MODELLING HYDROTHERMAL FLUID FLOW IN A HIGH ANDEAN SETTING

Abstract

Northern Chile (17-28°S) is located in a very suitable tectono-magmatic setting for the development of geothermal energy. It is composed of a volcanic chain associated with the active Nazca-South America plate boundary and quaternary volcanism is found along the high Andes and Altiplano, over a thick crust (~60 km), with climatic conditions ranging from arid to hyper arid. The hot fluids at shallow crustal levels in this region contribute to estimated geothermal resources in Chile in the order of 16000 MW (Lahsen et al. 2010).A preliminary TOUGH2 model has been developed for the Pampa Lirima basin, which is one of the characteristic hydrothermal systems in the Northern Andean region. Data from geological, geophysical and geochemical studies of the area were combined to develop a conceptual model of the system which was then implemented as a numerical model in TOUGH2. Care was taken to accurately represent the high altitude and the low level of meteoric recharge. The locations and flow rates of surface features were used to calibrate the model to ensure that the position of the unsaturated zone above the water table and the flow balance in the basin agree with observations. Temperatures recorded in the springs and estimated from geochemistry were used to carry out a preliminary calibration of the subsurface.The natural state model results agree well with the available data and suggest that the Pampa Lirima system is structurally controlled with a number of faults interacting to provide mechanisms for both upflow and recharge. Numerical experiments with the model also revealed that it is unlikely that a large steam zone exists within the system unless the reservoir temperatures exceed estimates obtained through geochemistry.The insights gained into the Pampa Lirima system demonstrate the usefulness of developing numerical models at an early stage, even prior to the availability of exploration well data.