Mechanical Stratigraphy and Properties for Saudi Arabia's Jurassic Reservoir - Caprock Sequences: Implications to CO2 Storage and Seal Integrity

ABSTRACT: Jurassic reservoir-caprock sequences in Saudi Arabia play a critical role in both hydrocarbon systems and future CO2 storage, where long-term structural trapping relies on the hydraulic and mechanical integrity of the caprock. This work provides a mechanical characterization of these sequences, including the Manifa, Hith, and Arab A, B, and C formations. This paper focuses on a 210-meter continuous near outcrop core section from the Jurassic Sulay, Hith, and Arab formations in Saudi Arabia, marking the first published comprehensive and continuous petrophysical and rock mechanical analyses of this sequence. A series of laboratory measurements including scratch and ultrasonic tests as well as triaxial loading tests were conducted to evaluate petrophysical properties, assess mechanical stratigraphy, and determine brittle-ductile transition with a particular focus on the evaporite (anhydrite) layers, the seals. Additionally, facies and geochemical analyses were conducted to link depositional environments and mineral composition with mechanical properties. The results reveal significant variation in strength and stiffness across the formations, with a strong correlation between mechanical stratigraphy and facies. The brittle-ductile transition mapped within the core presents critical implications for the caprock hydro-mechanical integrity during CO2 injection. Ultimately, these findings offer key insights into the mechanical behavior of evaporitic seals and strategies for safe CO2 injection and permanent storage.