Caprock characterization of Upper Jurassic organic-rich shales using acoustic properties, Norwegian Continental Shelf

Characterization of Upper Jurassic Organic-Rich Caprock Shales in the Norwegian Continental Shelf

“…The studied areas, i.e., the Barents Sea and the North Sea, share similar depositional and structural setups. Yet, there are substantial differences, mainly in the Cretaceous-Cenozoic burial history and exhumation [35,40,41]. All the provinces in NCS are dominated by NW-SE-oriented rifting, followed by rapid subsidence, siliciclastic deposition, infill, and the draping of rift topography in the Early Cretaceous.…”

“…However, in the Late Cretaceous, regional transgression and deposition of thick carbonate sequence characterized the North Sea, while time-equivalent marine deposits are highly condensed because of uplift, erosion, and non-deposition within the Barents Shelf deposits. Rock properties are affected by Cenozoic uplift and erosion in the entire NCS region; however, the Barents Sea area has experienced multiple episodes and maximum net erosion, estimated to be around 1-1.2 km in the Goliat Field area and approximately 2 km in the Hoop area [35,[41][42][43]. Net uplift in the central North Sea is estimated to be from zero to 0.7 km, while 0 to 1.3 km uplift is assessed in the northern North Sea area [44][45][46].…”

“…An effective caprock shale has very low matrix porosity and permeability [3,11,32,33]; hence, very high capillary entry pressure prevents fluid from escaping. However, leakage may occur if the permeability is sufficiently high or injection-induced pressure-driven caprock fracturing occurs [34][35][36]. Shear failure or the fracturing of seal rock occurs when shear stress exceeds shear strength and is controlled by the brittleness of that rock [37].…”

Top seal assessment of Drake Formation shales for CO2 storage in the Horda Platform area, offshore Norway

“…It is also unlikely to have caprock failure due to capillary breakthrough because of the low permeability in most shales. Instead, pore-pressure-driven fracturing and fault reactivation are likely scenarios regarding fluid escape/leakage from the storage sites (Bjørlykke et al, 2015;Hansen et al, 2020;Ingram et al, 1997).…”

“…Therefore, it is crucial to characterize shale brittleness property to evaluate caprock integrity. However, the brittleness property, which is also classified as fracability (Holt et al, 2015(Holt et al, , 2011Jin et al, 2014;Rybacki et al, 2016;Wang and Gale, 2009;Yang et al, 2013), is a complex function of rock strength, lithology, texture, effective stress, temperature, fluid type (Handin et al, 1963;Handin and Hager, 1957;Nygård et al, 2006), diagenesis, TOC type, amount and maturation (Walles, 2004;Hansen et al, 2020), natural fractures and other planes of weakness (Gale et al, 2007;Zhang et al, 2016;Johnson et al, 2022), etc. There is no firm definition of the brittleness indices; instead, different quantifying methods have been employed (e.g., Fawad and Mondol, 2021;Grieser and Bray, 2007;Guo et al, 2012;Josh et al, 2012;Kivi et al, 2018;Liu et al, 2020;Mondol et al, 2022;Rickman et al, 2008).…”