Page 346 - Reservoir Formation Damage

326 Reservoir Formation Damage

migration, and redeposition of fine mineral particles and therefore cause
formation damage (Chang and Civan, 1991, 1992, 1997).
Formation damage resulting from the injection of incompatible waters
into reservoirs can be avoided if the initial rock-fluid equilibria and,
hence, the initial reservoir quality can be maintained (Schneider, 1997).
Injecting oxygenated waters into reservoirs and can oxidize the reduced
Fe and S species present in the pore water and can cause precipitation
and plugging of pores (Schneider, 1997). Geochemical models are important
for predicting the complications that will result from the interactions of
the various drilling and production fluids with the reservoir formation
(Schneider, 1997).
Yeboah et al. (1993) draw attention to the fact that most models use
limited solubility or thermodynamical data and ignore the effects of ion
pairs, presence of other ions (such as magnesium) on the solubility, and
the kinetic and transport phenomena factors. Therefore, Yeboah et al.
(1993) caution that "the available models predict only scaling tendency
and with a high degree of uncertainty," but "a positive scaling potential
does not necessarily imply that scale will form."

Geochemical Phenomena—Classification,
Formulation, Modeling, and Software
Fluids and minerals in petroleum-bearing formations may undergo
various interactive chemical reactions in response to the alteration of the
in-situ conditions by various operations, including drilling, workover, and
improved recovery. Geochemical models provide scientific guidance for
controlling adverse reactions that may result from rock-fluid interactions.
Excellent treaties of the geochemical reaction modeling are available
from several sources, including Melchior and Bassett (1990), Ortoleva
(1994), and Bethke (1996). This subject is extremely complex, therefore,
only the fundamentals of the overall subject are outlined here. The readers
are encouraged to resort to literature for details and to use ready-made
software available from various sources.
Petroleum-bearing formations can be generally viewed as being geo-
chemical systems in which fluids consisting of oil, gas, water, and
immobile solid phases formed from an assemblage of minerals interact
through various chemical reactions. Lichtner (1985) classified such
reactions into four categories: (1) aqueous ion complexing, (2) oxidation
and reduction, (3) mineral precipitation and dissolution, and (4) ion
exchange and adsorption reactions. As stated by Kharaka et al. (1988)
and Amaefule et al. (1988), such reactions occur in response to changing
temperature, pressure, and fluid composition by various factors, including