Hydraulic and thermal impact modelling at the scale of the geothermal heating doublet in the Paris Basin, France

13 pagesInternational audienceThe Paris Basin is extensively developed for the geothermal district heating (GDH) of approximately 150 000 dwellings. As of late 2010, thirty four GDH systems apply the doublet concept in the Paris suburban area and mine the heat of the Dogger reservoir, a limestone formation of Mid-Jurassic age at depths ranging from 1500 to 2000 m. As the brine is fully reinjected, cold water bodies progressively invade the reservoir around injector wells inducing both thermal and hydraulic interactions at the doublet scale. The premature production well cooling and the sustainable development of the resource highlight two critical parameters, the thermal breakthrough time (tB) and the extent of the cooled fluid bubble(S) respectively. First, a set of benchtest simulations was launched to compare the sensitivities of tB and S parameters to selected reservoir conceptual model typologies. These simulations were applied on a GDH doublet undergoing a suspected thermal breakthrough. Five reservoir modelling teams validated their “in house” simulations by (i) checking an analytical (Gringarten-Sauty, 1979) solution, and (ii) testing three candidate reservoir structures on the doublet considered remotely located (i.e. not interfering with nearby exploitations) for a first step. The outcome resulted in a rewarding insight into the variability of simulation outputs. An additional segment will enable the actors to compare their modelling expertise on the same doublet considered in interaction with the other GDH operations located in its environment. Second, BRGM carried out a survey towards various rehabilitation schemes (a new doublet or a triplet) and their contribution toward sustainability standards. From a hypothetical, twenty five year life, doublet simulation, an initial hydraulic/temperature field was derived. Then, several new well locations were simulated and isotherms, alongside production well cooling kinetics, compared accordingly. A two-stage rehabilitation scheme, i.e. triplet then a new doublet, seems to reconcile the resource longevity and the economic demand. Further work is required to compare the different designs with a method integrating both the impact of the geothermal exploitation on the resource and the lifetime of the exploitation in a single mathematical factor

Geothermal Field Development in the European Community Objectives, Achievements and Problem Areas

Achievements and problem areas are reviewed with respect to various engineering implications of geothermal field development in the European Community (EC). Current and furture development goals address three resource settings. (a) low enthalpy sources (30-150{degrees}C), an outlook common to all Member states as a result of hot water aquifers flowing in large sedimentary units with normal heat flow, widespread thoughout the EC; (b) high enthalpy sources (<150{degrees}C) in areas of high heat flow which, as a consequence of the geodynamics of the Eurasian plate, are limited to Central and South-West Italy and to Eastern Greece; (c) hot dry rocks (HDR), whose potential for Europe, and also the difficulties in implementing the heat mining concept, are enormous. A large scale experiment conducted at medium depth in Cornwall (UK) proves encouraging though. It has provided the right sort of scientific inputs to the understanding of the mechanics of anisotropic brittle basement rocks

Estimating permeability in a limestone geothermal reservoir from NMR laboratory experiments

International audienceA wireline NMR (Nuclear Magnetic Resonance) logging tool has recently been deployed in the Dogger geothermal aquifer of the Paris Basin to provide a continuous permeability estimation throughout the reservoir. The complex pore structure of heterogeneous carbonate systems means that careful consideration must be given to standard permeability prediction. A laboratory study was performed on cores from a geothermal well at Bobigny, north of Paris. Petrographic and petrophysical analyses of thin sections, water permeability and laboratory NMR relaxation time T2 were conducted on 72 samples. A classification was established using four main facies and the impact of microporosity and micritization on flow properties was investigated. The range of permeability is wide [0.05–1000 mD] and the evaluation addresses different relationships between permeability and a combination of porosity and T2 distributions. Since the latter distributions can provide an estimation of the pore size distributions and in particular the fraction of microporosity within the total porosity, several possibilities arise for better constraining the permeability relationship. For one facies, permeability is nearly independent of porosity over a porosity range of [0.12–0.22], illustrating the well-known difficulty of predicting permeability in carbonate lithologies. The best permeability prediction is obtained when considering only macroporosity instead of total porosity in a classical power law

Characterizing facies and porosity-permeability heterogeneity in a geothermal carbonate reservoir with the use of NMR-wireline logging data

International audienceIf they are to be economically and technically sustainable, geothermal projects require the production of hot fluid at high flow rates over a 30-year thermal lifetime. The combined use of multiple logging tools in making petrophysical assessments of reservoir quality helps to optimize drilling in areas of high geothermal potential. The present paper focuses on four geothermal wells intercepting Middle Jurassic (Dogger) carbonate rocks of the Paris Basin where for the first time Nuclear Magnetic Resonance (NMR) log data have been successfully used to investigate reservoir porosity-permeability heterogeneities. A total of ten facies have been identified from recovered cuttings and cores and grouped into four facies associations along a schematic carbonate ramp profile. From the wells studied, four reservoir units exhibiting porosities exceeding 15% and permeabilities of up to 1 Darcy (D) were traced in the Calcaires de Comblanchien, the Oolithe Blanche and the Calcaires marneux à Pholadomyes formations. The well's sub-horizontal trajectory and well-logs correlations between two wells, made it possible a priori to identify porous and permeable layers extending over at least 500 m and up to 2000 m within the Bathonian reservoir, providing useful pointers for further 3D reservoir geomodeling. Permeabilities derived from well testing proved to be overestimated when compared with NMR-derived permeabilities, illustrating the upscaling problem that is invariably a challenge in carbonate systems. NMR can be combined with production logging tool (PLT), that provides data on the distribution and thickness of productive layers, to give indications for example about continuous permeability record along the geothermal wells or about the proportion of micro and macroporosities in rocks. Based on the geological classification derived from examination of cores and cuttings, four rock-types (including mean T2 pore-size distributions) have been identified and attributed to a given sedimentary facies and depositional environment by extending a clustering method to NMR log distributions from wells

NMR contribution in sub-horizontal well for porosity-permeability heterogeneity characterization in limestones: implications for 3D reservoir prediction and flow simulation in a world class geothermal aquifer

International audienc

NMR contribution in sub-horizontal well for porosity-permeability heterogeneity characterization in limestones: implications for 3D reservoir prediction and flow simulation in a world class geothermal aquifer

International audienc

NMR contribution in sub-horizontal well for porosity-permeability heterogeneity characterization in limestones: implications for 3D reservoir prediction and flow simulation in a world class geothermal aquifer

International audienc