Oil and Gas

Oil and Gas | Petrophysics

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

Course Code: N064
Instructors:  Martin Kennedy
Course Outline:  Download
Format and Duration
5 days

Summary

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

This is a clasroom 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.

Course Overview

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.

Topic 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.

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

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

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

Topic 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.

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

Martin Kennedy

Background
Martin Kennedy, is a consultant petrophysicist based in Perth, Western Australia. He began his career as a wireline-logging engineer. After leaving the field, Kennedy worked in R&D, for government and for several mid-sized British independents before moving to Perth as Woodside’s Chief Petrophysicist in 2003. He left after six years to concentrate on training and consulting. His career has spanned everything from field studies to quick-look evaluations as well as managing the petrophysics skill-pool for two companies. Kennedy has worked on most of the classic petroleum provinces outside North America (and a few within) as well as some more exotic areas. He now consults for a wide range of companies ranging from small Independents to Majors and specializes in areas that do not readily yield to standard techniques. His particular interests are carbonates; the way logging tools interact with geology; image logs; and interpreting old logs, bad logs, and bad/old logs. Kennedy holds a degree in chemistry from Bristol U. and a PhD degree in electrical engineering from Edinburgh U.

Affiliations ans Accreditation
PhD Edinburgh University - Electrical Engineering
BSc Bristol University - Chemistry

Courses Taught
N003: Geological Interpretation of Well Logs
N030: Rocks & Fluids: Practical Petrophysics (Isle of Wight, England)
N360: Quantitative Log Analysis and Petrophysics

CEU: 4 Continuing Education Units
PDH: 40 Professional Development Hours
Certificate: Certificate Issued Upon Completion
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