AAPG Bulletin, V. 83, No. 12 (December 1999), P. 1901-1926.

Delaware Mountain Group, West Texas and Southeastern New Mexico, A Case of Refound Opportunity: Part 1--Brushy Canyon

Scott L. Montgomery,¹ John Worrall,² and Dean Hamilton³

©Copyright 2000. The American Association of Petroleum Geologists. All rights reserved.
¹Petroleum Consultant, 1511 18th Avenue East, Seattle, Washington 98112.
²Scott Exploration Inc., 200 W. First Street, Suite 648, Roswell, New Mexico 88201.
³Consulting Geologist, Midland, Texas.

ABSTRACT

Exploration in Permian (Guadalupian) deep-water sandstones of the Delaware Mountain Group, west Texas and southeast New Mexico, represents a success story 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 Canyon reservoirs in particular previously were overlooked due to indications of poor reservoir quality from log and well test data; however, oil shows observed on mud logs across the northern Delaware basin led to new completion 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 variably interpreted as deposited by turbidity or saline density currents. Significant clay content, lamination, and close interbedding between oil- and water-bearing units make log analysis and reserve estimates problematic. As a result, the mud log remains the cheapest, most practical indicator of pay. Reservoir sandstones can be divided into a series of major productive trends related to proximal/slope and more distal/basin-floor depositional settings. Well productivity is variable within each trend, but primary recovery rarely exceeds 10%. Options for enhanced recovery include pressure maintenance, waterflooding, and carbon dioxide flooding. Early indications suggest that carbon dioxide flooding may be most appropriate in these low-permeability, clay-bearing reservoirs.