formation fluid?
    21 hours ago

Post a comment