The Dineh-bi-Keyah field is producing oil from a porous and fractured Oligocene syenite sill which intruded dark gray dense limestone and shale of Early Pennsylvanian age. The field is at the northwest end of the Toadlena anticline, a northwest-trending surface feature on the northeast flank of the Defiance uplift, but the oil accumulation is primarily stratigraphic. The initial production of individual wells is as high as 3,300 bbl of oil per day.

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