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ABSTRACT: A Case Study of Exploitation in the Lovington Strawn Trend, Permian Basin, Lea County, New Mexico

K. A. Shanks, M. C. Williams

The Lovington, New Mexico area, located in the northwest shelf of the Permian basin, produces oil from Pennsylvanian-age phylloid algal bioherms within the lower Strawn limestone. Strawn carbonates were deposited on the northwest flank of the Central Basin axis in a low-energy midramp setting. Algal bioherms developed as steep-sided, loaf-shaped buildups elongate in a dip direction. Mounds range from 20 to 180 ft (6-55 m) thick and average 112 mi (0.8 km) wide by 0.5 to 1 mi (0.8-1.6 km) long and occur at an average depth of 11,300 ft (3444 m). Porosity occurs in the mound facies, usually in one massive zone with values ranging from 4 to 14%. Porous mounds are sealed by nonporous lime mudstones (intermound facies), the predominant facies within the Strawn limestone. A bas nal black shale overlies the Strawn limestone across the play fairway and provides a source for Strawn oil. In the downflank portion of the play, skeletal grainstones occur beneath the Strawn shale, onlapping the mound and intermound facies. Areas of thick grainstone development are associated with poor production due to reduced porosity/permeability and possible loss of sealing facies.

Prediction of undrilled mounds between well control is difficult from log, dipmeter, or drill cuttings data. Isolated Strawn limestone isopach thicks coincident with anomalous seismic character can be used to predict mound locations. Disrupted or anomalous seismic character is caused by thickening of the Strawn interval when porous and abrupt facies/velocity changes between mound and intermound limestone facies. Correct spatial imaging of the steep-sided algal mounds is critical in developing an accurate subsurface target. Once a prospect has been identified, a well-defined bottom-hole location is required to ensure a valid test of the prospect.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990