(289c) Permeability and Porosity of Tuscaloosa Mudstone at CO2 Injection Site

Saline formations are promising targets for large-scale geologic carbon storage – likely representing billions of tons of potential resource in the conterminous United States, alone. One such candidate target is the Lower Tuscaloosa Formation into which the Southeast Regional Carbon Sequestration Partnership’s (SECARB) Cranfield Project has injected more than 1 million metric tons of CO₂, into the saline part of the field comprised of primarily sandstones. The Tuscaloosa Formation is generally heterogeneous and composed of gravel, sand, and clay lithologies. In this work, composition, porosity, and permeability of the mudstone samples from the NETL-supported Cranfield Project were studied, before and after exposure to CO₂–brine environment. Specifically, a core sample was exposed to CO₂-saturated brine at the sequestration temperature and pressure for a period of six months. Powdered Tuscaloosa mudstone samples were also studied using optical microscopy and X-ray diffraction (XRD) to observe the mineralogical, textural, and geochemical changes resulting from CO₂-brine exposure.

Two pieces of core extracted from the depth of 3104-3105 m measured 10 cm in diameter and about 9 cm and 13 cm in length, respectively. Core sample densities were measured to be 2.39 g/cc and 2.51 g/cc for the first and second samples, respectively. Porosity and permeability of both samples were characterized prior to their exposure to CO₂-saturated brine; the second sample was subsequently used in the geochemical studies. Exposure of this sample to CO₂-saturated brine led to some chemical alterations and a significant increase in the permeability. Because of the relatively low initial permeability and relative thickness of the Tuscaloosa mudstone, the observed increase in permeability in response to CO₂-brine exposure is likely insufficient to substantially impact the interval’s effectiveness as a natural seal.