[H-RE12] New Developments in Engineering Geology

[HRE12-03] Feasibility study on geothermal power generation system by CO₂ circulation

*Hiroshi Suenaga¹, Yoshinobu Nakao¹, Toshiaki Fukada¹ (1.Central Research Institute of Electric Power Industry)

Keywords:Carbon dioxide, Geothermal Power, Laboratory test, Numerical simulation, Feasibility study, Generated energy

Three types of method exist to extract geothermal heat with CO₂ circulation: a coaxial method to circulate CO₂ inside and outside of a duplex tube in a well, a closed-loop method to circulate CO₂ in a looped well connected an injection well and a production well at the bottoms, and an open-loop method to circulate CO₂ in an injection well, reservoir rock, and a production well. For a closed-loop and an open-loop methods, numerical simulation models were constructed to calculate water and CO₂ flow in reservoir rock and drilled wells and applied them to Ogachi and Hijiori site where hot dry rock (HDR) research was conducted in the past. As a result, suitable conditions for the geothermal power system by CO₂ circulation could be found using the numerical simulation models to acquire high thermal power at the Hijiori site where showed the deeper reservoir depth and higher bottom hole pressure than the Ogachi site. A generated energy prediction method for the geothermal power generation system by CO₂ circulation was also constructed to calculate the generated energy for the combined cycle of CO₂ turbine and binary generator at the Hijiori site.
Laboratory experiments which simulate the geothermal power system by CO₂ circulation were conducted in this study. As a result, thermosiphon phenomena in which CO₂ could circulate in the looped pipe spontaneously caused by its density with temperature were demonstrated within injection pressure of 8 – 18 MPa and reservoir temperature of 75 – 200 degree-C. The results of the laboratory experiment were also reproduced by using the numerical simulation model.