Page 125 - Reservoir Formation Damage

Characterization of Reservoir Rock 107

X-Ray Diffraction (XRD)

The X-ray powder diffraction analysis (XRD) is a nondestructive
technique that can provide a rapid and accurate mineralogical analysis
of less than 4 micron size, bulk and clay contents of sedimentary rock
samples (Amaefule et al., 1988). This is accomplished by separately
analyzing the clays and the sand/silt constituents of the rock samples
(Kersey, 1986). The X-ray diffraction technique is not particularly sensitive
for noncrystalline materials, such as amorphous silicates and, therefore,
an integrated application of various techniques, such as polarized light
microscopy, X-ray diffraction, and SEM-EDS analyses, are required
(Braun and Boles, 1992). Hayatdavoudi (1999) shows the typical X-ray
diffraction patterns of the bulk and the smaller than 4 micron size clay
fractions present in a core sample.

X-Ray CT Scanning (XRCT)

X-Ray CT (computer-assisted tomography) scanning is a nondestructive
technique, which provides a detailed, two- and three-dimensional exami-
nation of unconsolidated and consolidated core samples during the flow
of fluids, such as drilling muds, through core plugs and determines such
data like the atomic number, porosity, bulk density, and fluid satura-
tions (Amaefule et al., 1988; Unalmiser and Funk, 1998). This technique
has been adapted from the field of medical radiology (Wellington and
Vinegar, 1987).
As depicted by Hicks Jr. (1996), either an X-ray source is rotated
around a stationary core sample or the core sample is rotated while the
X-ray source is kept stationary. The intensity of the X-rays passing
through the sample is measured at various angles across different cross
sections of the core and used to reconstruct the special features of the
porous material. The operating principle is Beer's law, which relates
the intensity of the X-ray, through the linear attenuation coefficient, to
the physical properties of materials and different fluid phases in the
sample (Wellington and Vinegar, 1987; Hicks Jr., 1996). A schematic of
a typical X-ray scanning apparatus is shown by Coles et al. (1998). The
image patterns can be constructed using the linear attenuation coefficient
measured for sequential cross-sectional slides along the core sample as
shown by Wellington and Vinegar (1987). These allow for reconstruction
of vertical and horizontal, cross-sectional images, such as shown by
Wellington and Vinegar (1987). Three-dimensional images can be recon-
structed from the slice images as illustrated by Coles et al. (1998).
Tremblay et al. (1998) show the cross-sectional and longitudinal images
of a typical wormhole, perceived as a high permeability channel, growing