Structural control on fluid flow and shallow diagenesis: Insights from calcite cementation along deformation bands in porous sandstones

Abstract

<jats:p>Abstract. Porous sandstones are important reservoirs for geofluids. Interaction therein between deformation and cementation during diagenesis is critical since both processes can strongly reduce rock porosity and permeability, deteriorating reservoir quality. Deformation bands (DBs) and structural-related diagenetic bodies, here named Structural and Diagenetic Heterogeneities (SDH), have been recognized to negatively affect fluid flow at a range of scales and potentially lead to reservoir compartmentalization, influencing flow buffering and sealing during production. The hydraulic behavior of DBs is not yet fully constrained, and it remains poorly understood also how diagenetic processes interact with DBs to steer fluid flow mechanisms and evolution. In this contribution we present two field-based studies from Loiano (Northern Apennines, Italy) and Bollène (Provence, France) that contribute to elucidating the structural control exerted by DBs on fluid flow and diagenesis recorded by calcite nodules associated with the bands. We relied on careful field observations and a variety of multiscalar mapping techniques (photography, string mapping, and drone aerial photography), integrated with optical, scanning electron and cathodoluminescence microscopy, and stable isotope (δ13C and δ18O) analysis of nodules cement. In both case studies, at least one set of DBs precedes and controls selective cement precipitation. Cement texture and cathodoluminescence patterns, and their invariably negative δ13C and δ18O value ranges, suggest a meteoric environment for nodule formation. In Loiano, DBs acted as low-permeability barriers to fluid flow and promoted selective cement precipitation. In Bollène, clusters of DBs restricted fluid flow and focused diagenesis in parallel-to-band compartments. Our work shows how low-permeability DBs in porous sandstones can actually affect fluid flow and localize diagenetic processes (in the shallow crust) that, in turn, could further enhance the sealing capacity of these structural features. </jats:p>

Structural diagenesis in ultra-deep tight sandstones in the Kuqa Depression, Tarim Basin, China

“…In addition, the dominant gas-bearing Lower Cretaceous Bashijiqike Formation is buried to an ultra-deep depth of 5500-8000 m (Lai et al, 2019a). The ultra-deep burial depths, complex structure patterns and concentrated stress will result in complex diagenetic modifications and pore evolution histories (Laubach et al, 2010;Wu et al, 2019;Del Sole et al, 2020). Previous studies have individually unraveled the structural evolution, in situ stress, fracture and diagenesis of Bashijiqike Formation in the Kuqa Depression (Jia and Li, 2008;Lai et al, 2017a;Shen et al, 2017;Nian et al, 2018;Ju and Wang, 2018;Lai et al, 2019a).…”

Fault zone fluid pathways in the carbonate Irecê basin, NE Brazil

“…Fluid pathways in carbonate rocks are strongly dependent on depositional petrofabrics and their tectonic and diagenetic history (Agar & Geiger, 2014;Pili et al, 2002). Current approaches to better understand fluid flow in carbonate rocks and associated structures from large to small scale include seismic-scale data (Masaferro et al, 2004;Melville et al, 2004), field observations (Agosta et al, 2010;Del Sole et al, 2020;Ferrill et al, 2011Ferrill et al, , 2017Ferrill & Morris, 2008;Michie et al, 2014;Peacock, 2002;Peacock et al, 2016Peacock et al, , 2017Peacock & Sanderson, 2018;Petracchini et al, 2012), petrophysical and micro-CT data (Beaudoin et al, 2018;Healy et al, 2014;Lézin et al, 2009), isotope geochemistry (Agosta et al, 2008;Bertotti et al, 2017;Gomez-Rivas et al, 2014;Zaarur et al, 2013), physical modelling (Cilona et al, 2012;Spratt et al, 2004) and numerical modelling including fluid flow and reactive transport (Antonellini et al, 2014;Bisdom et al, 2017;Corbella et al, 2014;Fitz-Dias et al, 2011).…”