Sussex Sandstone
Powder River Basin Upper Cretaceous Target - Shallow Marine Sandstone Producer
Location
Key Reservoir Properties
Upper Cretaceous (Campanian, 75-80 Ma)
Marine shelf sandstones with stratigraphic and structural traps
6,000 - 10,000 ft
14-22%
36.0° API
Executive Summary
The Sussex Sandstone represents an important Upper Cretaceous reservoir interval in the Powder River Basin, producing from marine shelf sandstones deposited during the Campanian stage of the Late Cretaceous. This thin but productive interval has yielded significant volumes from stratigraphic and structural traps across eastern Wyoming.
- Prolific Upper Cretaceous Target: One of multiple productive Cretaceous intervals in the basin
- Shallow Marine Origin: Shelf sandstones with favorable reservoir properties
- Moderate Depths: Production from 6,000-10,000 feet enables reasonable well costs
- Light Oil: 36 API gravity crude with associated gas
- Multiple Trap Types: Both stratigraphic and structural traps provide exploration targets
- Horizontal Potential: Amenable to modern horizontal development techniques
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Historical Background
The Sussex Sandstone has been developed across the Powder River Basin as one of several productive Cretaceous targets.
Development History: Sussex production was established as operators explored the multiple Cretaceous intervals exposed in the basin. The formation's favorable reservoir properties and combination of trap types supported sustained development activity.
Stacked Development: The Sussex is often developed alongside other Cretaceous targets including the Shannon, Muddy, and Frontier sandstones, maximizing value from established acreage positions.
Geological Characteristics
The Sussex Sandstone comprises an Upper Cretaceous (Campanian) marine shelf sandstone sequence deposited in the Western Interior Seaway.
Depositional Environment
Sussex sediments accumulated on a shallow marine shelf during periods of active sediment supply from western highlands. The resulting sandstones exhibit good reservoir quality where preserved.
Stratigraphic Position
The Sussex lies within the Cody Shale equivalent section, representing a regressive sandstone tongue within the predominantly shale sequence.
Trap Types
Production occurs from both stratigraphic traps related to sand body geometry and structural traps on basin-margin anticlines.
Reservoir Thickness
Net pay ranges from 15 to 60 feet depending on depositional setting and preservation.
Reservoir Properties
Sussex reservoir properties reflect its marine shelf sandstone origin. Porosities range from 14% to 22% with permeabilities of 20-150 millidarcies in productive intervals. The well-sorted marine sandstones provide favorable reservoir quality.
Oil gravity averages 36 API with gas-oil ratios of 400-1,000 scf/bbl.
Production History
The Sussex Sandstone produces from approximately 2,200 active wells across the Powder River Basin. Development activity peaked in the 1990s but continues today as part of multi-zone programs.
Drilling & Completion Economics
Sussex development employs conventional techniques with wells reaching 6,000-10,000 feet. Well costs average $4-5 million. Horizontal drilling offers potential to improve recovery from thin but laterally extensive reservoirs.
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
Sussex economics benefit from moderate depths and proven production. With breakeven prices around $40/bbl, the play remains attractive where reservoir quality is favorable.
Remaining Potential & Future Opportunities
The Sussex Sandstone retains development potential in less-developed areas and through application of horizontal drilling techniques to improve recovery from thin pay zones.
Conclusion
The Sussex Sandstone represents a proven Upper Cretaceous target in the Powder River Basin, with marine shelf sandstones providing quality reservoir development opportunities across eastern Wyoming.
Data Sources & References
- Wyoming State Geological Survey - Cretaceous reservoir studies
- USGS - Powder River Basin assessment
- Wyoming Oil and Gas Conservation Commission - Production records
- Pruitt, Sean - Owner, Kingdom Exploration
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.
