A PETROGRAPHIC ANALYSIS OF THE RELATIONSHIP BETWEEN POROSITY AND ORGANIC MATTER IN THE PHOSPHORIA FORMATION OF NORTHEASTERN UTAH

The Phosphoria Formation is a reservoir for oil and gas in the western United States, as well as a major source of phosphate. The relationship between the relative phosphate levels and porosity was examined by performing a petrographic analysis of the Phosphoria (Park City) Formation north of Vernal Utah, on the southern flank of the Uinta Mountains.

The research concluded that the differences in porosity in the Phosphoria Formation are controlled by lithology, amount of compaction, weathering and the amount of fecal pellets, the source of phosphate in this formation. The beds with a higher abundance of organic material, including fecal pellets, tended to have reduced porosity. While the beds with low abundance of organic material tended to have higher porosity.

Levels of phosphate within the Phosphoria Formation represent a good model for determining levels of porosity in possible subsurface hydrocarbon reservoirs. While high porosity exhibited at the surface would represent low phosphate levels, which is important for phosphate exploration and future surface mining operations.