3D seismic for design and derisking of dual geothermal boreholes in sedimentary sequences and new prospects in the Paris Basin (Adapted methodology using petroleum industry techniques)

Abstract

The use of existing geological and structural maps, previous 2D seismic profiles, boreholes and correlation models between these data is sufficient to understand basin structure and thermal systems on a regional scale. However, this is not sufficient on a scale of a geothermal site to be sure of the hydraulic connectivity (or of the presence of a permeability barrier) between two boreholes 1.5 or 2 km apart. To ensure that there is enough hydraulic connectivity, it i s necessary to understand the controls on the network of fractures which affects the aquifer (fracture permeability) and the physical properties of the rock, namely the porosity and clay content in order to obtain a matrix permeability. The latest generation of broadband (six octaves) 3D seismic reflection will provide the following information: the similarity attribute will give an accurate structural map of the fault network at the seismic resolution and, in many cases, at a higher resolution than seismic; seismic velocity anisotropy analysis techniques will make it possible to visualize a 3D volume of information on the fracture network [Michel et al. (2013) Application of Azimuthal Seismic Inversion for Shale Gas Reservoir – Proceedings of the 11th SEGJ International Symposium, Yokohama]; acoustic impedance inversion or petrophysical inversion techniques will predict the porosity throughout the whole volume of the aquifer from a porosity log recorded in a pilot-hole. It allows a real 3D mapping of predicted porosity inside the aquifer much more reliably than from modelling alone. These seismic techniques were initially developed for petroleum exploration and development. They have rapidly progressed throughout the last decade, both in acquisition, processing and interpretation with new methodologies and high-performance softwares. They are efficient for modelling reservoirs to be produced. And, consequently, they can be used for geothermal applications as data to design dual deviated drillings with horizontal drains in carbonate and clastic reservoirs – not only for new projects, but also to revisit old ones to improve their performance or develop another reservoir. Broadband 3D seismic will secure the exploration of Triassic sandstones which stay an interesting prospect for deep geothermal projects. New prospects are proposed in the Paris Basin: Regional faults overlap the substratum. Inside faulted zones, hydrothermal circulations arriving by convection at the top of granitic basement could be geothermal objectives, as in the Alsace Upper Rhine Graben. A production pilot site is suggested to test superimposed aquifers and a regional fault and, at the same time, two different architectures of boreholes doublets: horizontal drains for aquifers and deviated wells for crossing a regional fault. The first site that will use this approach could be instrumented and used as an experiment with a small addition of measurements and sensors, thus becoming a showcase for geothermal energy in France. The objective of this experiment would be to determine the transit time, the heating time of the re-injected water and the circulation speed to define the optimal direction, spacing and length of drains, and also, to realize the thermal modelling of the site for different options.

Contribution of drone photogrammetry to 3D outcrop modeling of facies, porosity, and permeability heterogeneities in carbonate reservoirs (Paris Basin, Middle Jurassic)

“…Micritized grains are generally microporous throughout the log section. Micropores measure less than 10 µm and are well expressed by the greenish/bluish colour of resin in micritic grains (after the definition of Deville et al, 2011). Microporosity is homogeneously present within the model.…”

“…The choice of this site is motivated by the fact that the Basin is well studied, mainly because of its importance as petroleum and geothermal reservoirs and for CO 2 storage (Mougenot, 1999;Lopez et al, 2010;Brigaud et al, 2014;Regnet et al, 2015;Drouiller et al, 2019). In particular, Massangis quarry in Burgundy has been studied as a reservoir analogue of the Oolite Blanche Formation (Purser, 1985;Casteleyn et al, 2010Casteleyn et al, , 2011Makhloufi et al, 2013;Regnet et al, 2015), a major geothermal reservoir in the Paris Basin (Lopez et al, 2010).…”

Upscaling of geological properties in a world-class carbonate geothermal system in France: From core scale to 3D regional reservoir dimensions

“…3D seismic is proving to be a very promising tool to strengthen the predictions of geothermal resources (Casini et al, 2010;Lüschen et al, 2011;Drouiller et al, 2019;Salaun et al, 2020).…”

“…Use of 3D seismic data is increasing in the exploration and production of geothermal resources in European basins (Munich, Vienna, …). This kind of data is, however, not available in this study area, but it would be an excellent addition to de-risk the implementation of new doublets as it could help to localize areas of high potential in zones where well data is not present nearby and its general use should be seriously discussed also for the Paris area (Drouiller et al, 2019). Deep neural networks are also promising to estimate porosity and permeability in the Middle Jurassic geothermal reservoir from old 2D seismic lines acquired in the 1980s and well log data (Allo et al, 2021).…”