Structural
Style and Timing in the Narraway Area, Foothills
Belt,
Richards, David R.1, Rob
Scammell2, Martin Armitage2, Michael Doe1 (1)
Midland Valley, Golden, CO (2)
The Narraway
area is in the frontal foothills portion of the Alberta Rockies fold and thrust
belt. The deformation is a mixture of detachment folds and small displacement
thrusts in the Permian through Cretaceous section. It is an area of substantial
gas production from several tight Cretaceous sandstone units. Fractures are
critical to economic production in this area.
Details of the relative timing of the
structural events are displayed on regional 2D seismic. A new depth-migrated 3D
volume provided additional detail on the structures and timing. The depth
migration included a considerable advance on the velocity model as well as
insight into the anisotropy due to dipping shale above.
There is clear evidence of early
thrusting on ramps through parts of the Cretaceous section. These faults are
imaged basinward of the main Narraway
folded zone. In the Narraway area some of the thrusts
are folded by the later detachment folding, and they were inactivated by the
change in geometry. There is disharmony vertically through the section,
indicating the location of detachments in shales, and
compartmentalizing the shortening into sections of harmonic detachment folding
or ongoing thrusting. Steep limbs are primarily kink folds, rather than faults.
Existing wells show that production rates
are related to fractures. 3D seismic, production and field examples suggest
that, at least in part, fractures are related to faulting and folding. As
production is not restricted to structural highs, detailed mapping of the
faults and fold shapes in 3D can aid in exploration and step-out drilling.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California