Page 236 - Shale Shakers Drilling Fluid Systems
P. 236
218 SHALE SHAKERS AND DRILLING FLUID SYSTEMS
value is tested prior to adding the water to the hydroxide. After settling, the water was pumped
mud system. Neutralization of the acid coagulants into another holding tank where it was given a
is commonly accomplished using caustic soda, final treatment with chlorine prior to returning to
magnesium hydroxide, or sodium carbonate. Of the active mud system.
these neutralizing agents, magnesium hydroxide This technique removes dry solids and returns
works at the lowest level of concentration. Using the recovered water to the active mud system,
magnesium hydroxide in conjunction with phos- which has no suspended solids, a minimum of dis-
phoric acid produces only water and an insoluble solved solids, and a pH in the 7 to 10 range.
phosphate precipitant. Treatments with the other
neutralizers, such as caustic soda and soda ash,
produce significant amounts of water soluble salts. POLYMER TECHNOLOGY
Continued use of these products will create an un-
acceptable buildup of the salts and increased tur- A number of additives may be used to coagu-
bidity levels. Chlorine, called "everclear," may be late and flocculate solids in waste water, but poly-
added to the recovered water to precipitate the mers are the most effective and least expensive.
colloidal solids and increase the pH. Understanding the dewatering process requires
Oil muds are more difficult to dewater than some knowledge of polymers.
water-based muds. The cuttings travel from the
shaker to a wash tank containing a detergent and
an agitator where the oil is removed from the Polymer Chemistry
cuttings. The water/oil mixture is then put into
a pit where the oil is removed by a "skimmer," A polymer is a chemical chain of organic mol-
or it is processed through a small ID-high pres- ecules that is produced by the joining of primary
sure hydrocyclone. chemical units called monomers. The word "poly-
Dewatering of oil-based muds follows approxi- mer" comes from the Greek word polymeros, mean-
mately the same procedure as that of water-based ing, "many parts."
muds. First, the emulsion must be broken down, Depending on their ionic character, polymers
which is accomplished by adding an acid and ad- used in water treatment applications can be di-
ditional water. The oil separates and rises to the vided into three major types: nonionic, anionic,
surface where it can be removed by a skimmer. and cationic. Nonionic polymers possess no ionic
The remaining solids are then sent to the process- charge, anionic polymers possess net negative
ing tank where they are treated in the same man- charges, and cationic polymers possess net posi-
ner as water-based mud. Additional washing may tive charges. The basic polymer structure for wa-
be required if the remaining oil content in the ter treatment polymers is polyacrylamide, which is
sludge exceeds acceptable environmental levels. made from acrylamide monomer. Straight poly-
Vacuum filtration is another method of remov- acrylamide is nonionic. Charge can be imparted to
ing solids from the liquid. Chemical flocculation the polymer by chemically adding functional groups
may be used to aggregate the solids, or the mud that possess the desired charge type. In this man-
can be processed through a filter depending on the ner, anionic or cationic polymers can be generated.
properties of the filter. The solids can then be Polyelectrolytes, as these polymers are some-
dried to further reduce any residual water. Chemi- times called, encompass the entire family of wa-
cal flocculation and removal by a centrifuge has ter treatment polymers. Nonionic polymers, al-
f
proven the least expensive of the two methods, though they do not possess ne ,uc,rge, are still
however, the filtration method is continuously be- classified as polyelectrolytes because they tend to
ing improved and should be given consideration. exhibit similar solution properties, as do ionically
In comparison field studies the most effective charged polymers.
and economical treatment method has been chemi- Another important characteristic of water treat-
cal treatment, settling, and centrifuging of the ment polymers is molecular weight, which refers
mud. In these field tests, mud from the active sys- to the polymer chain length. The longer the chain
tem was treated with anionic polyacrylamide poly- length, the higher the molecular weight. Polymers
mers, flocculants, and phosphoric acid coagulants. with molecular weights between 5,000 to 200,000
The flocculated mud was processed through a high- behave as coagulants in water. These polymers,
speed (1500 to 2000 times the force of gravity) cen- carrying positive charge, neutralize negatively
trifuge. The "dry" solids removed contained ap- charged colloidal matter in waste water to form
proximately 50% solids by volume. The recovered small floe particles. Conversely, polymers with
water, or filtrate, was placed in a holding tank molecular weight between 500,000 and several
where the pH was neutralized with magnesium million, act as flocculants in water. These polymers
