Abstract
Abstract. Microporous carbonate rocks form important reservoirs with permeability variability depending on sedimentary, structural, and diagenetic factors. Carbonates are very sensitive to fluid–rock interactions that lead to secondary diagenetic processes like cementation and dissolution capable of modifying the reservoir properties. Focusing on fault-related diagenesis, the aim of this study is to identify the impact of the fault zone on reservoir quality. This contribution focuses on two fault zones east of La Fare anticline (SE France) crosscutting Urgonian microporous carbonates. Overall, 122 collected samples along four transects orthogonal to fault strike were analyzed. Porosity values have been measured on 92 dry plugs. Diagenetic elements were determined through the observation of 92 thin sections using polarized light microscopy, cathodoluminescence, carbonate staining, SEM, and stable isotopic measurements (δ13C and δ18O). Eight different calcite cementation stages and two micrite micro-fabrics were identified. As a main result, this study highlights that the two fault zones acted as drains canalizing low-temperature fluids at their onset and induced calcite cementation, which strongly altered and modified the local reservoir properties.
Highlights
Microporous carbonates form important reservoirs (Deville de Periere et al, 2017; Lambert et al, 2006; Sallier, 2005; Volery et al, 2009), with porosity values up to 35 % (Deville de Periere et al, 2011)
Porosities measured on the 92 samples show a strong decrease towards the fault core (Fig. 3): dropping from more than 10 % in the host carbonates to less than 5 % within fault zones
– In the D19 Fault zone, the lowest porosity values are found in narrow zones around the faults and in the lens between F4 and F5
Summary
Microporous carbonates form important reservoirs (Deville de Periere et al, 2017; Lambert et al, 2006; Sallier, 2005; Volery et al, 2009), with porosity values up to 35 % (Deville de Periere et al, 2011). Faults can act as barriers (Agosta et al, 2010; Tondi, 2007), drains (Agosta et al, 2007, 2008, 2012; Delle Piane et al, 2016; Evans et al, 1997; Molli et al, 2010; Reches and Dewers, 2005; Sinisi et al, 2016; Solum and Huisman, 2016), or mixed hydraulic behavior zones (Matonti et al, 2012) depending on their architecture and diagenetic evolution Because of their hydraulic properties, fault zones influence the fluid flows in the upper part of Earth’s crust (Bense et al, 2013; Evans et al, 1997; Knipe, 1993; Sibson, 1994; Zhang et al, 2008) and are capable of increasing the fluid– rock interactions. In case of a polyphasic fault zone, repeating fluid pathways–barriers behavior in time leads to very complex diagenetic modifica-
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