| Title | NUMERICAL MODELLING OF THE INTERACTION BETWEEN BRINE-NCG SOLUTIONS AND GREYWACKE |
|---|---|
| Authors | D.E. Altar, E. Kaya |
| Year | 2018 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Carbon dioxide, hydrogen sulphide, NCG, co-injection, TOUGHREACT, modelling, brine, fluid-rock interaction, chemical kinetics |
| Abstract | Global warming as an impact of human activities is a widely accepted theory. It is imperative that greenhouse gas (GHG) emissions be reduced as early as is practicable, especially in the energy production sector. For the geothermal power sector, it is important to explore alternative disposal technologies for GHG emissions in place of the common practice of releasing the separated non-condensable gases (NCG) into the atmosphere. One alternative which has received widespread focus is geologic sequestration, or the injection of NCG deep into the earth. Co-injection of NCG with the reinjected fluids (i.e. brine and condensate) is considered a prime option compared to supercritical injection. Another potential impact of the co-injection of NCG is pH-lowering which may lead to reservoir permeability stimulation. In theory, the increased acidity of the resulting solution will dissolve minerals in the formation, improving permeability, or even creating new permeability zones over time. GNS Science conducted a series of experiments on the interaction of brine with greywacke. In 2015, Passarella et al. simulated the interaction between brine with dissolved CO2 and H2S, and a sample of greywacke from the Waotu quarry in South Waikato. To investigate the physicochemical processes of NCG-brine-reservoir rock interaction and quantify the effect of NCG on petro-physical properties of geothermal reservoirs it is necessary to carry out numerical simulations. This work aimed to simulate the results from the experiments of Passarella et al. (2015) with the use of TOUGHREACT. The goal of the study is to develop numerical simulation techniques to model and understand the effects of the reinjection of brine with dissolved NCG. The resulting model provided insights into the geochemical behaviour of greywacke-brine-NCG under reservoir conditions and impacts of this interaction on permeability and porosity. The numerical simulation also assesses the evolution of mineral reactive surface areas as a result of the degree of dissolution and injection flow rate, and investigates the potential for NCG sequestration. |