Numerical and thermodynamic modeling for estimating production capacity of NW Sabalan geothermal field, Iran

Abstract

In this paper, a new estimate of the power production capacity of the NW Sabalan reservoir is presented based on an evaluation of the recent field data. An improved three-dimensional numerical model (EOS1) was created utilizing the Tough2 simulator code. A rectangular prism with a length of 11.5 km and a width of 8 km (92.9 km) and a depth of 5.11 km is assumed for modeling. Also, 17 horizontal layers were considered for the model, with a layer thickness ranging from 100 to 1000 m, extending from the elevation of -1000 to 4110 masl. The model was validated using temperature and pressure profiles at ten deep exploration wells. The best-fit model of the natural state demonstrated the existence of an upflow of high-temperature fluid in the southern part of the area (with a recharge rate of 108 kg/s). For evaluating and predicting the power production, a thermodynamic model of the single-flash geothermal power plant was developed for the NW Sabalan field. The optimum separation pressure of approximately 5.1 bar was obtained, assuming the quality of the turbine outlet steam is equal to 0.86. At this pressure, the system yields about 31 MW of electricity as a best estimate. Then simulations of four scenarios of 25, 50, 100, and 150 MWe were carried out for 30 years using the TOUGH2 code. The results of the scenarios showed that the main factors controlling the production capacity in the NW Sabalan field are the expected pressure drop and the enthalpy of the produced fluid. This field cannot provide the required enthalpy of the produced fluid for more than 150 MWe. The field can provide enough high enthalpy fluid for a maximum capacity of 114 MWe for 70 years. For this capacity, a limit of 3.125 km2 was identified on the area of the main production zone.