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Geology of the Billy (Abo) Field: Lamb County, Texas

J. Michael Party1 and A. E. “Tony” D'Agostino
1 Wagner & Brown Ltd

Wagner & Brown, Ltd., with its partner Burlington Resources, spudded the Billy C #1 well in November 1994. This well was completed flowing 37 barrels of oil on January 13, 1995 and is the discovery well for the Billy (Abo) Field. The Billy (Abo) Field is located in southern Lamb County (Fig.1), south of the town of Littlefield, and produces from the Leonardian Abo formation (Fig. 2). Production in and around the discovery had only occurred previously from overlying San Andres and Clearfork formations. To date, the Billy (Abo) Field has produced 1,543,303 barrels of oil.

The Abo formation is a time-transgressive formation of early to middle Leonardian age. Early Leonardian depositional geometry in the northern Permian Basin was that of a rimmed shelf margin. Several outcrop and subsurface studies have documented the existence of well-defined continental, sabkha/supratidal, intertidal, subtidal, and basinal environments along the northern rim of the Permian Basin. These same facies tracts are very evident within the 2,000 plus feet of core taken from 19 wells within the Billy (Abo) Field. These cores were studied in great detail to determine the depositional environments and porosity types as they relate to production and subsequent exploration. The main producing intervals in the Billy (Abo) Field are interpreted as intertidal peloid grainstones deposited in tidal channels or as bars and shoals along the paleo-shoreline (Fig. 3).

Overall porosities in the Abo reservoirs of the field range from 2% up to over 30%, with the average being around 12%. Porosity varies greatly from facies tract to facies tract. As examples, the depositionally high intertidal to supratidal facies have been heavily occluded with anhydrite, greatly diminishing their porosity values. The grainstones of the intertidal facies were dolomitized very early and have been subjected to a later stage diagenetic event that has leached out some of the dolomite rhombs, enhancing the porosity (Fig. 4). The better porosity in the subtidal facies tract is interparticle and intraparticle (moldic) porosity. This porosity type is a good producing facies when found above the field’s oil- water contact of –3200’ (Fig. 5).