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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