New well architectures assessment for geothermal exploitation ofthe Triassic sandstones in Paris basin

Abstract

The deep geothermal resource of the center of the Paris basin (Ile-de-France, France) has been exploited since the mid-1980s, the main target being the Dogger limestone aquifer (1,500–2,000 m deep, 55–80°C). Currently, the Triassic sandstone units below the Dogger aquifer are envisaged as new targets. This paper presents a modelling 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 and to enable the exploitation of the Triassic sandstones with lower permeabilities compared to the Dogger aquifer. The results of the modelling 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. 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. However, improvements in drilling technologies and further experience from new operations will lead to substantial cost reductions in the future.