Abstract: Stratigraphic Traps in the Wilcox and Yegua of the Upper Gulf Coast

By

Stewart Chuber

Stratigraphic loss of porosity and permeability accounts for oil production in the Milbur Wilcox Field, Milam County, Texas, and in several Yegua fields of central Beauregard Parish, Louisiana.

The Milbur field produces from a barrier bar which has formed a pure stratigraphic trap (one whose edges are entirely controlled by lithologic or permeability discontinuities). It is six miles long, two miles wide and has a maximum thickness of 30 feet. Only the updip lagoonal edge is productive. Although the field is small, it is significant because it extends a producing stratigraphic trend 100 miles to the north.

Combination stratigraphic-structural traps are common in the Yegua of Beauregard Parish. Longville and East Longville produce from dip-fed distributary channel sandstones. Hurricane Creek production is trapped in a strike-oriented redistributed sandstone which developed on a low relief roll-over fold along a major fault.

Environmental interpretations can be made by using a combination of subsurface and petrographic techniques. Isopach maps and electric log cross sections demonstrate the external form of the sandstone body. Quartz size/quartz content plots of sandstone cores show texture and composition which help confirm the interpretations made from the logs. The electric log character of strike-fed and dip-fed sandstone bodies can be diagnostic of depositional environment.

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