Abstract

Andy’s Mesa Field was discovered in 1967 on the northeast flank of the Gypsum Valley salt anticline. Over 60 producing wells have been drilled to date, 45 wells in the Andy’s Mesa Federal Unit and 21 in the Double Eagle Federal Unit. This paper will only discuss Andy’s Mesa Federal Unit (AMU) which is currently operated by EnCana Oil & Gas (USA) Inc. Andy’s Mesa Field continues to be developed 40 years after the discovery well was drilled by Union Oil Co. of California (UNOCAL). Between 1967 and 1998 there were only seven producing wells in AMU. Full development within the AMU did not begin until after UNOCAL shot 3-D seismic in 1998.

AMU has produced over 66 Bcfe and has a current estimated ultimate recovery (EUR) of approximately 118 Bcfe, based on cumulative production and proved reserves. Production is from arkosic sandstones in the Pennsylvanian Honaker Trail and Permo-Penn Cutler Formations trapped in complex structural and stratigraphic accumulations created by intermittent movement of the Paradox Salt. Complex faulting, which can only be mapped with 3-D seismic, has compartmentalized the field.

Depositional environments for the sandstone reservoirs are interpreted to include meandering and braided fluvial with some eolian, delta front, and distributary channel environments. Reservoirs have average porosities up to 15%, water saturations less than 50%, and permeabilities as high as 150 md. Pore pressure gradients range from 0.33 to 0.4 psi/ft and increase with depth. The under-pressured nature of these reservoirs makes them highly susceptible to formation damage from overbalanced drilling and prone to fluid loading if and when water production begins. Issues impacting AMU net pay determination include low contrast and low resistivity pay. However, with careful evaluation of subtle log characteristics, “pay” can successfully be determined with considerable confidence.