Page 259 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

230 Xingru Wu

Figure 5.7 Nucleation process from supersaturation to crystal growth for homoge-
neous and heterogeneous nucleation. Modified based on Crabtree et al. (1999).

formation or imperfections on metal surfaces of tubing. For scale deposi-
tion in porous media resulting in formation damage, pore size distribution
can also affect the nucleation process, because of its stochastic nature. The
crystal growth is more limited in small pores because the probability of
collision is less in smaller pores than larger pores. Owing to the complex-
ity of scale deposition in porous media, the scaling prediction from a lab-
oratory may result in significant errors if they are directly used to predict
scaling in heterogeneous porous media (Fig. 5.7).
For scale to form from a supersaturated solution once nucleation has
occurred, there must be sufficient contact time between the supersatu-
rated solution and the nucleating sites on the reaction surface. The con-
tact time required varies depending on the degree of supersaturation, type
of mineral, temperature, pressure, agitation, and others. In the contacting
duration, these factors can exacerbate the risk of scaling and scale precipi-
tation by influencing the fate of the crystal nuclei. Given the nature of
the kinetic process of scale formulation and precipitation, crystal growth
remains understood only in qualitatively terms. The rate of precipitation
from a scale-forming solution varies according to the crystalline form that
the solid adopts. Also, scale deposits change with time as the continuous
process of dissolution and precipitation takes place at the surface.