1. Dr. Tark Hamilton Camosun College
Sedimentary Geology Geos 240 – Chapter 2 Collecting the Data Part 1 Geological, Stratigraphic & Petrophysical Data
Dr. Tark Hamilton
Camosun College

2. Collecting the Data Stratigraphic Sections from Surface Outcrops
Petrophysical logging of boreholes
Well cuttings and cores
Regional Geophysics
Labwork on sediments, rocks, fossils, fluids
Computer/Office: Mapping, Interpretation & Modelling
Alternatively there is always the Russian Method (make it up) or the American Method (industrial espionage or warfare)

3. Measuring a Stratigraphic Section
You can do this on the scale of a soil profile, a river bank or the cross section of a Mountain range!
Methods use Jacob’s Staff (ruled meter stick), measuring tape, altimeters or trigonometry e.g. thickness = baseline cos alpha where baseline is hypoteneuse and alpha is dip angle
Gayna River near Norman Wells NWT
Western Canada Sedimentary Basin

4. Measuring with a Jacob’s Staff
Use a 1.5 m stick with a level or dip arrow
Site along to next 1.5 m position in true thickness position and add!
One potato two potato three potato four!, Five potato Six potato…

5. Strip Log – Stratigraphic Section
Grain Size increases to right = resistance to weathering
Sands>> stick out while Shales<< are recessive

6. Castlegate Sandstone: Utah
Horizontal Photos & Line Drawing showing bedding, sequence boundaries & paleocurrent directions
~1 week’s work

7. Components of a Modern Exploration Rig on Land

8. Drilling Details: Mud Lubricates, Cools, Prevents Blowouts, Carries Cuttings & Fluids

9. Roller Bits For Various Hole Sizes
For Hard Rocks (Sandstones & Limestones)
Blade Bits are used for clays, coals and soft shales

10. Core, Core Boxes & Cuttings
Description is the major work of most wellsite geologists
Core “libraries” at ISPG Calgary & Charlie Lake, NEBC

11. Coring Tools: Full Core & Sidewall

12. Energy Resources Conservation Board: ISPG & University of Calgary

13. Detailed Well Log Formation Symbols at Left, SP & Gamma Logs
Lithologic interpretation, Detailed descriptions

14. Table of Petrophysical Logs
Fluids vs Rock
Brine, Gas, Oil
Logs vary w/Diam
Low Dens Coal Salts
FMS TV Pictures Sedimentary structures
XRF Induced Gamma Ray Fluorescence Chemistry/Mineralogy

15. Physical Properties of Formation near a Borehole
It is hard to measure “limestone versus shale” or “oil versus water” but easy to measure conductivity, gamma ray attenuation, sonic velocity etc. So we use variation in natural physical properties as an analog of contrasting rocks and fluids.
Drilling Fluids: mud, salts, ions, water move

16. Natural Gamma Measures Shaliness due to 40K in clay minerals
Nunavut

17. Common Petrophysical Logs: SP
Shales have high cation exchange capacity ~>100 meq/g and although not very permeable, Na+ from salty clays migrates into fresh drilling mud
Permeable sands are negatively charged mineral surfaces but containing salty water. The sands hold onto their cations and allow chloride to move into well bore.
Cl->Na+ for size but ions are solvated so for both reasons above Cl- is less strongly held and moves into fluid.
No one knew this ahead of time. They just started measuring things and found out what they meant later!
Shales have + SP response, high CEC, Na+ moves into mud
Permeable Sands have –SP response. Cl- is more mobile as mineral surfaces are negatively charged (silicates)

18. Petrophysical Logging: SP & Resistivity
Saltiness of porous sand causes more resistivity variation for laterolog with distance from borehole than for constant impermeable shale. This is easy as the lateral log just has 2 or 3 different electrode or coil spacings and thus variable depths of penetration into the formation.
Shale lines and Sand lines are baselines relative to that tool and the salinities (density and conductivity) of fluids in this formation at this region.
Empirical not absolute measurements this makes lithostratigraphy from logs easy for anyone but exact fluid salinities or gas and oil saturations are difficult and hard to calibrate.
No wonder oil and gas are so expensive!
SP –Sand line to left, +Shale Line to right
Resistivity tool has different depths of penetration

19. Petrophysical Logs: Caliper & Resistivity
Mudcake
Fresh Water Invasion
Mudcake
Low resistivity with insulating fresh mudcake but high resistivity with fresh water invasion of porous/permeable layer.
Shales are soft so hole cuts to a bigger diameter

20. Petrophysical Logs: Neutron & Density
Approximate interpretation is for any geologist to tell lithologies, track reservoir zones, facies etc., however calibrated porosity estimates require a well log analyst who is a specialized engineer whose calculations mean $$ and drill or quit!

21. Petrophysical logs: Dipmeter & FMS
Dipmeter from 4 resistivity tools can even measure sedimentary structures like cross beds.
FMS is a 4 way fiber optic TV camera scan in colour for formation bedding contacts in borehole walls.

22. Channel Sands in Shales
L.Cretaceous
Jurassic

23. THIS COVERS MOST CONVENTIONAL SEDIMENTARY GEOLOGY FOR RESOURCE EXPLORATION End of Chapter 2 Part 1 (Strata, Sedimentary Rocks & Well Logs)
Mining Exploration, Environmental, Geotechnical, Aquifer, Academic & Archeological studies all do similar things but with smaller tools, areas of interest and way smaller budgets!