Novel chemical stimulation for geothermal reservoirs by chelating agent driven selective mineral dissolution in fractured rocks

Abstract

Improving geothermal systems through hydraulic stimulation to create highly permeable fractured rocks can induce seismicity. Therefore, the technique must be applied at a moderate intensity; this has led to concerns of insufficient permeability enhancement. Adding chemical stimulation can mitigate these issues, but traditional methods using strong mineral acids have challenges in terms of achieving mineral dissolution over long distances and highly variable fluid chemistry. Here, we demonstrate a novel chemical stimulation method for improving the permeability of rock fractures using a chelating agent that substantially enhances the dissolution rate of specific minerals to create voids that are sustained under crustal stress without the challenges associated with the traditional methods. Applying this agent to fractured granite samples under confining stress at 200 °C in conjunction with 20 wt% aqueous solutions of sodium salts of environmentally friendly chelating agents (N-(2-hydroxyethyl)ethylenediamine-N, N′, N′-triacetic acid and N, N-bis(carboxymethyl)-l-glutamic acid) at pH 4 was assessed. A significant permeability enhancement of up to approximately sixfold was observed within 2 h, primarily due to the formation of voids based on the selective dissolution of biotite. These results demonstrate a new approach for chemical stimulation.

Reactivity and Dissolution Characteristics of Naturally Altered Basalt in CO2-Rich Brine: Implications for CO2 Mineralization

“…Furthermore, the groundwater in the potential CO 2 storage site usually contains significant amounts of divalent cations, which potentially impedes the leaching of more cations from rocks due to the dissolution/precipitation equilibrium. To overcome these challenges and vary the dissolution/precipitation equilibrium, recent studies, including our previous work, have demonstrated that the incorporation of additives, such as chelating agents, can effectively enhance mineral dissolution by selectively extracting metals. , The utilization of such advanced approaches should also be considered for the advancement of the CO 2 mineralization technology.…”

“…To overcome these challenges and vary the dissolution/precipitation equilibrium, recent studies, including our previous work, have demonstrated that the incorporation of additives, such as chelating agents, can effectively enhance mineral dissolution by selectively extracting metals. 44 , 45 The utilization of such advanced approaches should also be considered for the advancement of the CO 2 mineralization technology.…”

Velocity-dependent heat transfer controls temperature in fracture networks

“…These changes in the hydraulic behavior of a reservoir can also benefit geothermal exploitation, as flow paths inside the fracture network might become altered so that thermal exploitation in previously neglected parts of the reservoir is increased. Clogging and opening of fractures can also be triggered through anthropogenic stimulation techniques 38 , 39 and might provide future optimization techniques for geothermal reservoirs.…”

CO2 Injection-Induced Shearing and Fracturing in Naturally Fractured Conventional and Superhot Geothermal Environments

“…Second, the resulting fractures within the CFN have narrow apertures in both conventional and superhot geothermal environments, reducing their potential to provide additional connections for the natural fractures. Therefore, further stimulation, such as a longer pressurization duration (Goto et al 2021) or the use of chemical stimulation to dissolve rock-forming minerals at conventional geothermal temperatures (Watanabe et al 2021b), may improve the permeability of the CFN. Third, the low viscosity of CO 2 may also impose challenges during field-scale operation: CO 2 could flow far within the natural fracture network, especially under conventional geothermal conditions, such that increasing the pressure is difficult.…”