• Number 341  |
• July 11, 2011

Seeing the Effects of Rock Heterogeneity on CO₂ Movement

All three DOE's National Energy Technology Laboratory X-ray CT scanners were recently used to characterize flow patterns during CO₂ flooding of a sandstone sample from China. This work was part of a U.S.-China Energy Partnership that involves the Chinese Academy of Sciences (CAS), NETL, and PNNL. A delegation of scientists from the CAS brought a core sample from a sandstone formation in the Ordos Basin, China, that is of interest for potential CO₂ storage. NETL’s medical CT scanner and industrial CT scanner were initially used to determine macro-variations in the sample structure, which included visually distinguishable bedding planes. Petrographic analysis of this core revealed that the lighter-colored bedding planes contained a high level of calcite. The figure above left shows the results from the medical CT scanner and industrial CT scanner in the two left-most images. Note the higher resolution that is capable with the new industrial CT scanner.

A small sub-core was analyzed with NETL’s micro-CT scanner to determine the pore scale features of these bedding planes. A region was scanned that contained both a calcite-rich bedding plane and a calcite-lean region next to it. This scan is shown in the right-most image in the figure above. The resolution of this image is 2 microns/pixel and shows that some of the calcite (lighter gray) is not bonded to the sand grains (darker gray) and that there is some porosity (black), even in the calcite-rich region.

A CO₂ flood of a brine-saturated core was then performed in NETL’s medical scanner and the motion of the fluids was captured by multiple scans. The results, shown at left, illustrate that the CO₂ preferentially flowed through the bedding planes that contained less of the calcite in-fill. This multi-scale tomography clearly showed that preferential flow paths existed in the sandstone sample that would impact its use for storage of CO₂. Such information is vital for deciding on the applicability of a formation for storage and helps to guide estimates of what percentage of the pore space could be filled if sequestration were to occur. Combining NETL’s imaging capabilities with traditional core-scale petrographic analysis enables researchers at NETL to characterize samples and understand how they will behave in a CO₂-rich environment.

[Linda Morton, 304.285.4543,
Linda.morton@netl.doe.gov]