The Dineh-bi-Keyah field on the Navajo Indian Reservation in northeastern Apache County, Arizona, is producing from a porous and fractured primary igneous intrusive rock. Production first was established in the field with the completion of the Kerr-McGee No. 1 Navajo in January 1967. As of December 1967, 14 oil wells had been completed on 160-acre spacing and the field still was being developed. The initial potential of individual wells is as high as 3,300 bbl of oil per day. Cumulative production to January 1, 1968 was 2,815,205 bbl of oil.

The field is at the northwest end of the Toadlena anticline, a NW-SE-trending surface feature on the northeast flank of the Defiance uplift. The sedimentary section penetrated in the field conforms with that which has been described in the geologic literature for the Defiance uplift and surrounding area. The sedimentary rocks range in age from Cambrian through Tertiary. Several Tertiary volcanic rock bodies are exposed at the surface.

The production at Dineh-bi-Keyah is from a syenite sill which intruded Lower Pennsylvanian rocks. The sill is of Tertiary age and contains both intercrystalline and fracture porosity. Primary minerals are sanidine, biotite, diopsidic augite, glass, and minor magnetite. Glass is the primary cementing material. The porosity, permeability, and oil-saturation values measured in the igneous rock are similar to the reservoir parameters of many oil-producing carbonate rocks. At the present stage of field development, the sill is known to cover approximately 3,000 acres.