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Nanoscale imaging of organic matter and wettability of oil-window shales

Andrew Fogden, Terri Olson and Andrew G. Christy
Nanoscale imaging of organic matter and wettability of oil-window shales (in Imaging unconventional reservoir pore systems, Terri Olson (editor))
AAPG Memoir (2016) 112: 25-42


Five shale samples preserved from the oil window of four unconventional reservoirs were solvent-extracted using toluene and methanol for high-resolution, secondary-electron imaging with field emission scanning electron microscopy (SEM) of the textures of organic matter (OM) present at or near induced fracture surfaces. The samples represent calcareous, siliceous, and mixed mineralogy mudrocks. Based on their nanoscopic textures, nine categories of OM could be distinguished: (1) nonporous particles, (2) low-porosity masses (sometimes [3] with mineral crystallites), (4) spherule aggregates, (5) intermediate-porosity granular masses, and (6) high-porosity foamy frameworks between mineral grains, together with (7) thick, (8) thin, or (9) very thin coats on mineral surfaces. The frequency of occurrence of these OM categories was qualitatively assessed from all images and compared to those from siliceous gas-window maturity Barnett Shale. The various morphologies are interpreted to comprise types of kerogen, bitumen, and asphaltenic residues, and transformations between them due to maturation and migration are proposed. After the first stage of cleaning and imaging, the samples were re-cleaned with stronger solvents for re-imaging at the same locations. Chloroform/methanol azeotrope only mobilized the very thin coats on clays, which presumably comprise asphaltenic nanoparticles deposited from crude oil as later-stage wettability alteration in the reservoir. Tetrahydrofuran effected only a slight swelling of mature bitumen, while pyridine (at higher temperature) apparently induced further bitumen production from kerogen and partially dissolved some preexisting bitumen but did not dissolve most of the OM present.

ISSN: 0271-8529
Serial Title: AAPG Memoir
Serial Volume: 112
Title: Nanoscale imaging of organic matter and wettability of oil-window shales
Title: Imaging unconventional reservoir pore systems
Author(s): Fogden, AndrewOlson, TerriChristy, Andrew G.
Author(s): Olson, Terrieditor
Affiliation: FEI Oil and Gas, Canberra, A.C.T., Australia
Affiliation: Digital Rock Petrophysics, Golden, CO, United States
Pages: 25-42
Published: 2016
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 28
Accession Number: 2018-018674
Categories: Economic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Secondary Affiliation: Digital Rock Petrophysics, USA, United StatesAustralian National University, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 2018
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