Eastern Section Meeting

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Carbon Dioxide Sealing Capacity: Textural or Compositional Controls?

Abstract

The primary goal of this research was to investigate the factors controlling sealing capacity of the caprocks and their respective contributions to seal capacity. Better understanding of the elements controlling sealing quality will advance our knowledge regarding the sealing capacity of shales and carbonates. To assess the effect of textural and compositional properties on scCO2 maximum retention column height we collected 30 representative core samples from caprock formations in three counties (Cimarron, Texas, Beaver) in Oklahoma Panhandle. We used mercury injection porosimetry (MIP), scanning electron microscopy (SEM), and Sedigraph measurements were used to assess the pore-throat-size distribution, sorting, texture, and grain size of the samples. Also, displacement pressure at 10% mercury saturation (Pd) and graphically derived threshold pressure (Pc) were determined by MIP technique. Moreover, EDS (Energy Dispersive X-Ray Spectrometer), specific surface area, and total organic carbon (TOC) measurements were performed to study various parameters and their possible effects on sealing capacity of the samples. Based on statistical analysis of our sample measurements from Oklahoma Panhandle, we assessed the effects of each group of properties (textural and compositional) on maximum scCO2 height that can be hold by the caprock. We conclude that there is a relatively strong positive relationship (+0.40 to +0.69) between scCO2 column height based on Pc and hard/soft mineral content index in both shale and limestone samples. Average median pore radius and porosity display a strong negative correlation with scCO2 retention column height. Also, increasing bulk density is correlated with increasing scCO2 retention column height. One of the most important factors affecting sealing capacity and consequently the height of scCO2 column is sorting of the pore throats. We observed a strong positive correlation between pore throat sorting and height of scCO2 retention column especially in shales. This correlation could not be observed in limestone samples. This fact suggests that the pore throat sorting is more controlling the sealing capacity in shales than other lithologies and, consequently, shales with well sorted pore throats are the most reliable lithology as seal. We observed that BET surface area shows a very strong correlation with scCO2 retention column height in limestone samples while BET surface area did not show significant correlation in shales.