| Title | Reactive Transport Model of CO2 and H2S Mineral Sequestration at the CarbFix2 Reinjection Site, Hellisheiði Geothermal Power Plant, SW-Iceland |
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| Authors | Thomas RATOUIS, Sandra Ósk SNÆBJÖRNSDÓTTIR, Bergur SIGFÚSSON, Ingvi GUNNARSSON, Martin VOIGT, Edda Sif ARADÓTTIR |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | numerical model, toughreact, reactive tranport, geochemistry, carbon storage, climate change, sustainable resource management |
| Abstract | Non-condensable gases are being injected at the Husmuli reinjection site of the Hellisheiði Geothermal Power Plant in Iceland using the CarbFix method to dispose and permanently store CO2 and H2S by underground mineral storage. At current rate, about 10,000 tonnes of CO2 are injected annually along with about 5,000 tonnes of H2S. The injection of CO2 and H2 takes place in the Húsmúli reinjection area and has been an integral part of the operations at the Hellisheiði Geothermal Power Plant since 2014. Coupled modelling of fluid flow and reactive transport using the TOUGH2/iTOUGH2 and TOUGHREACT simulators is being developed to study the injection of dissolved CO2 and H2S in basaltic rocks. The model aims to evaluate the dynamic fluid-rock interactions to identify mineralization processes under reservoir conditions. The target reservoir is an altered fractured olivine tholeiitic lava extending from the Husmuli reinjection site to the Skardsmýrarfjall production zone at depths ranging from -700 to -2000 masl. One-dimensional reactive transport models of the CarbFix injection of a CO2-H2S fluid mixture in the fractured reservoir between the CarbFix reinjection site to the Skardsmýrarfjall production zone are developed. The models were set at an elevation comprised between -700 and -1800 masl where reservoir temperatures range from 220 to 260 °C. The CarbFix injection is modelled by integrating a simple wellbore mixing model with one-dimensional reservoir models at the depth at which the CarbFix fluid enters the host rock. The wellbore model simulation the mixing of the separated water and the gas-charged condensate and the resulting fluid is used as the initial chemistry for the fluid injected in the reservoir models. The average chemistry of the background reservoir chemistry as well as the primary and secondary minerals present in the basaltic reservoir were included in the model as the basis for the reactive chemistry. The simulations use the updated thermodynamic databases for mineral carbonation compiled at the University of Iceland as part of the CarbFix2 project. The simulation results showed successful mineral sequestration of CO2 and H2S under reservoir condition at the CarbFix site. CO2 will mainly be mineralized into calcite and to a lesser extent ankerite and H2S into pyrite. The results also show competition mechanism in form of clays and epidote precipitation. |