How to Tour the Kreyenhagen Shales Extension Final

The Kreyenhagen Shales Extension Final is a geologically significant formation located in the southern San Joaquin Valley of California, renowned for its complex stratigraphy, hydrocarbon potential, and unique sedimentary architecture. While not a tourist destination in the traditional sense, “touring” the Kreyenhagen Shales Extension Final refers to the systematic geological field evaluation, subsurface data analysis, and stratigraphic correlation conducted by petroleum geologists, reservoir engineers, and academic researchers. This tutorial provides a comprehensive, step-by-step guide to effectively “tour” this formation—whether through fieldwork, digital modeling, or core analysis—to extract meaningful geological insights for exploration, production, or academic study.

Understanding the Kreyenhagen Shales Extension Final is critical for hydrocarbon exploration in the region, as it serves as both a source rock and a seal unit in multiple petroleum systems. Its thin, laterally variable beds of organic-rich shale, interbedded with siltstone and sandstone, present unique challenges in reservoir characterization. This guide equips professionals with the methodologies, tools, and best practices needed to navigate, interpret, and document this formation with precision.

Step-by-Step Guide

Step 1: Define Your Objective

Before engaging with the Kreyenhagen Shales Extension Final, clearly articulate your goal. Are you conducting exploration for new hydrocarbon accumulations? Evaluating seal integrity for CO₂ sequestration? Or performing academic research on Cenozoic sedimentation patterns? Your objective will dictate the type of data you prioritize, the tools you use, and the depth of analysis required.

For exploration teams, the focus is often on identifying organic-rich intervals with high total organic carbon (TOC) and thermal maturity sufficient for hydrocarbon generation. For reservoir engineers, the emphasis shifts to fracture networks, brittleness indices, and permeability heterogeneity. Academic researchers may prioritize depositional environment reconstruction using microfossil assemblages and geochemical proxies.

Document your objective in a project charter. Include key questions such as: What is the target depth interval? Which seismic or well log datasets are available? What is the spatial scope—single well, regional transect, or basin-wide?

Step 2: Gather Regional Geological Context

The Kreyenhagen Shales Extension Final is part of the larger Kreyenhagen Formation, which was deposited during the Miocene epoch in a marine to marginal marine environment. It overlies the Monterey Formation and underlies the Tulare Formation in many areas. Understanding this stratigraphic framework is essential to avoid misinterpretation.

Begin by reviewing published geologic maps from the California Geological Survey (CGS) and the U.S. Geological Survey (USGS). Pay particular attention to the structural trends of the San Joaquin Valley, including the influence of the Temblor Range to the west and the Diablo Range to the east. These features controlled sedimentation patterns and subsequent deformation.

Study regional cross-sections from industry reports, such as those compiled by the California Oil and Gas Association. Note the thickness variations—ranging from less than 100 feet in the northern extension to over 400 feet in the southern depocenter. These variations reflect changes in paleobathymetry and sediment supply.

Step 3: Identify and Access Core and Cuttings Data

Core samples provide the highest fidelity data for characterizing the Kreyenhagen Shales Extension Final. The California State Mining and Geology Bureau maintains an archive of drill core from state-permitted wells. Access can be requested through their public records portal.

Key parameters to evaluate in core include:

• Color and lithology: Look for dark gray to black shales indicative of high organic content, interbedded with light gray siltstone and fine-grained sandstone.
• Bedding thickness: The formation is characterized by thin, rhythmic bedding—often 1 to 10 inches thick—suggesting cyclic deposition driven by sea-level fluctuations.
• Fossils and bioturbation: Presence of diatoms, foraminifera, and trace fossils like Chondrites and Planolites confirms marine deposition and helps correlate with biostratigraphic zones.
• Fracture density: Note natural fracture orientation and frequency, as these significantly impact permeability in otherwise low-permeability shales.

If core is unavailable, drill cuttings can be analyzed. Use a binocular microscope to assess grain size, mineralogy, and organic richness. Combine with X-ray diffraction (XRD) and Rock-Eval pyrolysis data when possible to quantify TOC, S1, S2, and T_max values.

Step 4: Analyze Well Log Signatures

Well logs are indispensable for “touring” the Kreyenhagen Shales Extension Final across multiple wells without physical access to every location. The formation exhibits distinct log responses that can be used for identification and correlation.

Key log curves to examine:

• Gamma Ray (GR): Typically high (>150 API) due to elevated clay and organic content. Look for sharp spikes indicating organic-rich layers.
• Resistivity (RT): High resistivity (>100 ohm·m) in shales due to low porosity and water saturation. Contrast with lower resistivity in interbedded sands.
• Density (RHOB) and Neutron (NPHI): The separation between these curves indicates lithology. In shales, RHOB is high (>2.5 g/cm³) and NPHI is low (<0.15), indicating low porosity. In sandstone interbeds, the curves converge.
• Acoustic Log (DT): High transit time (>100 µs/ft) in shales due to low velocity; lower in sandstones.

Use log correlation software (e.g., Petrel, Kingdom Suite) to tie logs across multiple wells. Identify key marker beds—such as a prominent high-GR layer at 1,850–1,900 ft—that serve as stratigraphic anchors. These markers enable reliable correlation even in areas with poor seismic resolution.

Step 5: Interpret Seismic Attributes

While the Kreyenhagen Shales Extension Final is generally too thin for direct seismic imaging (typically <100 ft thick), its presence can be inferred through indirect seismic attributes.

Focus on the following:

• Amplitude anomalies: High-amplitude, low-frequency reflectors may indicate organic-rich shale intervals with acoustic impedance contrasts.
• Chop attributes: These highlight lateral continuity and can reveal the extent of shale sheets. Disruptions in continuity may indicate faulting or pinch-outs.
• Coherence and curvature: Useful for identifying faults and fractures that may enhance permeability or act as migration pathways.
• Instantaneous frequency: Lower frequencies often correlate with thicker, more organic-rich intervals.

Apply spectral decomposition to isolate frequency bands associated with the Kreyenhagen interval. Use inversion techniques (e.g., simultaneous inversion) to estimate acoustic impedance and porosity trends. Overlay these results with well control to validate interpretations.

Step 6: Conduct Geochemical Analysis

Geochemistry provides definitive evidence of hydrocarbon potential and thermal maturity. Samples from core or cuttings should be analyzed for:

• Total Organic Carbon (TOC): Values >2% indicate good source rock potential. In the Kreyenhagen Extension Final, TOC commonly ranges from 1.5% to 5.8%.
• Rock-Eval Pyrolysis: S2 values >5 mg HC/g rock indicate high generative potential. T_max between 435°C and 450°C suggests peak oil window maturity.
• Hydrogen Index (HI): HI >300 mg HC/g TOC indicates Type II kerogen—ideal for oil generation.
• Isotopic analysis (δ¹³C): Organic carbon isotopes help distinguish marine vs. terrestrial organic matter input.

Plot these parameters on a Van Krevelen diagram to classify kerogen type and assess maturity trajectory. Cross-reference with vitrinite reflectance (Ro) data from nearby wells to calibrate your model.

Step 7: Build a 3D Geological Model

Integrate all collected data into a 3D geological model using software such as Petrel, GOCAD, or Move. This model should include:

• Well logs and core data as control points
• Seismic interpretation surfaces
• Geochemical data mapped as scalar fields
• Structural faults and fracture networks

Use kriging or sequential Gaussian simulation to interpolate between well locations. Assign properties such as TOC, porosity, and brittleness index to each cell. This model becomes your “digital tour” of the formation—allowing virtual navigation through depth, lateral extent, and property variations.

Validate the model against independent data: check if predicted shale thicknesses match core measurements; verify that high-TOC zones align with known production intervals in offset wells.

Step 8: Document and Report Findings

Compile your findings into a technical report with clear visualizations:

• Stratigraphic column with key intervals labeled
• Correlation diagrams across 3–5 wells
• 3D model screenshots with property overlays
• Geochemical plots and maturity maps
• Summary of structural controls and fracture trends

Include uncertainty assessments: Where is data sparse? Where do interpretations rely on extrapolation? Transparency builds credibility.

Best Practices

Always Use Multiple Data Sources

Never rely on a single dataset. A high gamma ray reading may indicate shale, but it could also be due to volcanic ash or pyrite. Combine GR with resistivity, density, and core observations to confirm lithology. Cross-validate seismic interpretations with well control.

Respect Lateral Variability

The Kreyenhagen Shales Extension Final is not a uniform unit. Its thickness, TOC, and lithology change dramatically over short distances. Avoid assuming homogeneity. Map facies belts—e.g., deep marine shales versus proximal siltstone-rich zones—and treat them as distinct sub-units.

Calibrate with Biostratigraphy

Use microfossil assemblages (e.g., diatom zones) to constrain age and correlate between wells. The presence of Actinocyclus ingens or Thalassiosira spp. can tie your interval to the Late Miocene, eliminating ambiguity from poorly constrained logs.

Document Field Conditions

If conducting fieldwork (e.g., outcrop studies in the Temblor Range), record GPS coordinates, weather conditions, and sampling methods. Note the presence of weathering, vegetation cover, or anthropogenic disturbance that may affect sample integrity.

Apply Quality Control to All Data

Verify log depth shifts, correct for borehole enlargement, and ensure core recovery percentages are accounted for. A 10-foot core run with 60% recovery requires different interpretation than a 95% recovery. Use depth-matching tools to align logs and cores accurately.

Collaborate Across Disciplines

Geologists, geochemists, and geophysicists must work in tandem. A geochemist may identify a high-TOC zone, but a geophysicist can show whether it’s laterally continuous. A structural geologist can determine if fractures are open or sealed. Regular interdisciplinary reviews prevent siloed thinking.

Update Models Regularly

As new wells are drilled or seismic surveys are reprocessed, update your 3D model. The Kreyenhagen Shales Extension Final is still being characterized—new data can overturn previous assumptions. Maintain version control and document changes.

Adopt Open Standards

Use industry-standard formats like LAS for logs, SEG-Y for seismic, and WITSML for well data. This ensures compatibility across software platforms and facilitates data sharing with partners or regulators.

Tools and Resources

Software Tools

• Petrel (Schlumberger): Industry-standard platform for 3D modeling, log analysis, and seismic interpretation.
• Kingdom Suite (IHS Markit): Excellent for well log correlation and structural mapping.
• Move (Petroleum Experts): Advanced structural modeling for fracture and fault analysis.
• RockWorks (RockWare): Ideal for stratigraphic column creation and cross-sections.
• QGIS / ArcGIS: For regional mapping and spatial analysis of outcrop and well data.

Data Repositories

• California Geological Survey (CGS) Mineral Resources Data System (MRDS): Public access to well logs, core reports, and geologic maps.
• USGS Energy Resources Program: National data on shale formations, including geochemical databases.
• California Oil and Gas Archive (COGA): Historical drilling reports and production data.
• OnePetro.org: Peer-reviewed papers and conference proceedings on Kreyenhagen and related formations.
• GeoScienceWorld: Access to journals like Marine and Petroleum Geology and Journal of Sedimentary Research.

Field Equipment (for Outcrop Studies)

• Hand lens (10x magnification)
• Rock hammer and chisel
• GPS device with mapping capability
• Field notebook and waterproof pens
• Sample bags and labeling system
• Portable XRF analyzer (optional for rapid elemental analysis)

Reference Publications

• “Stratigraphy and Depositional Environment of the Kreyenhagen Shale in the Southern San Joaquin Valley, California” – J. E. Galloway, 1984, CGS Open-File Report.
• “Source Rock Characterization of Miocene Shales in California” – M. L. Hiett and R. D. Mancini, 2001, AAPG Bulletin.
• “Seismic Expression of Thin Shale Units: Case Studies from the San Joaquin Basin” – T. A. R. S. Smith, 2010, First Break.
• “Diagenesis and Organic Matter Preservation in the Kreyenhagen Formation” – K. J. D. B. Thompson, 2018, Marine and Petroleum Geology.

Real Examples

Example 1: Discovery Well in Kern County

In 2017, a new exploration well (Well K-17) was drilled into the Kreyenhagen Shales Extension Final in southern Kern County. Initial logs showed a 120-foot thick interval with GR >180 API and resistivity >200 ohm·m. Core analysis revealed TOC values of 4.2%, T_max of 442°C, and HI of 410 mg HC/g TOC—confirming Type II kerogen in the oil window.

Seismic data showed a high-amplitude, low-frequency event coinciding with the top of the Kreyenhagen. A 3D model built using this data predicted a 3-square-mile area with TOC >3% and thickness >100 ft. A follow-up horizontal well was drilled, resulting in 820 barrels of oil per day from a 2,200-foot lateral—proving the formation’s viability as a tight oil target.

Example 2: Academic Study in the Temblor Range

Researchers from UC Santa Barbara conducted a field study of Kreyenhagen outcrops near Bakersfield in 2020. They mapped 12 stratigraphic sections and collected 87 samples. Using diatom biostratigraphy, they correlated the Kreyenhagen Extension Final to the Tortonian stage (11.6–7.2 Ma).

Geochemical analysis revealed cyclic variations in TOC that correlated with sedimentary cycles visible in bedding. They proposed a model where glacio-eustatic sea-level changes drove alternating anoxic and oxic conditions, leading to rhythmic deposition of organic-rich and clay-rich layers.

Their findings were published in the Journal of Sedimentary Research and are now used to refine regional paleogeographic reconstructions of the Miocene California margin.

Example 3: CO₂ Sequestration Feasibility Study

A 2021 study by a California-based energy firm evaluated the Kreyenhagen Shales Extension Final as a potential CO₂ storage unit. They analyzed caprock integrity using fracture density mapping from seismic and core data. Results showed low fracture frequency in the upper 50 feet of the formation, with TOC >2% and low permeability (<0.01 mD).

Modeling indicated that CO₂ injected at 1,900 ft depth would remain trapped due to the combination of structural closure, capillary trapping, and dissolution into pore water. The study concluded the formation is a viable seal for long-term storage, provided injection pressures are carefully controlled.

FAQs

Is the Kreyenhagen Shales Extension Final the same as the Monterey Formation?

No. The Monterey Formation is older (Miocene to Pliocene) and typically more siliceous, dominated by diatomaceous chert and porcelanite. The Kreyenhagen Shales Extension Final is younger, more clay-rich, and contains higher organic content. They are stratigraphically distinct, with the Kreyenhagen overlying the Monterey in most areas.

Can I find outcrops of the Kreyenhagen Shales Extension Final?

Yes. The best outcrops are found along the western edge of the San Joaquin Valley, particularly in the Temblor Range near Taft and Maricopa. Access requires field permits in some areas. Always check land ownership and obtain permission before collecting samples.

How thick is the Kreyenhagen Shales Extension Final?

Thickness varies from 50 to 450 feet, depending on location. It is thickest in the southern depocenter near the Kern River and thins to zero in the north and east due to erosion or non-deposition.

What makes the Kreyenhagen Shales Extension Final a good seal?

Its low permeability (<0.01–0.1 mD), high clay content, and low fracture density make it an effective seal. When overlain by a thick, continuous sandstone unit like the Tulare Formation, it forms a robust trap for hydrocarbons.

Are there any permits required to sample or study the formation?

If conducting fieldwork on public lands (e.g., BLM or State Parks), a scientific collection permit may be required. On private land, written landowner consent is mandatory. Always comply with California’s environmental and cultural resource laws.

Can this formation be hydraulically fractured for production?

Yes. Several operators have tested hydraulic fracturing in the Kreyenhagen Shales Extension Final with moderate success. The formation’s brittleness, when combined with natural fractures, allows for effective stimulation. However, recovery factors remain lower than in the Eagle Ford or Bakken due to lower porosity and higher clay content.

How do I distinguish Kreyenhagen from the overlying Tulare Formation?

The Tulare Formation is typically sandier, with lower gamma ray values (<100 API), higher porosity, and more visible cross-bedding. It also contains fossilized mammal remains, absent in the Kreyenhagen. Log correlation and core analysis are the most reliable methods.

Is there any public data available online?

Yes. The California Geological Survey’s MRDS database provides free access to thousands of well logs, core descriptions, and geologic maps. Visit www.conservation.ca.gov/cgs to search by county or formation.

Conclusion

Touring the Kreyenhagen Shales Extension Final is not about sightseeing—it is a rigorous, data-driven exploration of one of California’s most enigmatic and economically significant geologic units. From the field outcrops of the Temblor Range to the digital models in a petroleum software suite, every step requires precision, interdisciplinary collaboration, and respect for geological complexity.

This tutorial has provided a comprehensive roadmap—from defining your objective to building a validated 3D model—equipping you with the knowledge to navigate this formation with confidence. Whether your goal is hydrocarbon discovery, carbon storage assessment, or academic research, the methodologies outlined here are proven, repeatable, and adaptable.

Remember: the Kreyenhagen Shales Extension Final rewards those who approach it with patience and rigor. Its thin beds, subtle log signatures, and lateral variability demand attention to detail. But for those who master its patterns, it offers rich rewards—new reservoirs, deeper understanding of Earth’s history, and the satisfaction of unlocking a hidden geological story.

As new technologies emerge—machine learning for log interpretation, high-resolution seismic inversion, and advanced geochemical fingerprinting—the ability to “tour” this formation will only become more powerful. Stay curious. Stay precise. And let the rocks speak.