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CO2-EOR Potential of the Muddy/Newcastle Sandstone Reservoir of Fiddler Creek Field, Weston County, Wyoming

Tomasso, Mark 1; Wo, Shaochang 1
1 Enhanced Oil Recovery Institute, The University of Wyoming, Laramie, WY.

Fiddler Creek Field, discovered in 1948 and divided into East and West units, lies on the eastern margin of the Powder River Basin in Weston County, Wyoming. The main reservoir is the Albian Newcastle Sandstone, which is the eastern equivalent of the Muddy Sandstone in the deeper Powder River Basin. Screening and simulation evaluation concluded that CO2 WAG flooding can be an effective EOR method for this reservoir. Injecting CO2 alternating with water improves the injection profile and reduces gas channeling.

Many of the fields within the Powder River Basin are structurally controlled by large-scale basement lineaments running along NE-SW and SE-NW trends. In the case of Fiddler Creek Field, the major control was a NE-SW trending lineament known as the Fiddler Creek Trend. This fault downthrows to the SE, and provided shallow topographic drainage to funnel sediment through to the deeper basin. The westernmost part of the field overlies the SE-NW trending Weston/Hat Creek Trend, which downthrows to the SW and offsets the Newcastle Sandstone by ~300’ in the study area.

A geological evaluation of the Muddy Sandstone was carried out in order to assess CO2-EOR potential. The study utilized closely-spaced SP wireline log data, in association with other logs and core-based petrophysical data. Seven separate SP log facies were identified. Isopach maps of the reservoir sandstone indicate that it is spread unevenly around the field, typical of a meandering fluvial belt within a confined low. The data indicate that there are probably two separate, vertically offset-stacked, sequences within the field. Structurally, it appears that the East Unit is heavily fractured, with fracture sets sub-parallel to the basement trends.

A static reservoir model of the field was generated, with SP log thicknesses used to estimate sandstone body widths using subsurface, outcrop, and numerical analogs. Over 600 stochastic runs were used to assess volumetric OOIP.

The relatively large pressure interval between the initial reservoir pressure and CO2-oil MMP measured from slim tube tests is considered favorable for miscible CO2 flooding. Simulation of CO2 WAG flooding was performed on representative sector models for the East and West units to examine the effect of flood pattern and fracture permeability on oil recovery. Four flood patterns were modeled. Simulation results were rescaled as dimensionless curves that were used to predict unit-wide performance of CO2-WAG floods.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009