Attapulgite
Attapulgite belongs to a quite different family of the clay minerals Attapulgite-based muds
have excellent viscosity and yield strength and retain these properties when mixed with salt
water. However, they have the disadvantage of suffering high water loss thereby giving poor
sealing properties across porous and permeable formations.
Organophillic Clays
Organophillic clays are made from normal clays (bentonite or attapulgite) and organic cations.
The organic cations replace the sodium or calcium cations originally present on the
clay plates. Organophillic clays can be dispersed in oil to form a viscous structure similar to
that built by bentonite in water.
POLYMERS:
Polymers are used for filtration control, viscosity modification, flocculation and shale
stabilisation. When added to mud, polymers cause little change in the solid content of the mud.
Polymers are chemicals consisting of chains made up of many repeated small units called
monomers.Polymers are formed from monomers by a process called polymerization. The
repeating units (monomers) that make up the polymer may be the same, or two or more
monomers may be combined to form copolymers. Structurally, the polymer may be linear or
branched and these structures, either linear, branched, or both, may be cross-linked, i.e. tied
together by covalent bonds.
1-Starch:
2-Guar Gum
3-Xanthan Gum:
4-Carboxymethylcellulose (CMC)
Sodium carboxymethylcellulose (usually abbreviated as CMC) is an anionic polymer produced
by the treatment of cellulose with caustic soda and then monochloro acetate. The molecular
weight ranges between 50,000 and 400,000. CMC is used for viscosification and filtration
reduction in heavily weighted muds and wherever little viscosification of the fluid phase of the
mud is desirable.
FILTRATION CONTROL MATERIALS:
Filtration control materials are compounds which reduce the amount of fluid that will be lost
from the drilling fluid into a subsurface formation caused by the differential pressure between
the hydrostatic pressure of the fluid and the formation pressure. Bentonite, polymers, starches
and thinners or deflocculants all function as filtration control agents. Bentonite imparts
viscosity and suspension as well as filtration control. The flat,"plate like" structure of bentonite
packs tightly together under pressure and forms a firm compressible filter cake, preventing
fluid from entering the formation.Polymers such as Polyanionic cellulose (PAC) and Sodium
Carboxy-methyl-cellulose (CMC) reduce filtrate mainly when the hydrated polymer chains
absorb onto the clay solids and plug the pore spaces of the filter cake preventing fluid seeping
through the filter cake. Thinners and deflocculants function as filtrate reducers by separating
the clay flock’s or groups enabling them to pack tightly to form a thin, flat filter cake.
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