John C. McCaslin
Exploration Editor
One can always count on Wyoming's Powder River basin for exploratory success/The third Minnelusa oil well in WD field has been completed in eastern Campbell County, 9 miles southeast of Gillette. Two other wells in the new field have also been good producers. In the past few months, continued success in wildcatting, offsetting, and development work, have kept the big and prolific Wyoming basin in the forefront of oil news pages. There have been new Cretaceous Dakota producers in North Buck Draw Unit, Pennsylvanian Minnelusa wells have been added to several areas, including West Prong. The latest new strike at WD promises to become another in a long line of excellent Minnelusa pools.
CONTINUED SUCCESS
Last summer, Ampolex (Wyoming) Inc. opened WD field at 34-34 Wolff in SW SE 34-49n-71w.
The well made 359 b/d of 28.3 gravity oil and some gas from the Pennsylvanian Minnelusa "A" sand at 9,925-58 ft. Petroleum Information reported in November that the discovery well had produced 15,726 bbl of oil in its first 3 months of life, June through August.
Ampolex then confirmed the excellent strike at a south offset, the 21-3 C-T in NE NW 3-48n-71w. This one made 320 b/d of oil from the Minnelusa at 9,950 ft. PI notes that this well made 4,697 bbl of oil and 303 bbl of water during its first month of production last August.
Newest producer to tie this new field down as an excellent producer is 24-34 Federal in SE SW 34-49n-71w. Completed on pump got 290 b/d of 25.5 gravity oil with no water from perforations at 9,956-70 ft. The well was drilled by Exeter Drilling Co. Rig 20.
PI adds that Ampolex is the Denver based subsidiary of Ampol Exploration Ltd. of Sydney, Australia, and LASMO Energy Corp., a unit of LASMO plc of England. The two are doing exploratory work in a 15 wildcat campaign on prospects developed by Ampolex and Denver's McAdams, Roux & Associates.
FOR 100 YEARS
The Powder River basin is the largest in Wyoming. It is also one of the most lucrative places to look for oil in the world. Years of wildcatting and development work began in 1889 at Salt Creek where seeps were examined. The structure itself was drilled in 1906, opening Salt Creek field, the largest in the Rockies until many years later. Drilling peaked in the 1950's with an avalanche of Cretaceous strikes, followed by a series of important and flush Cretaceous Muddy sand pools.
Cretaceous objectives were favorites for the oil hunters for many years. This interest has not died down, either. Looking for Pennsylvanian Minnelusa oil is now one of the highlights of Rocky Mountain exploration. It has become the prime target in the shallower section on the eastern side of the basin. Minnelusa hunting offers pays at 7,000-10,000 ft. The zone also offers lower drilling costs with total reserves generally lower, about 100-400 bo/d, but wells may be drilled on 40-80-acre spacing, offering good exploration economics in any one's book.
Those interested in basin economics note that high volume initial production, 500-1,000 b/d of oil, is part of the appeal of looking for Cretaceous oil. Total reserves per well typically fall in the 200,000-300,000 bbl range, along with significant amounts of gas, according to an article by Mary Fritz in AAPG's Explorer. Quoting James Barlow of Casper, she notes that the 13,000-14,000 ft wells offer the advantage of quicker payout and an overall higher success ratio than the Minnelusa, but higher drilling costs, 640 acre spacing, and well quality are risk factors.
Copyright 1990 Oil & Gas Journal. All Rights Reserved.