Characterization and mischaracterization of authigenic magnesium-bearing minerals: Examples from Norphlet Sandstone, Alabama, Florida, and Mississippi

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6020780

Kugler, R L ^[1]

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1. Geological Survey of Alabama, Tuscaloosa, AL (United States)

Jurassic Norphlet sandstones are significant gas, condensate, and carbon dioxide reservoirs in the eastern Gulf Coast region. Diagenetic factors affecting the quality of these reservoirs are variable at microscopic to megascopic scales. Major authigenic components of the reservoirs include quartz, albite, K-feldspar, a variety of carbonate minerals, anhydrite, pyrite, illite, and chlorite; minor components include zeolite, tourmaline, apatite, and anatase. Although the diagenetic character of Norphlet sandstone has been intensely investigated, diagenetic pathways and the origin of porosity remain controversial. Characterization of chemically variable authigenic minerals is crucial to understanding fluid migration pathways and rock-water interactions. Detailed polarized-light and electron microscopy, energy- and wavelength-dispersion X-ray microanalysis, and X-ray diffractometry reveal that common authigenic Mg-bearing minerals in Norphlet reservoirs have been overlooked or improperly chemically characterized. Breunnerite has not been identified by other investigators, although it is abundant in cores from some wells. Authigenic chlorite, which is widespread in offshore reservoirs, commonly has been described as being Fe-rich, whereas electron probe microanalyses indicate that this chlorite is Mg-rich. Qualitative chemical characterization of authigenic minerals commonly is determined by EDX analysis during routine observation of textural relationships with a SEM. This type of analysis typically is performed with little regard for beam-sample-detector geometric relationships and other operational parameters. Peak intensities on EDX spectra collected using a lower electron beam potential (10 kV) more closely reflect proportions of Mg and Fe in breunnerite and chlorite. Thus, SEM operating parameters should be carefully considered, even for qualitative chemical analysis.

• OSTI ID: 6020780
• Report Number(s): CONF-9304188--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:4
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
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CARBON DIOXIDE
CARBON OXIDES
CARBONATES
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