N064 Uncertainty in Petrophysics: Shaly-Sands, Carbonates, and other Problem Areas

Course Facts

Course Code:
5 days
4.0 Continuing Education Units
40 Professional Development Hours
Certificate Issued Upon Completion


The course looks at the sources of uncertainty in petrophysical properties and how to cope with them. This can involve both properly defi ning the range of uncertainty and/or applying tools and techniques to reduce the uncertainty: both aspects are covered in the course. Having carefully distinguished the various sources of uncertainty -which are always present- it looks in detail at plays and reservoir types where they can be a signifi cant component of the overall volumetric uncertainty. Examples include carbonates, shaly-sands, thin bed pays, fractured reservoirs and tight gas sands and several of these will be studied during the course. 

Duration and Training Method

A five-day classroom course taught through a series of lectures with exercises, case studies and group discussions. Problems are designed to be tackled with calculators, charts and graph paper but a laptop with Excel may be useful.

Participants will learn to:

  1. Estimate the various sources of error and uncertainty in petrophysical data.
  2. Understand the reasons why conventional log analysis can fail to produce satisfactory answers in carbonates. Appreciate that petrophysical properties may be subject to much higher uncertainty in carbonates.
  3. Quantify and account for the effects of clay and/or shale in log analysis, particularly when computing saturation. Use special core analysis data to quantify excess conductivity.
  4. Appreciate tools and techniques that can be used to evaluate thin bedded reservoirs.

For many reservoirs petrophysical properties can be calculated with a high degree of confidence so that they make only a small contribution to the overall uncertainty of volumetric estimates.  For some plays however petrophysics can contribute a lot of uncertainty and even lead to gross errors. This course looks at the fundamental reasons for errors and uncertainty and the tools and techniques used to handle them. The concepts are illustrated with examples from a range of different reservoirs that are known to cause problems. These include carbonates, fractured reservoirs, tight gas sands, thin beds, low resistivity pays, classical shaly sands and complex lithology. This is an advanced course which presupposes a working knowledge of basic quantitative log interpretation in clastics.

Day 1 Introduction and Administration. Revision Review? of the Petrophysical Workflow and inherent assumptions. Handling Errors and Uncertainty. Sources of errors and uncertainty in petrophysics. Introduction to Tools and techniques (Image logs, NMR, geochemical logs, petrography). Case Study: Tight Gas sands.

Day 2 Case Study on Carbonates. Pore systems in Carbonates. Heterogeneity. Porosity estimation. Saturation estimation. Permeability Prediction.

Day 3 Classical Shaly Sand reservoirs. Total and Effective Porosity (Vshale Estimation). Excess Conductivity. Waxman-Smits/Cation Exchange capacity. Permeability Prediction.

Day 4 Thin Bed Pays. Recognition and Characterisation. Total/Effective porosity.  Sand-Shale ratio estimation (Vshale). Thomas-Steiber methodology. Resistivity and saturation estimation. Resistivity Modelling.

Day 5 Fractured Reservoirs. Diagnostics. Characterisation. Administration and close.  Tool response to fractures; designing logging suites; electrical v hydraulic conductivity; real v artifact fractures in the borehole wall; integrating petrophysical, drilling and dynamic data.

Who should attend

Geoscientists and Engineers working with such problem reservoirs, petrophysicists seeking to extend their log analysis skills beyond well-behaved pore systems.

Prerequisites and linking courses

Due to the higher technical content within this class, It is advantageous, but not essential, to have attended N083 (Introduction to Petrophysics and Formation Evaluation) or N030 (Rocks and Fluids - Practical Petrophysics). Having attended N003 (Geological Interpretation of Well Logs) and/or N121 (Modern Petrophysical Interpretation of Well Logs) would be beneficial.

Linked courses for further understanding relate to specific interest or areas of work. N054 (Petrophysics in Reservoir Evaluation), M105 (Carbonate Petrophysics), and M187 (Low Resistivity, Low Contrast Pay) are all classes for which attending N064 prior to those class would be of benefit.

Click on a name to learn more about the instructor

Martin Kennedy