Dual Porosity Models of a Two-phase Geothermal Reservoir

Abstract

The research reported here is part of a general study aimed at determining when dual-porosity models should be preferred ahead of single porosity models for modelling geothermal systems. The Mt. Apo geothermal reservoir, in Mindanao, Philippines, was simulated using both single and dual porosity (MINC) models and inverse modelling was used to estimate rock parameters such as permeability and porosity. The forward simulations were carried out with AuTOUGH2 (O\'Sullivan, 2000), a modified version of TOUGH2 (Pruess, 1991) while the inverse problem of determining the best-fit parameters for the dual natural-state and production history model calibration was solved using PEST (Doherty et al., 1994). The data for calibration were steady-state temperatures and pressure, and average monthly enthalpy transients for 16 years The results were compared for a single porosity model and various dual porosity (MINC) models with the aim of determining whether or not one type of model clearly fitted the data better than the others.