Pore Space Quantification of Sedimentary Rocks before-after Supercritical CO2 Interaction by Optical Image Analysis

Abstract

Optical image analysis (OIA) allows a quantitative characterization of pore space measured through thin sections. Together with petrographic studies, by using optical microscopy (OpM), OIA could provide a reproducible pore characterization of sedimentary rocks in applications related to the geological storage of CO2. This research is focused on the application of the OIA technique to measure porosity on thin section samples of sandstones from Spain before and after CO2 injection to supercritical (SC) conditions in autoclave (P ≈ 7.5 MPa and T ≈ 35°C). The aim of this article is to show preliminary measures by OIA using images acquired with high-resolution scanner (HRS). Mineral images were acquired from thin sections before and after SC-CO2 injection. The optical measures of porosity on the thin sections of sandstones showed an effective pore segmentation considering different images in cross-polarized light conditions (90°/0°; 120°/30°) and plane-polarized light conditions (90°/-) of the same petrographic scene. Mineralogical studies by OpM and OIA-HRS have allowed an exhaustive characterization of the samples studied and a preliminary approximation of the CO2-rock interactions. This study shows a fast, effective and reproducible methodology that allowed the researchers to obtain qualitative information about changes in the pore network (optical porosity) distribution on the thin section that could be applied to similar experimental injection tests.