Delaware Mountain Group, West Texas and southeastern New Mexico, a case ofrefound opportunity: Part 1 - Brushy Canyon

Exploration in Permian (Guadalupian) deep-water sandstones of the Delaware Mountain Group, west Texas and southeast New Mexico, represents a success s tory of the 1990s derived from reevaluation of reservoirs previously deemed uneconomical. Recent discoveries have concentrated on the Brushy Canyon in New Mexico and, to a lesser extent, the Cherry Canyon in Texas. Brushy Can yon reservoirs in particular previously were overlooked due to indications of poor reservoir quality from log and well test data; however, oil shows o bserved on mud logs across the northern Delaware basin led to new completio n efforts in the late 1980s and 1990s using gel-sand fracture stimulations. Productive reservoirs are very fine to fine-grained arkosic to subarkosic sandstones with porosities of 12-25% and permeabilities typically of 1-5 md . Better reservoir quality is concentrated in massive channel sandstones va riably interpreted as deposited by turbidity or saline density currents. Si gnificant clay content, lamination, and close interbedding between oil- and water-bearing units make log analysis and reserve estimates problematic. A s a result, the mud log remains the cheapest, most practical indicator of p ay. Reservoir sandstones can be divided into a series of major productive t rends related to proximal/slope and more distal/basin-floor depositional se ttings. Well productivity is variable within each trend, but primary recove ry rarefy exceeds 10%. Options for enhanced recovery include pressure maint enance, waterflooding, and carbon dioxide flooding. Early indications sugge st that carbon dioxide flooding may be most appropriate in these low-permea bility, clay-bearing reservoirs.