Preliminary design study of wellbore heat exchanger in binary optimization for low - medium enthalpy to utilize non-self discharge wells in Indonesia

Indonesia has a large potential in geothermal energy resources. However, the development of the geothermal industry in Indonesia is still focused on high-temperature or high-enthalpy fields. There are 246 geothermal areas in Indonesia which classified into low to medium enthalpy, which is potentially able to be developed with binary system. In this paper, an experimental design was studied by modifying the Organic Rankine Cycle at the wellhead generating unit. This design utilizes non-self-discharge wells to be used as "heat exchanger" where the working fluid is pumped into the well through a U-pipe and heated by the geothermal fluid. The outflow of the working fluid from the U-pipe is expected to be steam-phased and directly flowed into the turbine. Several working fluids have been studied to determine maximum power generation at a certain reservoir temperature. In this study, pressure and temperature profile of well XX-02 is used for case study. XX-02 is non-self discharge well and medium temperature-water dominated reservoir.The working fluids evaluated were Isobutane, Propane, Isopentane, and Butane. The maximum generation output was found in Isobutane and Butane with generation output 294 kW and 241 kW respectively, and flow rate needed was 5 kg/s. This un-significant generation give flexibility in working fluid selection. Sensitivity analysis of the temperature decline from near wellbore was conducted to evaluate the feasibility of the design for 30 years project lifetime. Economics analysis was also have been done to study the feasibility of the design and electric price produced. ORC (Organic Rankine Cycle) price used in economic analysis is the average price of ORC (3,000 USD/kWh), resulting electricity price produced is 7.76 USD cents/kWh. This result conclude that Wellbore Heat Exchanger design is feasible to improve non-self discharge well to be economically developed.