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 2 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 generated an anticlinal feature in the upthrown block on the east flank of the Delaware basin that is the reservoir for the Langley Deep field Devonian strata, and the fault is the possible trap at the Ellenburger formation.

This discovery was the result of an ongoing seismic program that started with a regional group shoot in 1968 on the Central Basin platform and the Delaware basin in Lea County, New Mexico. This survey obtained data that has at best only short discontinuous reflectors in the present area of interest. It could be used only to obtain dips of unknown geologic horizons. ARCO Oil and Gas Co. has been in additional group shoots or has acquired seismic data in each year from 1973 through 1981 in the Delaware basin and Central Basin platform of New Mexico. Each vintage is an improvement in the quality of the section in terms of both the continuity of events and resolution of events. New acquisition and processing techniques contribute to the enhancement of the data. Even though better record s ctions are obtained with each successive vintage, the improvement is limited in each case. The most improvement in record section quality is between the data acquired in 1968 and 1973.

The exploration play developed when data acquired in 1973 was reprocessed in 1975 including diffraction migration, which clearly demonstrated the presence of the critical east dip on Devonian and older formations. Subsequent seismic programs define the limits of the closure. The 1978 discovery well confirmed the existence of the seismic structure. Seven wells have been drilled to date on the Langley Deep seismic feature. Six wells have been completed and are producing gas from Devonian and Ellenburger formations. The seventh well had shows but is considered noncommercial. The only other deep well on the structure was drilled in 1962 to Conoco Inc. to the Ellenburger formation on the northern end of the Langley Deep feature, but was over 500 ft (150 m) lower at the Devonian formation w en compared with the shallowest penetrations of these formations on the Langley Deep structure.

The success of finding the Langley Deep field is due to recognizing that the potential for finding reservoirs exists in the no-data zones on seismic. By continually investigating and searching for the causes of the no-data zones, new and improved acquisition and processing techniques revealed a gas field that would never have been found if exploration stopped after the initial efforts to define the subsurface. The continued efforts to specify the subsurface along the western edge of the Central Basin platform and eastern edge of the Delaware basin not only resulted in the discovery of the Langley Deep field, but also renewed interest of the majors and independents in this area. Conoco Inc., ARCO Oil and Gas Co., and Shell Oil Co. have drilled additional deep

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gas producing wells on similar features that are on trend with and to the south of the Langley Deep field. Thus, the effort of improving the quality of seismic reflections not only led to the discovery of the Langley Deep field but also generated the impetus that discovered additional reserves on other features along the same general trend.

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