Exploring for Subtle Traps with High-Resolution
Paleogeographic Maps
T. B. Bulling, J. A. Breyer
High-resolution
paleogeographic maps depicting the depositional history of
the Reklaw 1 interval provide a basis for prospecting for subtle traps in the
updip Reklaw trend in south Texas. The Reklaw 1 interval began with sand being
carried southwestward by longshore currents to form the barrier bar that forms
the reservoir in Atkinson field. The hydrocarbons are trapped by the updip
pinch-out of barrier-bar sand into a lagoonal mud. Stratigraphic traps similar
to Atkinson field could be present along depositional strike if the sand in that
field were part of a more extensive barrier-bar system. After the barrier bar
formed, distributary-mouth bars prograded seaward depositing the bar-finger
sands that are the reservoirs in Hysaw and Flax fields. Subtle structural traps
co ld be present where small down-to-the-north faults associated with the Sample
fault system cut the bar-finger sands downdip from the established production.
Farther down paleoslope, the distributary channels began to bifurcate and the
distributary-mouth bars coalesced to form a broad delt-front sheet sand.
Burnell, Hondo Creek, and Runge West fields produce from this sheet sand near
the unstable shelf margin. A rapid rise in relative sea level terminated
deposition of the Reklaw 1 interval. Many of the oil and gas fields remaining to
be discovered in the United States are in mature petroleum provinces where much
of the remaining oil and gas probably resides in subtle traps. High-
resolution
paleogeographic maps may be a key to finding these subtle traps.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.