2006 Volume 28 Issue 1 Pages 19-36
A numerical simulation was conducted to evaluate the Appi reservoir under the Geothermal Promotion Survey project of NEDO between 2000 and 2003 fiscal year. To estimate an electrical generation potential, we constructed an adequate numerical model based on the conceptual model, and predicting a production performance due to field operation using that model, leading to the following findings. 1. Permeability is estimated to be 2.5×10-15m2 for higher formations, 0.25×10-15m2 for lower ones, and 0.02×10-15m2 for the lowest ones based onpressure interference tests. Such low permeabilities were required to reproduce conductive temperature profiles observed at the Appi field. 2. Conductive heat flow of 0.5Wt/m2 was assigned in the southern part of the grid bottom blocks, and upflow of steam with 2, 700kJ/kg internal energy and 0.6kg/s rate in two bottom blocks around Mt. Appi-dake to obtain a good match between observed and calculated temperature profiles. Total recharge rates of energy are 8.125MWt and 1.62MWt from conduction and convection. respectively, which indicates conductive-dominated heat transport at the Appi. 3. Simulations of production performance were carried out for several operation scenarios. It was estimated that the geothermal reservoir in the Appi field is capable of generating 20MWe for 30 years by a single flash power generation system. 4. Although steam discharge without liquid water was recognized under a long term production test, the simulation results predict small amount of water discharge from a few production wells after several years of operation. It is considered that the distribution of two phase region is limited in the southwestern area and decrease of reservoir pressure associated with steam production causes liquid water around the two phase region to migrate into production area.
