Pore Structure and Seal Capacity of Ilaro Formation Shales in the Eastern Dahomey Basin: Implications from Mercury Injection Capillary Pressure and Spontaneous Imbibition Analyses (original) (raw)

A petrophysical evaluation of caprock pore characteristics and seal capacity is critical for geologic storage of CO 2. In this study, integration of X-ray diffraction, mercury injection capillary pressure (MICP), and spontaneous imbibition analyses is used to evaluate the pore characteristics and seal capacity of shale samples from the Ilaro formation, which could serve as a seal for CO 2 injected into the reservoir units of the eastern Dahomey basin. X-ray diffraction reveals the samples as clay-rich and early diagenetic, while spontaneous imbibition reveals pore connectivity heterogeneity. MICP analysis shows the samples as being characterized by a low breakthrough pressure and reveals the mesopore dominance with majority of pore volumes dominated by 5 to 10 nmsized pore throats. Furthermore, high CO 2 column heights are obtained from conversion of MICP data (at 20% saturation) for mesopore-dominated samples containing ankerite and kaolinite. The study reveals that should injected CO 2 migrate upward from the reservoir units of the onshore eastern Dahomey basin, portions of the Ilaro formation may function as a good seal due to the mesopore mineralogical composition influence on the CO 2 −brine−rock interaction. This result should therefore serve as an important insight for future caprock sealing studies conducted on the onshore eastern Dahomey basin.