Observations of carbon dioxide saturation distribution and residual trapping using core analysis and repeat pulsed-neutron logging at the CO2CRC Otway site

Abstract Time-lapse pulsed-neutron well logging has been applied at the CO2CRC Otway site to measure changes in carbon dioxide saturation profiles across an injection interval. Three stages of contrasting saturation were logged: when the formation was fully water saturated; after CO 2 was injected; and after water was injected to drive the CO 2 to residual saturation. This allowed for a unique opportunity to observe changing fluid saturation responding to relative permeability hysteresis at the field scale as part of a controlled experiment. The high vertical resolution of the logs ( 2 saturation were obtained in the upper portion of the 7 m thick injection interval where higher initial CO 2 saturations were reached. In a comparison study with core-scale fluid saturation measurements from the same interval, it was found that the correlation between initial and final saturation from the field measurements gives a similar fit to a Land coefficient derived from the laboratory measurements. Observations of the spatial variation in the trapped gas from both core and logs show that residual trapping is a function of the initial saturation achieved and is sensitive to geological heterogeneity.