Preprints
https://doi.org/10.5194/egusphere-2024-435
https://doi.org/10.5194/egusphere-2024-435
15 Feb 2024
 | 15 Feb 2024

Naturally fractured reservoir characterization in heterogeneous sandstones: insight for Uranium In Situ Recovery (Imouraren, Niger)

Maxime Jamet, Gregory Ballas, Roger Soliva, Olivier Gerbeaud, Thierry Lefebvre, Christine Leredde, and Didier Loggia

Abstract. This study delves into the characterization of a complex reservoir, the Tchirezrine II sandstone unit in North Niger, crucial for potential Uranium In Situ Recovery (ISR) in a naturally fractured and faulted context. Employing a multifaceted approach, including well log data, optical borehole imagery, and hydrogeological tests, alongside satellite-based lineament analysis, this study provides a comprehensive understanding of the structures and its impact on fluid flow. Lineament analysis reveals scale-dependent patterns, consistent with spatially homogeneous joint networks restricted to mechanical units, as well as nearly scale-invariant patterns, better corresponding to spatially heterogeneous fault networks. Various deformation structures are detected from borehole imagery, including Mode I fractures, cataclastic deformation bands, and brecciated-cataclastic fault cores. The Tchirezrine II reservoir displays heterogeneous porosity and permeability related to its fluviatile sedimentary context. These data differ from traditional porosity-permeability relationship obtained in sandstone reservoir matrix but are instead consistent with Nelson’s classification, emphasizing the impact of deformation structures on such petrophysical properties. Hydrological tests have been implemented into a zone of E-W trending deformation structures, revealing a strong permeability anisotropy of this heterogeneity. This strong E-W anisotropy is consistent with the presence of the observed E-W structures, i.e. with a drain behaviour of Mode I open fractures and a sealing behaviour of both cataclastic bands and fault rocks. Considering implications for ISR mining, this study allows discussing the interplay between fractures, faults, and fluid flow properties. It suggests that a well pattern perpendicular to the main permeability orientation can attenuate channelled flow, thus improving contact of the leach solution with the mineralized matrix. These results provide an integrated approach and multi-scale characterization of Naturally Fractured Reservoir (NFR) properties in sandstone, offering a basis for optimization of NFR production such as ISR development.

Maxime Jamet, Gregory Ballas, Roger Soliva, Olivier Gerbeaud, Thierry Lefebvre, Christine Leredde, and Didier Loggia

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2024-435', Giacomo Medici, 15 Feb 2024
    • EC1: 'Reply on CC1 by AE', Stefano Tavani, 15 Feb 2024
  • RC1: 'Comment on egusphere-2024-435', Anonymous Referee #1, 06 Mar 2024
  • RC2: 'Comment on egusphere-2024-435', Anonymous Referee #1, 06 Mar 2024
  • RC3: 'Comment on egusphere-2024-435', Nikolas Aleksi Ovaskainen, 10 Mar 2024
Maxime Jamet, Gregory Ballas, Roger Soliva, Olivier Gerbeaud, Thierry Lefebvre, Christine Leredde, and Didier Loggia
Maxime Jamet, Gregory Ballas, Roger Soliva, Olivier Gerbeaud, Thierry Lefebvre, Christine Leredde, and Didier Loggia

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Short summary
Naturally fractured reservoirs are governed by multi-scale transfer properties from matrix to large-scale structures. In this paper, using a multi-method/-scale analysis, we characterize the structural network of a NFR. This characterization is obtained via analysis on satellite images, structure measurements, logs and hydrogeological tests. We found that clustered structures have a significant impact on permeability anisotropy compared to distributed sub-orthogonal joint sets.