Integration of core sample velocity measurements into a 4D seismic survey and analysis of SEM and CT images to obtain pore scale properties

Abstract

The Scurry Area Canyon Reef Operators Committee (SACROC) field, located in the Permian Basin of West Texas is an enhanced oil recovery (EOR) site into which large volumes of CO2 have been injected. We acquired core samples and 3D seismic surveys from the site in order to better characterize the movement of the CO2 injection plumes. The samples of SACROC reef limestone were used for ultrasonic velocity measurements, detailed mineralogy and Scanning Electron Microscopy (SEM) characterization, Computed Tomography (CT) scanning, thin section studies, and porosity measurements. Using a NER AutoLab 1500 at the National Energy Technology Laboratory (NETL) Core Flow Lab we have measured P and S wave velocities, porosity, and permeability at varying pressures, temperatures, and fluid saturations that simulate reservoir conditions after successive floods. Measurements were also taken with supercritical CO2 at in situ pressures and temperatures. We also modeled the expected velocities for our samples using the standard Gassmann and other rock physics. We created a tool that groups grayscale ranges into three categories, cleans boundaries between groups, and produces a polygon map of the macropores, micropores, mineral grains, and matrix. In addition, the CT and SEM pore maps were analyzed to reveal pore shape statistics. Pore volume, area, and connectivity is essential for chemistry experiments that will emulate time exposure of CO2 to limestone. Further, this analysis technique allows us to obtain pore orientation information, which is important in understanding the anisotropic conditions that may affect seismic data. This multi-scale approach can help to characterize what is occurring inside of the reservoir. Fine scale measurements of how CO2 affects pore-space dissolution can help to inform us of any changes in overall reservoir storage capacity due to changing porosity. Core-scale velocity measurements under in situ conditions will allow us to predict changes in future well log or seismic surveys. Combining microscale, mesoscale, and macroscale information should lead to a better understanding of the various processes at work when CO2 is sequestered in a limestone reservoir.