Assessment of complex well architecture performance for geothermal exploitation of the Paris basin: A modeling and economic analysis

The deep geothermal resource of the center of the Paris basin (Ile-de-France region, France) has been exploited since the mid-1980s, the main target being the Dogger aquifer (1500-2000 m deep, 55-80 °C). Currently, the Triassic sandstone units below the Dogger aquifer are envisaged as new targets. This paper presents a modeling and economic analysis used to assess new well architectures (sub-horizontal, horizontal or multilateral wells) in comparison with standard geothermal operation, with a view to increasing doublet hydraulic performance. The reservoir modeling covers the Dogger carbonate aquifer, which can be described by a relatively homogeneous permeability distribution, and the Trias fluviatile sandstones, with higher temperature but lower permeability and far more heterogeneous petrophysical properties. The results of the modeling analysis are expressed in terms of a doublet performance index (DPI, in m3/(h bar)), which is the average between the productivity and injectivity indices. Economic analysis results are given in terms of a doublet cost-performance index (CPI, in k€/year/DPI). The results suggest that both DPI and CPI are better for complex well architectures compared to standard deviated wells. Moreover, better doublet performances are achieved in the Dogger reservoir for which DPI is 4-5.5 times that of the Trias reservoir, depending on well architecture. The extra costs of complex well architectures compared to the cost of standard wells are largely offset by the relative benefits of increasing doublet hydraulic performance. The economic analysis also demonstrates that the cost of any additional unit of DPI in the Trias reservoir is 5-7 times that of the same unit in the Dogger reservoir. However, improvements in drilling technologies and further experience from new operations will lead to substantial cost reductions in the future.