Sustainable Production Assessment of the Bacon-Manito Geothermal Reservoir, the Philippines

Abstract

Sustainable production capacity of the Bacon-Manito geothermal system (BacMan) is assessed by two models of different complexity. Base case of 150 MW electrical generation is considered and constant production up to end of Geothermal Service Contract for BacMan (year 2031). Models considered are based on the lumped-parameter and a full scale, 3D well-by-well methods. Conceptual reservoir model is 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 240C to 320C. 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 to 5 milli-Darcies while the productive wellfield ranges from 25 to 100 milli-Darcies. Stable enthalpies of production wells are predicted for the 23 years studied, indicating that reservoir temperature drawdown will be moderate. Instead of predicting reservoir performance for tens or hundreds of year, it was decided to stop production in year 2031 and monitor recovery of heat and mass reserves using lumped and distributed parameter models.