Geothermal energy is clean, renewable, sustainable, and is independent of weather, place, and time. To harness this energy form requires drilling two or more wells in a crystalline formation to create a reservoir. However, field experiments are expensive to perform, but with the aid of modelling, the reservoir behaviour during exploration/exploitation can adequately be predicted. The dual-porosity modelling approach has been widely adopted in describing most naturally fractured geothermal reservoirs with two contiguous (i.e. matrix and fractures), but there are still some shortcomings when employing the dual-porosity model to represent deep geothermal reservoirs with multiple pore media, such as reservoirs with natural fractures, micro-fractures, and faults. In this study, the concept of triple porosity-permeability is proposed to represent reservoir heterogeneity better in naturally fractured and faulted reservoirs. The triple porosity-permeability modelling approach proposed in this study describes flow through naturally fractured reservoirs with different petrophysical properties, among which porosity and permeability are of primary interest. The media resides in a formation that is formed by three distinct continua of matrix, fractures, and faults, such as the graben formation of the Soultz geothermal system. In the Soultz graben, the series of fractures are interconnected with large faults, and fluid and heat are transmitted via these structures. The study develops a numerical model based on finite element methods for analysing coupled heat transport and fluid flow responses of the Soultz (France) deep heterogeneous geothermal reservoir. The model proposed here can reflect transient temperature distributions during a long-term simulation of 30 years, as well as pressure distribution among multiple pore media. Further, the model also considers density and viscosity variation in deep geological formations during production.

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