Comparing thresholding techniques for quantifying the dual porosity of Indiana Limestone and Pink Dolomite

• Evaluation of thresholding methods to find the pore space from rock volume images.
• Basic imaging or thresholding methods alone cannot be used for all carbonate rocks.
• Calculated porosities are functions of microporosity, mineral, and image resolution.

Carbonate reservoirs, and in particular, saline aquifers are globally abundant and promising for carbon dioxide (CO2) storage. Pore network modeling of CO2 storage in porous networks extracted from imaged carbonates provides a tool for evaluating potential storage sites. Capturing the multi-scale porosities (porosity at multiple length scales from nanometers to millimeters) inherent in carbonates is key to producing reliable pore network simulation results. Thresholding techniques that can extract the multi-scale pore space from micro computed tomography (microCT) or scanning electron microscopy (SEM) are needed. In this work, the application and evaluation of thresholding techniques originally developed for sandstones were applied and evaluated for Indiana Limestone and Pink Dolomite, carbonates that exhibit dual porosities (porosities that represent two distinct pore size distributions). The objective was to determine whether there is a single method or imaging technique that can reliably evaluate the porosity of carbonate rocks. The evaluation of the thresholding techniques applied to carbonate rocks showed that one single imaging technique or thresholding method cannot be solely used for all carbonate rocks. Instead, the evaluated porosity is a function of the microporosity, rock type and image resolution. The sensitivities of existing methods to thresholding techniques, imaging method and material structure were shown. This work provides a preliminary assessment of thresholding dual porosity carbonates.

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