--> Abstract: Detrital Mica Influence on Reservoir-Scale Diagenesis; #90063 (2007)

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Detrital Mica Influence on Reservoir-Scale Diagenesis

 

Boles, James R.1 (1) University of California, Santa Barbara, Santa Barbara, CA

 

Detrital muscovite and biotite are important to sediment diagenesis at the reservoir scale. Although the two mica types have similar structures and compositions, surprisingly, they exhibit different mechanical and chemical behavior. Muscovite tends to remain largely undeformed throughout the compaction history of the sediment. This is partly because muscovite resists compaction by dissolving silicate grains upon contact. In contrast to muscovite, biotite readily deforms during compaction, and can show both plastic and brittle deformation styles. Early carbonate-cemented rocks have undeformed biotite whereas the mica is extensively deformed in deeply buried uncemented sediment. Thus a measure of the relative timing of carbonate cement can be deduced from the extent of biotite deformation.

 

Mica cleavage faces produce a micro chemical environment which has a different chemistry than the bulk pore fluid. In certain chemical environments, biotite cleavage is an important nucleation site for early-formed diagenetic pyrite or carbonate minerals, such as dolomite and siderite. The carbonate crystals can greatly expand the original mica causing porosity reduction. The effect is believed to be a result of locally high pH near the biotite surface due to H+ exchange onto the surface. Carbonate growth is almost never observed in muscovite, yet in contrast to biotite, it is an important catalyst for pressure solution of quartz and feldspar. In all examples of cleavage surface effects, the micas do not breakdown, but rather provide a substrate which catalyzes reactions.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California