Algal-Bearing Carbonate Reservoirs of Pennsylvanian Age, West Texas and New Mexico: ABSTRACT

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Leafy, platy, or phylloidal algae have been observed in many well cores from hydrocarbon reservoirs at various localities in the Permian basin of west Texas and southeastern New Mexico. These algae have a significant bearing on the quality, and in some cases the existence, of the reservoir. Three examples have been chosen to illustrate these relations. Nena Lucia field, Nolan County, Texas, produces from massive limestone of Desmoinesian (Strawn) age on the east side of the Midland basin. Inferences of eolian depositional environment published previously are not supported, for the dominant reservoir lithofacies is algal calcareous wackestone. Saunders field, Lea County, New Mexico, produces from both massive and well-bedded limestone of Permo-Pennsylvanian age on a well-defined structure just north of the Delaware basin. Although diverse elements contribute to the different porous zones, platy or phylloidal algae are a dominant factor in some of the zones. Conley field, Hardeman County, Texas, produces from three separate formations, including a limestone reservoir in the early Missourian (Canyon) Palo Pinto Formation. This unit is articularly noteworthy for the profusion of algae and the nearly complete dependence of reservoir development on the organisms. Though much smaller in volume, this reservoir is petrologically very similar to that described from the Aneth field complex of the Paradox basin. Phylloid algal reservoirs commonly are surrounded by nonporous mudstone and wackestone and thus fall in the class of reservoirs wherein sediment genesis is an important factor in pore origin. An initial pore network End_Page 726------------------------------ controlled by plate morphology helps localize later diagenetic events, which ultimately produce a well-connected, predominantly large-pore network. This provides for large initial production rates and relatively high recovery factors, which are very desirable reservoir attributes from an economic standpoint. End_of_Article - Last_Page 727------------