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Water base mud

Water base mud

Consists of:
1-Liquid water, continuous phase
2-Reactive solids, for viscosity and yield point
3-Inert solids, for density
4- Chemical additives, to control properties

Hydration of clays
Clays with high cation exchange capacity exchange large amount of water into the exchangeable layer and adsorb water onto the outer surface of plates
This effect gives high viscosity and high yield point
Adsorption of water causes a very sticking expansion of clay
Overall hydration transform clay from dry power to plastic slurry
Clay yield depends on: purity, nature of atoms in exchangeable layers and salinity of water

Bentonite and attaplugite
Bentonite consists primarily of montmorillonite
Came from French town Montmorillon, where first mined 1874
Basic structure is close to pyrophllite.
There are a small number of exchangeable ions, sodium calcium and magnesium
Most common bentonite are those with sodium and calcium as exchangeable ions
Attapulgite belongs to a different family of clay minerals
Instead crystallizing as platy crystals, it forms needle like crystals
Have excellent viscosity and yield strength when mixed with salt water
Disadvantage is suffering high water loss and poor sealing properties

Dispersion, flocculation and defloccullation
Agitating of clay suspension in water gives three modes: edge to edge; face to edge; and face to face
Dispersion occurs with no face or edge association
It results in increase in viscosity and gel strength
Aggregate occurs with face to face association
Aggregate results in a decrease in viscosity and gel strength
Flocculation occurs with face to edge association
It causes excessive gelation
Flocculation can be broken by chemical thinners
The resulting suspension is called deflocculated
Inert solids
Include low gravity and high gravity
Low gravity include sand and chert
High gravity are added to increase mud weight or density
Referred to as weighting materials
Mud named as weighted mud, they are:
                                1)Barite (barium sulphate, BaSO4) sp.gr. 4.2
                                   Used to prepare mud in excess of 10 ppg
                                  Refened to as weighting agent for low cost and high purity
2)Lead sulphides (galena) sp.gr. 6.5-7.0
Allowing mud weight up to 35 ppg
Iron ores, sp. gr. 5+ More erosive
Contain toxic materials
 
 
 

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