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.