T183 Geochemistry of Geologic Sequestration of CO2: Understanding Gas-Water-Mineral Interactions over Wide Temporal and Spatial Ranges (Posters)

Tuesday, 2 November 2010
8:00 AM - 6:00 PM
Hall D

INITIAL CHARACTERIZATION OF MUDSTONE NANOPOROSITY WITH SMALL ANGLE NEUTRON SCATTERING USING CAPROCKS FROM CARBON SEQUESTRATION SITES

Paper number: T183-6
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Geological carbon sequestration relies on the principle that CO2 injected deep into the subsurface is unable to leak to the atmosphere. Structural trapping by a relatively impermeable caprock (often mudstone such as a shale) is the main trapping mechanism that is currently relied on for the first hundreds of years. Many of the pores of the caprock are of micrometer to nanometer scale. However, the distribution, geometry and volume of porosity at these scales are poorly characterized. Differences in pore shape and size can cause variation in capillary properties and fluid transport resulting in fluid pathways with different capillary entry pressures in the same sample. Prediction of pore network properties for distinct geologic environments would result in significant advancement in our ability to model subsurface fluid flow. Specifically, prediction of fluid flow through caprocks of geologic CO2 sequestration reservoirs is a critical step in evaluating the risk of leakage to overlying aquifers.

The micro- and nanoporosity was analyzed in four mudstones using small angle neutron scattering (SANS). These mudstones are caprocks of formations that are currently under study or being used for carbon sequestration projects and include the Marine Tuscaloosa Group, the Lower Tuscaloosa Group, the upper and lower shale members of the Kirtland Formation, and the Pennsylvanian Gothic shale. Total organic carbon varies from <0.3% to 4% by weight. Expandable clay contents range from 10% to ~ 40% in the Gothic shale and Kirtland Formation, respectively. Neutrons effectively scatter from interfaces between materials with differing scattering length density (i.e. minerals and pores). The intensity of scattered neutrons, I(Q), where Q is the scattering vector, gives information about the volume of pores and their arrangement in the sample. The slope of the scattering data when plotted as log I(Q) vs. log Q provides information about the fractality or geometry of the pore network. Results from this study, combined with high-resolution TEM imaging, provide insight into the differences in volume and geometry of porosity between these various mudstones.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under contract DE-ACOC4-94AL85000.