Review articleImaging pores in sedimentary rocks: Foundation of porosity prediction

- Pore imaging for sandstones and limestones fostered understanding that led to predictive models for porosity prediction.
- Pore categorization based on the primary texture and composition has particular relevance for predictive modeling.
- Imaging mudrock pores requires special sample preparation and imaging methods for which there have been recent advances.
- At the nano-scale, pore categorization relative to primary textures (paragenesis) is poorly understood.
- Knowledge about pore walls is fundamental to placing pores into a correct paragenesis.
- Nascent modeling efforts suggest that pore evolution in mudrocks departs in significantly from pore evolution in sandstones.

This review examines the history and current practice of technologies for imaging of pores in sedimentary rocks. Pores are that portion of the rock volume occupied by components of relative mobility such as water of various salinities, microbial life, petroleum liquids, gases, and supercritical fluids. Through a rock's history the contained pores evolve as the primary detrital assemblage responds chemically and mechanically to changing conditions in the subsurface. Description and classification of pores based upon their paragenesis depends upon inspection by imaging that allows the pores to be seen and interpreted in the context of historical processes responsible for formation of the pore walls.Since the late 1960s, sample preparation and imaging methodologies that clarified our understanding of pores in their correct historical context have been at the root of important advances in prediction of porosity and related bulk properties in the subsurface. These older approaches are now joined by new technologies that serve current efforts to extend predictive capabilities to nm-scale pores in the fine-grained, low-permeability rocks that dominate in the deeper parts of sedimentary basins, and indeed, in the sedimentary record as a whole. Placing the smallest pores into their proper paragenetic context presents a challenge in the quest to develop predictive models for porosity evolution in fine-grained rocks.