Reinjection of CO2 in Geothermal Fields

Abstract

In this study, reinjection of NCGs (non-condensable gases) released from geothermal plants was investigated. NCGs are formed mainly CO2 ( more than %98). The purpose of this study is to protect environment, prevention of geothermal plants from being subject to the carbon tax and providing them take a share from the carbon reduction revenues by injecting NCG into geothermal reservoir with reinjected water. Furthermore, it was observed during this research and studies that productivity of the wells will be reduced with a decrease in partial pressure of NCG in the reservoir for fields emitting NCG, even if the reservoir pressure and temperature are maintained. In this way, it was seen that reinjection of NCG into the geothermal reservoirs will make a major contribution to the sustainable production as well as the environmental protection. Here, unlike many carbon capture projects, CO2 is not injected into the reservoir in gas phase, but after dissolved in the reinjected water. In the study, NCG released into the atmosphere from the geothermal plant is injected into the water injected via a compressor and, then, injected into the injection well by compressing it up to a value above the dissolution pressure. As a case study, Dora-II with 11.7 MW binary power plant’s wells examined and investigated what would happen when CO2 reinjected into the reservoir by using a TOUGH2 modelling. Increased pressure in the injection wells increases the pumping and compressor operating costs. To decrease operating costs and reinjection pressure, it is the most cost-effective solution to solve all NCG to be injected in the injected water. In case this study is implemented in geothermal fields, the geothermal plants emitting carbon dioxide will take carbon reduction revenue and not pay carbon tax and, furthermore, since partial pressure of carbon dioxide is maintained, it will be possible to generate much more energy on the field by preventing reduction of productivity of wells.