Description of Geothermal Reservoir Simulator "NSCGREATS" and a Preliminary Simulation of the Kirishima Field

Abstract

A numerical simulator for geothermal reservoirs(NSCGREATS) is presented, that includes sub-simulator for flow in geothermal wells. The flow in reservoir is expressed on the basis of mass and energy transport i n porous media. The flow toward the well in the wellblock are treated as a steady horizontal radial flow. The vertical flow i n geothermal wells is expressed by a new set of correlations. Its details are presented in another paper by the author in these proceedings. NSCGREATS has been applied to a preliminary simulation of the Kirishima geothermal field. The simulation revealed several mechanisms at work in the transition of the reservoir. The important mechanisms are: (1) steam/ water counterflow which forms a steam cap in shallow levels but remains liquid water a t deep levels, and (2) recharging from outside of ,the reservoir which compensates for production to a considerable extent. It has been predicted by the simulation that an enthalpy Qf 1500 GJ/h may be produced by wells drilled a t intervals of 20Om in a main fault wne having a length of 1.2Km. However, further investigations into the deep levels i n the field are necessary to make more accurate prediction, since production depends strongly on recharging from the fluid source deep below the reservoir.