Abstract
Deeply buried sandstone reservoirs are targeted in the Upper Rhine Graben (URG) for geothermal and hydrocarbon resources. These reservoirs are affected by a convective heat flow along fault zones and have a complex diagenetic and deformation history recorded in their paragenetic sequence. Here, the focus is made on siderite and barite cementation characterisation, which trace paleo geothermal circulations within the fracture network affecting the Buntsandstein Gp. sandstones. A double approach on geochemistry and fracture network features is used to characterise fluid-flow episodes in the rift basin and on its shoulders. Barite sulphur isotopic signature suggests a common source for all the locations. However, Rare Earth Elements distribution patterns, oxygen isotopic ratios, and fluid inclusion study suggest two distinct flow regimes for fluids associated with barite precipitation along the shoulders and at depth in the middle of the graben. The barite has a higher content in total REE and contains non-saline fluid inclusions on the graben shoulders, suggesting that fluid circulations within the border faults interact with sulphate rich layers and precipitate at temperature above 150 °C. In deep-seated samples from the central part of the basin, barite fluid inclusions show a wide range of salinities, suggesting a higher contribution of sedimentary brines and precipitation at lower temperatures (< 150 °C). According to their REE signature, these barite mineralisations are associated with siderite and apatite with a diagenetic source. A conceptual model for fluid circulation within the basin is built from this new dataset. Fast and deep down- and up-flows occur along the major border faults, locally leaching evaporitic horizons. A part of the infiltrated meteoric waters reaches the centre of the basin, where it then mixes with the brines in sedimentary. This new characterisation of fluid pathways in the targeted reservoir brings insights into geothermal circulation compartmentalisation at the basin scale.
Highlights
Fluids are involved in widespread deformation processes in many geological contexts such as rift basins, foreland basins and oceanic ridges
This study aims to characterise the origin and conditions of fracture mineralisation within the Buntsandstein Gp. sandstones within the Upper Rhine Graben (URG)
The analysed sandstones consist of fine to medium-grained sandstones belonging to the Buntsandstein Gp
Summary
Fluids are involved in widespread deformation processes in many geological contexts such as rift basins, foreland basins and oceanic ridges. The enhanced thermal regime at the rift initiation stage provides a high heat flow caused by lithospheric thinning (Ranalli and Rybach, 2005; Cloetingh et al, 2010) This thermal regime can be recorded in mineralisation in fault and fractures planes and in the matrix of sedimentary formations (Gleeson et al, 2001; Wilkinson, 2003; McKinley et al, 2011; Olivarius et al, 2015; Kristensen et al, 2016). The tracking of the origin of fluids is crucial to understand the processes that affect the hydraulic properties of the sedimentary formations and their evolution in space and time These aspects have to be integrated into characterisation studies for mineral and nonmineral (hydrocarbon, water) resource exploration and production (Bense et al, 2013; Griffiths et al, 2016; Vidal and Genter, 2018). Reservoir compartmentalisation can affect field productivity due to sedimentary features and fault zones architecture, including vein occurrence
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
