Production capacity assessment of the Bacon-Manito geothermal reservoir, Philippines

Abstract

A sustainable production capacity of the Bacon-Manito geothermal system (BacMan) is assessed in this study by three numerical models of different complexity. A base case of 150 MW electrical generation is considered and production is constant up to end of Geothermal Service Contract for BacMan (year 2031). The numerical models considered are based on volumetric, lumped-parameter and a full scale, 3D well-by-well methods. A conceptual reservoir model is first proposed based on previous geoscientific research and downhole data. The geothermal reservoir has an estimated area of 23 km2, its thickness exceeds 1500 m and temperatures range from 240 to 320°C. A volumetric model, using Monte Carlo style simulation, indicates that a production capacity of 200 MWe can be maintained for another 25 years with 90% probability. The lumped model predicts an annual pressure drawdown of 0.67 bars, resulting in a manageable total drawdown of 25 bars in year 2031. For the well-by-well method, a distributed parameter numerical model was developed using the simulator iTOUGH2. The simulator reduces poor matching between observed and simulated response by optimizing a set of 15 model parameters. These include mass and enthalpy of hot and deep recharge and 12 permeability values. Optimization resulted in far-field permeability of 0.5-5 milli-Darcies while the productive wellfield ranges from 25 to 100 milli-Darcies. The deep recharge was calibrated as 98 kg/s of 1830 kJ/kg enthalpy. Sensitivity analyses show that the model is most sensitive to pressure drawdown data followed by enthalpy....