Intergranular Pressure Solution and Porosity Evolution in Quartzose Sandstones: ABSTRACT

Abstract

Compared to cementation by quartz, carbonates, and clay minerals, intergranular pressure solution has long been viewed as a minor control of porosity evolution in quartzose sandstones. However, quantitative cathodoluminescence petrography and scanning electron microscopy of Paleozoic and Mesozoic sandstones from various geologic settings suggest that intergranular pressure solution is the diagenetic process that most fundamentally influences porosity and permeability evolution in a majority of cases. Intergranular pressure solution dictates tightness of grain packing, size and geometry of primary pores, and diameter and morphology of contacts between framework grains; it also commonly predates pervasive cementation. Consequently, intergranular pressure solution is the fundamental control of minus-cement porosity. Although there is a close relationship between intergranular pressure solution and cementation in some sandstones, they are independent in others. For this reason, the percentage of minus-cement porosity actually occluded by cement is not systematic and is therefore difficult to predict. Numerous geologic variables have been documented that influence the amount of intergranular pressure solution that occurs in quartzose sandstones. On a local scale, relatively fine-grained sandstones and sandstones containing between 3 and 9% early authigenic clay have experienced more intergranular pressure solution than other sandstones. Regionally, among sandstones of equal age, grain size, and clay percentage, those that have been exposed to greater rates of burial, greater total depth of burial, and higher temperatures have experienced more intergranular pressure solution. These results suggest that an enhanced understanding of intergranular pressure solution may lead to a capability of predicting quartzose sandstone reservoir quality. End_of_Article - Last_Page 487------------