Pore systems in carbonate formations, Weyburn field, Saskatchewan, Canada: Micro-tomography, helium porosimetry and mercury intrusion porosimetry characterization

Abstract

Capturing the multi-scale porosities inherent in carbonate rocks is critical for the understanding of their transport and elastic properties and how these are affected by pore and confining pressures. To ensure accuracy of such an assessment, sample selection, sample preparation and measurement techniques need to be fit for purpose. In the recent years, micro-computed tomography (micro-CT) has been increasingly used for the analysis of pore characteristics in rocks. One of the recurrent problem with respect to rock physics characterization, however, is that the values of porosity it can determine often differ from conventional laboratory measures. Today, for example, to our knowledge, there is no systematic workflow that will allow for a full characterization of microstructure details of carbonates. We expect the development of such workflow to go through testing and comparison of different porosity measurement strategies. In this regard, we provide in this paper a number of examples where micro-CT was used in addition to standard petrophysical measurements (helium and mercury intrusion porosimetry) to get estimates of porosity in dolomites and limestones from the Weyburn oilfield in southwestern Saskatchewan, Canada. Optical microscopy and SEM were used to have an overview of the pore shapes and sizes and, whenever needed, to condition the micro-CT image segmentation parameters.On about half of the studied twelve samples, the micro-CT porosity agrees within ∼2% with the mercury and helium porosities and is lower (up to 16%) on the rest of the samples. On an oolitic limestone, we show how combining micro-CT and mercury porosimetry can allow quantitative estimation of connected and non-connected pores.