Fault
Characterization and Reservoir Development
at Kuparuk River Field, Part 1:
Fault
Styles and Deformation Models
By
M.R Longden and R.W. Krantz (Phillips Alaska, Inc.)
Access to the 1 billion barrels of remaining reserves
at Kuparuk requires efficient water flood and EOR performance and optimum-infill
drilling, which rely on detailed geologic characterization. Faults represent a
fundamental reservoir complexity; accurate fault
mapping is a critical first
step in
fault
characterization.
The main reservoir contains thousands of seismic scale faults. Lateral and vertical variations in structural style are due to both facies and time-dependent controls on the mechanical stratigraphy of the Kuparuk Formation. Thicker C-sand corresponds to discreet faults with greater lateral extent. Areas with thicker intra-reservoir shales show enhanced decoupling of faulting at top and base Kuparuk. Another variation relates to the degree of lithification at the time of faulting.
The faults define two sets with different strike and
age. Early, northwest-striking faults commonly show more offset at the base of
reservoir than the top. Top offset generally exhibits a component of folding or
distributed faulting. In contrast, later, north-striking faults often display
the opposite relationship, with more offset at top reservoir and multiple faults
combined with folding at the base. Evidence from core within the fault
zones
also shows differences in micro-structure. Only north-striking faults show
evidence of bedding plane slip.
In the context of North Slope tectonic evolution, the
deformation models contrast an early, near-surface fault
episode and a later,
deeply buried episode. Facies-dependent mechanical stratigraphy and lithologic
maturity interact to control deformation styles. The resulting faults can be
grouped into structural domains according to age and facies distribution, which
can then be used to guide interpretation.
AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.