Petrophysics is the study of the physical and chemical properties of rocks and their included fluids, if any. Petrophysical data can be obtained from well logs and from laboratory data. Petrophysical data is used both qualitatively and quantitatively. Both forms are discussed in appropriate sections of this Handbook.

Although "petrophysics" was used by G. E. Archie in the 1940's, the word  has only become popular in the last 20 years. The terms "log interpretation" or "log analysis" are widely used in the literature (inaccurately) to mean the same thing.

Petrophysics is a more inclusive term, encompassing core analysis, sample descriptions, X-ray diffraction, petrography, scanning electron microscopy, and other forms of detailed laboratory data, in addition to well log data. lab data can also be considered as a "well log", because the depth of each sample is usually known.

The term "Integrated Petrophysics" is now widely used to suggest that all forms of rock physics data is being analyzed in a coherent fashion. In some cases, an adequate log analysis model cannot be constructed without the integration of XRD, thin section petrography, geochemistry (organic carbon), electrical properties, and capillary pressure measurements, in addition to the more conventional core porosity and permeability measurements.

Petrophysicists offer services in the areas of well logging supervision, log analysis and interpretation, computer analysis of logs, seismic modeling, synthetic seismograms, and reconciliations of log data with geological, geophysical and exploration prospects, field studies and simulations, reserves estimates, and submissions to regulatory agencies.

These services are essential functions in modern oil and gas companies and cannot be accomplished without input from trained petrophysicists. The financial health and long-term success of a company depends on the central role of petrophysicist in all aspects of the company’s exploration and development activities.


Where petrophysics fits in the scheme of reservoir description (courtesy of GeoNeurale)

Well log and lab data seldom tell us what we really want to know. They might tell us  the resistivity and density of a rock. These are nice things to know but are not the final answers. We really want to know if there is oil or gas in that rock, how much is present, how fast can it be produced, and will it make a profit while doing so. Logs and lab data alone cannot tell us!

Thus the art and science of "petrophysical analysis" was born. A petrophysicist is the person who does the analysis of the data. Log analysis and log analyst are terms still widely used as synonyms.


grated Petrophysics" is the most recent buzzword, but is a little redundant, as the combined use of well logs and lab data has always been a fact of life for anyone trying to calibrate well log analysis results to "ground truth".


After analysis comes answers, and after answers comes interpretation, followed hopefully
by understanding. This Handbook deals mostly with data analysis. The numerous
case histories will provide the material needed to interpret and understand your results.

Data analysis, or data reduction, gives us "answers" that can be ambiguous at best or dead-wrong at worst. To consider "answers" as the final result of petrophysics is not adequate; the answers have to make sense when compared to all known facts and probably need calibration to those other facts. This step may be iterative, so petrophysical analysis is usually not a one-pass process. . The next step is to interpret the answers, and hopefully, gain an understanding of the answers. There is a huge gulf between getting answers and understanding the answers. Most of this Handbook deals with getting answers. However, numerous case histories are provided to help start the understanding process. Trial and error, experience, and a great memory will continue the process.

Petrophysics is much like crime scene investigation (CSI). In the early days, we used Sherlock Holmes as our model detective  Today, CSI shows on television (every channel, every night) show us how to gather evidence, analyze it in the lab, draw conclusions from the evidence, eliminate the impossible and improbable, and finally understand "who-dun-it". By treating petrophysics in the same fashion, we can use proven scientific methods to reduce doubt and uncertainty, but of course never eliminate them entirely. We still convict the innocent once in a while.

 Calgary Herald cartoon circa 1978, showing the public's impression of reservoir evaluation. That's me in the parka, looking into the borehole, while supervising a logging crew for PanArctic Oils Ltd on Melville Island in the Canadian High Arctic.

By integrating the data from other geoscience disciplines, we can do more than mere log analysis. We can actually define the rocks and fluids AND calibrate our work.

When petrophysics, in its inclusive sense, is combined with depositional environment, well performance, and pressure data, the result is called "reservoir description" or "reservoir characterization", and often leads to a reservoir simulation or full-field study.

Integrated Petrophysics is more than mere log analysis

State of the art well log analysis involves the intelligent use of a multiplicity of log curves and lab data in complex computer programs which evaluate many unknowns at once. Calibration of results usually requires statistical analysis, correlating laboratory and log analysis parameters. Sophisticated analysis of this type requires highly trained technical staff for programming, data entry, and evaluation. Software is often deterministic, using a fixed or user-defined sets of mathematical equations to derive answers from raw data and parameters supplied by the analyst. Other programs use probabilistic, statistical, or neural network methods, in addition to some deterministic code, to obtain answers. No known software can do the interpretation and understanding phase of the job - that is up to YOU.

To reduce dependence on the expertise of the programmer and user, a number of companies are studying the use of artificial intelligence (expert systems) to guide less experienced analysts through the analysis procedures. However, after more than 25 years of research, none have become commercial products.

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