Figure 12: Madison limestone cluster analysis at the different threshold
values: (A) 0.35, and (B) 0.55 that correspond to cluster valleys in
Figure11.
The imaging and analysis processes previously described were also
applied to fractured Indiana and Madison limestone samples, with the
goal of observing both fracture and pore systems simultaneously. As
previously seen in Figure 9 (non-fractured Indiana limestone), the
cluster valley for this sample are observed at threshold values for the
non-fractured Indiana limestone are 0.60, and 0.80. The fractured
Indiana limestone sample shows similar characteristics to the
non-fractured Indiana limestone of small and large vugs as shown in
Figure 13. There is a new valley at the threshold 0.30, Figure 14A,
because the sample is now more connected than before (the small pores
and vugs are more accessible due to the fracture) and intense features
in fractures and their vicinity exhibit less signal relaxation. This is
exemplified by the threshold value of 0.60, which remains the same for
both the fractured and non-fractured Indiana limestone samples, but the
number of clusters reduces in the fractured Indiana Limestone (at
threshold 0.60) changing from 6 cluster in Figure 10A to 2 clusters in
Figure 14B. A cluster valley has also appeared at the threshold value of
0.70, suggesting that there is a new feature that has a proton density
that is not a part of the small pore system or the vug system. This new
proton density is assigned to the fracture that was manually created in
the sample. Figure 14C clearly shows the fracture through the sample
(green and gold feature). This fracture has made the vugs more
accessible in the Indiana Limestone as shown in Figure 14D (threshold
0.80). There are more vugs present in the fractured sample when compared
the non-fractured sample. This result is consistent with the fracture
connecting the sample more so than before. Based on this analysis, the
pore space in the sample has become more accessible to water, now that a
fracture has been introduced. The pores, whether small or vug like, are
more connected and therefore could allow better transport through the
sample.