--> ABSTRACT: Seismic Delineation of Algal Mound Reservoirs, Humble City South Field, Lea County, New Mexico, by Charles A. Caughey; #91030 (2010)

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Seismic Delineation of Algal Mound Reservoirs, Humble City South Field, Lea County, New Mexico

Charles A. Caughey

Pennsylvanian algal mounds near Lovington, New Mexico, typify the targets remaining for exploration in the Permian basin. The Strawn trend near Lovington comprises numerous small (200-800 ac) reservoirs of clean algal limestone encased in unfossiliferous carbonate mudrocks. Vuggy porosity occurs in algal micrites and sporadically in crinoidal or foraminiferal grainstones associated with the mounds.

Some of the Lovington area fields encountered downdip water, but difficulty in finding the mound facies remains the principal dry-hole hazard. Vague acoustical boundaries complicate seismic detection of relatively minor (50-150 ft) carbonate buildups at depths of 11,200-11,600 ft. Stratigraphic interpretation of high-resolution seismic data recently led to several new field discoveries and major extensions. Development drilling, however, can be an even greater challenge to reservoir prediction.

Humble City South field illustrates the difficulty of developing a stratigraphic oil field in an area of poor seismic definition and sparse well control. A shooting program following the wildcat discovery only heightened confusion about the size and shape of the new reservoir. Two subsequent dry holes missed the mound entirely and provided only negative control. Seismic modeling, careful stratigraphic interpretation, and saturation coverage with a three-dimensional seismic project ultimately defined the existing reservoir and revealed the presence of a separate, nearby pool. Exact reservoir delineation remains difficult, but this program presented the first clear picture of overall mound geometry. The Humble City experience showed that three-dimensional seismic can be an important too in the critical period following a wildcat discovery.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.