Print this pageCharacterizing and Evaluating Tar-Sand Reservoirs with Scanning Electron Microscope--an Example from Sunnyside, Utah
Richard M. Pollastro, Christopher J. Schenk
The presence of authigenic clays and other minerals in tar sand reservoirs
presents problems during stimulation and recovery of bitumen. Therefore, it is
important to characterize the authigenic mineralogy, morphology of pores, and
surfaces of framework grains. Such reservoir characterizations provide insight
into the subsequent fluid-flow properties, water-rock chemical interactions, and
mechanical stability of reservoir pore systems so that effective and efficient
in-situ recovery 
methods
can be implemented.
The scanning electron microscope (SEM), combined with energy-dispersive x-ray
analysis (EDX), optical petrography, and x-ray powder diffraction (XRD), was
used to characterize bitumen-impregnated rocks from the Sunnyside, Utah, area.
The bitumen is hosted mostly in lenticular, fluvial, and lacustrine sandstones
of the Tertiary Green River and Colton Formations. Samples from core and outcrop
were analyzed by SEM before and after extraction of the bitumen with chloroform;
XRD and EDX were used after bitumen extraction.
SEM analysis reveals that the surfaces of grains making up the pore systems
of these bitumen-saturated rocks are extremely complex in morphology and
mineralogy. Framework grains are commonly coated with a variety of authigenic
clay minerals, including nearly pure smectite, illite, illite/smectite, and
chlorite. Kaolinite, however, occurs in booklets or vermicules as a pore-filling
or replacement phase. Other minerals found as surface growths or cements include
zeolites (analcime, chabazite, erionite) and carbonates (calcite, dolomite,
ankerite).
The diversity in grain morphology and authigenic mineralogy revealed through
the SEM demonstrates that the bitumen-impregnated rocks near Sunnyside are a
complex reservoir system. Therefore, complications are expected using
conventional in-situ recovery methods
for these tar sands.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.