The Yegua genetic unit of the Gulf Coast Basin (Bartonian, upper Middle Eocene; includes the Cook Mountain Formation) contains multiple lowstand events that have generated significant “mid-dip” (updip of the shelf margin) and “downdip” (shelf margin and beyond) production trends. (Figure 1, page 27.)

The mid-dip trend has produced 1.04 tcfg and 68 mmbc (1.4 tcfe) from 113 fields in two fairways. The Victoria–Fort Bend Fairway (545 bcfe) produces from incisedvalley sandstones discovered using “bright spot” and AVO anomalies. The Evangeline Fairway (876 bcfe) produces from Cockfield incised-valley sandstones, in large part from salt structures in St. Landry Parish.

The downdip trend has produced 2.35 tcfg and 96 mmbc (2.9 tcfe) from 221 fields in six fairways. Major production is from expanded shelf-edge and deepwater sandstones of the Liberty Delta System of southeast Texas and its flanks: the Fort Bend-Liberty Fairway in the delta core (1008 bcfe), the Jefferson-Orange Fairway on the eastern flank (703 bcfe) and the Victoria-Wharton Fairway on the western flank (651 bcfe). The first two are the least mature, as evidenced by recent, prolific wells drilled on 3D seismic data. Lesser fairways are the Calcasieu Fairway in southwestern Louisiana (180 bcfe) and the Duval-Jim Wells Fairway in South Texas (188 bcfe). The Camargo Fairway in northeastern Mexico and southernmost Texas is a complex of downdip and mid-dip environments (189 bcfe).

Four sparsely-drilled frontier areas are identified. The Brooks Frontier in deep South Texas has some production (21 bcfe), but its depositional systems are poorly known. The Goliad Frontier is an area of limited sand at the shelf edge. The Deep Frontier is a broad swath downdip of the Liberty delta system where wildcats discover substantial thicknesses of sandstone, but have so far failed to produce. Salt movement complicates the search for traps in this area. The Acadia Frontier represents the poorly tested Yegua/Cockfield shelf-margin in central Louisiana.

The Yegua shelf-margin trends contain seven major fields (>100 bcfe recovered) and 45 significant fields (20-100 bcfe). Perhaps 1.5 tcfe will be added to the current production of 4.36 tcfe— considerably more if the keys to trapping in the frontier areas can be found.

Figure 1. Trend map of the Yegua genetic unit showing areal extent and depositional systems. The location of fairways and frontiers is shown.

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