Abstract

Over twenty-three million barrels of oil and thirty billion cubic feet of gas have been produced since 1963 from a stratigraphic trap in Desmoinesian age Strawn chert conglomerates in the Arenoso Field area, Winkler County, Texas. The Arenoso sub-basin on the Central Basin Platform was the site of deposition of an alluvial fan created from the erosion of weathered Devonian and older cherts off the surrounding exposed, faulted structural uplifts. This alluvial deposit filled the southeast corner of the small sub-basin while shallow marine Strawn limestones filled the remainder of the sub-basin. Numerous periods of minor sea level rise deposited shallow marine carbonates between alluvial fan debris flows; subsequent subaerial exposure created terra rossa surfaces and other evidence of soil horizon development observed in cores from the field. The alluvial deposit was drowned by Late Strawn sea level rise and buried by younger Pennsylvanian shelf carbonates. During Wolfcampian regional deformation the deposit was tilted to the west. The preservation of this coarse alluvial fan deposit created an excellent hydrocarbon trap. Updip proximal-fan facies produce in isolated small pods of porosity; medial and distal braided stream and shoreface deposits are the most prolific producing depositional facies.