Wang, Tokunaga Win ACS Editors’ Choice Award2 min read

Source: Shibo Wang, Tetsu Tokunaga, and Dan Hawkes

ESD scientists Shibo Wang and Tetsu Tokunaga recently won an American Chemical Society (ACS) Editors' Choice Award for their paper on supercritical CO₂-brine capillary pressure-saturation relations in limestone sands. The Editors’ Choice award is given by ACS to new research of importance to the global scientific community. These peer-reviewed, open access articles consist of research that exemplifies the ACS commitment to improving people's lives through the transforming power of chemistry. This particular work was done through the Center for Nanoscale Control of Geologic Carbon (NCGC), a DOE Energy Frontier Research Center led by LBNL-ESD.

As Wang and Tokunaga describe in their paper, published online this past week (May 6, 2015) in Environmental Science & Technology, geologic carbon sequestration (GCS) relies on understanding and predicting CO₂ interactions with saline reservoirs and caprocks.

In GCS, pressure differences between the injected supercritical carbon dioxide (scCO₂) and native water control the saturations of both phases in reservoir pore spaces. This pressure difference, termed the capillary pressure (P_c), is related to water saturation (S_w), because it depends on the wetting behavior and wetting history of the rock formation (water drainage versus imbibition). Capillarity and its hysteresis in porous media have been extensively studied in water-air and water-oil systems, but few measurements have been reported for scCO₂-water.

Wang and Tokunaga studied P_c-S_w relations of scCO₂ displacing brine (drainage), and brine rewetting (imbibition), to understand CO₂ transport and trapping behavior in carbonate reservoirs. Drainage and imbibition P_c-S_w curves were measured in limestone sands at 45˚C under elevated pressures (8.5 and 12.0 MPa) for scCO₂-brine, and in limestone and dolomite sands at 23˚C (0.1 MPa) for air-brine, using a new computer-programmed porous plate apparatus. Measured large shifts in scCO₂-brine drainage and imbibition curves to lower Pc relative to predictions, based on pore size and surface tension, showed that the water wettability of the limestone was significantly reduced. Amounts of trapped scCO₂ were about three times larger than for air, and increased with pressure (depth), initial scCO₂ saturation, and time.

These results have important implications for scCO₂ distribution, trapping, and leakage potential, and have motivated further experiments on capillary behavior under reservoir conditions.

Congratulations, Shibo and Tetsu!

To read the paper, go to: http://pubs.acs.org/doi/abs/10.1021/acs.est.5b00826

Citation:  Wang, S., and T. Tokunaga (2015), Capillary pressure–saturation relations for supercritical CO₂ and brine in limestone/dolomite sands: Implications for geologic carbon sequestration in carbonate reservoirs.  Environmental Science & Technology, DOI: 10.1021/acs.est.5b00826.