Production capacity estimation by reservoir numerical simulation of northwest (NW) Sabalan geothermal field, Iran

A three dimensional numerical model of the northwest (NW) Sabalan geothermal system was developed on the basis of the designed conceptual model from available field data. A numerical model of the reservoir was expressed with a grid system of a rectangular prism of 12km×8km with 4.6km height, giving a total area of 96km². The model has 14 horizontal layers ranging in thickness between 100m to 1000m extending from a maximum of 3600 to -1000ma.s.l. Fifteen rock types were used in the model to assign different horizontal permeabilities from 5.0×10^-18 to 4.0×10^-13m² based on the conceptual model.Natural state modeling of the reservoir was performed, and the results indicated good agreements with measured temperature and pressure in wells. Numerical simulations were conducted for predicting reservoir performances by allocating production and reinjection wells at specified locations. Three different exploitation scenarios were examined for sustainability of reservoir for the next 30 years. Effects of reinjection location and required number of makeup wells to maintain the specified fluid production were evaluated. The results showed that reinjecting at Site B, immediate adjacent to production zone, is most effective for pressure maintenance of the system.On the base of existing data and assumptions the reservoir can sustain producing fluid equivalent to 50MW_e of electricity for more than 30 years. The reservoir can produce the maximum amount of fluids equivalent to 90-100MW_e for only 5 years, but the production capacity decreases to 50MW_e after 20 years of operation because of pressure and enthalpy drop. The reservoir can sustain 50MW_e over 100 years that can be defined as a sustainable production level of the field.