Revisiting the Importance of Secondary Dissolution Pores in Tertiary Sandstones Along the Texas Gulf Coast
Robert G. Loucks
Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin 78713-8924
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 sandstones along the Texas Gulf Coast have a mineralogical composition of subarkoses, lithic arkoses, and feldspathic litharenites. Dissolved feldspars and volcanic rock fragments produce abundant secondary pores in these sandstones. Some of the pores are filled with kaolinite or carbonate cement. Most of the dissolved material, however, does not appear to be reprecipitated in nearby pores. More than half of the 235 Texas Tertiary sandstones analyzed that are between burial depths of 2,500 and 18,000 ft are dominated by secondary pore networks. In the sandstones deeper than 10,000 to 11,000 ft nearly all the pore networks are dominated by secondary pores. These observations are important for three reasons: (1) secondary pores are very common in Gulf of Mexico sandstones, (2) numerical 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 predicting reservoir quality in sandstones where abundant feldspars and volcanic rock fragments are expected.
AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana