Subsurface Laboratory Methods 289 



These beds also include the Weber sandstone of Colorado and Utah and 

 the Quadrant formation of Montana. 



The greater part of the oil production of the Rocky Mountain 

 region now comes from Pennsylvanian beds. Larger and more productive 

 fields producing from Pennsylvanian beds include Lance Creek (Minne- 

 lusa), Elk Basin (Tensleep), Salt Creek (Tensleep), Steamboat Butte 

 (Tensleep), Wertz (Tensleep), Rangely (Weber), and Lost Soldier (Ten- 

 sleep) . The Quadrant formation of Montana has yielded a negligible 

 amount of oil in central Montana but for the most part produces only 

 copious quantities of water. 



In general, Pennsylvanian waters are saline, with the salinity being 

 due principally to the sulphate ion. Like the Permian waters previously 

 discussed, the Pennsylvanian waters are marked by persistent and appre- 

 ciable secondary characteristics; bicarbonate is usually low. Hydrogen 

 sulphide is commonly present but usually not in any great quantity. 



The Weber water in Colorado and Utah is a chloride-saline type 

 with appreciable quantities of sulphate. At Rangely a brine varying from 

 about 100,000 parts per million to 150,000 parts per million total solids 

 is associated with oil, and this is the highest-concentrated oil-field water 

 from a producing field in the Rocky Mountain region. The Rangely brine 

 is principally sodium chloride, the chloride ion ranging from 60,000 to 

 100,000 parts per million and the sodium from 35,000 to 60,000 parts per 

 million; calcium averages 5,000 parts per million and magnesium about 

 650 parts per million. 



The Quadrant waters of Montana are typical Pennsylvanian waters. 

 They average about 3,000 parts per million total solids and consist prin- 

 cipally of the sulphates of sodium, calcium, and magnesium. Secondary 

 salinity occupies from forty to seventy percent of the chemical system, 

 and traces of hydrogen sulphide are usually found in the fresh water. 

 Artesian flows, usually hot, of 10,000 to 125,000 barrels a day are en- 

 countered in the Quadrant formation in the Montana fields tabulated in 

 table 14, and these waters are the youngest encountered in north-central 

 and central Montana that consistently contain large quantities of sulphate 

 and the alkaline earths. 



The area in Montana embracing the new fields of Big Wall, Melstone, 

 and Ragged Point is now controversial as to the age of the producing hori- 

 zon. Water analyses seem to indicate that the three fields are producing 

 from lithologically identical units, but present opinion places Big Wall 

 and Melstone production as Amsden and Ragged Point as Kibby of 

 Mississippian age. The author has placed all analyses in the Pennsyl- 

 vanian table as Amsden(?) , but further study of the formation may change 

 this grouping. 



Tensleep and Minnelusa waters in Wyoming vary from dilute to mod- 

 erately concentrated (from a low of 200 parts per million at Derby Dorne 

 to 13,000 parts per million at Quealy Dome) but on the whole average 



