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Geology of Avalon (Delaware) Field, Eddy County, New Mexico

Timothy Maxwell

The Avalon (Delaware) field is located along the northwestern margin of the Delaware basin, in Eddy County, New Mexico. Siliciclastic sediments at Avalon represent part of an extensive lowstand wedge deposit that interfingers on the north with shelf-margin carbonates of the ancient Goat Seep reef and extends to the south (basinward) for many tens of kilometers. These sediments were deposited by channelized sand underflows and silt-clay interflows flowing off the shelf edge into the basin through breaches in the shelf edge reef-carbonate bank complex. Best characterized as a basin-margin sand lobe, Avalon field is developed as a depositional high that was later enhanced both by differential compaction of the more peripheral finer grained sediments and by channel scouring along its flank.

Production at Avalon is from the basinal quartz siltstones and sandstones of the Brushy Canyon and Cherry Canyon Formations. Three distinct lithofacies have been identified: (1) light-brown, very fine-grained, bioturbated sandstone, (2) medium-gray, very coarse-grained, finely laminated siltstone, and (3) dark-gray to black, medium to coarse-grained, clay-rich siltstone. Oil production is from bioturbated sandstones and finely laminated siltstones. Within the productive parts of these facies, primary intergranular porosities range to 20% and permeabilities to 25 md. Productive limits of the field cover approximately 1,100 ac, and it is currently fully developed on 40-ac spacing. Since discovery in 1982, Avalon field had produced more than 1.6 million bbl of oil with an average product on of 850 BOPD and water cuts of 60-65%.

AAPG Search and Discovery Article #91034©1988 AAPG Southwest Section, El Paso, Texas, 21-23 February 1988.