Sandstones of the Bone Spring formation (Leonardian) with significant potential in the northern portion of the Delaware basin include the Avalon sandstone and third Bone Spring sandstone intervals. The Avalon sandstone is a very fine to finegrained submarine-fan deposit, 10–18 m thick, distributed across parts of southern Eddy and southwestern Lea counties, New Mexico. The Avalon consists of a series of individual sandstone zones separated by carbonaceous and shaly siltstones. The sandstone zones display moderate porosities (7–17%) and low permeabilities (0.5–7.2 md) and require artificial stimulation to produce. Net pay is commonly 4–8 m. Reserves per well seldom exceed 100,000 bbl, and the Avalon interval is considered a secondary reservoir.
The third Bone Spring sandstone is widely distributed across the northern Delaware basin and is especially prospective within the deeper basinal area to the east. In contrast to the Avalon sandstone, which was sourced from the north and northwest, submarine-fan systems of the third Bone Spring sandstone were supplied from the northeast and east, with detritus derived from the Central Basin platform (CBP). Productive sandstone zones are very fine grained channel and levee/overbank facies, with porosities of 7–18% and permeabilities of 2.0 md or less. Well productivity is significantly enhanced by overpressure, which affects the lower portion of the Bone Spring formation and underlying Permian, Pennsylvanian, and Mississippian units. Wells in Red Hills and War-Wink fields, productive from the third Bone Spring sandstone, have yielded oil at rates of 700 bbl/day or more and required mud weights of over 12 lb/gal at depths of 3446 m. Estimated ultimate reserves for these wells are 300,000–375,000 bbl. The minimum prospective area is 64 ´ 16 km, lying between Red Hills and War-Wink fields on the west and the CBP on the east. Mapping of channel sandstone fairways should be possible through a combination of existing log data and three-dimensional seismic surveying.