American Oil and Gas Reporter - May 2015 - 71

SpecialReport: Study In Geophysics
entations in Silo Field. The top of Figure
3 shows the lineament analysis with the
Niobrara most negative curvature map. Interpreted faults are on bottom. The possible wrench faults are labeled as syncline
faults on the lineament map. Possible corresponding lineaments and faults are labeled A and B on both maps, indicating
there may be some basement control on the
orientations of the polygonal faults.
As noted, basement structure also exerts
some control on the location and orientation of the Permian salt dissolution edge in
the Silo Field. An isochron of the Permian salt to the Wolfcamp horizons shows the
irregular nature of the salt edge and confirms that the edge was caused by salt dissolution, as shown in Figure 4 (warm colors represent areas where the salt is thick).
The edge follows the trend of the possible basement wrench faults, indicating
that the basement structure is controlling
the location of the salt edge. The structural monocline in the upper horizons also follows the trend of the Permian salt edge.
Differential compaction over the edge partially explains the monocline. Since the

monocline does not follow the salt edge
perfectly, it is likely that basement structure is also a component in the location of
the monocline.

FMI Log Analysis
SM Energy provided FMI logs from the
Patriot 1-19H and the Sego Lily 14-5 wells
for the study. Both wells are located outside of Silo Field, to the south. Rex Energy, courtesy of Kaiser Francis, provided
the FMI log from the Silo State 41-22H
well, which is located in the southern end
of Silo Field. All three logs are outside the
survey area.
As part of the Silo Field study, resistive
natural fracture orientations in the Silo State
41-22H well were compared with natural
fracture orientations in the Patriot 1-19H
and Sego Lily 14-5 wells. The Silo State
41-22H FMI log shows that the orientation
of the vertical natural fractures is northwestto-southeast. This is the typical fracture orientation in the field, and the maximum
principle stress is oriented in the same direction, causing the fractures to be open.
Less than five miles to the south,

however, fracture direction changes to
north-to-south, as indicated in the Patriot
1-19H and Sego Lily 14-5 FMI logs. This
change in fracture direction requires careful consideration in Niobrara development
outside the main field area.
The 3-D seismic characterization
demonstrates that the majority of structures
present in Silo Field are controlled, at least
partially, by basement structure. A lineament analysis shows that basement features may be exhibiting some control of
fault orientation in the potential polygonal fault system in the south-central part
of the survey area. The possible basement
wrench faults appear to be controlling the
location of the Permian salt edge, and both
the basement faults and the salt edge play
a role in the structural monocline.
Open fracture directions within the field
follow the trend of the possible basement
wrench faults. Considering the changing
fracture orientations moving toward the
south of Silo Field, analyzing basement
structure outside of the 3-D survey area
could help predict orientations of features
in other areas around Silo Field.
r

American Oil and Gas Reporter - May 2015

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