The two fold increase of heat production from deep seated geothermal resources anticipated within the next decade by the French energy decarbonising policy acted as a strong stimulus among concerned designers and operators, in particular those active in the Paris Basin Dogger (mid-Jurassic) carbonate reservoir, the Word largest geothermal district heating (GDH) system developed to date. Summing up, the ambitioned goals would result here in doubling the existing GDH farming capacity (ca 1,500 GWhth supplied to the Paris suburban heating market) via the completion of thirty (30) new doublets each rated 50 000 to 60 000 MWhth yearly. Such a challenging out come required appropriate mining schemes based on well architecture taking advantage of the prevailing multilayered reservoir structure, a distinctive attribute of a number of sedimentary settings, in order to secure both thermal longevity along larger well to reservoir exposure. Another concern addressed the reclamations of moderately to poorly productive areas, which otherwise have remained unchallenged. Several innovative candidate designs, due to replace progressively the prevailing conventional well architectures candidated among which the so-called subhorizontal (SH) well concept first initiated in 2018 on the Cachan, moderately performant (15 dm transmissivity) site south of Paris, with a view to replace two, 33 years old doublets cumulating 350 m3/hr nominal production rating. The philosophy behind the concept aimed at intersecting via a step wise, en echelon type, trajectory, the layering sequence inferred from either from temperature/flowmetering (PLT) logs on offset wells or straight forwadly from direct drilling assessment. This first geothermal SH well achievement, awarded as a world premiere in geothermal engineering recorded a 450 m3/hr nominal rating and has been operating safely, over 4,5 years after completion of two 1 000 m long drains. The concept, replicated in 2022 on a poorly productive (10 dm transmissivity) site achieved similar performances, benefitting from a modified Ecoscope/Periscope HD (TM of Schlumberger, SLB) geosteered assembly, elsewhere confirming the early pilot hole design strategy as non essential. The multiradial (MR) well concept came second. Initially conceived as a substitute, in cas of a failure, to the former SH design, its advantage lies in its limited space occupation. Its efficiency however requires a three legged 75 to 80° inclined reservoir configuration and 80 to 85° top reservoir landing angle in order to avoid excess sharp angle steering and (upwards/downwards) trajectory reversals likely to generate, either or both, navigation difficulties and/or interlayer pressure interferences and subsequent production losses. The concept implemented in year 2021 in a low permeability frontier sector South West of Paris, is operating since 2022 in spite of design and operating features deemed non fully orthodox by the authors. Ultimately the multilateral well architecture extensively applied and documented by the Oil and Gas industry is raising increasing interest among geothermal engineers and operators, given its structural advantages among pilot hole prerequisite added to the flexibility in managing a number of laterally and multilayer distributed drains play a dominant role. On the well services side the availability of easier if not cheaper access to such facilities as drain re-entry/locator, intelligent coiled tubing units and high (up to 80°) angle tool convergence centralisers is regarded as the most efficient response to well design architectures in stratified media. Typical programmes and workflows along architecture modelling are documented and the figures of merits of the three candidate, SH, MR and ML, well designs addressed. Technological and economic issues are also discussed.

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