Project Media:
Study Year: 2011-2012

EORI Tensleep ROZ Study Summary 2011‐2012

Nick Jones of EORI explores the application of Permian Basin ideas to the Bighorn Basin through the use of cores, cuttings, well logs, PI cards, and more.

Apply Permian Basin idea to Bighorn Basin.

  • Importance of ROZ
  • Recovered oil from ROZ.

Data collection

  • Cores, cuttings, well logs, PI cards, completion, workover, operator communications.
  • Create database to organize the data.

Recognition &. Mechanisms

  • HC shows below and around MPZ.
  • Information provided by reservoir geologists and engineers.
  • Oil migration and accumulation history.


  • Select Frannie‐Sage Creek‐Homestead region as an example.
  • From data collection to potential ROZ reserve.

Tensleep Potential ROZ reserves in Bighorn Basin.

  • Potential Tensleep ROZ reserve.
  • ROZ fairway.


Deformation, Migration, and Accumulation

Early Mesozoic – Oil begins migrating into stratigraphic traps

Note: The uppermost sequence of the Tensleep Formation has already been eroded prior to deposition of the overlying Phosphoria Formation creating an erosional unconformity.

Late Mesozoic– Structural traps begin developing and charging

Regional dip is down to the southwest (present day) allowing migration to proceed up gradient, as migration occurs connate formation water is displaced and reduced to residual saturation.

Early Tertiary – Fracturing, faulting and compartmentalization?

Developing thrust faults begin to compartmentalize anticlinal structures affecting continued migration and accumulation of oil. Early stages of meteoric influx begin to degrade updip oil accumulations resulting in low API gravity oil and in some places result in tar layers at the OWC.

Late Tertiary– Hydrodynamic charging flushes existing oil accumulations?

Over time cementation of crestal fractures degrades fluid movement resulting in the majority of accumulations of oil to occur down dip of the fault plane and crest of the anticline. Water influx and tilted OWC’s need to be reevaluated with respect to initial reported production and drainage of off structure fractures.


Why is it different in Wyoming?

  • Lessons from early development in the Bighorn Basin
  • Water wet below the Main Pay Zone (MPZ) – Noneconomic!

Source rocks are younger than reservoir rocks.

  • Deposition, deformation, and erosion of upper Tensleep
  • Permian facies (deep marine shales to shallow marine carbonates)

Severity and timing of structural deformation.

  • Encroachment of the Antler Arc
  • Impact of the Sonoma, Nevadan, and Sevier Orogenies
  • Impact of Greybull Arch (Permian)
  • Affect of the Laramide Orogeny
  • Regional Uplift and Rotation (Colorado Plateau)

Uplift, timing and erosional exposure.

  • Laramide (~50‐100 mya) Upper Cretaceous – Early Tertiary
  • Exacerbated structural deformation in Tertiary Paleocene Time

A different perspective on opportunities

  • Main Pay zone only represents a small percentage of rock volume
  • Economic limits – Wettability – Primary Strata – Reservoir Geometry



Lessons from early development in the Bighorn Basin

  • Early on pay was defined based on economic saturations and porosity
  • Drilling costs and water handling were key factors
  • Undeveloped zone (ROZ) volumes far exceed developed pay volumes (Undeveloped zone oil saturations range from 30‐50% from evaluation of Frannie‐Sage Creek area)

Geologic Setting

  • Rocky Mountain tectonics vs Permian Basin tectonics
  • System source rocks – Just not there anymore!
  • Closed vs Open fracture networks
  • Timing and style of migration
  • Isolated and compartmentalized structures


  • Form and Fill?

Opportunities & Challenges for CO2‐EOR in Wyoming

  • Bighorn Basin – Needs pipelines
  • Wind River Basin – Active work by Denbury
  • Casper Arch – Active Fleur De Lis
  • Sand Wash Basin – Active Memorial Resources


Acknowledgements & Credits: • Enhanced Oil Recovery Commission • Wyoming Oil & Gas Conservation Commission • Wyoming Geological Association • Wyoming Pipeline Authority • University of Wyoming School of Energy Resources • Peigui Yin • Matt Johnson • Steve Fryberger