Page 117 - 4637

Oil-emulsion muds

Red-lime, oil-emulsion fluids were popular in the late 1950s,
and appeared to give good drill pipe protection. This was in part
due to the high pH (12 to 12.5) and oxygen (O 2) scavenging
dispersants such as Quebracho.
The emulsified diesel formed a protective "oil-wet" film on
the metal and allowed the drill pipe to be isolated from the fresh or
saltwater environment. This acted as a corrosion inhibitor; and
many drill strings were clean, bright and shiny when they were
pulled. A low corrosion rate, and minimum pitting was normal with
this system.

Oxygen inhibitor, plastic coating

Internally plastic coated drill pipe reduces O 2 attack on the
pipe ID and can lengthen string life. Without the protective coating,
high-pH and an inhibitor based on organic phosphate esters can be
used effectively in the drilling environments to protect the tubulars.
In systems containing a high level of soluble cations like calcium
and magnesium, the pH cannot be economically raised due to
precipitation of insoluble hydroxides.
Control of pitting is desired as this will decrease washouts
and failure many times. There was some use of the soluble base
ammonium hydroxide, especially during sour drill stem tests. But
the ammonia release has some environmental safety restraints, and
due to new regulations, that product is not used as a chemical of
choice anymore.

1960-Era Systems

During the 1960s, low- or neutral-pH, gypsum-treated fluids
were popular as an "inhibited" system to drill with. They were
"sulfate-saturated," and contained high filtrate calcium. They

116