Alterations to unconfined compressive strength in limestone cores due to injection of carbon dioxide at supercritical conditions

For decades, carbon dioxide has been used in the petroleum industry for enhanced oil recovery (EOR) to increase oil production from nearly depleted fields. Recent issues associated with climate change have raised concerns about atmospheric concentrations of "greenhouse" gases, mainly carbon dioxide. Long-term geological sequestration of carbon dioxide (CO2) into underground formations has been identified as one way to mitigate atmospheric concentrations of CO2. In the near future, possible regulations on CO2 emissions may provide economic motivation for using CO 2 in EOR or sequestration operations.;When CO2 is injected into underground formations, the carbon dioxide reacts with the formation water producing carbonic acid. The carbonic acid reacts with carbonate formations by dissolving the rock. The effect of this dissolution on the compressive strength of carbonate rocks has not been extensively studied.;This research examines the compressive strength changes due to CO 2 injection in the presence of reverse osmosis (R/O) water. Forty Indiana limestone cores were used for the experiment. Two groups of 10 cores were subjected to carbon dioxide at two different flow rates (high flow rate of 1.0 cc/min; low flow rate of 0.5 cc/min). Two groups of 10 cores were used as control groups (no CO2 injection), one of which was saturated with R/O water and then dried, and the other control group remained dry.;The groups subjected to CO2 experienced a minor loss of peak compressive strength. However, the results showed the dissolution of the rock matrix was not sufficient to significantly reduce the compressive strength of the Indiana limestone. The CO2 exposure did cause changes to the core's permeability values, which could affect CO2 injection during EOR or sequestration operations.