Reinjection of cooled water into sandstone geothermal reservoirs in China: a review

Abstract

Low injectivity of sandstone geothermal reservoirs during reinjection of geothermal waste water is a problem generally encountered in China, and has become a main obstacle for sustainable development of the geothermal resources. Over the last few decades, researchers have made much efforts to solve it based on the studies of reinjection schemes, hydrogeology of the reservoirs, well completion, reinjection water disposal techniques, and water-rock interactions focused on precipitation/dissolution reactions during reinjection. These studies have been very helpful in improving the injectivity. However, there are still many problems remaining for further investigations, among which characterization of the complete process of water-rock interactions during reinjection with the change in redox conditions, CO2 partial pressure, non-isothermal transport process of the reinjection water, and the mechanism of release, transport and sedimentation of colloidal particles on reservoir permeability being taken into account are considered to be the most necessary. This paper gives a brief review of the history and state of the art of the research works on reinjection of cooled water into sandstone geothermal reservoirs, and outlooks the research demands in water-rock interactions during reinjection in the future.