Experimentally determined rock physics properties, MicroCT to reservoir scale.

Summary In order to monitor a CO2 injection site with seismic surveying, the dynamic rock matrix must be thoroughly understood. To assist in this understanding, we present our approach to upscaling micro-scale rock matrix properties to reservoir scale and seismic velocity ranges based on theoretical rock wave propagation models and show the richness of useful data produced by micro computed tomography (µCT). We have acquired and processed µCT images of limestone samples to gain understanding of 3-D pore orientation, pore volume distribution and pore surface area geometry at a resolution of 1.3 to 3.9 microns. By comparing µCT scans from before and after timed CO2 exposures, rock density, and pore volume changes are quantified. In an 18.5% porosity limestone sample, our analysis identifies and describes over twelve thousand pores in a 26 cubic millimeter volume at 4X zoom (3.9 micron/pixel). By observing available reactive surface area of the porosity and mass change over a series of time increments and comparing results to chemical model predictions, we refine limestone-CO2 interaction models to predict how, over time, a carbonate reservoir will change due to storage of CO2. This porosity and density change model will be applied to a larger-scale reservoir model that detects the presence of CO2 density signatures. This application will be implemented to produce theoretical seismic volumes of uncompromised future reservoirs that can be compared to repeat surveys for leak detection.