--> ABSTRACT: Burial History Simulations of the Wilcox Group of the Texas Gulf Coast: The Effects of pCO<SUB>2</SUB>, Organic Acids, and Organic Acid Anions on Clastic Diagenesis, by Regina N. Tempel, Wendy J. Harrison; #91020 (1995).
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Burial History Simulations of the Wilcox Group of the Texas Gulf Coast: The Effects of pCO2, Organic Acids, and Organic Acid Anions on Clastic Previous HitDiagenesisNext Hit

Regina N. Tempel, Wendy J. Harrison

The separate effects of pCO2, organic acids, and organic acid anions on clastic Previous HitdiagenesisNext Hit have been investigated using burial history simulations of the Wilcox Group of the Texas Gulf Coast (Tempel and Harrison, 1991, Abstr. with Programs, GSA Ann. Meeting, p. A436). Results reveal that increased levels of pCO2 and high levels of organic acid anions in pore fluids increase the amount of Previous HitcarbonateNext Hit cement in a sandstone and reduce porosity. Conversely, dissociating organic acids destabilize Previous HitcarbonateNext Hit cements and inhibit precipitation of illites thus enhancing porosity development.

Increased levels of pCO2 cause precipitation of Previous HitcarbonateNext Hit cements in sandstones because the pH in Previous HitcarbonateNext Hit-silicate systems is buffered by the precipitation of alumino-silicate mineral phases. In particular, kaolinite is a common result of conditions of increased pCO2 in burial history simulations. The presence of both kaolinite and Previous HitcarbonateNext Hit in abundance in Wilcox sandstone paragenetic sequences thus suggests that increased levels of pCO2 influenced Previous HitdiagenesisNext Hit.

High levels of organic acid anions (OAA) in solution also promote stability of Previous HitcarbonateNext Hit phases by buffering the pH of the system. OAA achieve the buffering effect by acting as sinks for H+ ions. High levels of OAA do not appear to have a significant influence on the amounts of illite precipitated so that a predominance of Previous HitcarbonateNext Hit cement in Wilcox sandstones suggests that Previous HitdiagenesisNext Hit was affected by OAA.

Rapidly dissociating organic acids (OA) destabilize Previous HitcarbonateNext Hit cements and inhibit precipitation of illite cements by acting as a source for H+ ions. The resultant significant reduction in pH enhances porosity and also increases quartz stability. An influence on Wilcox sandstone Previous HitdiagenesisNext Hit by OA is therefore indicated by secondary porosity in Previous HitcarbonateTop cements, diminished amounts of illite cement, and a predominance of quartz cement.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995