Principal Additives of KCl Polymer Muds

KCl-Polymer Muds with low KCl concentrations (typically 3-5 wt%) and low densities are easy to maintain when drilling harder formations. However, when increased densities are required, mud composition is more complicated and mud properties are more difficult to control. Materials and concentration ranges for KCL-Polymer Muds are listed in Table 32. Not listed is poly (propylene glycol), or PPG, such as DCP-208, which is gaining increasing popularity as an inhibitor aid. This low-molecular weight polymer is usually added at levels up to 15 lb/bbl.

Principal Additives of KCl-Polymer Mud

Additive

Concentration, lb/bbl

Function

Prehydrated Bentonite

5 - 15

Viscosifier, Filtration Control

Potassium Chloride

5 - 60

Inhibition Source of K+ion

Caustic Potash

0.25 - 0.75

Alkalinity Control, Source of K+ion

Starch

3 - 6

Filtration Control

PAC

0.5 - 1.0

Filtration Control

Lignosulfonate

3 - 6

Deflocculant

^Lignite

2 - 4

HTHP Filtration Control

Bentonite - Prehydrated bentonite is used to viscosify KCl-Polymer Muds. Bentonite also provides a colloidal solid that can improve filter cake quality in freshly- prepared muds. Since bentonite will dehydrate from the high salt content of the mud and lose viscosity over time, constant additions of bentonite may be needed. When feasible, API "Nontreated" bentonite is recommended because it provides a noticeable reduction in material requirements and also provides better mud performance. Typically, concentrations of 5-15 lb/bbl of prehydrated bentonite are adequate for mud viscosity and filtration control. Dry bentonite additions will not give adequate viscosity for suspension in high chloride and hardness environments, but small additions in the range of 1-3 lb/bbl may enhance particle size distribution of the mud and improve filtration control, particularly at temperatures in the 225-275 °F range.

Potassium Chloride (KCl) - Potassium chloride is used to inhibit clay hydration. The amount of KCl actually needed for inhibition is difficult to determine. Older formations which contain nonswelling clays, require KCl levels in the 3 to 5 wt% range; whereas, younger shales containing hydratable clays, require KCl levels up to 15 wt%. Other sources of K+ may also be used - especially if there are environmental restrictions on chlorides - with little or no effect on performance, e.g., KNO3, KC2H3O2, K2CO3, and K4P2O7.

Caustic Potash - Caustic potash (KOH) is added for alkalinity control in a KCl-Polymer Mud rather than caustic soda because it provides pH control without introducing potentially destabilizing sodium ions. Generally, a pH range of 9.5-10.5 is considered optimum for running KCl-Polymer muds since high pH has a detrimental effect on polymer adsorption. However, in some cases, particularly in coring applications, a neutral pH (7-8) is desired.

Xanthan Gum - Biopolymers such as XC or XCD are used for viscosifying KCl-Polymer Muds either by replacing or supplementing prehydrated bentonite. Although KCl-Polymer Muds may display a high yield point, they may not be capable of adequately suspending barite; therefore, small quantities of xanthan gum are added to provide the required suspension properties.

Polyanionic Cellulose/Carboxymethylcellulose (PAC/CMC - Cellulosic polymers are added for filtration control. When chloride concentrations are below 50,000 mg/L, either technical-grade or regular-grade CMC are used for filtration control rather than PAC. High-viscosity CMC is generally not used because it can have a deflocculating effect; therefore, pilot testing should always be performed prior to treatment.

Starch - Starch is added for filtration control in KCl muds. A modified starch (starch treated with a bio-cide) is preferred. Modified starches are generally potato-based rather than corn-based and have a thermal stability of approximately 250°F. Conventional pregelatinized corn starch may be used. However, it has a slightly lower thermal stability and can bacterially degrade.

PHPA - Partially hydrolyzed polyacrylamide (PHPA) is primarily added to encapsulate solids and provide inhibition. Since PHPA purities vary from vendor to vendor, actual PHPA concentration should be ascertained to prevent over or undertreatment of the mud. PHPA is sensitive to calcium and magnesium ions. Calcium hardness should be less than 400 mg/L before adding PHPA.

Gilsonite - A mined asphalt-like powder, gilsonite is used to plug microfractures and bridge depleted sands.

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Responses

  • allyson
    Can KCl replace Na in Bentonite?
    7 years ago
  • Michaela
    How to prepare cmc with kcl powder for drilling?
    3 years ago
  • ute
    How to prepare KCL with bentonite mud?
    3 years ago
  • ASPHODEL
    How to make standard kcl drilling fluid mud?
    11 months ago
  • hagos yonas
    What formations require kcl?
    1 month ago

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