Rock physics and petrophysical evaluation of diagenetic effects in the Broom Creek CO2 sequestration site

Abstract

The Pennsylvanian–Permian Broom Creek Formation, a deep saline aquifer in the Williston Basin, North Dakota, is an important target for large-scale CO${}_2$ sequestration. Preserving long-term CO${}_2$ storage integrity in this reservoir hinges on a systematic assessment of how geological and diagenetic processes modify rock properties. This study investigates the impact of diagenetic alterations on the elastic properties of the Broom Creek sandstone through an integrated rock physics modeling approach. Multi-mineral petrophysical evaluation was conducted using geophysical well logs calibrated with X-ray diffraction and cuttings data. Rock physics models, including the contact cement, soft-sand, and stiff-sand models, were employed to establish diagenetic trends in compressional wave velocity and porosity space. Velocity-porosity trends and mineral volume fractions data were then used to quantify the contributions of contact cement and pore-filling materials to the rock framework. The findings reveal Upper Broom Creek eolian quartz arenite deposits exhibit diagenetic contact cementation by quartz overgrowths and dolomite, which stiffen the rock matrix while preserving porosity and permeability. In the lower, near-shore sandstone intervals of the formation, quartz overgrowths and dolomite cementation persist, but pore-filling anhydrite and clay dominate as non-contact cements. These results provide understanding into the mechanical properties of the reservoir and the role of diagenesis in modifying porosity and stiffness. The study’s outcomes are useful for modeling CO${}_2$-brine-rock interactions and evaluating the long-term stability and effectiveness of CO${}_2$ sequestration in the Broom Creek Formation.