Comparative pore surface area in primary and secondary porosity in sandstones

Daniel R Nolansnyder,John Parnell

doi:10.1016/j.petrol.2018.09.095

Daniel R Nolansnyder, John Parnell

Open Access

https://doi.org/10.1016/j.petrol.2018.09.095

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Abstract

Primary and secondary porosity in sandstones possess different pore geometry characteristics, but these are not well quantified. The pore surface area in 2 suites of sandstones exhibiting only primary porosity (Permo-Triassic, Northern Ireland) and only secondary porosity (Cambrian, England) were measured using JMicrovision software. The data show pore surface areas per unit pore volume ∼2.5 times as great in the secondary porosity compared to the primary porosity. This difference is great enough to have a significant impact on properties dependent on pore surface area, including oil production and capacity for microbial colonization in the deep biosphere.

Highlights

Pore geometry is a subject for study for petroleum geologists and engineers who are concerned with the potential of subsurface rocks to function as hydrocarbon reservoirs
The development of secondary porosity, i.e. porosity generated during mineral dissolution during burial, is ubiquitous in sandstones that contain feldspars, as the feldspars are readily dissolved by acidic pore fluids (Schmidt and McDonald, 1979)
We present data based on image analysis of two sets of sandstones, one containing just primary pores and the other containing abundant secondary pores due to partial dissolution of feldspar grains, and compare their pore surface areas

Summary

Introduction

Pore geometry is a subject for study for petroleum geologists and engineers who are concerned with the potential of subsurface rocks to function as hydrocarbon reservoirs. One of the most fundamental approaches to documenting pore geometry is image analysis This study utilizes a simple image analysis procedure to assess the difference between two fundamental pore types, primary and secondary porosity in sandstones. Secondary porosity is of fundamental importance to the prospectivity of siliciclastic reservoirs. The development of secondary porosity, i.e. porosity generated during mineral dissolution during burial, is ubiquitous in sandstones that contain feldspars, as the feldspars are readily dissolved by acidic pore fluids (Schmidt and McDonald, 1979). Numerous studies (e.g. Giles and de Boer, 1990; Taylor et al, 2010) conclude that secondary porosity is the norm for sandstone successions, and in some cases it represents the majority of the porosity

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