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| From
Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005 How Important Are Secondary Dissolution Pores in Siliciclastic Sandstones? Data from the Tertiary Sandstone Section along the Texas Gulf Coast Abstract: Secondary pores are a well-documented diagenetic
dissolution feature in siliciclastic sandstones, especially immature feldspar-
and rock-fragment-rich sandstones. The importance of dissolution pores,
however, is still controversial. In quartzarenites this pore type may
be minor, but in arkoses and litharenites, this pore type may be dominant.
The Tertiary sandstone section along the Texas Gulf Coast has a mineralogical
composition of subarkoses, lithic arkoses, and feldspathic litharenites.
Dissolved feldspars produce abundant secondary pores in these sandstones.
Some of the pores are filled with kaolinite or carbonate cement. The amount
of dissolved material does not appear to be reprecipitated in nearby pores.
More than half the Texas Tertiary sandstones analyzed that are between
burial depths of 700 and 3300 m are dominated by secondary pore networks.
Nearly all the sandstones deeper than 1300 m are dominated by a secondary
pore network. These observations are important for three reasons: (1)
secondary porosity can be very common in selected basins, (2) models that
focus on destruction of primary pores are missing an important component
of the pore network, and (3) secondary pore networks may produce porosity
versus permeability relationships different from those of primary pore
networks. Each of these factors is important in understanding reservoir-quality
prediction in sandstones where abundant feldspars and rock fragments are
expected. |