Sandstone Compaction: Basis for Porosity Predictive Capabilities

Abstract

Prediction of sandstone porosity must be based on understanding physical and chemical processes that are genetically linked to geologic history. Petrographic studies of sandstones of diverse geologic history indicate that reduction of intergranular volume (IGV) by compaction is the primary control of porosity in most cases. Moreover, these studies demonstrate that compaction can commonly be related to geologic history. Maximum depth of burial exerts a primary control on compaction in nondeformed and mildly deformed basins. For example, Miocene sandstones of Louisiana and Tertiary and Cretaceous sandstones of the Green River basin display progressive compaction to the depth limit of conventional core control. Compaction has reduced average IGV to less than 20% at 7.5 km (25,000 ft) depth in Miocene sandstones of Louisiana and to less than 10% at 5.3 km (17,500 ft) depth in Cretaceous sandstones in the Green River basin. Differences in absolute values of IGV in these basins reflect other geologic variables that have influenced compaction, including thermal maturity and age. In both basins, a progressive gradation from predominantly mechanical compaction-shallow to predominantly chemical compaction-deep is observed. Previous work in older basins indicates that chemical compaction remains an important agent of porosity modification in sandstones that undergo additionalmore » physical, chemical, and thermal stress. Compaction progressively reduces the intergranular volume of sandstones, thereby directly controlling intergranular porosity and influencing chemical diagenesis by modifying plumbing systems. Thus quantification of compaction in sandstones of diverse geologic history is fundamental to the development of porosity predictive capabilities.« less