Origin and distribution of grain-coating and pore-filling chlorite in deltaic sandstones for reservoir quality assessment

Automated mineralogy (SEM-EDS) approach to sandstone reservoir quality and diagenesis

“…(B) Detrital quartz-dominated Lower Jurassic deltaic sandstones from Halten Terrace, Norway (mineral colour index in Figure 3), with minor feldspars, locally pore-filling chlorite (Ch), Fe-ooids (FO) and some remaining primary porosity (Pp). The yellow dashed outline shows the outline of a burrow, possibly Skolithos (Griffiths et al, 2021). The creation of the burrow has disturbed the mineralogy, resulting in a relatively "clean" central burrow fill, an intermediate layer with pores filled with illite (Ilt) and then an outer layer with pore-filling chlorite.…”

“…Illite cement in sandstone has three main sources: conversion of Al-rich dioctahedral smectite (e.g., montmorillonite), breakdown of K-feldspar and reaction of K-feldspar with kaolinite (Bjørkum and Gjelsvik, 1988;Worden and Morad, 2003). Chlorite cement in sandstone has five main sources: conversion of Fe-Mg-rich trioctahedral smectite (e.g., saponite), reaction of siderite with kaolinite, conversion of berthierine, possibly supplied by Fe-ooids, reaction of Fe-oxides such as ilmenite and the breakdown of Fe-Mg lithics such as volcanic rock fragments (Worden and Morad, 2003;Gould et al, 2010;Worden et al, 2020b;Charlaftis et al, 2021;Griffiths et al, 2021).…”

“…Quartz cement has many possible sources in sandstones (Worden and Morad, 2000) including: feldspar-to-clay breakdown reactions Gjelsvik, 1988), smectite-illitisation (McKinley et al, 2003), dissolution of amorphous siliceous bioclasts (Vagle et al, 1994), inter-facies redistribution (Trewin and Fallick, 2000), as well as from quartz dissolution at macro-and micro-stylolites (Heald, 1955). Quartz cement can be inhibited by a number of processes such as the development of chlorite (Pittman and Lumsden, 1968;Worden et al, 2020b;Griffiths et al, 2021), illite (Pittman et al, 1992), microcrystalline quartz (Aase et al, 1996;French et al, 2012;Worden et al, 2012;French and Worden, 2013;French et al, 2021) or siderite (Karim et al, 2010) grain coats, the early emplacement of petroleum fluids (Worden et al, 1998;Worden et al, 2018a;Worden et al, 2018b) and the early development of overpressure (Osborne and Swarbrick, 1999;Nguyen et al, 2013). The effectiveness of oil emplacement and overpressure for the inhibition of quartz Feldspar fabrics in sandstones (mineral colour index in Figure 3).…”

“…Primary pores, those that were present at the time of deposition, can be visualised using SEM-EDS, especially for images collected with a 2 μm or less spacing (Figures 3,4,5B,FIGURE 15 Examples of quantitative data that arise from SEM-EDS analysis and their relation to other techniques (A) Comparison of core analysis porosity and SEM-EDS porosity from some Lower Jurassic sandstones from Halten Terrace, Norway (Griffiths et al, 2021). The repeatability of core analysis measurements are typically 0.5%; the SEM-EDS porosity measurements probably have smaller degrees of uncertainty.…”

Insights into Carbon Dioxide Hydrate Nucleation on the External Basal Surface of Clay Minerals from Molecular Dynamics Simulations

“…Clay minerals (e.g., montmorillonite [Mnt], illite [Ilt], mica, kaolinite [Kln], and chlorite [Chl]) are pore-filling materials and found to ubiquitously coat quartz or feldspar grains in marine sediments. 14 Studies have identified clay minerals as important constituents of carbon storage. For instance, increased swelling of smectite in deep ocean-floor environments allows the formation of intercalated methane hydrate in the smectite interlayers, with a d 001 value of ∼2.2 nm.…”