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

Abstract

One solution to attain net zero CO2 emissions is the sequestration of CO2 in subterranean formations. Deep limestone saline aquifers provide excellent storage sites for CO2 due to their high solubility in water and vast aquifer volumes. This study investigates the potential changes in rock petrophysical and geomechanical properties caused by the reaction of carbonated brine (CO2+brine) and limestone rock, as well as the effect of temperature on wormhole generation. Three samples of Indiana limestone (100% calcite) with dimensions of 1.5 inches in diameter and 3 inches in length, 15% average porosity, and 2 mD average permeability were used. The samples were flooded at 1 mL/min and 2000 psi with a carbonated brine consisting of total dissolved salts of 120,000 ppm. To evaluate the effect of temperature on limestone-carbonated brine reaction at CO2 underground storage conditions, the experiments were conducted at three different temperatures (35, 60, and 85 °C). The samples' Young's modulus and Poisson's ratio at different confining pressures were measured before and after carbonated brine coreflooding. Additionally, we used a medical Computed Tomography (CT) scanner to visualize the created wormholes and quantify their volumes. We observed the generation of a wormhole in each of the experiments after 19.7, 26.7, and 46.9 pore volumes (PVs) of CO2-saturated brine were injected at 35 °C, 60 °C, and 85 °C, respectively. Moreover, the lowest temperature treatment created a straight wormhole with less void volume compared to the other temperatures. Wormhole generation at 85 °C showed the largest reduction in rock strength in terms of Young Moduli (YMs) than the other experiments despite showing the lowest reactivity. To the best of our knowledge, this is the first study to reveal the impact of temperature on wormhole generation due to the injection of CO2-saturated brine in limestone. This study also demonstrates that wormhole generation increases CO2 storage capacity; however, CO2 relative permeability increases, implying that CO2 will flow faster and accumulate primarily underneath the caprock. Furthermore, before injecting CO2, the well integrity in hotter carbonate reservoirs should be thoroughly examined. Conversely, this study reveals that CO2 or carbonated water could be utilized for acid stimulation.