The Effect of Weighting Materials on Cement

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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