Impact of Salinity and Temperature on Wormhole Generation Due to CO2 Sequestration

Abstract

Abstract Deep saline aquifers are good candidates for carbon dioxide (CO2) sequestration. The reaction between the CO2 gas and the saline water aquifer creates carbonic acid (live brine) that reacst with the formation rock to generate wormholes. As a result, the rock mechanical properties will be altered. The goal of this study is to understand the impact of salinity and temperature on creating wormholes due to live brine injection. Limestone core samples (1.5 × 3 inches) with a permeability of 2 – 4 mD and 15-17% porosity values were selected to perform the study. Coreflooding experiments were performed, after which the samples were scanned to observe the wormhole generation and the change in the pore structure. Carbon dioxide was mixed at 2,000 psi with a ratio of 30% CO2 to 70% brine to formulate a live brine. The live brine was injected into the rock samples at different temperatures (35 °C, 60 °C, 85 °C). Also, CO2 was mixed in the brine width with different salts concentrations (40,000 ppm, 120,000 ppm, 200,000 ppm), which were then injected into the rock samples to test the impact of salinity. The mechanical properties of the samples before and after wormhole generation were studied using impulse hammer and acoustics. The injection of the live brine generated wormholes in all low-permeability rock samples. Due to the wormhole's generation, the rock samples' porosity and permeability increased significantly. The time to generate the wormholes has a positive relationship with the salinity and temperature. For instance, it took around 5.5 hrs of live brine injection at 1 cc/min to create a wormhole at 35 °C, while it took more than 10 hrs at 85 °C. Similarly, it took only 3 hrs to generate womrhole in the low salinity samples while double the time for the high salinity ones. This research's novelty stems from its application to CO2 sequestration by investigating the salinity and temperature of saline aquifers. These two parameters are significant ones that distinguish aquifers. This is the first study to understand the impact of salinity and temperature on wormhole generation due to CO2 sequestration.