Soft-stimulating Injection Procedures to Improve Geothermal Reservoir Performance

Abstract

Geothermal plants may face a large variety of operational problems caused by scaling, particle clogging and inefficient injection strategies. Flow obstruction is well known in surface facilities and wells but difficult to observe and mitigate in the reservoir. A key challenge in geothermal energy production is the decline of injectivity over time. Rather than diverting to harsh reservoir fracking to improve injectivity we aim to develop gentle and low-cost techniques to overcome low injectivity. The technologies include thermal and CO2-(re)injection soft-stimulating injection procedures. Cooling of water and gas exsolution during geothermal energy production disturbs the chemical equilibrium of the water, frequently causing scaling (mineral precipitation). Alternatively, similar chemical and physical changes of the produced water may result in mineral dissolution, improving reservoir flow properties. Mineral (e.g. calcite) dissolution could be stimulated by both cooling and increasing the dissolved CO2 content. The effects of thermal and CO2-(re)injection soft-stimulation on the geothermal reservoir are assessed with reactive transport simulations with TOUGHREACT software and laboratory batch experiments. Experiments are performed with both the produced water and the original cuttings of a Dutch geothermal well targeting the Delft sandstone. A field-scale model is developed using site data on water, gas and rock compositions, pressure and temperature conditions and flow properties. Ultimately, optimization of production and injection procedures is crucial for good flow and injectivity would create more energy output and improve cost-effectiveness.