Simulation of the Habanero Enhanced Geothermal System (EGS), Australia

Abstract

A TOUGH2 reservoir model has been developed for the Habanero EGS, located in the Cooper Basin. The reservoir, interpreted to be the sub-horizontal Habanero fault, was defined by the extent of the stimulated seismic cloud. A 1D natural state model was used first to calibrate the rock properties: specific heat capacity, thermal conductivity, heat generation and the heat flux at the base of the model. The temperature distribution was matched against measured down-hole data from well Habanero 1. A 3D model was then developed with 9 horizontal layers and aligned along an impermeable eastern boundary fault. Gravity potentially plays an important role so the model was tilted to the west-south-west. Since the fine 72,000 cell model only extends to 20 km2 whilst the reservoir rock (Innamincka Granite) extends to over ~1,000 km2, Dirichlet boundary condition (large block volumes) was used for the sides with closed boundaries at the top and bottom. These large cells simulate the extension of the reservoir beyond the limited dimensions of the basic model. The permeability of the stimulated and mud damaged zones was calibrated using stable closed-loop (doublet) production and injection history data. The porosity was calibrated by simulating the two tracer tests carried out at Habanero. In preparing future production forecasts, three different well layouts were considered: staggered line drive; inverted 4-spot and regular 5-spot. For each scenario, closed-loop circulation was modelled for a production period of 20 years. For a larger-scale development plan, recommendations to provide the best outcome, balancing short-term temperature against long-term extensibility are presented.