The rationale for assessment of undiscovered, economically recoverable oil and gas in central and northern Arizona: Play analyses of seven favorable areas

Abstract

Seven oil and gas plays, totalling about 12,750 square miles, have been identified in the northern Arizona assessment province of the U.S. Geological Survey. This province is roughly north of 34°15' N. lat. in its western half and north of 33°15' N. lat. in its eastern half. These seven plays have good potential for the future discovery of economic oil and gas accumulations in reservoirs of middle and late Paleozoic age. Assessments are based on favorable attributes of potential source and reservoir rocks plus geothermal maturity, trap development, migration and timing. Arizona's only petroleum production occurs in the northeast corner of Apache County where the first oil field was discovered in 1954. Currently, Arizona's oil and flammable gas are extracted from Pennsylvanian rocks with minor production from Mississippian and Devonian rocks. Six plays are outlined in the Colorado Plateau physiographic province and one in the Cordilleran overthrust belt in the Basin and Range province of extreme northwestern Arizona. Plays are: 1) Devonian, Mississippian, and Pennsylvanian reservoirs in the Cordilleran overthrust structures; 2) Devonian through Permian reservoirs in primarily structural traps of the Hurricane Fault Uinkaret Plateau area of northwestern Arizona; 3) Devonian reservoirs in both structural and stratigraphic traps in the greater Black Mesa basin of northeastern Arizona; 4) Pennsylvanian bioherm and carbonate mound reservoirs along the southern margin of the Paradox basin in extreme northeastern Arizona; 5) Pennsylvanian reservoirs along the northern, western, and southern flanks of the Defiance uplift in northeastern Arizona; 6) Pennsylvanian and Permian reservoirs in the Holbrook anticline region of the southwestern Holbrook basin of east-central Arizona; and, 7) Pennsylvanian and Permian reservoirs in anticlines and updip stratigraphic pinchouts within the northeastern Holbrook basin of east-central Arizona. 1 All Arizona plays are speculative except for: 1) the extreme northeastern part of the greater Black Mesa basin which has very minor oil production, 2) the Paradox basin (Blanding basin subprovince) which has minor Pennsylvanian oil and gas production in seven fields, and 3) the northern flank of the Defiance uplift which contains Arizona's largest producing field, Dineh-bi-Keyah. The latter is a 20-million-barrel (ultimate recovery) field discovered in 1967. It produces from a fractured igneous sill of Oligocene age within the Pennsylvanian section. Regional anisotropy of basement rock and paleotopography have strongly influenced the growth of younger tectonic features and depositional patterns and are expressed in northwest-northeast geophysical trends. Continued analyses of these trends may provide one of the keys to finding more oil and gas in northern Arizona. Northern Arizona is a frontier exploration area with inviting targets and favorable potential. There are approximately 800 boreholes in the assessment province; almost half of these were drilled for oil and gas. The remainder were drilled exploring for geothermal, helium, and mineral resources, and as stratigraphic tests. About 130, or 35 percent, of the oil and gas boreholes are between 5,000 and 8,500 feet deep with none being deeper than 8,500 feet. Excluding development wells in existing oil, gas, and helium fields, drilling has been geographically uneven with an overall average drilling density of about one borehole per 140 square miles. In many instances drilling has been too shallow to reach the best potential reservoirs, and strategies have not always been based on modern exploration principles. Very few boreholes have tested the sedimentary section beneath the volcanic rock cover. Over 26,000 square miles (40 percent) of the study area is Indian reservation lands; unfavorable leasing policies have sometimes discouraged exploration in these areas (Peirce, 1982).