Fairways in the Downdip and Middip Yegua Trend— A Review of 25 Years of Exploration

Thomas E. Ewing
Yegua Exploration Associates LLC, 19240 Redland Rd., Ste. 200, San Antonio, Texas 78259

The Yegua genetic unit of the Gulf Coast Basin (Bartonian, late middle Eocene; includes the “Cook Mountain”) contains multiple lowstand events that have generated significant “middip” (updip of the shelf margin) and “downdip” (shelf margin and slope/ basin) production trends.

The middip trend has produced 1.04 TCFG (trillion cubic feet of gas) and 68 MMBC (million barrels of condensate) (1.4 TCFE [trillion cubic feet of gas equivalent]) from 113 fields in two fairways. The Victoria – Fort Bend Fairway (545 BCFE [billion cubic feet of gas equivalent]) in Texas produces from incised-valley sandstones discovered using ‘bright spots’ and AVO (amplitude versus offset) analysis. The Evangeline Fairway (876 BCFE) in Louisiana 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, and have yielded 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 (189 BCFE) is a complex of downdip and middip environments.

Four sparsely-drilled frontier areas are identified. The Brooks Frontier in 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 have discovered 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 sparsely 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—more if the keys to the frontier areas can be found.

AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas