Application of
Structural Analogs to Enhance Understanding of Tectonically Inverted Settings
Reynolds, David J.1, John R.
Underhill2 (1) ExxonMobil Exploration
Company, Houston, TX (2) The University of Edinburgh, Edinburgh, United Kingdom
Integration of field and subsurface data
from the Wessex Basin (UK) and Doseo Basin (Chad) has provided important
new insights into petroleum prospectivity in
structurally inverted settings. Using these data it has proved possible to
refine models of inversion anticline development and recognition criteria for a
variety of polyphase deformation scenarios. In the Wessex Basin, structures are exposed
that are typically difficult to image seismically, such as the steeply dipping,
highly deformed forelimb of inversion anticlines. These regions are
particularly important to resolve when mapping trap geometry, field extent, and
fault displacement for fault seal analyses. In all cases the inversion
anticlines are related one-for-one with early rift faults,
regardless of their trend and that relaying normal faults produce en-echelon
inversion anticlines. Thus, en-echelon folds do not indicate strike-slip
faulting a priori. In addition, maximum inversion is coincident with the center
of the fault segment where maximum subsidence occurs during extension. As a
result, much can be interpreted about the pre-inversion structure by mapping
the inversion anticlines themselves. Application of these observations has
aided in the interpretation of subsurface data from the Cretaceous Central African
rift system (Doseo and Doba Basins) in Chad, which contain up to 10
km of non-marine sediments and record a complex tectonic history from the Early
Cretaceous to the present. Combining results of the seismic interpretation,
structural analysis and direct field observations leads to the construction of
a new, unifying, generic model for inversion and criteria for differentiating
inversion anticlines from strike-slip fault zones which can be used to improve
our understanding of trap geometry and risk.