In May 1978, ARCO Oil and Gas Co. completed the Langley Deep Unit 1 well in Lea County, New Mexico, discovering a deep gas field with production from two horizons. The discovery well produces gas from a northwest-southeast-trending anticline that has a reverse fault at the Ellenburger formation on the northeast flank of the structure. This reverse fault, possibly persistent to the base of the Wolfcamp Formation, generated an anticlinal feature in the upthrown block at the Devonian level. The fault itself is the trap at the Ellenburger formation.

Major seismic evaluation of the eastern flank of the Delaware basin had proceeded for 10 years prior to the discovery of the Langley Deep field. The first major seismic group shoot, conducted in 1968, started on the Central Basin platform and proceeded into the Delaware basin. These seismic records had good, continuous, shallow reflectors. Deeper reflectors were present only on the Central Basin platform or in the deeper part of the Delaware basin but not on the eastern flank of the basin. By changing the field acquisition parameters and later the processing techniques, ARCO Oil and Gas Co. was able to improve the quality of the data and to identify continuous reflectors from the Delaware basin up onto the Central Basin platform, at least at the Devonian level. These improved seismic ata delineated an anticlinal feature with an associated fault trap that is the Langley Deep field.

Since the discovery of the Langley Deep field in 1978, a new geologic interpretation has been proposed for the eastern rim of the Delaware basin. A major conclusion, based on seismic control, the well control from this field, and on subsurface control throughout southern Lea County, New Mexico, is that a strike-slip fault was activated during the Late Pennsylvanian and Early Permian and caused deformation resulting in the formation of the Langley Deep structure.

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