ABSTRACT

The Downdip Yegua Trend of overpressured gas-condensate reservoirs has produced over 600 BCF and 15 MMBBL of oil and condensate, mostly since 1979. The trend has indicated reserves in the range of 1.6--2.0 TCF, and substantially higher potential.

The trend was opened only in the late 1970s and early 1980s because its sandstone fairways are for the most part separated from the updip sandstone-rich Yegua section, which has produced since the 1930s, by a "mid-dip" region where sandstones are scarce. The trend is also separated from overlying Frio and Vicksburg targets by over 1000 ft of highly overpressured Jackson shale.

Five fairways can be defined:

1. The Duval-Jim Wells Fairway, with thin but continuous sandstones and little expansion of section,
2. The Wharton-Jackson Fairway, with thick but discontinuous sandstones of high quality and very active faulting and expansion,
3. The Fort Bend-Brazoria Fairway, with deeply buried sandstones affected by growth faulting and salt movement,
4. The Harris-Jefferson Fairway, with abundant sandstones, no mid-dip region separating it from updip deltaic sediments, abundant salt structures, and growth faulting,
5. The Orange-Calcasieu Fairway, with widespread sandstones deposited in a narrower belt of growth faults and traps.

Fairway 4 has the most production to date (250 BCF). It was also one of the earliest to be developed beginning in 1953. Fairway 2 has produced 122 BCF since its discovery in 1982, and is the most active fairway to date. Fairway 1 has produced 30 BCF since 1979, and Fairway 5 has produced in the vicinity of 8 BCF. Fairways 3 and 5 are in the least mature stage of development.

At present, activity is mainly concentrated on detecting "sweet spots" of a few hundred acres or less; evaluating downdip and lateral extensions of known trends; and in defining large, potentially prolific structures in frontier areas using integrated geologic and geophysical analyses.