Erslev, Eric A.1, Peter H. Hennings2
(1) Colorado State University, Fort Collins, CO
(2) ConocoPhillips, Houston, TX
ABSTRACT: Variations in Predicted Reservoir Heterogeneity Due to Multiples Modes of Folding in Basement-Involved Foreland Anticlines
Petroliferous anticlines in basement-involved foreland systems can be explained as
second-order accommodation features formed during first-order basement arching above
master, listric thrust faults. These anticlines can be classified by their mode of
occurrence as backlimb tightening, backthrust tip, forelimb wedge, and subthrust splay
anticlines.
Although many of these anticlinal geometries can be replicated by shear-based
fault-propagation-folding algorithms, recent field observations and kinematic analyses
show that an additional component of flexural slip is commonly required to produce their
geometries and deformation patterns, particularly in shale-rich basins. Out-of-the-basin,
layer-parallel shear is required by the geometry of back-limb tightening, backthrust tip,
and forelimb wedge anticlines. For subthrust splay anticlines, into-the-basin,
layer-parallel shear can be driven by gravitational spreading of basement arches during
movement on their master thrust faults.
The mode of folding controls fault-generated reservoir heterogeneity. In competent strata
near the basement interface, triangular shear zones form arcuate folds as forelimb strata
are thinned and thickened by distributed faulting. The resulting reservoir-scale faulting
and heterogeneity is proportional to the dip of units within the shear zones. In contrast,
flexural slip folding concentrates layer-oblique faulting at fold hinges, particularly in
the upper and lower layers of more competent stratal packages underlain by less competent
strata. The degree of reservoir-scale deformation and heterogeneity will be dependent on
the local curvature of layers, not their dip, and their position relative to other strong
and weak strata. As a result, determining the distribution of fold mechanisms is essential
to the prediction of reservoir heterogeneity in basement-involved anticlines.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.