About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 956

Last Page: 956

Title: Burial Diagenesis of Illite/Smectite, a Kinetic Model: ABSTRACT

Author(s): D. G. McCubbin, J. W. Patton

Article Type: Meeting abstract


X-ray diffraction analysis of clay-rich sediments of Miocene and younger age from 14 wells in offshore Louisiana supports the published conclusion that diagenetic changes in the mixed-layer illite/smectite (I/S) clays involve a progressive downward increase in the proportion of illite layers, followed by a change from random to regular interstratification and a further increase to about 80% illite layers. We also found that the depth at which these diagenetic changes begin and the degree of alteration at any given depth vary substantially from well to well and are related to the age and burial rate of the sediments as well as to present-day subsurface temperatures.

This burial alteration was modeled using a first-order reaction equation with a term to describe a non-linear increase in temperature with time. For each of several wells where we had complete data, we solved this equation for values of activation energy (E) and frequency factor (a). The resulting values of (E) are fairly consistent among wells and are close to those determined experimentally by others. The calculated values of (a) are lower by two orders of magnitude than the reported experimental values, but range considerably. The same equations can be used to calculate the degree of reaction for different times and temperatures, assuming these or other values of (E) and (a). This kinetic model should be helpful in deciphering the influences of I/S reactions on interstitial fluid p essures, fluid and rock chemistry, and shale physical properties.

End_of_Article - Last_Page 956------------

Copyright 1997 American Association of Petroleum Geologists