Page 26 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Overview of Formation Damage During Improved and Enhanced Oil Recovery 9

damage unique to the production of heavy oil by hot water, steam and
in-situ combustion (Schembre and Koscel, 2005), including, transforma-
tion of kaolinite to water-sensitive clay, such as smectite in excess of

200 C, and dissolution of carbonate and silica due to increase of tempera-
ture, and reprecipitation of calcium, magnesium, and silicate solids caused
by an abrupt change of temperature, and wettability alteration due to
the decrease of adsorption of oil components as the temperature
becomes higher.

1.6 PRODUCED-WATER-RE-INJECTION (PWRI)

Produced water compositions usually contain toxic pollutants, vary-
ing significantly from field to field, potentially posing a great threat to
environment and increasing field oil and gas production costs. Produced
water can contain contaminants of organic materials and inorganic mate-
rials, including: (1) dissolved and dispersed oil, (2) dissolved minerals, (3)
treatment chemicals, (4) produced solids, (5) dissolved gases, and (6) bac-
teria and scales (Hansen and Davies, 1994). During production of oil/gas,
the compounds contaminating the produced water may change over
time, while other water enters the production zones, derived from water
flooding or produced water re-injection (Sheng, 2013). For conventional
oil and gas wells, as a well’s production life advances, the volume of pro-
duced water typically increases associated with a decrease in produced
volumes of oil and gas and an increase in waste-management costs; espe-
cially, after the breakthrough of injected water. The produced water in
conventional oilfields usually contains emulsion, solution, suspension, par-
ticulates and adsorbed particles, and treatment chemicals, injected water,
and bacterial contaminants (McCormack et al., 2001). The biggest differ-
ence of produced water in conventional gas fields is that usually no
injected water is present in gas formations (Jacobs et al., 1992). In coalbed
methane fields, a large amount of produced water is pumped out of coal
seams at the early stage of production, and its produced volume decreases
significantly as production advances (Nghiem et al., 2011). It is the
uniqueness of requiring large amounts of fracturing fluids and sands for a
large-scale fracture stimulation of unconventional reservoirs that distin-
guishes their produced water compositions from conventional reservoirs