--> ABSTRACT:  Intraorganic Nanoquartz Associated with Algal Bituminite within the Devonian Marcellus Formation, Ritchie County, West Virginia: Potential Origins and Implications, by Warner, Travis B.; #90142 (2012)

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 Intraorganic Nanoquartz Associated with Algal Bituminite within the Devonian Marcellus Formation, Ritchie County, West Virginia: Potential Origins and Implications

Warner, Travis B.*1
(1) EQT Production, Pittsburgh, PA.

The association between organic matter and authigenic quartz is a critical relationship to understand as organic-richness and formation brittleness are two primary controls on organic-rich mudstone reservoir productivity. Argon-ion milling and field emission scanning electron microscopy / energy dispersive X-ray spectroscopy was performed on a Marcellus Fm. sample from Ritchie Co., WV (11% TOC by weight; 24% TOC by volume). Observed within algal bituminite were nanometer-scaled quartz crystallites (~125 nm aggregates of smaller <50nm ‘blobs’) in a chain morphology - likely a ‘lattice’ in 3D. ‘Nano-quartz lattices’ (NQLs) were often observed emanating from authigenic ‘in situ’ quartz silt. Bacterial metabolism, having been shown to mediate silica dissolution (Birnbaum & Wireman, 1984; Rageuneau et al., 2000; Warren, 2006) and later biomineralization (Bhaskar & Bhosle, 2005; Douglas, 2005), suggests both ‘in situ’ quartz and NQLs were biogenic in origin and formed during eogenesis. Laboratory observations (Furukawa & O’Reilly, 2007) of nanometer-scaled amorphous silica globules forming in chains bound to organic matter, mediated by Fe(III)-reducing bacteria appear to be analogous to the Marcellus NQLs. The potential implications of NQLs within organic macerals are 1) where present, NQLs constitute a previously unrecognized volume of quartz which, due to the individual cystallites’ nanometer-scale, are generally undetecteded by standard microscopy techniques; 2) NQLs appear to preserve original algal microstructures as intraorganic fracture nanoporosity - which may be enhanced later during catagenesis, and 3) NQLs likely outline planes of weakness by which organic macerals might ‘cleave’ upon hydraulic stimulation and therefore may be the first high permeability pathway connecting intraorganic nanoporosity with hydraulic fractures and eventually the well bore. Given the volume and spatial arrangement of organics in the Marcellus’ organic-rich intervals, and given that organic matter (via intraorganic nanoporosity) appears to contain the majority of the system’s retrievable hydrocarbons (Wang & Reed, 2009; Ambrose et al., 2010; Loucks et al., 2009; Laughrey et al., 2011), the realization that some organic matter itself is prone to cleaving is important. Further analyses are necessary to evaluate the prevalence of the NQL phenomenon.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California