Page 53 - Environmental Control in Petroleum Engineering

Drilling and Production Operations 41

hundreds of parts per thousand (ppt). For comparison, seawater con-
tains 35 parts per thousand.
In addition to salt, many produced waters also contain high levels
of calcium, magnesium, and potassium, with lower amounts of alumi-
num, antimony, arsenic, barium, boron, chromium, cobalt, copper, gold,
iron, lead, magnesium, manganese, nickel, phosphorus, platinum,
radon, radium, silicon, silver, sodium, strontium, tin, uranium, and
vanadium. The concentrations of seven major heavy metals found in
produced water in the Gulf of Mexico are summarized in Table 2-6.
Lead, nickel, chromium, zinc, nickel, and copper were found to have
the highest concentrations (Stephenson, 1992). Produced water also
contains low levels of naturally occurring radioactive materials. Radio–
active materials are discussed below.

Hydrocarbons

Produced water normally contains dissolved and suspended droplets
of hydrocarbons and other organic molecules that are not removed by
the separations equipment. Hydrocarbon effluent concentrations vary
widely with equipment used. The majority of the hydrocarbon concen-
trations in produced water from the Gulf of Mexico are between 10
and 30 mg/L, with virtually all levels less than about 100 ppm (Burke
et al., 1991; Stephenson, 1992). The current U.S. Environmental
Protection Agency limits for the discharge of hydrocarbons in water

Table 2-6
Heavy Metals Concentrations in Produced Water

Average Concentration Standard Deviation
Metal (micrograms/L) (micrograms/L)
Cadmium 27 12
Chromium 186 68
Copper 104 180
Lead 315 670
Nickel 192 307
Silver 63 17
Zinc 170 253

Source: from Stephenson, 1992.
Copyright SPE, with permission.