Effects of Microcracks Closure/Pore Collapse in Ultrasonic Analysis in Carbonates During CO2 Core-Flood Experiments

Abstract

This study evaluates how sample modification promotes ultrasonic velocities increase in laboratory analysis due to porosity collapse/microcracks closure during the buildup pressures related to supercritical CO2 injectivity from offshore carbonate fields in Malaysia. The evaluation considered the significant increase in confinement stress and pore fluid pressure acting on the ultrasonic velocity results. The variation of the effective stresses was also considered. One sample had different stresses conditions evaluated throughout the experiment and the ultrasonic velocities results were compared with sonic log derived compressional velocities. Eight other samples were evaluated for ultrasonic velocities only at the original reservoir conditions. A comprehension of the pore and microcracks behavior under stress during the ultrasonic experiment is conjectured as the sample condition was not directly accessed during the experiment development. A discussion of possible mechanisms for the verified velocities variations is supported by literature data comparison, targeting the causes for such behavior during the experiments.