Modeling of smectite illitization in burial diagenesis environments

Report on THMC Modeling of the Near Field Evolution of a Generic Clay Repository: Model Validation and Demonstration

“…The overall illitization rates encompass great uncertainties as well, because the assumptions regarding starting point and temperature history of the formation vary significantly from one case to another. For example, the illitization rate calibrated in Kamei et al (2004) is two orders of magnitude higher than that in Cuadros (2006). However, even though they observe quite high illitization rate, Kamei et al (2004) conclude that there would be little illitization if the temperature of the nuclear waste disposal repository is kept under 100 o C. In general, the natural analogue studies agree that temperature and the availability of K + (Casciello et al, 2011) are the primary factors that affect illitization.…”

“…Fairly extensive studies have been conducted to evaluate the occurrence of illitization in bentonite and clay formation; some of these studies are listed in Table 5-2 and a brief summary of each study is given below. Illitization is clearly evidenced in geological system (Wersin et al, 2007), as exemplified by several natural analogue studies (Pusch and Madsen, 1995;Kamei et al, 2004;Cuadros, 2006;Casciello et al, 2011). Illite/smectite mixed-layer clay is commonly observed in the clayey sediments, and typically the deep formation contains more illite than shallow formation (Cuadros, 2006), which lead to a conclusion that smectite is gradually transformed to illite during diagenesis.…”

“…Illitization is clearly evidenced in geological system (Wersin et al, 2007), as exemplified by several natural analogue studies (Pusch and Madsen, 1995;Kamei et al, 2004;Cuadros, 2006;Casciello et al, 2011). Illite/smectite mixed-layer clay is commonly observed in the clayey sediments, and typically the deep formation contains more illite than shallow formation (Cuadros, 2006), which lead to a conclusion that smectite is gradually transformed to illite during diagenesis. Pusch and Madsen (1995) investigated the illitization of kinnekulle bentonite, a 5 m thick illite/smectite interlayers with upper and lower part having 50-70% illite and the central part 30-50% illite.…”

“…Illitization is typically described in the clay science community with a kinetic model that relates the time derivative of illite (or smectite) mass fraction in the illite/smectite mixed layer to temperature, activation energy, and concentration of K + , etc. But the details of the kinetic equations vary a great deal, as detailed in Cuadros (2006). The overall illitization rates encompass great uncertainties as well, because the assumptions regarding starting point and temperature history of the formation vary significantly from one case to another.…”

“…However, even though they observe quite high illitization rate, Kamei et al (2004) conclude that there would be little illitization if the temperature of the nuclear waste disposal repository is kept under 100 o C. In general, the natural analogue studies agree that temperature and the availability of K + (Casciello et al, 2011) are the primary factors that affect illitization. But as to the importance of availability of K + in illitization, Cuadros (2006) realized that this is a more complicated issue and therefore proposed to use 'effective K + concentration" in the illitization kinetic model to accommodate the effect of other actions like Ca +2 , Mg…”