A Characterization of Tight Sandstone: Effect of Clay Mineralogy on Pore-Framework

Abstract

Macro-, meso-, micro-pore systems combined with clay content are critical for fluid flow behavior in tight sandstone formations. This study investigates the impact of clay mineralogy on pore systems in tight rocks. Three outcrop samples were selected based on their comparative petrophysical parameters (Bandera, Kentucky, and Scioto). Our experiments carried out to study the impact of clay content on micro-pore systems in tight sandstone reservoirs involve the following techniques: Routine core analysis (RCA), to estimate the main petrophysical parameters such as porosity and permeability, X-ray diffraction (XRD), and scanning electron microscopy (SEM) to assess mineralogy and elemental composition, Mercury Injection Capillary Pressure (MICP), Nuclear Magnetic Resonance (NMR), and Micro-Computed Tomography (Micro-CT) to analyze pore size distributions. Clay structure results show the presence of booklets of kaolinite and platelets to filamentous shapes of illite. The Scioto sample exhibits a micro-pore system with an average pore body size of 12.6±0.6 μm and an average pore throat size of 0.25±0.19 μm. In Bandera and Kentucky samples illite shows pore-bridging clay filling with an average mineral size of around 0.25±0.03 μm, which reduces the micro-pore throat system sizes. In addition, pore-filling kaolinite minerals with a diameter of 5.1±0.21 μm, also reduce the micro-pore body sizes. This study qualifies and quantifies the relationship of clay content with primary petrophysical properties of three tight sandstones. The results help to advance procedures for planning oil recovery and CO2 sequestration in tight sandstone reservoirs.

The Power of Characterizing Pore-Fluid Distribution for Microscopic CO2 Injection Studies in Tight Sandstones

“…It ought to be mentioned that the micropore system represented a significant proportion of the tight rock's total porosity [88,89]. Our study confirmed that the micropore systems of the studied sandstones significantly contributed to overall sandstone porosity, with contributions of 38% in the Bandera, 48% in the Kentucky, and 50% in the Scioto samples.…”

“…Hence, the low clay content of the other sandstones (50.1% for Scioto and 48% for Kentucky) leads to the presence of high micropore-system proportions, and to the relatively high contribution of the micropore-throat system (60% for Scioto and 50.9% for Kentucky sandstone). It ought to be mentioned that the micropore system represented a significant proportion of the tight rock's total porosity [88,89]. Our study confirmed that the micropore systems of the studied sandstones significantly contributed to overall sandstone porosity, with contributions of 38% in the Bandera, 48% in the Kentucky, and 50% in the Scioto samples.…”

“…Our results demonstrate that T 2 cut-off values of the tested sandstones were 17.8, 12.2, and 24.6 ms for Bandera, Kentucky, and Scioto sandstones, respectively, which lie in the typical range for sandstone rocks (Table 4). Based on these results, we may assert that the T 2 threshold value is not always 33 ms for sandstone rocks, as recommended by other scholars [86][87][88]. The cumulative NMR-porosities of partial saturation conditions represent the bound-fluid volume of these sandstones.…”