--> Abstract: Geological Controls on Formation Water Salinity Distribution, Southeastern Greater Natural Buttes Field, Uinta Basin, Utah, by Tuba Evsan, Marc Connolly, and Matthew J. Pranter; #90169 (2013)
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Geological Controls on Formation Previous HitWaterNext Hit Salinity Distribution, Southeastern Greater Natural Buttes Field, Uinta Basin, Utah

Tuba Evsan, Marc Connolly, and Matthew J. Pranter
University of Colorado at Boulder

Use of conventional petrophysical evaluation techniques at Greater Natural Buttes Field in the Uinta Basin is challenging. One reason for this is that sandstone gas reservoirs of the Upper Cretaceous Mesaverde Group have variable fluid saturation along with low matrix porosity and permeability. For petrophysical analysis, the study interval was divided into seven stratigraphic zones based on net-to-gross ratio and variation in resistivity. Pickett plot analysis was conducted for these zones in each well to determine formation Previous HitwaterNext Hit resistivity. Because many Mesaverde Group sandstones do not exhibit 100% Previous HitwaterNext Hit saturation, Pickett plot analysis often relied on interpreting irreducible Previous HitwaterNext Hit saturation. Moreover, Previous HitwaterNext Hit resistivity was used with formation temperature to determine formation Previous HitwaterNext Hit salinity. Temperature data from production logs show that the Wasatch Formation and Mesaverde Group have higher geothermal gradients than formations that are stratigraphically above. Therefore, formation temperature was estimated using these gradients which are consistent through the study interval. Total, irreducible, and free-Previous HitwaterNext Hit saturation were determined in order to evaluate the relationship between movable Previous HitwaterNext Hit saturation and salinity variations. Previous HitWaterNext Hit saturation calculations based on the Archie equation are higher than values based on the Waxman and Smits equation due to Previous HitboundNext Hit Previous HitwaterNext Hit associated with shale and clay. Petrophysical analysis indicates more fresh Previous HitwaterNext Hit is present in the eastern part of the study area, while salinity increases and Previous HitwaterNext Hit saturation decreases stratigraphically upward. This may be due to natural fractures enhancing imbibition of fresh Previous HitwaterNext Hit into deeper zones creating the observed variability in salinity and Previous HitwaterNext Hit saturation. Basement faults are believed to create these natural fractures impacting gas and Previous HitwaterTop production across parts of the field.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013