Abstract

Block 16 is located in south-central Ward County, Texas on the eastern flank of the Delaware Basin. It is one of the more prolific fields of the deep Paleozoic gas play in the Delaware Basin. Primary producing reservoirs are present in the Devonian chert and Lower Ordovician Ellenburger dolomite.

Block 16 is an anticlinal structure with closure extending nine miles northwest and three miles northeast. The structure is asymmertic to the southwest with both independent and fault closure on that flank. Maximum gas column thickness in the Ellenburger is approximately 1300 feet which equals the Ellenburger thickness. Demonstrable structural growth on both the anticline and bounding faults dates from early Desmoinesian or Strawn (Middle Pennsylvanian) into Wolfcampian (Lower Permian). Structural terracing occurs on younger Permian data horizons.

The discovery well was the Exxon Pyote Gas Unit 4-1 completed in 1968. At present the field is nearing final definition with 22 gas-condensate completions in each reservoir. Well spacing is 640 acres. Probable final field recovery should exceed 1.3 TCFG and 18 MMBC. Production through 1974 has totaled 540 BCFG and 10.2 MMBC. The Ellenburger reservoir is the larger producer, accounting for 54% of produced gas and 86% of produced condensate. Combined daily average production in January 1975 was 348 MMCFG and 5860 BC. Exxon and Mobil are principal operators in the field.

The Devonian reservoir averages 450 feet in gross thickness with an average net pay thickness of 83 feet (more than 4% porosity); average porosity is 6.1%. Storage capacity is present in fractured novaculitic chert and in vugular and intercrystalline porosity in dolomites. The Ellenburger is dolomite with low vugular and intercrystalline porosity. Storage capacity is augmented and rendered permeable by fracturing. Average gross pay in this unit is 800 feet. Drilled depth to the axis of the Devonian reservoir is 13,200 feet. The Ellenburger centroid is at 16,400 feet.