Shannon Sandstone
Marine Shelf Sand in Wyoming's Multi-Pay Powder River Basin
Location
Key Reservoir Properties
Late Cretaceous (Campanian)
Fine to medium-grained marine sandstone
7,500 - 10,500 ft
12-18%
36.0° API
Executive Summary
The Shannon Sandstone is a Late Cretaceous marine shelf deposit in the Powder River Basin that contributes to the region's stacked pay potential. Part of the Cody Shale interval, the Shannon was deposited in a marine environment as part of the Western Interior Seaway transgression-regression cycles.
While not as prolific as the Turner or Parkman, the Shannon provides additional completion targets in multi-zone development strategies, enhancing overall Powder River Basin economics.
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Historical Background
Shannon Sandstone production began from conventional vertical wells targeting shelf sand bodies with higher permeability. The formation contributed to Powder River Basin oil output for decades before horizontal drilling expanded the productive footprint.
From 2009 to 2014, combined Shannon, Sussex, and Frontier production grew from 8,900 bbl/d to 17,000 bbl/d as horizontal technology improved recovery from these marine sand targets.
Geological Characteristics
The Shannon Sandstone Member of the Cody Shale was deposited in a marine shelf environment during the Campanian age. The formation comprises fine to medium-grained sandstone with interbedded marine shales indicative of fluctuating water depths and sediment supply.
The Shannon is commonly developed with the Sussex Sandstone, which lies stratigraphically above. Both formations represent marine sand bodies encased in organic-rich Cody Shale.
Reservoir Properties
Shannon sandstones exhibit moderate reservoir quality with porosity of 12-18% and permeability of 0.1-5 mD. Higher permeability zones can be prolific producers while tighter intervals require stimulation.
Oil gravity ranges 36-44 API with moderate solution gas. The marine depositional setting creates laterally continuous sand bodies favorable for horizontal development.
Production History
Shannon production has increased with horizontal drilling, though it remains secondary to Turner and Parkman targets. The formation provides incremental resource capture in multi-zone development strategies.
Historical vertical production continues from higher-permeability intervals while horizontal wells access tighter resources.
Drilling & Completion Economics
Shannon horizontal wells cost $4.5-6 million depending on lateral length and completion design. The shallower depth compared to Turner reduces drilling costs. Multi-zone completions targeting Shannon and Sussex can improve capital efficiency.
Production Decline Analysis
The Shale Decline Reality
While industry headlines tout record production, the underlying data reveals a critical truth: shale wells experience dramatic production declines that require constant drilling just to maintain output. This creates a "treadmill" effect where massive capital expenditure is needed simply to prevent production collapse.
Industry Expert Analysis
"New wells drilled in 2023 may ultimately produce roughly half of what new wells from 2019 will ultimately produce. The industry is sacrificing future production to maximize short-term output."
— Art Berman, Petroleum Geologist (40+ years experience)The Lateral Length Paradox
Since 2014, the industry has nearly tripled average lateral lengths from 5,000 ft to 14,000+ ft. While this increases initial production rates, it also accelerates decline—effectively using "wider straws" to drain reservoirs faster.
Key Investment Considerations
Decline Risks
- Hyperbolic Decline: 65-75% production loss in year 1 (vs 5-6% for conventional)
- Child Well Problem: 85% of new wells produce less than expected
- Inventory Exhaustion: Tier 1 acreage running out within 3-5 years
- Treadmill Economics: Continuous drilling required just to maintain output
Counter-Perspectives
- Technology continues improving operational efficiency
- Infill drilling potential may extend productive life
- Multi-zone development can maximize recovery
- Higher commodity prices improve economics on marginal wells
Decline Analysis Data Sources
- IEA - International Energy Agency, "The Implications of Oil and Gas Field Decline Rates" (2024)
- EIA - U.S. Energy Information Administration, Production Decline Curve Analysis
- SPE/JPT - Society of Petroleum Engineers, "Shale Wells Producing More Early On, Then Declining Faster Than Ever"
- Art Berman - Petroleum Geologist, artberman.com - Shale decline analysis
- David Hughes - Geoscientist, Post Carbon Institute - Shale production studies
- Goehring & Rozencwajg - Natural Resource Investors, Permian Basin analysis
- Novi Labs - Delaware Basin and shale well performance data
Economic Analysis
Shannon economics benefit from lower drilling costs and moderate reservoir quality. Breakeven prices around $50-55/bbl make the formation economic at constructive oil prices.
Stacked pay potential with Sussex and other targets enhances project economics when multiple zones can be completed from common wellbores.
Remaining Potential & Future Opportunities
The Shannon Sandstone offers continued development potential as part of multi-zone Powder River Basin strategies. The formation's marine sand character and lateral continuity support efficient horizontal development.
Conclusion
The Shannon Sandstone contributes valuable incremental production to Powder River Basin development. While not a standalone play driver, the formation enhances overall basin economics through stacked pay development.
Data Sources & References
- Wyoming State Geological Survey - Cody Shale and Shannon studies
- USGS - Powder River Basin petroleum systems
- Wyoming OGCC - Production and well data
- EIA - Regional production statistics
Important Disclaimer
This geological review is provided for educational and informational purposes only. The author, Sean Pruitt, is not a licensed geologist. Information presented here has been compiled from publicly available sources including USGS reports, state geological surveys, academic publications, and industry data. Reservoir properties and production data represent ranges observed across productive areas and may vary significantly by location. Kingdom Exploration makes no representations or warranties regarding the accuracy, completeness, or reliability of this information for any specific purpose. This content does not constitute investment advice, geological consulting, or professional engineering recommendations. Investors and operators should conduct their own due diligence and consult qualified licensed professionals including petroleum geologists, reservoir engineers, and financial advisors before making any investment or operational decisions.
