Traps and Reservoirs in the Phosphoria and Tensleep Formations of the Big Horn Basin: ABSTRACT

Abstract

Phosphoria and Tensleep traps in the Big Horn basin are contrasted as to those controlled by strong artesian water flow, and others where subsurface water movement is at a minimum. Fresh waters cause changes in the nature of the entrapped petroleum as a result of lower temperatures and replenishment of oxygen at the oil-water interface. Closures protected from the regional direction of movement for artesian waters are less affected by these factors and contain crudes of abnormally high gravity, or gases with high concentrations of H2S. It is concluded that reservoirs modified least by mechanical and chemical effect of artesian waters are those which most closely approximate the original conditions of petroleum generation and entrapment. These reservoirs are in the deeper part of the basin, or in traps where pressure alone--rather than motion and pressure--holds the hydrocarbons and associated substances in place. End_of_Article - Last_Page 2613------------