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

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

Specifications for the application of the United Nations Framework Classification for Fossil Energy and Mineral Reserves and Resources 2009 (UNFC 2009) to Geothermal Energy Resources

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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

Application of the United Nations Framework Classification for Resources (UNFC) to Geothermal Energy Resources - Selected case studies

Over the last century, different energy and raw material sectors, as well as countries, adopted a range of approaches to classify and manage resources. New challenges to the production, distribution and utilization of energy and raw materials have, however, emerged in recent years that demand innovative approaches for an integrated resource management system. The 2030 Agenda for Sustainable Development defines a clear pathway to address these challenges in a holistic manner. The United Nations Framework Classification for Resources (UNFC) was developed under the auspices of the United Nations Economic Commission for Europe by a dedicated community of experts drawn from a range of fields, but with the common goal to develop an internationally applicable scheme for the classification, reporting and management of energy and mineral resources. Though initially developed for the mineral and petroleum sectors, UNFC has recently expanded its scope to include renewable energy. Growing awareness and interest in renewable energy resources, including geothermal resources, has highlighted a need to standardize the way in which renewable energy potential is classified and reported. To facilitate improved global communication in the geothermal sector, the ECE Expert Group on Resource Classification, under the framework of a Memorandum of Understanding between the United Nations Economic Commission for Europe and the International Geothermal Association (IGA), developed specifications for applying UNFC to geothermal energy resources. The specifications were issued in September 2016. A set of 14 case studies from Australia, Germany, Hungary, Iceland, Italy, Netherlands, New Zealand, Philippines and Russian Federation are presented here to facilitate a better understanding of the specifications and the uniform application of UNFC to geothermal resources. These application examples illustrate the classification of a range of different geothermal resource scenarios in a manner consistent with other energy resources. The approach also provides valuable indicators to the value of UNFC as a tool to support attainment of the Sustainable Development Goals. Experts in geothermal energy resources, as well as those in other energy and mineral sectors, will find this collection of case studies a useful reference document in their efforts to apply a globally applicable integrated resource management system. I commend all those involved in the preparation, review and verification of these case studies and thank, in particular, the International Geothermal Association for its support