--> Abstract: Prediction of Fibrous Illite and Associated Secondary Porosity Formation in Sandstones, by Robert H. Lander and Linda M. Bonnell; #90078 (2008)

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Prediction of Fibrous Illite and Associated Secondary Porosity Formation in Sandstones

Robert H. Lander and Linda M. Bonnell
Geocosm, Austin, TX

We have developed a model for fibrous illite in sandstones where kaolinite is a primary reactant and potassium is derived from in-situ K-feldspar grain dissolution or imported into the model reference frame. Illite fiber nucleation and growth are modeled using Arrhenius expressions that consider saturation state in addition to temperature and time. Nucleation occurs on pore walls and muscovite and detrital illite are energetically favorable substrates. The model is integrated with other Touchstone models to account for interaction of diagenetic processes on surface area and reactant volumes and to incorporate results into permeability and microporosity models.

We tested the model on two datasets with differences in sandstone characteristics and burial histories: Jurassic samples from offshore mid-Norway experienced maximum temperatures ranging from 108-172 °C and are quartzose in composition whereas samples from offshore Southeast Asia are Miocene in age, rich in lithic fragments, and have maximum temperatures ranging from 154-173 °C.

The model matched measured illite, kaolinite, and K-feldspar abundances within measurement uncertainties for both datasets using identical kinetic parameters. Predicted K-Ar ages agree with published data from mid-Norway for samples with comparable maximum temperatures. Although no illite particle size data are available from the analyzed samples, modeled crystallite thicknesses are comparable to published measurements of ~40-120 Å from Jurassic North Sea samples with similar temperature histories. Predicted K-Ar dates for the southeast Asia dataset trend are comparable to measured values assuming 2 vol% detrital contaminants. Calculated δ18O values for samples from this dataset are within 1‰ of the measured values based on models that assume a constant water value comparable to the present-day value of ~ -4‰ δ18O SMOW

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas