The Patrick Draw oil field has been the site of research into surface and remote sensing methods for hydrocarbon exploration for nearly 10 yr. The oil field is a stratigraphic trap with conspicuous sage vegetation on the surface and an associated tonal anomaly within that sage (visible via Landsat") overlying the field's gas cap. This paper attempts to resolve the controversy of whether the Patrick Draw sage anomaly is related to oil field factors or to other independent factors.

Geology and production history of the field show the sage die-out anomaly results from upward migration of injected gases and waters used to maintain reservoir pressures in the field. These gases and waters produced anoxic, low-Eh (oxidation potential), high-pH, and high-salinity soils that are toxic to the overlying sage population. Stunted sage associated with the anomaly commonly occurs in marginal terrains in the western United States and is not tied uniquely to oil fields.

A velocity for the seeping gases of 250-1000 ft/yr (76-305 m/yr) was calculated from the reservoir to the surface. Failure to account for the lag time associated with movement of seepage to the surface has been a source of misinterpretation.