The impact of CO2 saturated brine salinity on wormhole generation and rock geomechanical and petrophysical properties

Abstract

Deep saline aquifers are good candidates for CO2 sequestration because of their huge reserves, wide distribution, cost-effectiveness, and relatively high security. The impact of CO2 sequestration on the rock's mechanical and petrophysical properties is a complex issue that depends on a number of factors, such as salinity. This study provides insights into the potential changes in rock petrophysical and geomechanical properties due to the reactivity of CO2-saturated brine with limestone. Specifically, this article provides insights into the impact of salinity on wormhole generation and the corresponding changes in rock properties. Three Indiana limestone samples with a 1.5-inch diameter and 3-inch length, 15% average porosity, and 2 mD average permeability were used. The samples were flooded at 1 mL/min, 2000 psi, and 60 °C with different brine concentrations mixed with CO2 at a 70:30 ratio. To examine the impact of salinity, CO2 was mixed with brine concentrations of 40,000 ppm, 120,000 ppm, and 200,000 ppm for the coreflooding experiments. The samples' Young's modulus (YM) and Poisson's ratio at different confining pressures were measured before and after coreflooding. A medical CT scan was also used to visualize the generated wormholes and quantify their volumes. Results showed that it took only 14.3 pore volumes (PVs) to create a wormhole at 40,000 ppm, while 24.8 and 25.6 PVs at 120,000 ppm and 200,000 ppm, respectively. Lower salinity live brine generated a thicker wormhole compared to the other salinities. The reduction in rock strength in terms of YMs was the highest at 200,000 ppm, followed by the 120,000 ppm and then the 40,000 ppm cases. This study demonstrates that wormhole generation can substantially increase CO2 storage capacity in low-salinity aquifers; however, an increase in CO2 relative permeability indicates that it will accumulate primarily beneath the caprock. In addition, this study reveals that fresh carbonated water or water with a low salinity can be used for acid stimulation.