Numerical Evaluation of Production Performance of Chingshui Geothermal Reservoir

Abstract

The Qingshui geothermal power plant was built in 1981 which was one of the representatives of geothermal development in Taiwan. However, the power plant was decommissioned in 1993 due to continued decline in production. Although some geothermal exploration and field tests had been exercised in the past, the production potential of Qingshui geothermal reservoir is still not well understood. The main purpose of this study is to investigate the reasons of production declination and evaluate performance of the Chingshui Geothermal plant through numerical modeling approach. In this study, a refined grid model was constructed for assessing the responses of the reservoir system under different production conditions and the influence of formation scaling on the well productions. The model integrated detailed geological features of the site. A wide variety of field measurement data were incorporated into the three-dimensional numerical model through model calibration. The model was first calibrated by adjustment of inflow rate from model bottom boundary until a good match obtained with the natural state condition. Inclusion of CO2 in the model as observed in the field has shown further improvement in simulation results. The calibrated model was then used to simulate the production history during 1981-1993. With the model, we intend to investigate the impact of availability of water resource on the production well performance. Moreover, the influence of formation scaling on well production was modeled through reduction of permeabilities at the skin zone surrounding the production wells. Simulation results confirm that the production failure of the Chingshui Geothermal plant is mainly due to the formation scaling. With the developed high definition model, we are able to calculate amount of total geothermal resource in place, optimize the design of reinjection and production schemes, investigate approaches for preventing formation scaling, and further re-evaluate the feasibility of resuming commercial exploitation of the Chingshui geothermal system.