Numerical model of the Habanero geothermal reservoir, Australia

Abstract

A TOUGH2 reservoir model has been developed for the Habanero enhanced geothermal system (EGS), located in the Cooper Basin, Australia. 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 thermal properties, 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 20km2 whilst the reservoir rock (Innamincka Granite) extends to over ∼1000km2, 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, four different well layouts were considered: staggered line drive (SLD); inverted 4-spot, regular 5-spot and east-west SLD. For each scenario, closed-loop circulation at 25, 35 and 45kg/s per well was modeled for a production period of 20 years. The well patterns were stretched to about the maximum well separation available within the existing seismic cloud, as well as hypothetical seismic clouds. For a larger-scale development plan the best outcome was chosen by balancing short-term temperature against long-term extensibility. The results within the existing seismic cloud indicate the 4-spot layout as the most optimum. The best temperature performance is obtained from an extended seismic cloud when using an east-west SLD.