How Important Are Secondary Dissolution Pores in Siliciclastic Sandstones? Data from the Tertiary Sandstone Section along the Texas Gulf Coast

Robert G. Loucks
The University of Texas at Austin, Austin, TX

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.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005