Review of Limestone Microporosity Occurrence Through the Phanerozoic Eon

Abstract

Micropores in carbonate rocks can, in many cases, hold significant percentages of a reservoir's in-place oil. This is especially true in giant and supergiant fields where the hydrocarbon column height is sufficient to forcibly charge these micron- and submicron sized pores. The vast economic potential of increased production from bypassed micropores in fields already developed has placed a new emphasis on characterizing carbonate microporosity, understanding its formation and diagenesis, and mapping its spatial distribution so it can be included into geological and reservoir simulation models. This global study, reviewing information from over two hundred previous works, characterizes the range of microporosity textures observed in limestone reservoirs throughout the world, and relates these textures to porosity and permeability values. This paper further describes how carbonate microporosity is spatially distributed and identifies depositional environments, facies, rock types, and allochems that are especially prone or resistant to microporosity formation. For example, mud-dominated facies tend to exhibit a higher relative abundance of microporosity in their pore system than grain-dominated rocks within the same depositional system. However, grain-dominated rocks in some cases can be almost entirely microporous. Furthermore, certain fossils, like foraminifera, green algae, and corals, are more susceptible to becoming microporous than are brachiopods and echinoderms. Because carbonates have themselves evolved throughout the Phanerozoic in response to the secular variation in seawater chemistry and the evolution of carbonate secreting organisms, this study reviews how the spatial distribution in microporosity occurrence varies through time. Specifically, the global dataset is used to test a recent hypothesis (Volery et al., 2009) that microporosity development is enhanced during so-called “calcite seas” like the Cretaceous and Early Paleozoic, while it is suppressed during “aragonite seas” during the late Paleozoic and today.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016