Development of Technique for the Coupled Simulator of Reservoir, Wellbore, and Fluid-Gathering Pipeline Networks to Provide Optimum Operation and Management of Geothermal Power Plant

Abstract

The mass flow rate of steam transported into a turbine for geothermal power plant is controlled by the discharge characteristics of production wells and their wellhead pressures, which are, in turn, influenced by not only reservoir properties, but also pressure loss occurred along pipelines during transportation. In order to calculate the pressure loss in the pipeline network a fluid-gathering pipeline simulator named TPGS (Two-Phase Gathering System), which treats the pipeline network, has been developed. In addition, a simulation method to individually couple a wellbore simulator and a fluid-gathering pipeline simulator to a reservoir simulator has been constructed to predict the generating power output. TOUGH2, MULFEWS, and TPGS are the reservoir, wellbore, and fluid-gathering pipelinesimulators, respectively, used for the coupled simulation. This method was applied to predict changes of power output of the Hatchobaru power plant, Japan, overtime. The simulation includes a total length of 4.7km pipeline networks. Predicted changes of power output gave good agreement with the actual power decline trend, meaning the successful coupling of three simulators. Furthermore, the decrease in wellhead pressures and discharge rates of some production wells due to reservoir cooling was predicted. On the other hand, both simulated pressures at wellheads of production wells and at interconnection pipelines were predicted to besmaller by 20% than the actual pressures. This shows that the pressure losses atpipelines calculated by TPGS are underestimated. It is concluded, therefore, that values of surface roughness of the pipelines and correction factors for calculating pressure losses at fittings of pipelines requires some modification to increase the accuracy for TPGS.