Page 58 - Environmental Control in Petroleum Engineering

46 Environmental Control in Petroleum Engineering

Coagulants commonly include polyamines and polyamine quaternary
ammonium salts.

Foam Breakers

Some crude oils generate a foam during production. This foam
inhibits the separation of the oil, water, and solids in the production
equipment. Although not commonly needed, foam breakers are avail–
able. Foam breakers include silicones, polyglycol esters, and alumi–
num stearate.

Surfactants

Surfactants (detergents) are regularly used to wash equipment and
decks on offshore rigs. These surfactants commonly include alkyl aryl
sulfonates and ethoxylated alkylphenols.

2.2.4 Well Stimulation

The oil and gas production rate of many wells is restricted by a
low permeability around the wellbore. To increase the production rate,
the permeability is often increased by stimulation. The two most
common forms of stimulation are acidizing and hydraulic fracturing.

Acidizing

Acids are used to dissolve acid-soluble materials around the well-
bore to increase the formation's permeability. These acid-soluble
materials can include formation rocks and clays, as well as any
materials added during drilling. A variety of inorganic and organic
acids can be used, depending on the formation. These acids include
hydrochloric, formic, acetic, and hydrofluoric. Additives are also
required to optimize the process.
The most widely used acid is hydrochloric acid. Its main application
is in low permeability carbonate reservoirs. The major reaction prod-
ucts produced during acidizing are carbon dioxide, calcium chloride,
and water. Spent acid returned from a well has a high chloride content.
The principal disadvantage of hydrochloric acid is its corrosivity on
tubulars, particularly at temperatures above about 250°F.