Regional
Reservoir Compartmentalization within offlapping,
Top-Truncated, Mixed-influenced Deltas, Wall Creek Member, Frontier Formation, Powder River
Basin, Wyoming
Sadeque, Junaid1, Janok P. Bhattacharya2 (1) Chevron ETC, Houston, TX (2) University of Houston, Houston, TX
This study utilizes a dataset of over
2000 well logs and 40 cores linked to the adjacent outcrops exposed along the
western margin of the Powder River basin, Wyoming in order to document
the stratal inter-relationships, sandbody
geometries and reservoir heterogeneity of the Upper Turonian
Wall Creek Member of the Frontier Formation. We show that the Wall Creek
Member, previously interpreted as an offshore bar or shelf ridge, is better
interpreted as a delta system formed during a lowstand,
individual lobes of which have been top-truncated by marine ravinement
during high frequency episodes of transgression. Basinwide
correlations and mapping reveal consecutive stacks of lensiod
shaped, offlapping deltaic parasequences
that prograde progressively basinward
towards the south-southeast. Sub-regionally, the Wall Creek compartmentalizes
into a two tier system of parasequence sets,
separated by a major flooding surface. Individual parasequences
within each set are locally farther compartmentalized into bedsets.
Differential accommodation caused by proto-Laramide
tectonics probably enhanced amalgamation and top-truncation of these parasequences towards the north.
Internal facies
architecture of preserved prodelta and delta front
deposits show varied influence by river, tide and wave processes. Sandbody isolith maps show
strike-elongate to lobate and dip-elongate paleogeomorphology, which also reflect different degrees of
reworking by waves and tides over time.